Dec 9, 2013 Evening Forecast: Snow Tomorrow

10:30 PM Forecast: Moderate Snow Expected Tomorrow

snowmapThis morning’s update noted that confidence has increased for a snowstorm to affect the area, as the model guidance trended in the short range to increase snow accumulations across the region as a wave of low pressure tracks along the frontal boundary. The NAM model, often notable for its low reliability in its longer range, has surprisingly handled this storm remarkably well, with the GFS alternating between light snow and isolated flurries. The GFS began trending towards more significant impacts on Sunday, with most of the foreign model guidance such as the ECM, UKMET and CMC not having fully caught on until only last night, less than 48 hours before the start of the event.

As a strong shortwave moves through aloft with strong forcing and a wave of low pressure developing southeast of the area, widespread precipitation is expected to spread in towards 8-10 AM from southwest to northeast. With temperatures aloft and at the surface cold enough, in the low 30s, this is expected to support precipitation type falling as snow. Along with favorable snow growth, this setup is expected to support a narrow band of heavy snow roughly along the I-95 corridor into parts of the area, with the heaviest snow falling between 10 AM and 2 PM. With a fast mid-upper level flow, the storm will remain fast moving, and will exit the area by 2-5 PM from southwest to northeast.

While the duration of precipitation will not be very long, heavy snowfall rates are likely under the aforementioned band, but with some uncertainty regarding where this sets up. At this time, the highest totals with 4-6 inches, locally up to 8 inches, is favored from Maryland to Philadelphia, with slightly lower totals forecast to extend into northeast NJ, NYC and Long Island. Elsewhere in the area, at least 2 to 4 inches of snow are likely. The heavy snow axis is subject to some revisions, and the main areas of uncertainty at this time are regarding the northern extent of the heavier snowfall, which may be revised southward, and how far northeast the heavy snow axis spreads, whether into the NYC area or central NJ, in which case interior parts of the area would see 1-2″ with at least 2-3″, locally 4″, for the rest of the area. Storm updates will be posted during the day on Tuesday to reflect on the latest conditions.

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