SPC AC 240517 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1217 AM CDT Thu Sep 24 2020 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS PARTS OF SOUTHEASTERN MISSISSIPPI...CENTRAL AND SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND THE FLORIDA PANHANDLE... ...SUMMARY... A few strong thunderstorms may impact parts of the eastern Gulf Coast states today, accompanied by at least some severe weather potential. This may include the risk for a couple of tornadoes, mainly this afternoon across parts of south central Alabama. ...Synopsis... Strong zonal flow emanating from the northern mid-latitude Pacific appears likely to rapidly overspread the Pacific Northwest through the northern Great Plains during this period. A vigorous short wave trough on the leading edge of this regime is now progressing inland of the British Columbia/Pacific Northwest coast, and is forecast to progress east-northeastward through the Canadian Prairies today through tonight. This probably will be accompanied by significant surface cyclogenesis from the lee of the Canadian Rockies through northern Saskatchewan by late tonight. A cold front may also surge southeastward to the lee of the northern U.S. Rockies by late this afternoon. This probably will be preceded by strengthening southwesterly low-level flow across the northern Great Plains, near/east of pre-frontal surface troughing, but initially modest moisture content beneath the eastward advecting nose of a plume of warm elevated mixed-layer air is expected to result in low convective potential. Models indicate that seasonably high precipitable water content will largely remain confined to a couple of northeastward advecting plumes, east of mid-level troughing, within a remnant branch of weak westerlies, gradually shifting east of the middle/lower Mississippi Valley toward the middle/southern Atlantic Coast. This includes mid-level remnants of Beta, which may become increasingly sheared/deformed while progressing across the central Gulf States through the lee of the southern Appalachians, slightly in advance of the associated weakening surface low. ...Southeast... Despite the lower/mid tropospheric moistening, relatively warm mid-level air may limit destabilization, and perhaps tend to suppress thunderstorm development across much of the region. Initially dry/potentially cool boundary-layer air emanating from surface ridging across the lower Ohio Valley into the southwestern Atlantic may also slow boundary-layer destabilization. However, an influx of lower/mid 70s F surface dew points, within a narrow plume off the Gulf of Mexico into the vicinity of the surface low center, may continue. And models suggest that this may overspread southern into central Alabama and the western Florida Panhandle by early this afternoon, contributing to mixed-layer CAPE on the order of 1000+ J/kg. Although stronger lower/mid tropospheric wind fields may tend to develop northeastward into the residual drier/more stable air, 30+ kt flow in the 850-700 mb layer may persist as far south/southwest as south central Alabama, as the boundary layer destabilizes this afternoon. This may contribute to sizable clockwise-curved low-level hodographs supportive of low-level mesocyclone development, as large-scale forcing for ascent and daytime heating aid widely scattered to scattered intensifying thunderstorm activity. Some of this could pose a risk for a tornado, before convection wanes late this afternoon or evening. ..Kerr/Wendt.. 09/24/2020 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z