Archive for atmosphere
Showers and thunderstorms through this afternoon
Posted by: | Comments07/29/10 9:20 AM
A cold front is currently moving through New York City and Philadelphia metropolitan area this morning. As the cold front slides to the southeast through the afternoon, showers and thunderstorms will remain a threat through the day.
The visible satellite tells us a lot about what to expect with this cold front. First, the fact that there is so much cloud cover ahead of this cold front limits the potential for the atmosphere to become unstable. In short, the temperature trends as the surface are not rising very fast and the air at the surface is as warm as temperatures at 850 MB and 500 MB. The lack of warming at the surface also leads to a very weak lapse rate throughout the atmosphere, which means that thunderstorms can not attain optimal strength. All this leads to a higher threat for heavy rainfall than any type of organized severe thunderstorm. Still, an isolated thunderstorm may exhibit a wind gust over 50 mph this afternoon, especially over and southeast of the Philadelphia metropolitan area. This is not expected to be a significant threat.
The other detail we can learn this morning from the visible satellite picture is that the clearing behind this cold front is going to develop rather quickly. Once the rain drops to the south of a location and the rain ends, the clouds will break up rapidly as dry air works south from the eastern Great Lakes and northern New York. So by this evening, skies will be generally clear with a nice northwesterly breeze, overall not a bad evening at all! This rapid clearing also means that temperatures will be able to rise into the 80′s and 90′s even behind the cold front as the July sun and some down sloping influences via the northwesterly wind enhances high temperatures this afternoon.
So overall, this cold front is not a major impact on the Northern Mid Atlantic. A few showers and thunderstorms this morning for the New York City metropolitan area, extending into the afternoon hours for the Philadelphia metropolitan area and points southeast, followed by clearing skies. High pressure will take hold tonight through Saturday with tranquil weather conditions, low humidity, and temperatures closer to normal in the 80′s.
The next disturbance to impact the Northern Mid Atlantic will be on Sunday with scattered showers. By this point, the high pressure system will be anchored over New England, which will lead to an easterly wind at the surface. The easterly wind will introduce a more stable air mass over the region, which will mean showers will be the primary threat with little chance for any strong or severe thunderstorms. The showers will be scattered on Sunday afternoon with temperatures remaining around 80 degrees for a high. The disturbance exits on Monday morning with slow clearing skies.
The break in the hot and humid pattern will come to an end on Monday as high pressure at the surface and upper levels becomes established off the Mid Atlantic coast and a new southwesterly flow begins to form. Temperatures will warm back into the upper 80′s to lower 90′s for highs, mid 60′s to lower 70′s for lows through next week with increasing humidity each day. There will be a constant threat for thunderstorms in the afternoon via mid level disturbances as well. So we head back into the sauna after a brief brake this week.
For details on your location, visit the NY NJ PA Weather Local Seven Day Forecast!
-- Weather When Posted --
- Temperature: 75°F;
- Humidity: 83%;
- Heat Index: 75°F;
- Wind Chill: 75°F;
- Pressure: 29.9 in.;
Isolated Thunderstorms developing
Posted by: | Comments1:05 PM 07/11/10
A mid level disturbance at 850 MB is enhancing lifting from the Hudson Valley down through eastern New Jersey this afternoon. This lifting is producing isolated yet strong thunderstorms over the region. These thunderstorms are producing very heavy downpours with rainfall rates of up to a half an inch per hour. Given the high low level moisture content in the atmosphere, there is potential for these thunderstorms to produce rainfall rates of an inch per hour leading to localized flash flooding.
I will continue to monitor to rapidly changing situation and update these developments.
-- Weather When Posted --
- Temperature: 82°F;
- Humidity: 58%;
- Heat Index: 84°F;
- Wind Chill: 82°F;
- Pressure: 29.89 in.;
Premium Discussion Overview for Thursday July 8, 2010
Posted by: | CommentsThe 100′s may be gone, but the heat and humidity remains. Today I discussed a variety of topics like the impacts of the upper low off the Mid Atlantic coast, the developments of Tropical Depression 2, and when another wave of upper 90′s and lower 100′s can be expected. Are you a Premium Member? Get the details on Premium Membership here!
-- Weather When Posted --
- Temperature: 78°F;
- Humidity: 65%;
- Heat Index: 80°F;
- Wind Chill: 78°F;
- Pressure: 30.08 in.;
Another hot and humid day, but some slight relief on the way
Posted by: | Comments07/07/10 7:35 AM
Yesterday, another day of record highs were recorded throughout the northern Mid Atlantic. Conditions today won’t be much better, however there is some good news going forward as high temperatures will be closer to 90 rather than 100 through the rest of this week.
A weakness in the atmosphere or a weak area of low pressure will hover around the New Jersey coast today, which will lead to a slightly better chance for thunderstorms this afternoon. Otherwise, another hot and humid day is expected with temperatures, already in the mid 80′s in some locations, rising rapidly into the mid 90′s to lower 100′s once again. Dew points will continue to increase as more low and mid level moisture builds into the region, leading to a heat index well into the 100′s once again. Use caution in these dangerous conditions and be sure to drink plenty of water.
