Archive for southeastern canada
Raw, cloudy, and wet
Posted by: | Comments05/12/10 8:30 AM
Today is the type of day that makes you want to stay in bed and sleep. Cloudy, wet, and raw with that chilled feeling running up your spine when you walk outside. Yes, Spring does have days like this, but hold on for just a bit because I have some good news.
The visible satellite picture this morning certainly shows that the northern Mid Atlantic and much of the Ohio Valley is covered in a well established overcast. There are little signs of a break in the cloud cover going back to Pittsburgh, so the conditions experienced this morning will continue on through the day today. So where did all these clouds come from? Glad you asked!
What is happening is that a warm front at 850 MB to 500 MB has surged north and east into New England and the northern Hudson Valley, however the surface warm front is still stuck over the Delaware Bay and Maryland. The reason why the warm front at the surface is stalled is due to the high pressure system that is sitting over Quebec and New England. This is a text book negative NAO induced pattern where strong convergence and confluence aloft over southeastern Canada and New England is enhancing surface high pressure to the northeast of the region. With the anti cyclonic circulation from the high pressure system firmly established, a marine air mass from the Atlantic will simply block the warm front from moving north until a stronger disturbance finally breaks up the log jam. The combination of the warm, moist air at the mid levels and the cool, moist air at the low levels will lead to overcast skies through the day along with drizzle and scattered showers from mid level disturbances.
Tomorrow afternoon, some breaks in the clouds will work in from north to south as drier air from the high pressure system to the north will sink into portion of the Hudson Valley, Connecticut, and potentially as far south as central New Jersey. However, I think those in southern New Jersey and Philadelphia will continue with the rather depressing overcast and wet conditions.
Now, the strong disturbance I was alluding to above is currently over the Southern Plains, which by the way may spawn some rather nasty severe thunderstorms once again for Oklahoma, Texas, and Arkansas this afternoon and evening. This area of low pressure and strong upper level disturbance will move towards the Mid Atlantic coast by Friday morning with another round of moderate to heavy rain. A few embedded thunderstorms will also be possible as the warm front surges north and the cold front approaches from the west. The low pressure system will exit by Friday afternoon with clearing skies by Friday evening. Now for the good news!
High pressure will take hold Friday night through Monday with clear skies and temperatures rebounding once again into the 60′s, 70′s, and potentially lower 80′s for the Delaware River Valley. I expect humidity to remain low, thus after a rather raw and ugly middle of the week, the weekend is looking excellent. Hey, I rather have the great weather on the weekend anyway, right?
Another cold front will approach Tuesday night into Wednesday with scattered showers, however the set up seen today is not expected for this approaching low pressure system as the upper level pattern begins to shift to a much warmer phase for the end of the month.
For details on the next seven days for your location, check out the NY NJ PA Weather seven day forecast!
-- Weather When Posted --
- Temperature: 48°F;
- Humidity: 98%;
- Heat Index: 48°F;
- Wind Chill: 43°F;
- Pressure: 30.08 in.;
MJO and Stratosphere point to active February
Posted by: | Comments7:50 AM
Premium Post
Stratospheric temperatures continue to rise steadily this morning with much of the atmospheric layer from 1 MB to 70 MB now averaging above normal. The warming at 1 M is starting to slow some as the temperatures approach record highs, however model guidance from the ECMWF suggest another period of warming is on the way at this level and may work down to the lower levels once again. Meanwhile, the 70 MB level continues to rise steadily and is starting to influence the troposphere as the Polar Vortex is forced towards southeastern Canada. The warming event that is on going is expected to impact the 500 MB pattern through much of February with a focus on a negative state of the EPO, AO, and 
NAO through the month. A positive PNA ridge (or ridge over the Rockies) is also showing up in various model guidance in the extended ensemble runs.
Meanwhile, the MJO is moving into a state with the phase is building and remain in phase 7. The model guidance on this feature vary from remaining in a strong phase 7 state to moving between stages 7 and 8 through the next 10 days. What this basically means is the Sub Tropical jet stream will remain active across the Gulf Coast and Southeast with more of an influence of tropical moisture into low pressure systems moving through the United States. One example of this influence is already clear with the storm developing over the Plains this morning.
So what does the combination of these factors that I’ve been illustrating over the past few days mean? Well, the trends of both of these features support an increasing potential and threat for cold conditions and an active weather pattern for much of February. Now, let me be clear. This is no guarantee that every location will get above normal snowfall or a snow storm every week. However, what this does show is that the potential to support such a pattern or at least a significant snowfall event will be present, and in long term forecasting that’s all one can really hope for. How the disturbances interact, like this present storm will give the details on who gets what, but the point of the long term data is that the threat is real, maturing, and will have to be monitored.
-- Weather When Posted --
- Temperature: 30°F;
- Humidity: 68%;
- Heat Index: 30°F;
- Wind Chill: 25°F;
- Pressure: 30.09 in.;
History points the way for Friday night
Posted by: | Comments7:40 AM
Clouds continue to increase this morning as two disturbances begin to impact the northern Mid Atlantic and much of New England. Although all is quiet in terms of the interaction of these two disturbances, it is interesting to note just how close this set up is to a potential winter storm if all the pieces present on the water vapor satellite picture had interacted just right. However, the disturbance over the Ohio Valley producing light snow will weaken under strong shear from the upper low developing to the north. The majority of the precipitation will weaken and dissipate over the Ohio Valley, however a few widely scattered snow showers are possible in the evening and overnight hours tonight.
As the upper low forms over northwestern New York tonight, a shot of Arctic air will drive towards the coast to reinforce the cold boundary layer in place. While temperatures will break the freezing mark once again over most locations this afternoon, a colder regime will take hold by tomorrow afternoon with most locations at or below freezing for highs. The push of the Arctic air will be supported by a strengthening high pressure system over southeastern Canada which will provide dry and cold conditions over the Philadelphia and New York City metropolitan areas through Thursday.
I discussed yesterday my concern for the period of Friday through Saturday, the upper level set up for this period is a near carbon copy of 500 MB patterns of previous significant ice storms. Model trends illustrate that the guidance is playing catch up here. Let’s consider the ECMWF 2 M temperatures of the past three runs. Along the coast, the high temperatures of the event have been dropped from the mid 50′s to now the mid to upper 40′s while the interior thermal forecast has also trended colder with temperatures in the mid 30′s rather than mid 40′s at the height of the warm advection of this storm. Further, the strength of the high pressure system over Quebec on Friday night and Saturday morning has trended significantly stronger from 1030 MB from yesterday’s 00Z guidance to now a 1040 MB high, an increase of 10 MB in the guidance is not something to take lightly.
At this time I feel I have a confident handle on some aspects of this storm. We know for the time that the storm impacts the Mid Atlantic, that the primary low pressure system is over the Great Lakes, not the coast. We also know that a fresh Arctic air mass is in place ahead of this storm and there is strong 500 MB support for a strong CAD to develop by Thursday night and continuing in through Saturday morning. That’s where we stand right now.
The map to the left is a preliminary threat map based on the data I have available and historical data from similar past events with a similar 500 MB configuration. Although guidance is not showing this threat yet, but is trending in that direction, I have the highest threat for significant ice over much of eastern Pennsylvania through the Hudson Valley. My hypothesis is that this Arctic cold air is not going to exit very quickly, especially with a 1040 MB high ridge down the coastal plain ahead of this warm front. While 850 MB temperatures will have no problem warming above freezing, I have my doubts that temperatures from 950 MB to the surface will ever break freezing over extreme northern Pennsylvania.
Closer to the coast, the power of the coastal front will eventually overwhelm the cold air at the surface, but not without a fight. The Delaware Valley should have a period of snow, sleet, and freezing rain before an eventual change over to rain on Friday night into Saturday morning. Meanwhile, snow may start out briefly along the New Jersey coast and New York City, however a change over to rain should be pretty quick given the expected east-northeasterly winds and then easterly wind behind the coastal front. I should note though that given the snow pack in place, temperatures will be hard press over most locations to break past 45 degrees at most and likely by the time the event is 24 hours away, most locations will be stuck in the upper 30′s along the coast rather than the warm 50′s seen forecasted for this period yesterday.
