Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0244 AM CST Wed Dec 09 2020 Valid 121200Z - 171200Z ...DISCUSSION... A low-amplitude shortwave trough embedded within a broader, large-scale trough centered over the Plains will eject northeast from the Midwest to the northeastern U.S. on Day 4/Saturday. At the surface, a low near the mid-MS Valley Saturday morning will develop northeast to the lower Great Lakes by Day 5/Sunday morning. A cold front attendant to the low will spread east/southeast across the Midwest and south-central U.S., extending from western NY/PA southwestward along the central and western Gulf coast vicinity. Showers and thunderstorms are expected across parts of the mid/lower MS Valley into the Mid-South and central Gulf coast on Saturday. While modest Gulf moisture will return northward ahead of the front, the boundary layer will remain shallow and meager instability is forecast, precluding severe thunderstorm concerns. By Day 5/Sunday, medium range guidance begins to vary considerably in the evolution of the larger-scale upper trough over the Plains, and the associated surface pattern. The aforementioned cold front will likely continue to push offshore the Atlantic coast and Florida through early Day 6/Monday morning, but severe potential will remain low. Beyond Sunday, predictability is low given model variability, but in the mean, a progressive pattern with a series of short wavelength troughs appears to be likely. This should limit severe potential as any deep, higher-quality Gulf moisture return would be unlikely.
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