SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1110 PM CST Wed Dec 16 2020 Valid 181200Z - 191200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from a corridor across parts of eastern Texas by daybreak Saturday, the risk for thunderstorms appears neglible across much of the U.S. Friday through Friday night. ...Synopsis... Much of North America will remain under the influence of westerlies branching downstream of a strong, zonal mid/upper jet across the western through central southern mid-latitude/subtropical Pacific. This regime will continue to include a number of modestly amplified, progressive short wave troughs, including one accompanied by a significant surface cyclone migrating away from the Atlantic Seaboard Friday through Friday night. Stable conditions will generally prevail east of the Rockies (in addition to much of the west) in the wake of this system, with little change forecast across most areas through this period. However, boundary-layer moistening and northward return flow may be ongoing by Friday morning across parts of the southwestern Gulf of Mexico, on the southwestern flank of elongated surface ridging encompassing much of eastern North America and the Gulf of Mexico. Models do suggest that the Eastern surface ridge axis will gradually shift toward the Atlantic coast during this period, coincident with the progression of mid-level troughing east of both the Canadian Prairies and the southern U.S. Rockies. It appears that this will be accompanied by surface troughing into the Upper Midwest, lower Missouri Valley and southeastern Great Plains Friday night, preceded by weak to modest southerly return flow. As this occurs, modest low-level moisture emanating from the southwestern Gulf of Mexico may reach upper Texas coastal areas by 12Z Saturday. ...Eastern Texas... Latest model runs, most notably the NAM, appear a bit slower with the low-level moisture return to the northwest Gulf coast vicinity, in addition to farther south and slower with the mid-level short wave digging to lee of the southern Rockies, before turning eastward. However, it does still appear that moisture return above a residual surface-based stable layer will contribute to the development of at least very weak CAPE by late Friday night. As weak mid-level cooling begins to overspread the Ark-La-Tex southward toward the upper Texas coastal plain, convection capable of producing lightning appears possible by around 12Z Saturday. ..Kerr.. 12/17/2020
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