The structure of this storm will be a key factor to keep an eye on. A secondary low at a triple point (where the cold front, occluded front, and warm front meets) is expected to form, however the storm track basically takes this low right over the Delaware River Valley and into the Hudson Valley. In a way, what we have is a large occluded front driving from southwest to northeast followed by a return to a much colder regime. The “warm period” basically lasts for roughly 12 to 18 hours along the coast as the pattern reloads.
Changes To Watch For:
There are a few issues I’m keeping an eye on for this period.
1. The position and track of the secondary low. The secondary low will eventually become the primary low and this process begins while this low pressure system moves over the northern Mid Atlantic. The transition develops due to the primary low over the Great Lakes becoming vertically stacked while the strongest PVA drives towards the New England coast. If this transition occurs sooner or the coastal low is further south and east, this would have a significant impact on the forecast. For one, the coastal front is slower to move east into the coastal plain, thus supporting a colder solution. Currently, I don’t think this will happen however it is something to keep an eye on.
2. The impact of the snow pack on the boundary layer gradient. This aspect of the forecast is going to have to wait until Wednesday night at the earliest. The snow pack influence on the boundary layer combined with a fresh Arctic air mass will set up the coastal front that will eventually drive west into Long Island and the New Jersey coast. The intensity of this boundary layer will not only determine the strength of low level lifting, but also the timing of change over to various precipitation types.
3. Dry air. Yes, that culprit will have to be monitored very carefully. The high pressure to the north is rather strong and last time the guidance and this forecaster under forecasted the impact of dry air on precipitation totals. The strong CAD can also support a persistent dry layer of air at 950 MB as well. The impact of such a layer would have two impacts. The first would be to support strong evaporational cooling leading to colder temperatures from the mid levels to the surface. The second is a delay in the start of precipitation, which could lead to a shorter period of precipitation.
4. The high pressure moves to the east faster and thus the warm air simply overwhelms the Arctic air at the surface. The models and historical analysis would suggest a trend away from this solution, but it is something to keep an eye on.
5. The high pressure is slower to exit. This aspect has me worried the most, especially for those in northeastern Pennsylvania and much of eastern/central New York. Already the 00Z ECMWF is much slower in the exit of the high pressure system over Quebec with a 1040 MB high over northern Maine on Sunday morning. This is one of the reasons why the ECMWF has trended colder. IF this high is in place for that amount of time, then one could make the argument that many locations just away from the coastal plain would be impacted with snow, sleet, and freezing rain for an extended period of time.
After this storm, a new cold regime sets in as the negative NAO is reestablished and a ridge builds over the Canadian west coast. A strong disturbance driven by the Sub Tropical jet stream is expected to cut through southern California and race towards the coast by the end of next week. With cold air in place and some minor blocking over the Atlantic, there is potential for a light to moderate accumulating snow event for the northern Mid Atlantic on New Year’s Eve. However, the details are unknown at this time.
-- Weather When Posted --
- Temperature: 26°F;
- Humidity: 68%;
- Heat Index: 26°F;
- Wind Chill: 18°F;
- Pressure: 30.09 in.;
Overview of the Pre-Christmas Blizzard of 2009
Posted by: | Comments8:09 PM
On December 18th to the 19th, 2009 an area of low pressure tracked from the Gulf of Mexico to the Mid Atlantic coast producing heavy snowfall throughout the Mid Atlantic. Record breaking snowfall was observed in both Philadelphia, Pennsylvania and Upton, New York. The heaviest snowfall was observed from southern and central New Jersey through central and eastern Long Island with lesser amounts to the north and west.
Model Guidance Performance:
Leading up to this storm, the model guidance performed relatively poorly for the most part. In the medium range, there was a strong suggestion by the majority of the model guidance that the low pressure system would remain well to the south and east of the northern Mid Atlantic. In fact, there was a strong suggestion by the GFS that the low pressure system would track through the Florida peninsula and out into the Bahamas at one point. The ECMWF did not perform much better with a strong suggestion that the storm would remain far enough out into the Atlantic to produce only a light 4 inches or less over southern New Jersey. This forecast solution was seen up until two days before the winter storm.
Within 48 hours of the actual storm, models still had a difficult time with the actual forecast. The GFS remained well south and east of the actual storm track up until 12 hours before the event. The ECMWF/UKMET/Canadian solution performed much better in this time period with a better handle on the storm track and potential precipitation. Once again in what has been a theme since late Fall, somehow the NAM lead the way in terms of forecasting the precipitation gradient, storm track, and intensity. Despite the handicap of resolution issues on the NAM compared to the other model guidance in the 48 hour period, the NAM overall performed very well.
The model guidance had a difficult time with three important factors in this storm.
The first was the handling of the 500 MB evolution over southeastern Canada. The support for the storm track remaining well south and east of the northern Mid Atlantic was due to the idea of a strong upper low over Quebec. The overall theme of the guidance was to suggest the a disturbance dropping south from the Hudson Bay would remain weak while a dominant upper low will remain over Quebec. Meanwhile, the 50/50 upper low over the Canadian Maritimes weakened was well. The position of these features would lead to a suppressed storm track. The reality however was the upper level disturbance dropping south from the Hudson Bay was much stronger and the disturbance over Quebec was much weaker. As a result, the long wave trough was in a better position to support a strong winter storm.
The second feature that was handled poorly was the strength of the Sub Tropical Disturbance. Up until 36 to 48 hours of the storm impact, the strength of the Sub Tropical Disturbance was under forecasted in strength. As a result, the forecast of the potential intensification of the surface low off the Mid Atlantic was not handled well. The implications of a strong Sub Tropical Disturbance would mean that the overall phase would be stronger and the potential for the 500 MB features could close off for at least a short time.
Finally, the magnitude of the dry air was also under forecasted, leading to exaggerated QPF totals over northern Pennsylvania, northwestern New Jersey, and the Hudson Valley. The dry air lead to a longer than expected duration of virga over these locations.
Storm Impacts:
The blizzard of 2009 started to impact the northern Mid Atlantic early on Saturday morning over southern New Jersey with light snow. The snow quickly expanded north and west into the Philadelphia metropolitan area by day break with a steady light to moderate snow. Meanwhile, surface temperatures had fallen to the mid 10′s to lower 20′s over the northern interior and mid 20′s to lower 30′s along the coast. Dew points however were a more influential factor with a range of the negative single digits over the Hudson Valley to the lower 10′s over much of the coastal plain.
As the low pressure started to intensify off the North Carolina coast, moisture continued to push north throughout the northern Mid Atlantic in the morning hours. The very dry air over much of eastern Pennsylvania, just northwest of Philadelphia, the northern half of New Jersey, and much of the New York City metropolitan area lead to a prolonged period of virga up through the afternoon hours. However, a much different story was unfolding over the New Jersey coast. A strengthening thermal gradient at the mid and lower levels of the atmosphere supported strong lifting over central and southern New Jersey and back through the immediate Philadelphia metropolitan area. As a result, steady moderate to at times heavy snowfall resulted.
By the evening hours, the low pressure system moved to 50 miles off the Virginia coast. Very heavy snow and strong wind gusts were experienced along much of the New Jersey coast and over the Philadelphia metropolitan area. Light snow finally broke through the dry air and was slowly starting to accumulate over locations north and west of Philadelphia and central New Jersey. As the low pressure system continued to deepen to 990 MB, mesoscale banding started to form over Monmouth and Ocean Counties of New Jersey. Snowfall rates started to increase to an inch per hour and visibility crashed to below a mile at times.
On Saturday night, the surface low moved into the southern New Jersey coastal waters and stalled briefly for roughly 3 hours from 7 PM to 10 PM. As the low pressure system deepened to 980 MB east southeast of Atlantic City, very strong mesoscale banding developed from central New Jersey through much of Long Island. Snowfall rates increased to 1 to 3 inches per hour within these bands. Additional weaker bands formed over much of New Jersey and along the western shores of the Delaware River.
Light snow continued over northeastern Pennsylvania and the Hudson Valley. These locations missed on the heaviest snowfall on Saturday night as the best dynamics remained focused to the south and east. The strong lifting along the coast limited the potential for snowfall in these locations.
The intensity of the snowfall was best illustrated over northeastern New Jersey and the five boroughs of New York City as much of the snowfall up until Saturday evening accumulated to around an inch. Six hours later after the snow bands, 10 to 15 inches accumulated over much of this region. That is a 1.5″ to 2.33″ of snow per hour.
