Sept 21, 2013: Storms Tonight, Chilly Start To Week

Forecast Highlights:

1958A strong cold front is currently moving through the region, producing moderate to heavy rain and thunderstorms over Pennsylvania, which will spread into the area late this evening into tonight. A much cooler air mass will follow behind this cold front, with temperatures back into the 60s for highs and the 30s/40s for lows, with frost possible for interior areas. A gradual warm up will take place throughout next week, with temperatures back into the mid-upper 70s by next weekend.


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Friday, September 20 Observations:

9.20.13Friday was the warmest day of the week following a gradual warming trend starting on Tuesday. Areas of fog were observed again inland, with otherwise mostly sunny skies and highs rising into the mid to upper 70s across the area. The highest temperature was 79 degrees in multiple locations, and the coolest high temperature was 73 degrees in Montauk, NY and New London, CT.





Weekend Outlook: Stormy Tonight; Cooler, Windy Sunday

1958The latest regional radar image from the National Weather Service was posted to the left, showing a line of rain and thunderstorms over central Pennsylvania and New York states, slowly moving east. The line of rain and storms is associated with a strong, slow moving cold front, with the line extending south to the Gulf of Mexico, providing a surge of tropical moisture leading to the heavy rainfall, and north into eastern Canada. While locations north and west of NYC have seen partly to mostly cloudy skies this afternoon, a weak shortwave just off the coast resulted in an area of locally heavy showers in Nassau county in Long Island and Fairfield county in CT, where up to 1/3 inch of rain was observed in the last 2 hours. A breezy SSE wind at 10-15 mph will continue through the afternoon and evening, up to 20 mph in coastal NYC/Long Island with gusts up to 25-30 mph possible.

The line will continue to slowly advance to the east, with rain expected to begin in western NJ/Orange County in NY towards 7-8 PM, the immediate NYC area towards 9-10 PM, and Long Island/south CT between 10-11 PM further west and 12-1 AM further east. A narrow line of heavy rain, thunderstorms and strong wind gusts is expected along the front end of the line, with otherwise moderate rain showers continuing for another 3-5 hours before gradually ending. Rain totals of at least 1/2 to 1 inch are expected across the area. A much cooler air mass will enter the region behind the cold front, with partly sunny skies on Sunday, a breezy NW wind at 10-15 mph gusting to 20-25 mph, and highs peaking in the mid to upper 60s towards western NJ/SE NY, upper 60s to low 70s in the north/west suburbs of NYC, and the low to mid 70s from NYC and further east.


Monday – Tuesday: Chilly Temperatures Return

Next week will somewhat resemble this recent week with a chilly start and a mild ending. A strong trough will be present over the region on Monday and Tuesday, with temperatures falling back to below average again. Clearing skies are expected on Sunday night, but with a breezy north wind at 6-12 mph preventing interior locations from significantly cooling down relative to the rest of the area, with lows in the low-mid 40s inland, mid to upper 40s in the north/west suburbs and southern CT, upper 40s to low 50s in Long Island, and low 50s in NYC. Sunny skies are expected on Monday with highs only peaking in the mid 60s in the immediate NYC area and low-mid 60s further inland.

With clear skies and light winds overnight, cold temperatures are expected on Monday night, falling into the mid 30s inland with areas of frost possible, upper 30s to low 40s in the higher elevations of CT and the Long Island Pine Barrens, low-mid 40s in the north/west suburbs of CT and the rest of southern CT, mid-upper 40s in Long Island, and the upper 40s to low 50s in NYC. The latest 7-day forecast has a forecast low of 49 degrees for Central Park, subject to minor revisions, which would make it the earliest September sub-50 degree reading in NYC since 2000. Sunny skies are expected again on Tuesday with highs in the upper 60s-low 70s, and overnight lows falling again into the upper 30s inland, low-mid 50s in NYC, and the 40s elsewhere.


Wednesday – Next Weekend: Gradually Warming Up

The cold front moving through the area tonight will become a cutoff low pressure over Atlantic Canada, stalling on Monday and Tuesday before beginning to slowly exit on Wednesday. This cutoff low has been gradually trending west with recent model runs, with the 12z ECM the most aggressive in keeping this further west, while the GFS and CMC keep it more to the east. Given the ECM’s handling of the synoptic pattern especially beyond the Day 6 range which is likely too exaggerated with an overly amplified ridge in western North America, I am siding closer to the GFS’ handling of the pattern but with a further west cutoff low. This scenario keeps the warmest temperatures to the west of the region, with temperatures in the area remaining near average with a northeast flow, gradually turning southwest towards the weekend as the high pressure builds overhead and later southeast.

Partly sunny skies are expected on Wednesday highs reaching the low to mid 70s as a weak shortwave likely moves through the region but without producing any precipitation. A strong trough will dig into the western US as a low pressure develops in the Midwest, with ridging amplifying over the central US in response, leading to a slow but gradual warm up in temperatures for the late week, with highs warming back up into the mid 70s for Thursday and Friday, possibly reaching the upper 70s by next weekend. There is some uncertainty regarding the timing and strength of the next cold front to approach the area, although the next potential for rain is towards early next week. Stay tuned for more information on the longer range outlook.

One thought on “Sept 21, 2013: Storms Tonight, Chilly Start To Week

  1. Anonymous Reply

    Sir, I have a question. Do you know if Bay Ridge, Brooklyn cools down more overnight than Manhattan’s Central Park?

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