Sept 10, 2013: Hot & Humid, Stormy, Then Much Cooler

Forecast Highlights:

nam-hires_namer_051_sim_reflectivityThe wild weather pattern continues across the region as just one day after an unseasonably cool air mass brought chilly temperatures into the region, a strong warm front plowed through today, bringing heavy storms to the north and a much warmer and humid air mass, with widespread temperatures in the 90s expected across the region on Wednesday. A cold front will bring widespread thunderstorms on Thursday, possibly strong for some, followed by another strong cool down for the weekend with highs struggling to reach the 70 degree mark.

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Monday, September 9 Observations:

9.9.13Another strong cool down affected the region behind Sunday’s cold front, with morning temperatures as low as 40 degrees in Sussex, NJ. Mostly sunny skies were generally observed as high temperatures peaked in the low to mid 70s across most of the area, with upper 60s in eastern Long Island and southeastern CT. The highest temperature was 75 degrees in Somerset, NJ, and the coolest high temperature was 68 degrees in multiple locations.




Tonight – Thursday: Hot, Humid, Then Stormy

As mentioned with yesterday’s forecast discussion, a strong warm air mass entered the region from the west today, with temperatures at 850 millibars rising as high as 20-22C. As a result, temperatures quickly warmed up into the mid to upper 80s from NYC and further north/west with noticeably higher humidity. This will continue tonight, with overnight lows only falling to the upper 60s to low 70s across the area, almost the equivalent of yesterday’s high temperatures. With partly sunny skies on Wednesday, temperatures will quickly warm up into the low 90s away from the coast, where highs are expected to reach the upper 80s with a southwest wind. The hottest temperatures are expected in northeast NJ, where temperatures may reach 95 degrees. With the humid conditions, heat index values are forecast to reach the mid to upper 90s across the area away from the coast, and may get near 100 degrees in northeast NJ. Scattered thunderstorms are possible in the late afternoon and evening hours, especially west of NYC, with storms capable of locally heavy rainfall.

A strong cold front will approach the region on Thursday, and with an unstable air mass in place over the region along with relatively steep mid level lapse rates and higher bulk shear, some storms may be strong to locally severe with heavy rain and strong wind gusts, especially north of NYC. Mostly cloudy skies are expected during the day; while humid conditions will continue, temperatures won’t be as hot, peaking in the low to mid 80s inland and near the coast, and the mid to upper 80s for the rest of the area. Thunderstorms are expected north and west of NYC especially in the afternoon and late afternoon hours, spreading into the rest of the area during the evening; most storms should end before midnight, although isolated storms can’t be ruled out through Friday morning. Overnight lows will range from the low 60s inland to the upper 60s in NYC and further east.


Friday – Weekend: Much Cooler, Less Humid

A sharp contrast in air masses is expected for the late week, as the unseasonably warm air mass will be followed by a strong cool air mass, bringing more fall-like temperatures across the region, at least 5-10 degrees below average. Temperatures on Friday are expected to range from the upper 60s inland to the mid 70s in NYC and further east, with overnight lows in the mid to upper 40s inland and the low to mid 50s in NYC. The trough looks to move slower than originally forecast through the region, however, as the recently re-developed tropical storm Gabrielle quickly tracks north and NNE, brushing Nova Scotia, with the upper level trough slowly moving through the region, briefly cutting off over eastern New England. This is expected to result in mostly to partly sunny skies, as opposed to sunny skies which earlier outlooks indicated, with high temperatures reaching the mid to upper 60s across the area. As the high pressure extends towards the area overnight, clearing skies are expected with lows in the low 40s inland, mid to upper 40s in the north/west suburbs, southern CT and interior Long Island, and the low 50s near NYC and the coast. Mostly sunny skies will continue on Sunday with highs peaking in the low 70s across the area.


Longer Range: Brief Warm Up, Then Chilly Again

Another trough will drop into the region on Monday and Tuesday, bringing another quick yet strong air mass through the region with chilly temperatures. The timing of the front is still somewhat uncertain, but at this time appears to be during the day on Monday, which would bring high temperatures into the mid 70s range, followed by another chilly night on Monday night with lows similar to those of Saturday night and slightly cooler temperatures on Tuesday. As the high pressure slides east of the region, another warm up is likely towards mid-late next week.

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