Archive for cold surfaces
Light rain and snow tonight leads to minor accumulations
Posted by: | Comments6:36 PM
I have been hinting for some time that the precipitation shield for tonight’s storm was going to be more expansive than what was being forecasted. However, I am not very impressed with the accumulation potential for this storm. The first and foremost is the warm boundary layer temperatures.
Besides the fact that the surface freezing line is located over central New York and central Pennsylvania, the dew points this evening range from the mid to upper 20′s over the interior and lower 30′s along the coast. The problem with these temperatures and dew points is that the wet bulb temperatures are generally above freezing. Further, there is little if any additional cold air advection to this storm, so basically what you have is what you’ll get as far as the state of the atmosphere.
Make no mistake about it, this storm is very dynamic and impressive. In fact, convection is developing throughout the southern Mid Atlantic coast down through Florida with numerous lightning strikes. The precipitation shield is expanding as far west as central Virginia and will like encompass the entire Philadelphia and New York City metropolitan area. The temperatures above 950 MB for most locations is below freezing, suggesting that the precipitation type that will dominate will be snow. The issue, as described above, is that the snow simply will not be able to stick on too many place.
The updated snowfall map is basically for grassy and cold surfaces where the snow will be able to accumulate. Most locations will receive an inch of snow while a few isolated convective bands can push snowfall totals up to 3 inches. Given that the coldest model guidance available had surface temperatures from 32 over northeastern Pennsylvania to 37 degrees along the coast, any accumulation on pavement will be extremely limited.
-- Weather When Posted --
- Temperature: 37°F;
- Humidity: 80%;
- Heat Index: 37°F;
- Wind Chill: 37°F;
- Pressure: 29.85 in.;
Minor snow threat for Tuesday night into Wednesday morning
Posted by: | Comments9:15 PM
A very energetic Sub Tropical disturbance is rapidly developing along the Gulf Coast this evening. However, a more important disturbance that will determine the forecast is actually along the West coast.
While the storm along the Gulf Coast certainly appears ominous, the progression of the Pacific storm this evening into the coast of Washington and Oregon confirm that the 500 MB pattern will be shifting east. As a result, there is rather strong support via the actual observations that the eventual storm track will be well south and west of the New Jersey coast on Wednesday morning.
Now, I’ve had a suspicion for several days now that the precipitation shield of this storm will be more expansive than the guidance was giving credit too. The model guidance of late, is starting to pick up on this idea for the immediate New Jersey coast with up to a half inch of precipitation expected. However, the other issue with this storm will be the relatively warm boundary layer in place with temperatures even on Wednesday morning roughly 4 to 6 degrees above freezing. As such, while I think that snow will be flying in the air on Wednesday morning, 99% of the snow that falls will likely melt on the majority of the surfaces. The snow that does accumulate will likely be most focused on the grass and especially cold surfaces. Otherwise, this storm is going to bring more of an impact via windy conditions on Wednesday morning than anything else.
Otherwise, the pattern will clearly be in a moderation trend over the next 10 days. While the ECMWF does suggest a strong Sub Tropical disturbance along the Gulf Coast by Thursday morning with some marginally cold air over the northern Mid Atlantic. Still there is very little support of the ECMWF solution on other guidance, but I will naturally keep an on the potential given the fact the MJO will still be in a supportive state for such a storm. As far as the cold air, that I am not convinced of.
-- Weather When Posted --
- Temperature: 37°F;
- Humidity: 64%;
- Heat Index: 37°F;
- Wind Chill: 32°F;
- Pressure: 29.86 in.;
Minor snow threat for mid week, but warmer conditions are on the way!
Posted by: | Comments6:45 AM
The water vapor this morning shows that one major storm is finally exiting and another is on the way over the southern Plains.
The winter storm over New England is the result of the lingering upper low from late weeks winter storm that interacted with another Sub Tropical disturbance over the Atlantic. This low pressure system continues to intensify and will produce some periods of gusty winds along the immediate coast and at times over the New York City and Philadelphia metro. Otherwise, any lingering impact, like snow showers over eastern Long Island, will quickly exit into the Atlantic with a generally pleasant day for much of the northern Mid Atlantic.
