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Cooler Conditions Hanging On, Changes Coming This Week

Good Evening! 

The storm that bombarded portions of the Northeast over the past day is quickly moving out over eastern Canada, but the storm certainly left its mark. Most of the Northeast saw heavy rainfall totals in the range of about 2-5″, but the main event from this system were the winds that roared in overnight last night. As the low pressure area rapidly deepened and moved ashore over NJ and eventually progressed into New York state, it carried a large an impressive area of high winds just above the surface over portions of Long Island, Connecticut, Rhode Island, Massachusetts, Vermont, and Maine. As the storm began to fill in with warmer air and weaken, these winds just above the surface were able to rapidly crash down to the ground and cause an impressive amount of tree damage. Hundreds of thousands of folks are still without power in many of the states above, with over 400,000 customers without power in Maine alone. While these winds were rather impressive, the main story west of the immediate area of low pressure were the torrential rains that fell. Deep tropical moisture streamed northward into the Mid Atlantic and Northeast states, and when this moisture was met with the strong dynamics aloft, heavy rain became focused over New Jersey and portions of New York for several hours. Some locations were able to rack up rain totals in the 4-5″ range when all was said and done, with some minor street and river flooding noted. As we stated last week, the reason that these rains were not a bigger story was because an existing minimal drought muted out the overall impacts.

Sunday nights radar near the peak of the coastal storm that brought heavy rains and high winds over the region

As day broke today, a strong westerly jet associated with the backside of the low pressure system was working its way over the Northeast. Due to more mixing of dry air in the atmosphere, this low level jet was able to bring gusts down to the surface in the range of 30-40 mph, which brought some additional tree damage to the region. It also made for a cooler and more classic fall day as cooler Canadian air was briefly tapped. With partly sunny skies and cooler temperatures aloft, highs were able to make it into the middle 50’s across much of the region, but cooler conditions to the north and west kept highs down in the low to upper 40’s-with some stations in New York state even reporting snow showers! As the massive low pressure system continues to pull away this evening, wind have shifted from northwest to southwest as high pressure begins to build in from the south. As the winds shift, the gusty 20-30 mph conditions will begin to die down as the pressure gradient from the two opposing systems weakens with time. Given the clear skies and low humidity, conditions will be marginally supportive for radiational cooling to occur tonight which should knock temperatures down into the upper 30’s and lower 40’s across the area.

High resolution visible satellite imagery and surface observations over the northeast showing cooling and windy conditions

High resolution visible satellite imagery and surface observations over the northeast showing cooling and windy conditions

Tuesday and Beyond

The area of high pressure just south of the area will continue to build north throughout the day tomorrow, which will allow for dry conditions and generally clear skies. Highs will likely be limited to the middle to upper 50’s  during the day tomorrow despite winds coming from southwest winds at the surface, but cooler Canadian air continues to work in at the lower levels of the atmosphere. Winds will also likely die down completely by tomorrow afternoon, so as we work our way into the evening hours, we should see ideal conditions for radiational cooling to take place over the entire area. Low level temperatures will likely be below freezing already, so expect lows to drop into mid to upper 30’s, with some of the more interior locations possibly even dropping below-freezing and into the upper 20’s. With little to no winds, frost will be increasingly likely the farther away from the coast you move.

By Wednesday some changes will be in the works as a large area of low pressure begins to move towards the Great Lakes region. As this low heads northeast, it will bring a surge of warmer air along a warm front over the area, which should work to bring highs back into the upper 60’s and lower 70’s once again. Given the breadth of this system, we will likely be in between the cold front and warm front until Friday, when the cold front will finally pass, bringing a marginal chance of showers during the afternoon hours. Highs will likely remain in the upper 60’s to lower 70’s through this period, before the cold front knocks temperatures back down to more seasonable levels.

By this weekend temperatures should once again cool down with northwesterly flow returning from Canada, but we may have to watch for a threat of showers once again later in the weekend as a potential wave of low pressure rides north along a stalled cold front over the area. There is still considerable uncertainty with this solution and we’ll have more details by Wednesday as the model guidance converges on a more clear solution.

Snapshot from the 12z ECMWF model showing slightly above normal temperatures during next weekend with the return of higher heights in the east

Snapshot from the 12z ECMWF model showing slightly above normal temperatures during next weekend with the return of higher heights in the east

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Have a great night!

Steve Copertino

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