The low pressure system exited on Sunday morning with lingering light to moderate snow from eastern New Jersey through Long Island and Connecticut. All snowfall ended by mid Sunday afternoon.
This winter storm produced record breaking snowfall for Philadelphia at 23.2 inches and in Upton, New York at 26.3 inches. East Patchogue, New York in Suffolk County had the most snowfall of all the northern Mid Atlantic with 27.5 inches. The following are official snowfall totals from the National Weather Service.
CONNECTICUT
…FAIRFIELD COUNTY…
NORWALK 12.5 735 AM 12/20 SKYWARN SPOTTER
DARIEN 11.5 1200 PM 12/20 CT DOT
NEW CANAAN 10.3 1200 PM 12/20 CT DOT
BRIDGEPORT 9.0 700 AM 12/20 SKYWARN SPOTTER
SHELTON 8.8 1056 AM 12/20 SKYWARN SPOTTER
DANBURY 7.0 1200 PM 12/20 CT DOT
…MIDDLESEX COUNTY…
EAST HADDAM 23.5 830 AM 12/20 SKYWARN SPOTTER
CLINTON 20.0 900 AM 12/20 HAM RADIO
OLD SAYBROOK 20.0 1200 PM 12/20 CT DOT
WESTBROOK 19.0 1030 AM 12/20 SKYWARN SPOTTER
CLINTON 16.0 830 AM 12/20 PUBLIC
MIDDLETOWN 12.0 830 AM 12/20 SKYWARN SPOTTER
…NEW HAVEN COUNTY…
MADISON 12.2 1027 AM 12/20 SKYWARN SPOTTER
NORTH BRANFORD 12.0 830 AM 12/20 PUBLIC
NEW HAVEN 11.0 1200 PM 12/20 CT DOT
BETHANY 10.1 1030 AM 12/20 SKYWARN SPOTTER
MILFORD 10.0 1200 PM 12/20 CT DOT
NORTH HAVEN 8.5 830 AM 12/20 SKYWARN SPOTTER
BRANFORD 8.0 1006 AM 12/20 SKYWARN SPOTTER
BEACON FALLS 7.5 600 AM 12/20 CT DOT
NAUGATUCK 7.4 1250 PM 12/20 SKYWARN SPOTTER
WATERBURY 6.3 1200 PM 12/20 CT DOT
MERIDEN 6.0 140 PM 12/20 SKYWARN SPOTTER
…NEW LONDON COUNTY…
BALTIC 26.0 1100 PM 12/20 PUBLIC
NORWICH 20.0 1200 PM 12/20 CT DOT
OLD LYME 20.0 940 AM 12/20 HAM RADIO
MONTVILLE 19.0 900 AM 12/20 SKYWARN SPOTTER
GALES FERRY 18.5 1045 AM 12/20 SKYWARN SPOTTER
GROTON 18.0 1200 PM 12/20 CT DOT
OAKDALE 17.4 1100 AM 12/20 SKYWARN SPOTTER
LISBON 15.2 1200 PM 12/20 SKYWARN SPOTTER
NORTH FRANKLIN 15.0 850 AM 12/20 SKYWARN SPOTTER
NEW JERSEY
…BERGEN COUNTY…
PARAMUS 9.5 515 AM 12/20 SKYWARN SPOTTER
SADDLE BROOK 9.0 1000 AM 12/20 SKYWARN SPOTTER
PALISADES PARK 8.8 1000 PM 12/20 SKYWARN SPOTTER
BERGENFIELD 8.2 900 AM 12/20 SKYWARN SPOTTER
RUTHERFORD 8.0 515 AM 12/20 SKYWARN SPOTTER
RAMSEY 7.8 1000 PM 12/20 SKYWARN SPOTTER
GARFIELD 7.5 1100 AM 12/20 SKYWARN SPOTTER
MAHWAH 7.2 830 AM 12/20 SKYWARN SPOTTER
RIVERVALE 7.0 700 AM 12/20 SKYWARN SPOTTER
TENAFLY 6.8 700 AM 12/20 SKYWARN SPOTTER
FORT LEE 6.2 1000 AM 12/20 SKYWARN SPOTTER
RIDGEWOOD 6.2 1000 AM 12/20 SKYWARN SPOTTER
FAIR LAWN 6.0 1002 AM 12/20 SKYWARN SPOTTER
GLEN ROCK 6.0 1000 AM 12/20 SKYWARN SPOTTER
NORTHVALE 5.5 1100 AM 12/20 SKYWARN SPOTTER
DUMONT 4.0 815 AM 12/20 SKYWARN SPOTTER
…ESSEX COUNTY…
NEWARK 11.2 1100 AM 12/20 FAA CONTRACT OBSERVER
MILLBURN 8.3 715 AM 12/20 SKYWARN SPOTTER
NEWARK 8.0 1100 AM 12/20 PUBLIC
…HUDSON COUNTY…
JERSEY CITY 10.0 515 AM 12/20 SKYWARN SPOTTER
HARRISON 9.5 515 AM 12/20 SKYWARN SPOTTER
KEARNY 7.0 800 AM 12/20 PUBLIC
…PASSAIC COUNTY…
CLIFTON 11.0 515 AM 12/20 SKYWARN SPOTTER
RINGWOOD 10.0 515 AM 12/20 SKYWARN SPOTTER
…UNION COUNTY…
ELIZABETH 11.0 515 AM 12/20 SKYWARN SPOTTER
CLARK 10.0 515 AM 12/20 SKYWARN SPOTTER
ROSELLE PARK 10.0 1200 PM 12/20 PUBLIC
WESTFIELD 10.0 200 AM 12/20 PUBLIC
SPRINGFIELD 8.0 1215 PM 12/20 SKYWARN SPOTTER
PLAINFIELD 6.8 1201 PM 12/20 SKYWARN SPOTTER
NEW YORK
…BRONX COUNTY…
BRONX 9.5 900 AM 12/20 SKYWARN SPOTTER
THROGS NECK 9.5 800 AM 12/20 SKYWARN SPOTTER
EAST TREMONT 9.2 830 AM 12/20 SKYWARN SPOTTER
CITY ISLAND 9.1 800 AM 12/20 SKYWARN SPOTTER
RIVERDALE 8.6 215 PM 12/20 PUBLIC
…KINGS COUNTY…
BROOKLYN MARINE PARK 14.0 700 AM 12/20 PUBLIC
SHEEPSHEAD BAY 13.2 430 AM 12/20 SKYWARN SPOTTER
BOROUGH PARK 12.5 1000 AM 12/20 SKYWARN SPOTTER
BROOKLYN 11.8 700 AM 12/20 SKYWARN SPOTTER
…NASSAU COUNTY…
WANTAGH 18.0 1100 AM 12/20 SKYWARN SPOTTER
OLD BETHPAGE 17.9 1022 AM 12/20 SKYWARN SPOTTER
MERRICK 17.6 1020 AM 12/20 SKYWARN SPOTTER
PLAINVIEW 16.8 800 AM 12/20 SKYWARN SPOTTER
BELLMORE 16.6 1100 AM 12/20 PUBLIC
ROCKVILLE CENTRE 15.1 1200 PM 12/20 PUBLIC
MINEOLA 15.0 800 AM 12/20 SKYWARN SPOTTER
WOODBURY 15.0 1200 PM 12/20 PUBLIC
WOODMERE 15.0 1100 AM 12/20 PUBLIC
BETHPAGE 14.6 800 AM 12/20 SKYWARN SPOTTER
MASSAPEQUA 14.2 1153 AM 12/20 PUBLIC
OCEANSIDE 14.2 700 AM 12/20 COOP
SEAFORD 14.0 959 AM 12/20 SKYWARN SPOTTER
FLORAL PARK 13.5 1000 AM 12/20 SKYWARN SPOTTER
LIDO BEACH 13.5 900 AM 12/20 SKYWARN SPOTTER
MALVERNE 13.1 1100 AM 12/20 SKYWARN SPOTTER
LYNBROOK 13.0 1100 AM 12/20 SKYWARN SPOTTER
LONG BEACH 12.5 330 AM 12/20 SKYWARN SPOTTER
MILL NECK 12.0 213 PM 12/20 PUBLIC
…NEW YORK COUNTY…
NEW YORK 11.4 1100 PM 12/20 SKYWARN SPOTTER – UPPER
NYC/CENTRAL PARK 10.9 700 AM 12/20 CENTRAL PARK ZOO
MANHATTAN 9.5 210 AM 12/20 SKYWARN SPOTTER
HARLEM 9.0 800 AM 12/20 SKYWARN SPOTTER
…ORANGE COUNTY…
TUXEDO PARK 6.0 545 AM 12/20 SKYWARN SPOTTER
WESTTOWN 3.8 830 AM 12/20 SKYWARN SPOTTER
WARWICK 3.7 811 AM 12/20 SKYWARN SPOTTER
GOSHEN 2.5 800 AM 12/20 SKYWARN SPOTTER
NEW WINDSOR 2.5 700 AM 12/20 SKYWARN SPOTTER
…PUTNAM COUNTY…
PUTNAM VALLEY 4.5 635 AM 12/20 SKYWARN SPOTTER
…QUEENS COUNTY…
NYC/JFK ARPT 14.2 700 AM 12/20 FAA CONTRACT OBSERVER
FRESH MEADOWS 12.5 900 AM 12/20 PUBLIC
BAYSIDE 11.5 900 AM 12/20 PUBLIC
WHITESTONE 11.1 1130 AM 12/20 PUBLIC
NYC/LA GUARDIA 8.8 700 AM 12/20 FAA CONTRACT OBSERVER
…ROCKLAND COUNTY…
MONSEY 5.5 715 AM 12/20 SKYWARN SPOTTER
NEW CITY 5.0 940 AM 12/20 SKYWARN SPOTTER
STONY POINT 4.0 927 AM 12/20 SKYWARN SPOTTER
PIERMONT 3.9 1000 AM 12/20 SKYWARN SPOTTER
…SUFFOLK COUNTY…
EAST PATCHOGUE 27.5 1200 PM 12/20 PUBLIC
