Sept 13, 2013: Cooler Temps Through Next Weds

Forecast Highlights:

northeastBehind yesterday’s cold front, a cooler air mass entering the region will bring much more fall-like conditions through the middle of next week, with highs generally in the upper 60s to mid 70s and lows in the 40s away from NYC and the coast. A warm up will gradually intensify towards the second half of next week, when highs may briefly return into the low 80s with additional storminess possible.




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Thursday, September 12 Observations:

9.12.13With the unseasonable warm and humid air mass still in place from Wednesday, overnight lows failed to fall below the low to mid 70s for most. Temperatures quickly warmed back into the low to mid 80s, peaking in the upper 80s in northeast NJ, but scattered strong thunderstorms moved through northeast NJ and Rockland county around 1-3 PM, producing heavy rainfall, locally up to 1-1.5 inches, and gusty winds. Sunshine returned behind these storms as a line of widespread strong to locally severe thunderstorms slowly approached east ahead of a cold front, with scattered storms redeveloping around 5-6 PM northwest of NYC. As the squall line entered northern NJ, widespread strong thunderstorm development took place between 6-7 PM, with a storm stalling over East Passaic, Bergen and S Rockland counties for nearly an hour, where flash flooding occurred with as much as 2-3 inches of rain, frequent lightning, and wind gusts up to 40-50 mph. The storms gradually spread into southern CT, where heavy rainfall over 1 inch was observed as well, entering NYC around 8 PM with a similar round of heavy rainfall, strong wind gusts and frequent lightning. The storms generally weakened as they progressed east of NYC around 9-10 PM, but a strong thunderstorm managed to stay intact over coastal CT and the northern coast of Long Island, where heavy rain, frequent lightning and strong wind gusts were observed as well. Storms mostly moved out of the area by 11 PM with additional scattered showers later overnight.

Selected rainfall totals include 1.66″ in Central Park, 1.93″ in Caldwell, NJ (Essex), and 1.36″ in Bridgeport, CT, with 1.13″ falling in 1 hour alone. Temperature observations will be added shortly.



Tonight – Tuesday: Cooler Than Average Temperatures

Forecast Pattern: As yesterday’s cold front pushed through the region, a much cooler air mass returned into the region today with partly cloudy skies and scattered thunderstorms, one which produced heavy rainfall in the Bronx and south Westchester county. The current pattern setup consists of a trough over the region with a briefly closed upper level low, slowly drifting to the east as a low pressure develops near eastern Maine and Nova Scotia associated with the remnants of tropical storm Gabrielle merging with yesterday’s cold front. This low pressure will consolidate and lift north into Canada late on Saturday, which will pull the trough north into Canada while allowing the surface high pressure, currently near the Midwest, to build into the region. This will result in chilly temperatures for Saturday and Saturday night, but with the trough lifting out and ridging briefly building into the region ahead of another incoming Canadian trough, slightly warmer temperatures will return for Sunday and Monday.

The next trough will enter the region on Monday into Tuesday; there is some uncertainty regarding its setup, with recent model runs trending towards a more detached trough that either splits from the main flow east of the region, or stays attached but flatter than the scenario supported by earlier model runs. The main impact this will have is on overnight lows on Monday night, as a slower trough that splits would support a further west high pressure, a higher chance of rain on Monday, and overnight lows a few degrees warmer than currently forecast across the region. At this time, I introduced a slight risk of rain for interior areas in the 7-day forecast on Monday, but otherwise left the forecast temperatures unchanged; should the aforementioned scenario become more likely, temperatures may be slightly raised for Monday night.

Forecast For NYC Area: Clearing skies are expected tonight with a continued breezy NW wind at 6-14 mph and overnight lows falling into the upper 40s inland, low 50s in the north/west suburbs of NYC, low to mid 50s in Long Island, and the mid 50s in NYC and the coast. Mostly sunny skies are expected on Saturday with highs in the mid to upper 60s inland and the upper 60s to low 70s for the rest of the area, with overnight lows falling into the low 40s inland, mid 40s to near 50 degrees in the north/west suburbs of NYC and southern CT, upper 40s to low 50s in Long Island, and low to mid 50s in NYC. A brief warm up will occur on Sunday and Monday with highs rising into the low to mid 70s across the area, with mostly sunny skies on Sunday and partly cloudy skies on Monday, with scattered showers possible especially inland. Monday and Tuesday nights are expected to be mostly clear with lows in the upper 30s to low 40s inland, mid to upper 40s in the north/west suburbs of NYC and southern CT, upper 40s in Long Island, and low 50s in NYC, along with sunny skies on Tuesday and highs in the mid to upper 60s across the area.


Late Next Week: Warming Up

Some changes in the synoptic scale pattern will take place later in the week, as troughing consolidates near Greenland and east central Canada while troughing shifts east from the northeast Pacific into the western US, resulting in rising heights aloft in the eastern half of the US. Meanwhile, a low pressure will develop in the northern US, which is expected to prevent another trough from entering the region in a setup similar to that of Tuesday, resulting in a warmer air mass returning into the region. No significant warmth is anticipated at this time, with temperatures likely climbing into the upper 70s to low 80s by the late week, with the next risk of storms on Friday or Saturday as the next cold front likely affects the region with another cool down possible behind it. More information on the longer range outlook will be posted with the next long range pattern discussion, to be posted on Saturday evening.

4 thoughts on “Sept 13, 2013: Cooler Temps Through Next Weds

    • NYC Area Weather Post authorReply

      Despite the cloud cover, showers are not expected in the area today. The next chance of rain in Long Island is on Monday morning with scattered showers.

  1. Anonymous Reply

    What is the weather expected to be on Long Island on Monday. Is it expected to be all cloudy with rain or partly sunny with scattered showers?

    • NYC Area Weather Post authorReply

      The morning hours are expected to be cloudy with scattered light rain, with mostly to possibly partly cloudy skies after noon but with a continued risk of isolated showers.

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