Nov 25: Storm Summary, Longer Range Update

Today ended up bringing the second snow/sleet event to parts of the area, as a storm approaching from the west led to several hours of snow/sleet falling west of NYC before changing over to rain.

The set up that took place today was already clear over the last several days, with the general idea of wintry precipitation, potentially accumulating, in most of PA into northern New Jersey, however there were some small uncertainties with the timing which led to some differences with the forecasts, as the NAM model was the slowest, bringing precipitation in only after 5 PM, and was correctly considered as a slow outlier for this storm as it tends to have a slow bias.

Today, we saw a broad area of low pressure from the Midwest into the Ohio Valley moving east, with the front end of the storm entering Pennsylvania in the early overnight hours, bringing heavy precipitation. Dew points were low across the Northeast, meaning that evaporative cooling, temperatures cooling down once precipitation starts, would take place. With a high pressure exiting the region, a Cold Air Damming scenario took place, where cold air was trapped over Pennsylvania despite the storm track, which would usually support a much warmer air mass. While surface temperatures in most of PA were cold, there was a small area of 850 mb temperatures below zero in central Pennsylvania, leading to heavy snow developing in those areas and moving east during the morning hours into eastern PA along with the pocket of sub-zero 850 mb temperatures.

The heavy snow in eastern Pennsylvania was a result of the factors mentioned above, and at least a period of moderate snow fell over most of eastern PA as well as southern and central New Jersey. The best dynamics were over eastern PA, where heavy snow for several hours accumulated up to 2-3 inches, with reports of slightly over 1 inch in Allentown. As the pocket of cold 850 mb temperatures was further east over eastern PA, central/western PA changed over to rain/freezing rain by the late morning.

As the precipitation pushed east into the dry air by the early afternoon, it began to weaken, leading to the dynamics becoming less favorable and the area of snow shrinking. Light snow/sleet managed to fall over northern New Jersey, with sleet mixing in with the rain in Bergen County and New York City. By 5 PM, 850 mb temperatures then went back above 0c, and with temperatures warming up, the area changed over to light rain.

As of 10 PM, the area is seeing cloudy skies and warm air advection starting to take place, with temperatures expected to rise tonight, however an area of heavy rain in western NY/PA associated with the cold front of the storm will lead to a wet start to Friday, followed by a cold weekend.

Tomorrow’s Outlook:

As the main storm will be north of the Great Lakes with a secondary low developing near Maine, a cold front will move through in the late morning hours, producing moderate rain late tonight into tomorrow morning, though the heaviest rain should be to the north of NYC. By the early afternoon, the cold front should clear the area, with clearing skies, and breezy conditions. High temperatures will be steady in the mid to upper 40s inland and lower to mid 50s for the rest of the area, dropping by the late afternoon.

With mainly clear skies and a much colder air mass tomorrow night, temperatures should quickly drop overnight, with the coldest temperatures so far this fall possible by Saturday morning, in the upper 10s to lower 20s inland, mid to upper 20s in S CT and the north/west suburbs of NYC, upper 20s to lower 30s in Long Island, and in the lower 30s in NYC.

Weekend Outlook: Dry, Cold

Saturday should be a very chilly day, with high temperatures expected to be in the upper 30s to lower 40s inland and in the lower to mid 40s for the rest of the area. Saturday night will have mainly clear skies again, but with a slightly weaker cold air mass, should be a little warmer than Friday night. Sunday should be warmer, with high temperatures in the lower to mid 40s inland and in the mid to upper 40s for the rest of the area, but with a high pressure in place and clear skies, Sunday night could be slightly colder than Saturday night.

Early To Mid Week Outlook: Storm Expected For Wednesday

As the high pressure exits the area and a low pressure moves through the Midwest, the trough will lift out of the Northeast on Monday with temperatures returning into the 50s for parts of the area. This storm will pull in an arctic air mass into the Dakotas, though not as strong as the one we saw over the last few days, and its cold front will start to slowly move east. On Tuesday, the storm should be north of the Great Lakes, with a large supply of cold air to its west and a slow moving cold front moving through the Ohio Valley and the Southeast, pulling in a warm air mass into the East along with heavy rain. On Tuesday, due to the high pressure to the NE of NYC, the air mass won’t get as warm as places to the west/south, however that will change in the overnight hours.

By Wednesday, a low pressure is expected to develop along this cold front, and while there is uncertainty on the exact track, it could end up between western Pennsylvania and a track just off the coast, taking a negative tilt overnight and moving more north, then NNW through the Northeast as cold air comes rushing into the southern side of the storm. This storm has the potential of producing heavy rainfall over an inch in the area, as well as the potential of a snowstorm to its west, further inland. Stay tuned for more details on this storm.

Longer Range: Colder, Then Another Potential Storm For December 4-6

Behind the storm, a moderated version of the arctic air mass will move into the region, producing yet another round of cold temperatures, potentially similar to those of this coming weekend for Thursday and Friday, however another storm will meanwhile be taking shape near the Rockies.

Even though there is uncertainty as this is in the long range, it appears that a storm could be moving east through the central US during this time frame. With another potential arctic air mass dropping into the north central US, this potential storm will be capable of producing snow to its north, affecting the area on the 5th and 6th. Due to a -PNA still in place, this storm is also likely to track inland to the north of the area, however the models are suggesting that if the storm does track inland, with a -NAO still in place, there could be redevelopment further east, however at this time, this time frame doesn’t appear to be favorable for a snowstorm in the northern Mid Atlantic. Stay tuned for more details on this time frame.

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