As for the thunderstorms, the weak area of low pressure along the coast will enhance the sea breeze front, which will create lifting along the New Jersey coast and New York city metropolitan area. These thunderstorms are likely to move very slowly if they develop, which would lead to very heavy rainfall. Flash flooding, occasional lightning, and wind gusts over 45 mph can be expected in these thunderstorms.
Through the rest of the week into this weekend, a slight change will take place over the northern Mid Atlantic. Over the past few days, 850 MB have ranged from 20 to 24 degrees Celsius which supports the high temperatures that have been observed. However, those hot 850 MB temperatures will reposition further to the south, which means that 850 MB temperatures will fall off slightly into the 16 to 20 degree Celsius range for tomorrow through Sunday, which will put high temperatures ranging from the upper 80′s to lower 90′s. However, dew points will not be decreasing at all. In fact, with temperatures in the lower 90′s and dew points remaining in the 60′s to lower 70′s, humidity in the atmosphere will actually increase. So those hoping from a break from the heat and humidity will be disappointed. On the some what positive side, the decrease in temperatures at 850 MB will allow for a higher potential for isolated to scattered thunderstorms each afternoon, which could provide a nice yet rainy break from the heat and humidity.
For more details on your location, visit the NY NJ PA Weather Local Seven Day Forecast!
-- Weather When Posted --
- Temperature: 80°F;
- Humidity: 61%;
- Heat Index: 82°F;
- Wind Chill: 80°F;
- Pressure: 30.03 in.;
Live Coverage of Severe Thunderstorms for Friday May 14, 2010
Posted by: | CommentsThis afternoon the atmosphere is rapidly become unstable as skies have cleared and an aggressive secondary warm front races northeast towards the northern Mid Atlantic. A cold front entering western Pennsylvania at 1 PM is expected to move towards the region later this afternoon and this evening with strong to severe thunderstorms.
I will be doing live coverage of this potential severe event through this afternoon and evening. You can also follow along on twitter, but all illustrations can be seen here!
View Severe Weather Potential for 5/14 in a larger map
-- Weather When Posted --
- Temperature: 73°F;
- Humidity: 64%;
- Heat Index: 76°F;
- Wind Chill: 73°F;
- Pressure: 30.08 in.;
Risk of showers still a threat
Posted by: | Comments05/04/10 7:30 AM
I think the best way to describe this morning’s conditions is refreshing. I decided to walk outside while getting the paper and you can just take in the seasonably cool, comfortable air.
However, there is a pesky disturbance over the Ohio Valley that will quickly move towards the Philadelphia and New York City metropolitan area this afternoon. The relatively low humidity in place with dew points falling into the 50′s suggest that little if any precipitation will be expected from this disturbance. However, a few widely scattered to isolated showers will be possible this afternoon as the disturbance moves through. Otherwise, scattered clouds and temperatures in the 70′s can be expected throughout the region.
High pressure will remain in control through Wednesday with equally pleasant weather conditions including low humidity and seasonably warm temperatures. Highs will generally range in the 70′s to lower 80′s for highs.
Another disturbance will clip the northern Mid Atlantic on Thursday, but again the atmosphere will be rather dry ahead of this disturbance so I don’t expect much in the way of wide spread precipitation. However, I still can’t rule out an isolated afternoon shower or thunderstorms. Tranquil conditions return once again for Friday with temperatures in the 70′s and 80′s for highs.
A strong cold front is expected for Saturday. Now, unlike the previous cold front from yesterday, the air mass ahead of this cold front is not expected to be hot nor humid. Still, the strong upper level support for the cold front leads to the threat of showers and a few thunderstorms on Saturday morning and early afternoon. Current guidance projects the strongest lifting over the northern Hudson Valley and New England, so there is potential for the region to only have a glancing blow. Still, temperatures will fall quickly behind this cold front with highs both Saturday afternoon and Sunday struggling in the 60′s. Not the best weather conditions for going down to the shore.
High pressure returns by Monday with moderating temperatures and dry conditions.
For more details, check out the seven day forecast!
-- Weather When Posted --
- Temperature: 62°F;
- Humidity: 77%;
- Heat Index: 62°F;
- Wind Chill: 62°F;
- Pressure: 29.84 in.;
Convective showers driving east
Posted by: | Comments04/22/10 2:10 PM
An upper disturbance approaching from the Great Lakes will produce a few scattered showers over the Philadelphia and New York City metropolitan area this afternoon and early evening.
These showers are convective in nature and are a direct influence of the boundary layer warming significantly faster than the upper levels. We can see this in a well illustrated manor when we examine the low level lapse rate where there is as much as a 6 to 9.5 degree Celsius difference from the surface to 700 MB.