The storm over the southern Plains appears menacing, and if the 500 MB pattern observed over the past 30 days was remaining in place, would have lead to a major winter storm. However, a Pacific disturbance racing towards the Northwest coast by Tuesday morning will force the 500 MB pattern to shift to the east, forcing the trough axis that has been over the central Gulf Cost through the Tennessee Valley towards the immediate coast line. The result of this trough axis shift to the east will force the storm track of this low pressure system well to the south and east of the region.
On Tuesday night through Wednesday morning, a strengthening coastal low will move east-northeast, roughly 250 miles southeast of the New Jersey coast. The precipitation shield will be expansive far enough to the northwest to push snow showers as far west as the Delaware River Valley, the southern Hudson Valley, and southern Connecticut. However, boundary layer temperatures, especially along the coast will be marginal at best for snowfall accumulation with only minor snowfall totals expected. Mostly locations will have a trace to 2 inches of snow and possibly as much as 4 inches on the grass and other cold surfaces along the immediate New Jersey coast. As the storm exits, the snow will likely mix with some rain, and by the afternoon temperatures above freezing will allow for a rapid melt of any snow that did fall.
High pressure positioned over the Tennessee Valley from Wednesday night through Sunday will provide dry conditions, scattered clouds, and moderating temperatures in the 40′s for most locations. By Sunday there is event the potential for some locations to break into the lower 50′s, likely found over the immediate Delaware River Valley. Any snow that is on the ground by Wednesday morning, including from the previous storms, will likely be a distant muddy memory.
-- Weather When Posted --
- Temperature: 33°F;
- Humidity: 69%;
- Heat Index: 33°F;
- Wind Chill: 23°F;
- Pressure: 29.67 in.;
Evening Thoughts- (Part 1) Saturday’s snow potential
Posted by: | Comments9:11 PM
Snow through Sunday morning
Over the past several days, there has been some excitement throughout the weather world (at least in the Mid Atlantic) for a potential snow event Saturday evening through early Sunday morning.
My thoughts the past few days focused on the boundary layer temperatures through the time which the majority of the precipitation with this low pressure system will occur. Through that time period, temperatures continue to be forecasted above freezing, ranging from the mid to upper 30′s from eastern Pennsylvania through Long Island.
On Saturday afternoon, a weak area of low pressure will develop off the North Carolina coast and move east-northeast over the Gulf Stream through Saturday night and early Sunday morning. Moisture associated with this low pressure system will stream northward over the Mid Atlantic and into southern New England. The best dynamics are clearly focused along the coast and over the coastal waters, which will support more steady light to moderate precipitation.
The issue with this minor snow producer is not lifting nor moisture, but boundary layer temperatures. Temperatures from 925 MB on through 500 MB all support snow. It is the low level boundary level that is the issue here, especially along the coast. If surface temperatures were going to be 30 to 32 degrees along the coast for this event, snowfall amounts could have easily ranged from 2 to 4 inches in accumulation. However, the based on all guidance, temperatures will range from 34 to 37 degrees throughout much of the northern Mid Atlantic up until the early morning hours on Sunday. As a result, while precipitation will fall as snow, that snow will be difficult to accumulate all that much.
The snowfall map illustrates the issue above very well. I am expecting a trace to an inch (likely on cold surfaces) over much of the coastal plain where the majority of the accumulation will occur at the end of this event. Locations with higher accumulation totals feature were temperatures will fall at or below freezing on Saturday night.
Now, there is potential for a snowier outcome although this is a slim potential, it should be addressed. Dew points will have to be monitored on Saturday afternoon as dew points below freezing would lead to a strong evaporational cooling along the coast, thus allowing temperatures to fall at or below freezing. This potential is small as basically no model guidance supports this outcome. However, models have under forecasted the state of cold air advection at the boundary layer before, so this potential will have to be monitored.
-- Weather When Posted --
- Temperature: 50°F;
- Humidity: 61%;
- Heat Index: 50°F;
- Wind Chill: 46°F;
- Pressure: 29.87 in.;
Freehold
77°
New York
75°
Sussex
73°
Allentown
77°
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