MASTIC 26.5 938 AM 12/20 PUBLIC
UPTON 26.3 156 PM 12/20 NWS OFFICE
HOLTSVILLE 25.0 900 AM 12/20 SKYWARN SPOTTER
MOUNT SINAI 25.0 1115 PM 12/20 NWS EMPLOYEE
BRIDGEHAMPTON 24.0 800 AM 12/20 SKYWARN SPOTTER
EAST SETAUKET 24.0 705 AM 12/20 SKYWARN SPOTTER
NORTH BABYLON 24.0 258 PM 12/20 SKYWARN SPOTTER
NORTH PATCHOGUE 24.0 1000 AM 12/20 PUBLIC
PATCHOGUE 24.0 335 PM 12/20 NWS EMPLOYEE
ISLIP 23.9 100 PM 12/20 FAA CONTRACT OBSERVER
STONY BROOK 23.7 940 AM 12/20 SKYWARN SPOTTER
MIDDLE ISLAND 23.5 1100 AM 12/20 NWS EMPLOYEE
SOUTHAMPTON 23.0 900 AM 12/20 NWS EMPLOYEE
CENTEREACH 21.0 1000 AM 12/20 NWS EMPLOYEE
MANORVILLE 21.0 130 PM 12/20 PUBLIC
RIVERHEAD 21.0 930 AM 12/20 SKYWARN SPOTTER
RONKONKOMA 20.5 949 AM 12/20 NWS EMPLOYEE
CUTCHOGUE 20.0 1147 AM 12/20 NWS EMPLOYEE
SAG HARBOR 20.0 730 AM 12/20 SKYWARN SPOTTER
SAYVILLE 19.8 700 AM 12/20 NWS EMPLOYEE
LINDENHURST 19.5 915 AM 12/20 SKYWARN SPOTTER
BAITING HOLLOW 18.9 1205 PM 12/20 NWS EMPLOYEE
EAST NORTHPORT 18.5 1000 PM 12/20 PUBLIC
HOLBROOK 18.5 310 AM 12/20 PUBLIC
COMMACK 18.2 500 AM 12/20 SKYWARN SPOTTER
DEER PARK 18.0 1000 AM 12/20 PUBLIC
MEDFORD 18.0 330 AM 12/20 SKYWARN SPOTTER
ROCKY POINT 18.0 157 PM 12/20 NWS EMPLOYEE
BAY SHORE 17.0 1000 AM 12/20 NWS EMPLOYEE
SMITHTOWN 16.4 620 AM 12/20 SKYWARN SPOTTER
WEST ISLIP 16.0 230 PM 12/20 SKYWARN SPOTTER
HUNTINGTON 15.2 1115 AM 12/20 SKYWARN SPOTTER
PORT JEFFERSON 15.0 900 AM 12/20 SKYWARN SPOTTER
MELVILLE 14.0 100 PM 12/20 PUBLIC
…WESTCHESTER COUNTY…
PORT CHESTER 12.5 733 AM 12/20 SKYWARN SPOTTER
YONKERS 12.2 1015 AM 12/20 SKYWARN SPOTTER
LARCHMONT 12.0 700 AM 12/20 SKYWARN SPOTTER
SCARSDALE 12.0 730 AM 12/20 SKYWARN SPOTTER
EASTCHESTER 11.5 1000 AM 12/20 SKYWARN SPOTTER
YONKERS 11.0 725 AM 12/20 SKYWARN SPOTTER
NEW ROCHELLE 10.0 900 AM 12/20 PUBLIC
MOUNT VERNON 9.5 1030 AM 12/20 PUBLIC
HASTINGS-ON-HUDSON 9.0 600 AM 12/20 SKYWARN SPOTTER
ARMONK 8.5 643 AM 12/20 SKYWARN SPOTTER
WHITE PLAINS 7.0 1200 PM 12/20 SKYWARN SPOTTER
HARRISON 6.4 800 AM 12/20 SKYWARN SPOTTER
BRONXVILLE 5.5 1100 AM 12/20 PUBLIC
CHAPPAQUA 5.5 1040 AM 12/20 SKYWARN SPOTTER
***********************PEAK WIND GUST***********************
LOCATION PEAK WIND TIME/DATE COMMENTS
GUST OF
(MPH) MEASUREMENT
CONNECTICUT
…NEW LONDON COUNTY…
GROTON/NEW LONDON 41 216 AM 12/20 ASOS
NEW JERSEY
…ESSEX COUNTY…
NEWARK 44 1108 PM 12/19 ASOS
NEW YORK
…QUEENS COUNTY…
NYC/JFK ARPT 43 1016 PM 12/19 ASOS
…SUFFOLK COUNTY…
FARMINGDALE 53 1037 PM 12/19 ASOS
MONTAUK 48 158 AM 12/20 ASOS
SHIRLEY 44 1136 PM 12/19 ASOS
ISLIP 40 1254 PM 12/20 ASOS
NEW JERSEY
…ATLANTIC COUNTY…
FOLSOM 25.7 800 AM 12/20
HAMMONTON 22.0 730 AM 12/20
GALLOWAY 18.0 1045 PM 12/19
ATLANTIC CITY 12.1 717 AM 12/20 INTERNATIONAL AIRPORT
PLEASANTVILLE 12.1 717 AM 12/20
ESTELL MANOR 12.0 1008 AM 12/20
…BURLINGTON COUNTY…
TABERNACLE 24.8 728 AM 12/20
MEDFORD 24.0 1050 PM 12/19
SOUTHAMPTON 21.4 130 AM 12/20
MEDFORD LAKES 21.0 1031 AM 12/20
WILLINGBORO 19.6 1100 PM 12/19
CINNAMINSON 19.2 807 AM 12/20
MOORESTOWN 19.0 1130 AM 12/20
WESTAMPTON 17.7 814 AM 12/20
BURLINGTON 17.5 1211 PM 12/20
BORDENTOWN 17.0 1132 AM 12/20
PEMBERTON 17.0 912 AM 12/20
MOUNT HOLLY NWS 16.6 720 AM 12/20
WRIGHTSTOWN 16.0 719 AM 12/20
DELRAN 15.0 1205 AM 12/20
…CAMDEN COUNTY…
ATCO 24.0 1100 PM 12/19
BERLIN PARK 22.5 1010 AM 12/20
ATCO 22.0 1002 AM 12/20
BLACKWOOD 22.0 1210 AM 12/20
MERCHANTVILLE 22.0 1000 AM 12/20
SICKLERVILLE 22.0 1205 AM 12/20
LINDENWOLD 21.5 1027 AM 12/20
MERCHANTVILLE 20.0 1050 PM 12/19
STRATFORD 20.0 1158 AM 12/20
CHERRY HILL 19.5 1158 PM 12/19
SOMERDALE 18.5 1153 AM 12/20
PENNSAUKEN 18.1 807 AM 12/20
ERIAL 17.5 930 PM 12/19
WINSLOW 14.0 1008 AM 12/20
…CAPE MAY COUNTY…
ELDORA 18.3 1202 PM 12/20
SEAVILLE 11.5 919 AM 12/20
DENNISVILLE 10.0 1207 PM 12/20
SOUTH DENNIS 9.5 1206 PM 12/20
GREEN CREEK 9.3 857 AM 12/20
SWAINTON 9.0 1126 AM 12/20
NORTH CAPE MAY 8.3 918 AM 12/20
DIAS CREEK 8.0 1204 PM 12/20
VILLAS 7.8 919 AM 12/20
GOSHEN 7.5 1203 PM 12/20
CLERMONT 7.0 1030 PM 12/19
ERMA 6.0 927 AM 12/20
WEST CAPE MAY 5.0 918 AM 12/20
WHITESBORO 5.0 1204 PM 12/20
CAPE MAY 3.0 920 AM 12/20
SCOTCH BONNET 1.5 918 AM 12/20
…CUMBERLAND COUNTY…
NEWPORT 24.0 200 AM 12/20
VINELAND 23.6 925 AM 12/20
SHILOH 20.0 958 AM 12/20
CEDARVILLE 19.0 1030 PM 12/19
BRIDGETON 16.0 1016 AM 12/20
…GLOUCESTER COUNTY…
SWEDESBORO 25.0 1130 AM 12/20
NATIONAL PARK 23.2 717 AM 12/20
SEWELL 22.5 1014 AM 12/20
FRANKLINVILLE 22.0 1017 AM 12/20
MALAGA 22.0 908 AM 12/20
MONROEVILLE 22.0 809 AM 12/20
TURNERSVILLE 20.5 1045 PM 12/19
CROSS KEYS 19.0 940 PM 12/19
TURNERSVILLE 19.0 940 PM 12/19
FRANKLINVILLE 17.0 930 PM 12/19
GIBBSTOWN 17.0 930 PM 12/19
…HUNTERDON COUNTY…
FLEMINGTON 10.3 1020 AM 12/20
LEBANON 7.5 1021 AM 12/20
HIGH BRIDGE 7.0 1019 AM 12/20
…MERCER COUNTY…
HAMILTON PARK 15.7 1148 AM 12/20
HAMILTON SQUARE 14.0 1045 PM 12/19
HIGHTSTOWN 12.0 1134 AM 12/20
LAWRENCEVILLE 12.0 909 AM 12/20
PRINCETON 12.0 1149 AM 12/20
HOPEWELL 12.0 1124 AM 12/20
ROBBINSVILLE 10.5 852 AM 12/20
EWING 10.0 730 AM 12/20
PENNINGTON 8.5 1022 AM 12/20
…MIDDLESEX COUNTY…
EAST BRUNSWICK 12.5 1157 AM 12/20
CRANBURY 12.0 1032 AM 12/20
METUCHEN 10.0 1001 AM 12/20
NORTH BRUNSWICK 10.0 1024 AM 12/20
METUCHEN 9.3 1140 AM 12/20
MILLTOWN 9.0 1136 AM 12/20
WOODBRIDGE 9.0 1137 AM 12/20
SOUTH PLAINFIELD 8.0 1045 AM 12/20
NEWTOWN 8.0 852 PM 12/19
SAYREVILLE 8.0 1137 AM 12/20
EDISON 6.0 1110 PM 12/19
…MONMOUTH COUNTY…
COLTS NECK 22.5 1147 AM 12/20
WAYSIDE 19.0 904 AM 12/20
RED BANK 17.5 1034 AM 12/20
MORGANVILLE 17.0 948 AM 12/20
