Sept 8, 2011: Heavy Rain Finally Ends

Forecasting the remnants of Tropical Storm Lee has been a challenge over the last few days, as the model guidance failed several times to show heavy rain that affected the area. Most models showed rain weakening on Tuesday when affecting the area, which failed to happen, and instead, a total of 1-3 inches of rain fell that day from NYC and further west. The majority of the models once again failed last night, as heavy rain and thunderstorms formed over New Jersey north of the warm front and moved into the area, bringing an additional 1 to 2.5 inches of rain from NYC and further west. The day before heavy rain started to affect the area, most of the models showed at least 1-2 inches for NYC with 2-4 inches west of NYC; instead, most areas from NYC and further west ended up with 5 to as much as 8 inches of rain, bringing flooding issues once again to places hit hard by Irene and pushing the monthly rain total above the average for September.

With Lee’s remnants having weakened over the last day, no longer producing widespread heavy rain in the region, no additional widespread heavy rain is expected to affect the area from Lee’s remnants. Regardless, scattered showers and thunderstorms will continue to affect the region through Saturday or potentially Sunday, bringing an additional 1/4 to 1/2 inch of rain across most of the area with potentially higher amounts in isolated areas. Drier conditions will return by Sunday as a high pressure briefly moves into the region, but the dry conditions will be short lasting, as a strong cold front will bring more rain around the middle of next week, which may be followed by unseasonably chilly temperatures to end the week.

Friday And Weekend: Rain Ending, Warming Up

Friday will bring mostly cloudy skies to the area with scattered showers and thunderstorms. These storms are not expected to affect all of the area, but may be capable of producing locally heavy rain. Temperatures will be warmer than the last few days, reaching the lower 80s inland, lower to mid 80s in the immediate NYC area, and the upper 70s to lower 80s in Long Island and southern Connecticut with a NW/WNW wind expected.

Drier conditions are expected this weekend, but scattered thunderstorms are still possible, especially on Saturday. Sunday will bring partly sunny skies, though an isolated shower or thunderstorm cannot be ruled out in the afternoon. Temperatures will be slightly cooler on Saturday, in the mid 70s to lower 80s across the area, but on Sunday, due to a SE wind, colder temperatures are expected, reaching the mid to upper 70s from NYC and further west and the lower to mid 70s east of NYC.

Next Week’s Outlook

Monday will start out with temperatures similar to those of Saturday but without the rain. Tuesday will bring partly sunny skies along with warmer temperatures, reaching the lower to mid 80s in the immediate NYC area. A strong cold front will then approach the region on Tuesday night into Wednesday associated with a strong trough moving into the north central US from Canada, bringing a risk of showers and thunderstorms into the area, which may potentially be strong or severe.

There is some uncertainty with the trough behind the cold front, as some models show the front stalling offshore with the trough weakening before reaching the area, while other models bring the strong trough into the region, resulting in an unseasonably strong cold air mass, with 850 mb temperatures as low as zero degrees Celsius close to NYC, which typically starts to happen more frequently around October. Such a scenario would bring low temperatures into the 30s in the interior parts of the NYC area. At this time, I am expecting the trough to reach the region, bringing below average temperatures into the area, but temperatures should not be as cold as some models are showing, especially the GFS, which only shows high temperatures in the upper 50s to lower 60s across the area. Stay tuned for more information on Wednesday’s thunderstorms and the potential cool spell for the end of next week.

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