May 30, 2011: Severe Weather On Wednesday

Behind the MCS that affected the area this morning, cloud cover cleared across the area, resulting in temperatures quickly rising into the upper 80s to lower 90s west of NYC, mid to upper 80s in NYC, and the upper 70s to mid 80s in Long Island and southern Connecticut, making today the warmest day of the year so far in most of the area. A back door cold front will move through tonight, lowering tomorrow’s temperatures, but Wednesday will slightly warm up again ahead of a cold front which may be capable of producing this year’s first significant severe weather event in the area.

Tomorrow’s Outlook: Colder

When first discussing the heat wave potential for early this week, the expectation was there for a large ridge to move into the region and stick around through Wednesday, producing widespread 90+ degree readings across the region. For most of the region, this is true, especially in the centrla/southern Mid Atlantic where mid to upper 90s were reported today and are expected again tomorrow, but changes in the set up resulted in the warmth being pulled further west, not over the area as originally expected.

The original expectation was for a low pressure just north of the Dakotas moving east/ENE, with a widespread ridge covering the region. Since then, however, the low pressure has trended further west, stronger, and more negatively tilted, pulling in more warmth to the west of the region while a trough near New England pushes more south. This brings a back door cold front through the area, pushing the warmest temperatures to the south and west of the area while bringing an east/ESE wind to the central/eastern parts of the area. As a result, high temperatures tomorrow will be colder, reaching the mid to upper 80s in northern New Jersey, upper 70s to mid 80s in the immediate NYC area, and the lower to upper 70s for Long Island and southern Connecticut with a few lower 80s possible further west towards NYC. Mostly sunny skies are expected with mostly dry conditions, though an isolated shower or thunderstorm cannot be ruled out.

Wednesday: Severe Storms Possible

The back door cold front will move through the area as a warm front on Tuesday night, bringing a southwest wind for Wednesday along with warmer temperatures once again. Even though the ridge will weaken as the cold front approaches, with enough sunshine in the morning and early afternoon hours, NYC and further west will once again reach the upper 80s with some lower 90s possible as well. Long Island and southern Connecticut will slightly warm up as well, with temperatures closer to today’s high temperatures.

The models are showing parameters supportive of severe weather, with CAPE up to 3000 and lift index up to -10. Additionally, lapse rates of around 7 are expected. The lack of shear in the area is the main issue, however, with only 30-40 knots of bulk shear expected. With the parameters in place, severe thunderstorms are still possible in the afternoon and evening hours, but the highest risk of severe weather is likely to stay to the north of the area. Stay tuned for more information on Wednesday’s severe weather risk.

Late Week And Weekend:

Behind the cold front, a colder air mass will approach, but the coldest temperatures won’t arrive immediately behind the front. Thursday will bring slightly colder temperatures, reaching the mid 70s to mid 80s across the area. By Thursday night, clearing skies will take place with a high pressure nearby, which combined with 850 mb temperatures below 10c, may bring low temperatures into the upper 40s for the interior north/westernmost parts of the area on Thursday night.
Friday will bring colder temperatures, in the lower to upper 70s across most of the area with a few lower 80s in the immediate NYC area. Saturday and Sunday will slightly warm up, with mid 80s possible again, before another cool down is possible by early next week. Stay tuned for more information on the longer range.

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