Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0335 AM CST Thu Dec 10 2020 Valid 131200Z - 181200Z ...DISCUSSION... A progressive/moderate amplitude flow field aloft is progged across the U.S. through Day 8, with medium-range models in reasonably good agreement through Day 6 (Tuesday Dec. 15), with respect to synoptic-scale evolution. During this first three days of the period, low-amplitude troughing -- rotating around the eastern fringe of a large northern Canada polar vortex -- is forecast to gradually depart northeastward/away from the northeastern states. Meanwhile, a second short-wave trough -- initially over the Plains -- is forecast to move quickly eastward across the Southeast Day 4 (Sunday Dec. 13) and then off the Atlantic Coast through the first half of Day 5. This feature will be followed by the next in a series of troughs, which will move inland over the West Day 4, across the Intermountain region and eventually into the Plains through Day 5, and then eastward to the Mississippi Valley region through Day 6. Both of these two, aforementioned troughs will be accompanied by associated surface cyclogenesis. However, at this time it appears that a cool/stable boundary layer will remain across the southern Plains/Southeast, and thus the primary surface low tending to evolve just offshore of the Gulf Coast -- along the main west-to-east zone of baroclinicity (separating the cool continental air from the Gulf airmass). Given this evolution, any severe weather potential would appear to be limited to the Florida Peninsula, and that risk appears too low at this time to warrant any introduction of severe-weather probabilities.
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