NEPTUNE CITY 17.0 1201 PM 12/20
CREAM RIDGE 15.8 1153 AM 12/20
FAIR HAVEN 14.0 1035 AM 12/20
HOLMDEL 14.0 1136 AM 12/20
MANALAPAN 14.0 1205 AM 12/20
LONG BRANCH 11.0 729 AM 12/20
WEST LONG BRANCH 8.5 900 PM 12/19
MARLBORO 6.5 1045 PM 12/19
…MORRIS COUNTY…
WHIPPANY 10.0 1138 AM 12/20
MORRIS PLAINS 9.5 1141 AM 12/20
LINCOLN PARK 9.0 1045 PM 12/19
RANDOLPH#MORRIS 7.0 1040 AM 12/20
BUTLER 6.5 1205 AM 12/20
MILTON 6.5 810 AM 12/20
PARSIPPANY 6.5 1040 AM 12/20
BOONTON 6.0 1036 AM 12/20
ROCKAWAY 6.0 1036 AM 12/20
MARCELLA 5.5 920 AM 12/20
FLANDERS 4.0 1045 PM 12/19
…OCEAN COUNTY…
JACKSON#OCEAN 23.5 1045 PM 12/19
BRICKTOWN 22.0 723 AM 12/20
SHIP BOTTOM 21.0 1205 PM 12/20
TOMS RIVER 21.0 1045 PM 12/19
POINT PLEASANT BEACH 20.5 1042 AM 12/20
HOLIDAY CITY 20.0 1046 AM 12/20 BERKELEY TWP
SURF CITY 20.0 1205 PM 12/20
BEACHWOOD 18.5 1205 AM 12/20
BAYVILLE 17.5 900 PM 12/19
BROOKVILLE 16.0 1030 PM 12/19 OCEAN TWP
WHITING 16.0 900 PM 12/19
MANAHAWKIN 14.5 900 PM 12/19
FORKED RIVER 14.0 900 PM 12/19
POINT PLEASANT 14.0 900 PM 12/19
LANOKA HARBOR 13.0 1045 PM 12/19
…SALEM COUNTY…
PITTSGROVE 23.5 959 AM 12/20
…SOMERSET COUNTY…
BRANCHBURG 12.0 1154 AM 12/20
BRIDGEWATER 10.0 1155 AM 12/20
HILLSBOROUGH 9.5 1202 PM 12/20
SOMERVILLE 8.5 1026 AM 12/20
ROCKY HILL 8.0 1100 PM 12/19
…SUSSEX COUNTY…
HARDYSTON 4.5 1049 AM 12/20
NEWTON 4.0 1132 PM 12/19
SPARTA 3.9 1145 PM 12/19
HOPATCONG 3.0 938 PM 12/19
WANTAGE 3.0 728 AM 12/20
LAFAYETTE 2.5 734 AM 12/20
…WARREN COUNTY…
STEWARTSVILLE 7.6 813 AM 12/20
HACKETTSTOWN 6.5 809 AM 12/20
BROADWAY 5.0 1210 PM 12/20
HOPE 4.5 1248 AM 12/20
WASHINGTON 4.0 1025 PM 12/19
BLAIRSTOWN 3.5 1155 PM 12/19
PENNSYLVANIA
…BERKS COUNTY…
MAPLE GROVE 10.0 1140 PM 12/19
MOHNTON 8.5 1058 AM 12/20
BOYERTOWN 7.0 920 AM 12/20
DOUGLASSVILLE 7.0 1200 PM 12/20
WEST LAWN 6.5 1052 AM 12/20
…BUCKS COUNTY…
FEASTERVILLE 13.8 954 AM 12/20
BENSALEM 12.5 1100 PM 12/19
RICHBORO 11.5 1115 AM 12/20
NEWTOWN 11.4 101 AM 12/20
FURLONG 11.2 1015 AM 12/20
BENSALEM 11.0 900 PM 12/19
WARRINGTON 11.0 957 AM 12/20
MORRISVILLE 10.2 856 AM 12/20
PERKASIE 9.6 205 AM 12/20
…CHESTER COUNTY…
WEST CALN 19.3 1220 AM 12/20
EXTON 16.3 910 AM 12/20
WEST CHESTER 15.4 100 AM 12/20
EAST NANTMEAL 15.0 737 AM 12/20
DOWNINGTOWN 14.0 1216 PM 12/20
EXTON 11.0 1227 PM 12/20
HONEY BROOK 10.0 732 AM 12/20
FRICKS LOCK 8.5 1149 AM 12/20
…DELAWARE COUNTY…
SHARON HILL 23.0 1003 AM 12/20
FOLCROFT 19.0 1000 PM 12/19
UPPER CHICHESTER 18.0 1000 PM 12/19
CLIFTON HEIGHTS 16.7 230 AM 12/20
DREXEL HILL 16.0 729 AM 12/20
SWARTHMORE 14.8 1144 AM 12/20
…LEHIGH COUNTY…
ALLENTOWN 5.6 100 AM 12/20 LEHIGH VLY INTL AIRPORT
EMMAUS 5.2 115 AM 12/20
ALLENTOWN 5.1 1105 PM 12/19
SCHNECKSVILLE 5.0 1045 PM 12/19
…MONROE COUNTY…
EAST STROUDSBURG 5.1 130 AM 12/20
TOBYHANNA 4.3 1240 AM 12/20
…MONTGOMERY COUNTY…
ROCKLEDGE 16.5 1114 AM 12/20
WYNNEWOOD 16.5 1230 AM 12/20
KING OF PRUSSIA 14.2 1230 AM 12/20
ROYERSFORD 14.2 1158 AM 12/20
WILLOW GROVE 13.3 1100 PM 12/19
ABINGTON 13.2 1100 PM 12/19
TRAPPE 12.6 1200 PM 12/20
ELKINS PARK 11.3 1015 PM 12/19
ELKINS PARK 11.3 1014 PM 12/19
MONTGOMERYVILLE 11.0 1246 AM 12/20
EAGLEVILLE 10.0 930 PM 12/19
KULPSVILLE 10.0 1105 AM 12/20
AMBLER 9.5 1133 PM 12/20
SPRING MOUNT 8.8 958 AM 12/20
ROYERSFORD 8.3 910 PM 12/19
HARLEYSVILLE 8.0 1059 AM 12/20
POTTSTOWN 8.0 729 AM 12/20
UPPER POTTSGROVE 8.0 1156 AM 12/20
SOUDERTON 7.0 1106 AM 12/20
NORTH WALES 6.0 1104 AM 12/20
…NORTHAMPTON COUNTY…
MARTINS CREEK 3.5 935 PM 12/19
…PHILADELPHIA COUNTY…
PHILADELPHIA 23.2 717 AM 12/20 INTERNATIONAL AIRPORT
PHILADELPHIA 18.3 1119 AM 12/20
SOMERTON 10.5 1030 PM 12/20
-- Weather When Posted --
- Temperature: 28°F;
- Humidity: 50%;
- Heat Index: 28°F;
- Wind Chill: 15°F;
- Pressure: 29.85 in.;
Major Snow Storm with Blizzard Conditions Expected Saturday through Sunday afternoon
Posted by: | Comments10:14 PM
Obviously tonight all of our focus is on the storm that is on the way for Saturday. This afternoon, the model guidance took a strong swing towards what I defined two days ago as scenario 3, which is a full phase intense winter storm that is capable of producing significant snowfall. Given the data in front of me this evening and the lessons from climatology, I am prepared to say we are on the verge of a historic winter storm for December that will likely be remembered for some time.
As I’ve been pointing out the past several days, I have had a strong suspicion that the models were not handling this pattern right. I have felt that the Sub Tropical disturbance is under forecasted and the idea of three closed or semi closed upper level features across southeastern Canada was not a stable solution. Changes were on the way, and those changes were going to move towards a snowier solution.
This evening, we see that the Sub Tropical disturbance is well on the way of pushing north and driving towards through the Gulf Coast and towards the Tennessee Valley. The precipitation with this Sub Tropical disturbance is already impressively organized with an area of heavy rain pushing through the central Gulf Coast. There is also convection firing up, which is enhancing the development of the surface low in the Gulf of Mexico, which is already down to 1008 MB.
