A strong shortwave in the Subtropical jet stream and a shortwave in the Polar jet stream began to phase together over the Tennessee and Ohio River Valleys on the evening of January 24th, which forced the phased shortwave to tilt into a negative orientation and build up the ridge on the East coast. Meanwhile, a fresh Polar air mass had settled into the Northern Mid-Atlantic ahead of the advancing shortwave.
Strong warm air and moisture transport began to invade the region on the morning of January 25th, which supported an increase of cloud cover throughout the region. However, dry air at 700 MB to 925 MB prevented the development of precipitation over the northern Mid-Atlantic through 8 AM on January 25th. While the entire region was cold enough to support snowfall from the surface to 850 MB, only a few bursts of light to moderate snow were observed through 8 AM due to this dry air.
From 8 AM to 10 AM on January 25th, the moisture and warm transport started to overwhelm the dry, cold air which had limited support to remain in place due to a lack of a blocking high-pressure system to the north. Between 8 AM and 11 AM, snow began to break out over much of eastern Pennsylvania aside from the Philadelphia metro through the Catskills and into the Hudson River Valley. The vertical atmospheric environment supported a snow ratio of 10:1 to 8:1 which featured large, wet snowflakes. The dry, cold mid-levels were also eroded on the coast, however by the time precipitation started for most regions, surface temperatures were well above freezing to support any snowfall for central New Jersey on to the south, and only non-accumulating snowfall for the rest of the I-95 corridor.
As the shortwave lifted into the eastern Great Lakes, a strong jet streak at 850 MB that ranged from 30 to 60 knots, drove above-freezing temperatures from the surface to 850 MB drove from the coast into the interior through the afternoon and evening hours, which supported a change over to rain for all locations.
FORECAST’
The forecast verified at a 90% level. All forecasted locations either reached the low end of the forecast or fell just below the expected snowfall. However, the idea of the heaviest snowfall in the Poconos, Catskills, mid-Hudson River Valley, and then central New England worked out well. The expected snowfall over 1″-3″ did not work out well in northwestern New Jersey, southern Hudson River Valley, or central Connecticut.
