SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0652 AM CST Fri Feb 12 2021 Valid 121300Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunderstorms are possible across parts of the Southeast, for another few hours in deep south Texas, and late overnight near parts of the northern California and southern Oregon coastline. ...Synopsis/Discussion... A high-latitude blocking pattern will continue over Canada, in mid/upper levels, anchored by a high over northern Yukon and a persistent cyclone centered over southern MB. The "undercutting" belt of westerlies to its south will persist with zonal to subtly cyclonic flow across the northeastern Pacific and northern CONUS. A shortwave trough was evident in that flow belt near 150W, around 40N. This perturbation will penetrate the mean ridge offshore from the Pacific Coast and move ashore in northern CA and OR between 09-12Z. Associated strong DCVA/cooling aloft is expected, under the left-exit region of a cyclonically curved upper jet max. Accordingly steepened low/middle-level lapse rates the last few hours of the period will lead to around 100-300 J/kg MUCAPE atop the marine layer, some of which will could deep enough to support isolated lightning. Meanwhile, a southern-stream trough now over central/northern MX and west TX will pivot northeastward and weaken, reaching the western Gulf by the end of the period. Countless minor vorticity lobes -- some convectively induced/enhanced -- will eject northeastward over the Gulf and Southeast in the foregoing, gently confluent southwesterlies. Beneath those, a slow-moving surface frontal zone was analyzed from a low near MCN southeastward across the GA coastline, and southwestward over the FL Panhandle to the northwestern Gulf. The bulk of thunder will remain over the open Gulf, where air/sea fluxes will optimize low-level theta-e. However, a broad sheet of low-level warm advection and moisture transport will persist in extending inland, largely elevated poleward of the front. Isolated, diurnal, surface-based, but disorganized thunderstorms also may form in an environment of modest deep-layer lapse rates and weak buoyancy south of the front in parts of GA and central/northern FL. ..Edwards.. 02/12/2021
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