The driving force that allows this storm to come together can be found in Canada tonight. A disturbance is currently on the way south from northern Canada and will head towards the Hudson Bay and eventually over eastern Ontario by Saturday morning. Meanwhile, the negative NAO has formed and is setting up the blocking needed to slow down the exit of the surface low that will be positioned over the southern Mid Atlantic coast on Saturday morning. The debate for the past few days has been how will the energy split off from the 50/50 low interact with the disturbance diving south over Ontario. I’ve been arguing for the past few days that the disturbance diving south is going to end up being the dominant feature, not the disturbance traveling through Quebec, due to the position of the jet streaks over eastern Canada and the development of the ridge building towards the Hudson Bay. The idea of the upper low over central Quebec never made physical sense to me, and it seems the models have caught on to that.
The position of the dominant upper low over eastern Ontario allows the long wave trough to remain neutral over the Mississippi Valley and supports the shortwave trough to tilt into a negative position and even close off as an individual upper low at 500 MB. The result is an area of low pressure that is able to bomb out over the Delaware and New Jersey coastal waters with heavy snow throughout the northern Mid Atlantic. However, it is clear the locations east of the Delaware River will get the worse from this storm.
Mesoscale Thoughts:
I have two concerns about the mesoscale environment with this storm.
The image to the left is from the 00Z NAM, however the overall thermal gradient that is seen here is very similar to the ECMWF, UKMET, Canadian, and several Ensemble guidance. The feature I want everyone to focus on is the tight thermal gradient along the New Jersey coast. From 25 mile east of the New Jersey coast to the Delaware River, there is a 6 to 10 degree thermal gradient found from 700 MB down to 950 MB in the vertical and horizontal sections of the atmosphere. What this means is that a strong mid level and low level frontal structure will develop just to the east of the northern Mid Atlantic coast. This type of development leads to significant banding development over much of New Jersey, the immediate New York City metropolitan area, and southern Connecticut. Locations over eastern Pennsylvania can develop banding as well, however the best dynamics will be to the east.
The other concern is that the atmosphere will likely become destabilized due to the strong frontogenessis and the areas of warming and cooling that will take place. While some warming may cause some sleet to mix in at times, the other threat will be the potential for convective snow or thunder snow from this storm. Mesoscale features will have a significant impact on snowfall totals on this storm.
Snowfall Forecast and Impacts:
So here is what everyone has been waiting for. The first snowfall map for this event. First, let me say, I know the NAM guidance since 18Z produces over 2 inches of QPF over much of the region. While such a solution is not impossible given the moisture loaded storm to the south and the strong Atlantic fetch that develops from Saturday afternoon through Sunday, I believe a wiser stance is to side with the drier ECMWF/UKMET solutions given the bias of the NAM to exaggerate precipitation totals.
Locations further north and west will have the least snowfall with 1 to 3 inches in far northeastern Pennsylvania and 2 to 4 inches from the central Hudson Valley down through interior northeastern Pennsylvania and off towards south central Pennsylvania. As we move closer to the coast, snowfall accumulation potential increases. Now, along the immediate coast, there is a threat of mixing of sleet and even a short period of freezing rain or rain, however as the low intensifies to the east of the New Jersey coast, all precipitation will turn back over to snow. Given the potential for mesoscale influence and the position of the coastal fronts, I am highlighting interior southern New Jersey through central New Jersey and off towards central Long Island as being the most likely places for significant snowfall accumulations. However, I want to stress that all locations east of the Delaware River will be under the threat for strong mesoscale banding and snowfall totals exceeding what I have forecasted at this time. In fact, if the banding works out right, I can see support for snowfall totals exceeding 15 inches in many places from Philadelphia on east.
As for other impacts, wind is going to be a major problem with this storm on many levels. The most obvious will be visibility issues as the winds will be capable of reaching sustained winds of 35 to 45 mph with gusts over 50 mph. The strength of the wind will be capable of reducing visibility to near zero at times and will significantly restrict travel conditions. The other threat from the wind will be coastal flooding, which I think will be a more significant issue than many think considering the impacts on the coast from storms this fall. Major coastal flooding will be a problem from southern New Jersey through the Long Island Sound from this storm.
Considering the limited amount of significant snow storms in December, the potential for this storm of being historic is pretty high. Remember, the average snowfall in December is usually around 3 inches in the northern Mid Atlantic.
From this point on I will focus on updating the snowfall map when needed and discussing the finer details and threats of this storm. All other forecasting interests will have a limited coverage for the time being.
