SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1239 AM CDT Wed Oct 21 2020 Valid 211200Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No severe thunderstorms are expected across the continental United States on Wednesday. ...Synopsis... Shortwave trough currently progressing through the Upper Midwest is expected to continue northeastward through eastern Ontario and western Quebec today, moving within the strong, broadly cyclonic upper flow extending from the Pacific Northwest through Quebec. An associated surface low will take a similar path, moving just ahead of the parent shortwave, while an attendant cold front extends from this low southwestward into the southern Plains. Isolated lightning strikes are possible near this weakening front early in the period. Limited instability will temper the overall severe potential. Another shortwave trough is forecast to drop from British Columbia into the northern Rockies. Progression of this shortwave will encourage a deepening lee trough, with the resultant increase in the surface pressure gradient contributing to a northward surge of low-level moisture across the southern/central Plains and mid MS Valley. A dynamically enhanced low-level jet will also develop ahead of the approaching shortwave, stretching from the southern High Plains through the mid MS Valley. Warm-air advection associated with this low-level jet will result in elevated thunderstorms across the mid MS Valley Wednesday night through early Thursday morning. Instability will be limited but vertical shear may be strong enough to support a few stronger, more persistent updrafts capable of hail. Likely low coverage coupled with low overall potential preclude introducing any hail probabilities in this outlook. Cold mid-level temperatures accompanying this shortwave may also result in enough instability for a few lightning strikes over the northern Rockies. Farther south, a weakening tropical wave will support isolated thunderstorms across FL and portions of the GA and the Carolinas. Moist easterly flow across the Gulf and into the middle/lower TX Gulf Coast could also support isolated afternoon thunderstorms. ..Mosier/Lyons.. 10/21/2020
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