SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0747 AM CDT Tue Oct 20 2020 Valid 201300Z - 211200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe storms are not expected through tonight. ...Synopsis/Discussion... In mid/upper levels, broadly cyclonic flow will continue to dominate the northern 1/2-2/3 of the CONUS, interspersed with several mostly minor shortwaves. The strongest shortwave trough -- apparent in moisture-channel imagery initially over the northern High Plains of eastern MT/WY -- will assume more-negative tilt today. By 00Z, the trough should extend from northern/eastern ND across southwestern MN, before ejecting northeastward across the upper Mississippi Valley, WI, and Upper MI late overnight. Meanwhile, a slow-moving mid/upper trough in the subtropics will continue to spread vorticity lobes and maxima across much of FL and southern GA, combining with a residual low-level baroclinic zone and a moist-weakly capped low-level environment, to support general thunder potential from FL to the eastern Carolinas. At the surface, a wavy/quasistationary frontal zone was analyzed from offshore of the Carolinas across northern FL and ear the northern Gulf Coast, becoming diffuse across southeast TX. This boundary will move little through most of the period, except for minor mesoscale oscillations. A cold front was drawn from the Adirondacks southwestward through a weak low between CVG-SDF, to near MEM, becoming quasistationary to weakly warm frontal over central AR to central/southwest TX. The western segment of this boundary should move northward as a warm front through the period, across parts of west/north TX into southern/central OK. Isolated to widely scattered thunderstorms are expected mostly west and north of the latter front, in a zone of largely elevated buoyancy. Convection will be supported by warm advection, moisture transport, and isentropic ascent to LFC, amidst weak CINH. With modest low/middle-level lapse rates, and strongest flow aloft displaced more poleward, the shear/buoyancy parameter space should remain insufficient for an organized severe threat. ..Edwards/Leitman.. 10/20/2020
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