-- Weather When Posted --
- Temperature: 24°F;
- Humidity: 49%;
- Heat Index: 24°F;
- Wind Chill: 13°F;
- Pressure: 30.3 in.;
A break between another storm threat
Posted by: | Comments10:07 AM
The storm that produced a light to moderate snowfall over much of the northern Mid Atlantic yesterday (review issued this afternoon), surface high pressure has taken hold. The snow storm from yesterday marked another step down into what is looking to be very cold and active end of December. As the low pressure system races into the Canadian Maritimes, the upper level pattern will begin a shift that will eventually force the Polar Vortex over north-central Canada towards southeastern Canada.
Today through Tuesday, a strong Polar high pressure system will be in control of the New York City and Philadelphia metropolitan areas. Clear skies to a few scattered clouds can be expected through Tuesday along with temperatures averaging near to slightly below normal. With temperatures in the 30′s and lower 40′s in the afternoon, much of the snow on the ground will melt rapidly due to the high water content of the snow. Conversely though, the melt water from the will refreeze and a threat of black ice will need to be monitored each morning.
On Tuesday night, a developing low pressure system over the southern Plains will track towards the Ohio Valley. This storm is setting up to be a very complicated forecast for many locations away from the coast. Model guidance generally agrees on several key points at this time. One, that the primary low pressure system will track through the St. Lawrence River Valley. This storm track, even with a secondary coastal low developing, will mean that eventually the warm sector of this storm will move through the northern Mid Atlantic. Two, strong Polar high pressure over the St. Lawrence River Valley on Tuesday will move towards southern Quebec. This high pressure system will develop a strong Cold Air Damning (CAD) signature that will force cold air down the eastern side of the Appalachian Mountains. Here in lies the threat.
Moisture will be racing to the northeast from the Tennessee and Mississippi Valleys towards the northern Mid Atlantic on Tuesday night. The CAD signature will force a weak secondary low to develop on Tuesday night along the warm front. However, it is clear on all guidance that the strongest PVA or energy is focused towards the eastern Great Lakes. The storm track of the primary low will therefore clearly move in that direction. However, before the warm front is able to drive through the New York City and Philadelphia metropolitan areas, the cold air will have to be eroded away at the surface. This is why a high pressure system to the north of a winter storm is so important as the high pressure will work against the warm front and will keep the cold air in place much longer than normal. Precipitation will break out throughout the northern Mid Atlantic on Tuesday night, likely scattered at first, but increasing in coverage as isentropic lifting intensifies. Along the southern New Jersey coast, the precipitation may briefly mix with snow at the 
onset, but this is clearly a rain event. For locations from Philadelphia through central and northeastern New Jersey, and the New York City metropolitan area; the precipitation will start as snow for a short time with a slight potential of minor accumulations before changing over to rain early on Wednesday morning. The main threat is clearly over the interior, specifically northeastern Pennsylvania, northwestern New Jersey, the Hudson Valley, and interior Connecticut where the low level cold air will remain in place through the morning hours on Wednesday which will support a wide variety of frozen precipitation before a change over to rain. My concern for the interior is that first the precipitation will start faster than guidance is suggesting right now. In cases of isentropic lifting, model guidance is usually to slow with the start of precipitation. With moisture air advection apparent along with warm air advection on Tuesday night, the threat is present for snow to start on Tuesday night for most locations. Over the interior, the focus will likely turn to ice accumulation potential rather than snow accumulation potential, however the details will have to wait until more data is available. However, if I was in the the locations I have highlighted this morning, I’d prepare for a rough start to Wednesday morning.
Warm air will eventually win out for all locations by late on Wednesday morning with another one day warm temperatures event. The warm conditions may be considered a cruel joke compared to what is to follow in the days after this storm. There is now very strong model guidance to support the the Polar Vortex is coming east. This storm that will pull into the St. Lawrence River Valley is the trigger that pulls the Polar Vortex south and east, and also establishes a negative NAO pattern to couplet with a building ridge along the West coast to replace the negative EPO ridge that will be slowly weakening.
A few points before I go on. Note that the forecasted “warm period” of the guidance in the long range from the past few days has been cut down to one day. One day due to a storm that will force an Arctic air mass into the center of the United States. As I’ve stated before, models are a tool, not a crystal ball of facts. No matter what the models due, one must start a forecast with a foundation of real observations. By the way, the MJO is in stage 7, which strongly supports the model guidance depiction through 240 hours.
I expect temperatures to average well below normal for Friday, Saturday, and Sunday. I am concerned about a potential storm for the period of Saturday evening through Monday morning. I don’t expect a storm to last that long, however in that time period a Sub Tropical Disturbance will be moving through the Mississippi Valley and towards the Mid Atlantic coast. With an arctic air mass in place, a strong thermal gradient along the coast, and plenty of available moisture via the Sub Tropical jet stream over the Gulf of Mexico; I’m very wary of this period. There is a threat, but for now the details are unknown. However, I’d keep next weekend circled for the next wide spread snow threat for the region.
-- Weather When Posted --
- Temperature: 35°F;
- Humidity: 59%;
- Heat Index: 35°F;
- Wind Chill: 26°F;
- Pressure: 30.28 in.;
Warm conditions return to the Mid Atlantic
Posted by: | Comments6:46 AM
Surface Map This Morning- NWS/HPC
The ridge axis for the high pressure system over the Southeast moved over the northern Mid Atlantic last night, providing clear skies and light winds. As a result, temperatures were able to fall into the 30′s and 40′s this morning. However, the ridge axis is now off the New Jersey coast and as a result, a warm southwesterly wind has developed.
Through Thursday, high pressure off the Southeast coast will have a strong hold on the Philadelphia and New York City metropolitan areas, which will lead to temperatures soaring into the 60′s and 70′s for highs throughout the region. High temperatures for the period will average 4 to 8 degrees above normal as a result. However, the warm conditions will not last long.
A cold front will move through the eastern Great Lakes on Thursday night and will bring a much cooler air mass to the forecast area by Friday morning. This cold front is moisture starved and the majority of the upper level dynamics will remain over southeastern Canada, however the return of a true Polar air mass will knock temperatures down to below normal levels on Friday as high temperatures struggle to rise into the 50′s.
The next cold front is starting to show signs of being a more complicated low pressure system than
Upper Level pattern for Wednesday afternoon- Penn State E-wall
earlier thought. Support continues to grow for the remnants of Hurricane Rick in the off the west coast of Mexico to become entrained in the upper level trough that will drive a strong low pressure system through the Hudson Valley this Saturday. There are many issues with the remnant energy that must be ironed out for Saturday. For one, how much enhancement of the trough in the Sub Tropical Jet will be realized in this interaction? For now, the guidance already suggests that this upper trough/upper low will already be mature in development and further intensification will be limited. What really stands out is the added moisture, which I warned about this past weekend in the live chat. The additional tropical moisture is showing up as an influence as QPF amounts are rather impressive for the forecast area when this moisture is included in the forecast. So here is how I see this situation play out.
On Friday, the cold front that moved through the forecast area will stall over Delaware and Maryland. A strong low pressure system will move into the Ohio Valley on Friday night and begin to drive the warm front northward. As a result, clouds will increase from south to north along with a strengthening veering east to southeasterly wind.
Give high pressure will be over New England by Saturday morning, I have doubts that this warm front will get much further north than from a line the Connecticut coastline through the southern Hudson Valley and off towards northern New Jersey where a cold/occluded front will be racing to the east. The question is just how much of a negative tilt develops with the upper low. The stronger the tilt, the faster the dry air advection over the forecast area. Usually a negative tilt in the trough would lead to longer periods of rainfall, and that will be true for much of New England. However, in this case, the transition from a neutral to negative tilt over the Mid Atlantic will throw this occluded/cold front through the forecast area quicker than normal. The latest guidance also suggest that the majority of the mid level moisture will be over the forecast area in the morning and exiting by the afternoon with strong dry air advection right on the tail of the moisture. So what this is all hinting at to me is the following:
1. The heaviest precipitation will be to the north of the warm front, basically over the Hudson Valley and Connecticut. The rainfall will move as basically a large line of precipitation marching southwest to northeast on the radar with a larger coverage area along and ahead of the warm front.
2. The heaviest rainfall, based on the best guidance in front of me, will be on Saturday morning as the warm front races north and the occluded/cold front approaches. Strong isentropic lifting ahead of the warm front may lead to elevated thunderstorms producing very heavy downpours. Wind damage from these thunderstorms may become a threat.