As the afternoon continues, there is a minor threat of an isolated thunderstorm associated with this line of showers. However, I should note that once the sun starts to set and temperatures cool, the atmosphere will stabilize and these showers will quickly weaken and dissipate.
By this evening, all that should remain will be a few isolated showers and scattered clouds followed by a dry and tranquil couple of days heading into the weekend.
The afternoon updates are on the way!!
-- Weather When Posted --
- Temperature: 66°F;
- Humidity: 48%;
- Heat Index: 66°F;
- Wind Chill: 66°F;
- Pressure: 29.71 in.;
Stormy overnight, but improving through the rest of the weekend
Posted by: | Comments04/16/10 5:23 PM
As expected, a wide variety of high temperatures was observed from eastern Pennsylvania were highs were in the mid 70′s to lower 80′s to Long Island and Connecticut rose into the lower to mid 50′s. The temperature gradient over the northern Mid Atlantic reached a 20 degree magnitude throughout the northern Mid Atlantic.
Tonight, a cold front is driving towards the northern Mid Atlantic with a line of showers and thunderstorms. The atmosphere is the most unstable over eastern Pennsylvania were severe thunderstorms are most likely. The thunderstorms will be capable of wind gusts over 40 mph, heavy downpours, small hail, and frequent lightning. The rest of the region can expect showers and strong thunderstorms through tonight, however because the air mass east of the Delaware River is more stable, the thunderstorms will not be as strong tonight. Thunderstorms will be capable of heavy downpours, frequent lightning, and wind gusts up to 40 mph.
The cold front will exit by early Saturday morning with linger showers continuing through the day. However, the showers will be widely scattered with most locations remaining dry. Scattered to broken cloud cover can be expected through the weekend with temperatures averaging near to slightly below normal. Highs will generally remain in the 50′s and 60′s.
The northwesterly pattern will return through next week with high pressure generally in control with tranquil conditions and moderating temperatures. However, a few isolated disturbances will bring a threat of isolated showers each evening. This is not expected to be a significant issue however. Overall, next week will feature tranquil conditions with temperatures moderating into the 70′s and possibly 80′s for highs.
A detailed seven day forecast can be found here.
-- Weather When Posted --
- Temperature: 48°F;
- Humidity: 70%;
- Heat Index: 48°F;
- Wind Chill: 42°F;
- Pressure: 29.82 in.;
Tranquil conditions continue, but active weather pattern expected to return
Posted by: | Comments7:45 AM
High pressure is slowly transitioning towards the Ohio Valley today, which will lead to a slight shift in the winds towards the northwest. Other than the wind shift, conditions will remain rather quiet throughout the northern Mid Atlantic, as least for now.
The water vapor satellite picture this morning shows an interesting separation between the Sub Tropical and Polar jet streams. Note that the low pressure over the Southeast will remain well south and east of the northern Mid Atlantic over the next 24 hours due to the Polar jet stream suppressing the low pressure system. An area of sinking air between the two jet streams is centered right over the Philadelphia metropolitan area through Long Island, which will lead to clear skies due to sinking air over the region. This sinking air will also support warm temperatures with many locations breaking well into the 60′s, possibly upper 60′s by this afternoon. Yes, it will be very difficult to concentrate this afternoon at work or school!
Now, these conditions are expected to continue through this weekend with clear skies and rather warm temperatures. In fact, I would not rule out the potential for highs hitting 70 degrees over the Delaware River Valley and some urban locations due to the strong sun shine and sinking motion of the atmosphere. However, the tranquil conditions will come to an end by the start of next week.
The upper level pattern will shift once again as the Sub Tropical jet stream begins to move north and west. This shift in the Sub Tropical jet stream will lead to a weak ridge over the Southeast coast and force a storm track through the Mid Atlantic. For example, the storm that is south and east of the region today would have been forced into the northern Mid Atlantic if this pattern shift had happened already. The first low pressure system is expected on late Sunday night through Monday in the form of a slow moving cold front. As the low pressure system moves through the Ohio Valley, the Polar jet stream will phase with the Sub Tropical disturbance to add a Polar air mass into the mix. The result will be periods of heavy rain with embedded thunderstorms through Monday evening.
The low pressure system will exit by Tuesday morning with a few lingering showers followed by clearing conditions. High pressure will take hold on Tuesday afternoon through Thursday with dry conditions, scattered to few clouds, and temperatures rebounding into the 50′s and 60′s. However, another area of low pressure with a similar storm track is expected by Friday and Saturday with periods of rain and potentially strong to severe thunderstorms.
Overall, the temperatures through the next seven days will remain relatively above normal, especially for this weekend. The new pattern that evolves for next week will bring a risk of severe weather returning to the region along with the potential for additional flash flooding.
-- Weather When Posted --
- Temperature: 39°F;
- Humidity: 64%;
- Heat Index: 39°F;
- Wind Chill: 35°F;
- Pressure: 29.88 in.;
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.;
Freehold
57°
Albany
59°
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