July 24, 2012: Hot, Stormy Ending To Week

Forecast Highlights:


– Very brief cool down for Wednesday only; highs in low-mid 80s
– Heat returns briefly for Thu/Fri; highs on Thu to surge near/above 95
– Severe storms possible on Thursday; more storms Fri-Sat


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Sunday, July 22 Observations:

A slightly warmer air mass moved into the region on Sunday, with temperatures slightly warming up across the region. Highs peaked in the lower to mid 80s from NYC and further north/west, and in the upper 70s to lower 80s in Long Island and southern Connecticut. Although these temperatures are still cooler than average, the negative departures were not as large as they were in the previous days following the chilly rain storm on July 20.

Monday, July 23 Observations:

As a warm front moved through the region, several rounds of thunderstorms were observed during the day focusing north/west of NYC. Morning storms were observed in SE NY extending into SW Connecticut, with amounts locally over 1 inch. After more sunshine in the second part of the day, two severe storms focused over NW NJ, both of them weakening once getting south/east of NW NJ, with only a weakening area of moderate rain moving through the immediate NYC area. Temperatures peaked in the mid 80s to lower 90s from NYC and further north/west, with lower 80s in most of Long Island/S CT except for eastern areas in the upper 70s.

Tonight – Wednesday Outlook:


The outlook originally called for dry conditions today; although the day has been dry so far, scattered storm activity is persisting as it’s making its way into the area. Scattered storms, staying below severe levels and quickly moving through, are expected in the evening in parts of the area, especially over southern Connecticut but with isolated storms further west as well.

A cooler air mass will briefly move into the region on Wednesday resulting in slightly cooler temperatures, with highs peaking in the lower to mid 80s across the area along with mainly sunny skies.



Thursday – Saturday: Hot, Humid and Stormy


The forecast becomes much more interesting by Thursday and next weekend as a low pressure and a slow moving cold front affect the region. There is decent agreement with the models for a MCS to move through the region early on Thursday morning; the exact location/timing remain uncertain but although the better potential appears to stay north of the area, morning storms, possibly strong or even low-end severe, are still possible, if not likely for early Thursday morning in the NYC area. Behind the storms, a much warmer air mass will push into the area with 850mb temperatures above 20C, with clearing in the cloud cover allowing for temperatures to warm up into the lower to mid 90s from NYC and further north/west, with slightly cooler temperatures in Long Island/S CT due to more clouds and a delayed impact from the morning storms compared to the western half of the area. Humid conditions are also expected with dew points in the lower 70s, pushing heat index values near or possibly above 100 degrees. Assuming no major changes in the forecast, I will likely issue a heat alert for Thursday with the next update.

By Thursday evening, widespread thunderstorms are expected to form ahead of the cold front which will slowly make its way into the region. The set up is favorable for severe weather with decent instability and supportive shear. The best risk at this time appears to stay to the north and west of the area, but the NYC area is close to the southern end of the severe weather potential for Thursday evening, and the potential will be monitored. Stay tuned for more information on Thursday’s heat and severe storm potential.

The cold front will slowly make its way through the region, with cooler temperatures for Friday reaching the mid 80s to lower 90s, possibly a bit warmer in the immediate NYC area. More clouds are expected along with scattered storms, some perhaps strong. Showers and storms will stick around through Saturday with highs in the mid 80s for most of the area, slightly cooler in some areas.

Sunday – Beyond: Sunday and Monday are expected to be mostly dry with highs generally around the mid 80s, with a few showers possible early on Sunday. The model outcomes diverge starting after Monday, with some keeping average conditions, the GFS drops a cold front through, and the ECM shows heat slowly building in. There is too much uncertainty to make any high confidence call for the longer range, although at least the next 7 days with the exception of Thursday do not appear to end up far from the average on either negative or positive side.

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