3. High temperatures will peak late in the morning or early afternoon before falling off in the late afternoon under the influence of strong cold air advection.
Behind this cold front, strong high pressure and a cool Polar air mass will become established from Sunday through Tuesday. Dry conditions, scattered clouds, and temperatures continuing to remain 4 to 8 degrees below normal can be expected.
-- Weather When Posted --
- Temperature: 37°F;
- Humidity: 80%;
- Heat Index: 37°F;
- Wind Chill: 32°F;
- Pressure: 30.16 in.;
A raw day setting up for tomorrow, a drier weekend possible
Posted by: | Comments2:21 PM
Surface Map Tomorrow Afternoon, NWS
A very raw and windy day is setting up for the forecast area tomorrow as high pressure positions itself over southeastern Canada over the next 24 hours.
The upper level trough that has been east of the Mid Atlantic will retrograde back towards the Great Lakes tonight. A strong disturbance will dive south from central Ontario and move through the forecast area by tomorrow morning. At the surface, a weak cold front will move through with showers early in the morning. However, the cold front will stall off the New Jersey coast by the late morning hours.
Note the surface map to the left, as the cold front stalls, the high pressure system to the north will enhance an easterly wind over the Mid Atlantic. The easterly wind will extend as far up at 700 MB, which will bring moisture in from the Atlantic Ocean. Weak forcing will develop as the moist air from the Atlantic rides up and over the dry, cool air moving in from the Great Lakes and Ohio Valley, which will lead to overcast skies and periods of showers. Clearly, Wednesday is not looking very nice for the region.
Support is increasing for high pressure to have a stronger influence over the Mid Atlantic this weekend. The latest guidance now suggests that the position of the trough axis will be further to the east by Saturday, producing convergence and confluence over the region. As a result, high pressure will be able to build south along the Mid Atlantic coast, thus leading to drier conditions. A lot of the forecast for this weekend strongly depends on the timing of the trough on Friday night and Saturday morning, however there is strengthening support for a more dominant high pressure system over the Mid Atlantic Saturday and Sunday, possibly leading to clearing skies over much of the region. Temperatures are still expected to remain rather cool.
-- Weather When Posted --
- Temperature: 75°F;
- Humidity: 57%;
- Heat Index: 77°F;
- Wind Chill: 75°F;
- Pressure: 29.94 in.;
Strengthening coastal low brings wet conditions to New Jersey Coast
Posted by: | Comments5:15 AM
Trouble is brewing off the Mid Atlantic coast this morning as a strong upper level disturbance continues to intensify over the Tennessee Valley.
As discussed the past several days, the upper level pattern that is developing over the eastern United States is more like a late fall or winter seasonal pattern than one seen in September. Strong blocking is developing over the Canadian Maritimes this morning, which is leading to strong convergence and confluence over northern New England and southeastern Canada as seen on the water vapor images where now red highlights are showing up. The red indicates strong sinking motion in the atmosphere as the air dries in these locations. This sinking air will support a strong surface high pressure system, which will be one of the important keys to this forecast. Meanwhile, the blocking pattern over the Canadian Maritimes is also forcing the disturbance over the Tennessee Valley to stall and continue to intensify. The strong lifting from this upper disturbance, which is forming a strong 500 MB low, is supporting the development of a coastal low off the Delmarva Peninsula coastal waters this morning. Meanwhile, the upper level pattern is also pulling a significant amount of moisture up the coast with three distinct moisture sources; one from the Pacific at the higher levels of the atmosphere, the second from the Gulf of Mexico at the lower and mid levels of the atmosphere, and the third from the Atlantic primarily at the lower levels of the atmosphere. Any way you slice it, the atmosphere is saturated with moisture off the coast this morning.
Up through early this morning, the best dynamics at all levels of the atmosphere have been focused off the coast, however that will change this afternoon as the upper low matures and pulls the surface low pressure system closer to the coast. Scattered showers will increase in coverage and transition to a steady rain along the coast. As the upper low intensifies, so too will the surface low tonight through Thursday and into Friday. The combination of the high pressure to the north and the low pressure to the south will send plenty of moisture into the forecast area from the Atlantic via a strengthening easterly fetch. The lifting will then take advantage of this additional precipitation and produce rainfall, heavy at times, throughout the forecast area. The best total dynamics will be focused along the New Jersey coast, especially from Monmouth to Atlantic Counties where rainfall amounts can exceed over 2 inches of rain by Saturday morning.
Rainfall Through Saturday Morning
Through early Saturday morning, the forecast area can expect periods of heavy rainfall, especially along the coast with an increasingly strong easterly wind. The pressure gradient between the low pressure system and the high pressure system to the north will support sustained winds from 15 to 30 mph by tonight with gusts exceed 40 mph at times along the immediate coast. Rainfall amounts throughout the forecast area will be over a half an inch with rainfall amounts exceeding 2 inches along the southern and central New Jersey coast. However, most coastal locations will remain in the range of 1 to 2 inches of total rainfall by Saturday morning. The persistent easterly wind will support the potential for coastal flooding, especially along the New Jersey coast.
A defined chance in the pattern can be expected by Saturday night. A strong upper low will dig into the Mississippi Valley, which will force the upper disturbance over the Mid Atlantic to move into the northwester Atlantic Ocean. The upper low will continue to deepen over the Mississippi Valley, which will build a ridge along the East coast extending from the Bahamas to the St. Lawrence River Valley. The orientation of the ridge will support high pressure to build over the region through Tuesday with generally clear skies, dry conditions, and near normal temperatures.
-- Weather When Posted --
- Temperature: 64°F;
- Humidity: 93%;
- Heat Index: 64°F;
- Wind Chill: 64°F;
- Pressure: 30.04 in.;
Developing low expected to impact region through this week
Posted by: | Comments7:15 AM
This morning, the water vapor satellite image clearly shows the new and rather interesting pattern developing over the eastern half of the United States. A strong upper level disturbance is diving into the Tennessee Valley this morning, carving a negatively tilted weak trough from the Mississippi Valley to the Southeast and Mid Atlantic coast.
Meanwhile, a deepening upper trough over northern Quebec is in the beginning stages of forming a powerful upper low that will park over the Canadian Maritimes. Note the darkening line over southeastern Canada, this line is representing convergence aloft which is sinking air. Sinking air dries, therefore the decrease in moisture and the dark line developing on the water vapor image. This sinking air will enhance a surface high pressure to the north of the Mid Atlantic, and once the upper low is established over the next 24 hours, high pressure will be located into place.
So we have high pressure locked into place over New England and a strong upper disturbance digging into the Tennessee Valley. This set up forces strong lifting along the Mid Atlantic coast, thus the explosive convection off the Southeast and Mid Atlantic coast this morning. The combination of a stationary front, which is supporting low level lifting, and the upper level disturbance producing additional lifting; is producing an environment favorable for cyclogenesis along the East coast. This low pressure system will tap into the ample moisture available along the coastal waters of the Southeast from the Caribbean.
Due to the developing blocking nature of this pattern, the players in this pattern described above will not move very quickly at all. As a result, the low pressure system developing this morning will slowly drift to the north and east over the next several days. The pressure gradient over the Mid Atlantic will produce a strong easterly fetch from the Atlantic into the forecast area from the surface to 700 MB. As a result, a marine air mass will become established, which will lead to increasing clouds through the day and an increasing threat of showers.
The low pressure system will move continue to drift northward towards the Delaware coastal waters by Tuesday night. This low pressure system will not be able to move much further north due to the high pressure system. However, the pressure gradient will be strongest from Tuesday night on through Wednesday leading to an increasing easterly wind with 10 to 25 mph sustained winds and higher gusts especially along the New Jersey coast. While showers can be expected throughout the region, periods of steady rain, heavy at times, can be expected on Tuesday night through Wednesday along the southern and central New Jersey coast.
This upper level pattern will not break down quickly and another potentially stronger upper low will dig into the Tennessee Valley by the end of the week. The orientation of this upper low will be key in determining the location of developing low pressure systems and precipitation. As of this morning, there is some uncertainty on the exact location and orientation of this upper low by the end of the week.
-- Weather When Posted --
- Temperature: 64°F;
- Humidity: 77%;
- Heat Index: 64°F;
- Wind Chill: 64°F;
- Pressure: 30.29 in.;
Freehold
77°
New York
75°
Sussex
73°
Allentown
77°
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