SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0730 AM CDT Wed Oct 21 2020 Valid 211300Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No severe thunderstorms are expected through tonight. ...Synopsis/Discussion... An upper-air pattern initially characterized by broadly cyclonic flow across the entire northern CONUS, from coast to coast, will flatten east of the Mississippi River and amplify over the West. This will occur as a northern-stream shortwave trough -- evident in moisture-channel imagery over southwestern coastal BC -- moves southeastward and amplifies through the period. By 12Z, the trough should reach central/eastern MT and northwestern WY, with height falls as far south as the Four Corners and southern Rockies. The approach of that trough will foster low-level cyclogenesis in the immediate lee of the central Rockies, shifting from WY toward northeastern CO near the end of the period. As that occurs, a broad low-level warm-advection and moisture-transport regime -- already in place and supporting sporadic thunder from the lower Missouri Valley to the Northeast near a low-level frontal zone -- will strengthen in its western portions. A 45-60-kt LLJ should develop overnight from the south-central High Plains northeastward to IA. Lift of increasingly moist parcels to LFC will support thunderstorm potential from parts of the Lower Missouri Valley region over the Corn Belt, spreading/shifting northeastward toward the southern Upper Great lakes by the end of the period. Meanwhile, widely scattered thunderstorms will remain possible in a deep, extensive regime of easterly flow, rich moisture and minimal CINH, from FL across much of the Gulf, spreading into portions of south Texas. Isolated to widely scattered thunderstorms also will be possible from southern GA northeastward, near an old frontal zone analyzed at 11Z near the Carolinas coast. ..Edwards/Leitman.. 10/21/2020
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