SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CST Tue Dec 22 2020 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER MISSISSIPPI VALLEY AND GULF COAST STATES... ...SUMMARY... Isolated severe thunderstorms are possible Wednesday afternoon/night from the middle/upper Texas Coast across much of Louisiana, Mississippi, Alabama, and the Florida Panhandle. ...Synopsis... A deep upper trough is expected to extend from the Canadian Prairie Provinces southwestward into the Four Corners early Wednesday morning. Several shortwave troughs will rotate through this parent upper trough, contributing to both eastward progression and continued deepening. Upper flow around the trough will also strengthen significantly throughout the period, with a corridor of 100+ kt 500-mb winds expected from the Lower Mississippi Valley into southern Ontario by early Thursday morning. At the surface, low associated with the lead shortwave embedded within the larger upper trough will begin the period centered over east-central Minnesota/northwest Wisconsin. A strong cold front will extend from this low southwestward through the Middle Missouri Valley and Oklahoma into southwest Texas. Fast eastward/southeastward progression of this front is expected throughout the day, and the front will likely extend from eastern Lower Michigan south-southwestward into the western Florida Panhandle by 12Z Thursday. ...Lower Mississippi Valley/Gulf Coast States... Low-level moisture will increase ahead of the southeastward-moving cold front, with low/some middle 60s F surface dewpoints becoming increasingly common by late afternoon/evening from the Texas coast into Louisiana/southern Mississippi. Semi-prevalent cloud cover will tend to limit heating with lapse rates remaining poor, resulting in only modest buoyancy. Regardless, surface-based storms are likely to develop near/just ahead of the front by late afternoon/early evening across the middle/upper Texas coastal plain into Louisiana. Low to mid-level wind fields will be strong, supporting stronger storms with any more persistent and deep updrafts. Although there are some uncertainties regarding the overall magnitude of the severe risk, damaging thunderstorm gusts will be possible and some tornado risk may exist as well. ..Guyer.. 12/22/2020
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