Periods of heavy rain, storms possible through Friday

The NAM forecast model showing heavy rain with embedded thunderstorms throughout the NYC Area on Friday morning, in response to a warm front passing the area.  Courtesy of Penn State University.

A strong upper level low over the Central United States, which produced severe weather from Missouri to Alabama last night, will slowly shift eastward during the day on Thursday and will near the area on Friday. As it does so, increasing moisture owing to a south/southeast flow will bring more humidity and a setup conducive to heavy rain and thunderstorms to the NYC Area. The threat of rain will begin Thursday night, after clouds stream towards the area during the late afternoon hours on Thursday. A strengthening low level jet (strong winds and advection of moisture in the low levels of the atmosphere) on Friday morning will aid in the development of heavy rain and embedded storms, and more storms are possible later Friday afternoon ahead of a cold front.

The most likely timing for the heaviest rain and potential storms is between 6 and 9 am on Friday, with the passage of a warm front and the strengthening low level jet. In addition to the heavy rain and potential storms, the aforementioned low level jet could bring strong southeast winds off the water which will be especially prevalent over the NJ Shore and Long Island. The second round of storms, is expected to be less widespread, with scattered activity Friday afternoon ahead of a cold front after temperatures rise into the 70’s.

Keep reading for potential severe weather impacts and details on the potential hazards…

Storm Prediction Center Day 2 Outlook, forecasting a 5% risk of severe weather over Eastern NJ, NY, and CT.

Severe weather is not currently anticipated throughout the area, but remains a possibility especially given the strength of the upper level system and the shear in both the mid and low levels of the atmosphere. The Storm Prediction Center has placed our area in a 5% risk for severe storms, essentially a tier below “Slight Risk” level of severe thunderstorm potential. In their outlook, pictured left, they mention

“THE PRIMARY THREAT WOULD BE FOR STRONG WIND GUSTS CONSIDERING THE MODELS SHOW 40 KT OF FLOW JUST ABOVE THE SFC. IF MORE INSTABILITY CAN DEVELOP THAN IS CURRENTLY FORECAST…THEN AN UPGRADE TO SLIGHT RISK OVER PARTS OF SE NEW YORK AND SRN NEW ENGLAND WILL CERTAINLY BE POSSIBLE IN LATER OUTLOOKS.”

The Storm Prediction Center issues two “Day 2” outlooks per day, so an update is expected this afternoon. Stay tuned for any information on a potential update to a “Slight risk” for severe thunderstorms in certain parts of the forecast area. In addition to the thunderstorm thread, rainfall totals could near 1″ in spots that receive heavier thunderstorms or prolonged periods of heavy rain.

The threat for thunderstorms, and isolated severe weather, would end with the passage of the cold front which is expected by early Saturday morning. West winds and cool air underneath the upper level low/trough are expected on Saturday, bringing us a return to seasonable weather and lower humidity.

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