Administrators NorthGeorgiaWX Posted January 12 Administrators Posted January 12 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0650 AM CST Fri Jan 12 2024 Valid 121300Z - 131200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL/NORTHERN MISSISSIPPI AND WESTERN ALABAMA... ...SUMMARY... Severe thunderstorm winds and a few tornadoes are possible across a large part of the Southeast through early this evening. The most intense gusts (potentially above 70 mph) are possible through midday over parts of the Mid-South and Tennessee Valley regions. ...Synopsis... Broadly cyclonic flow in mid/upper levels will cover most of the CONUS through the period, except for shortwave ridging on either side of a strong lead trough now over the central/southern Plains. That perturbation will be the primary upper-air influence on convection today. The southern part -- initially located over portions of OK and north TX -- should eject northeastward to the IN/MI border area by 00Z, while the northern part moves more slowly across IA toward the Quad Cities. Overnight, these will combine into a 500-mb cyclone over Lower MI to Lake Huron, increasingly stacked on the surface cyclone described below. The 11Z surface analysis showed an area of low pressure over central MO, along the northern segment of a cold front extending across parts of central/western AR to central TX. A synoptic warm front was drawn from the low across the lower Ohio Valley. A prefrontal trough/wind shift and remnant of a Pacific front was evident over central LA southwestward to deep south TX. The surface low should occlude and move northeastward to near ORD by 00Z, then across Lower MI overnight. The main/Arctic cold front is forecast by 00Z to overtake the Pacific boundary and reach WV, the western Carolinas, northern/western GA, central/eastern FL Panhandle, and the central Gulf. The front should move offshore from the Mid-Atlantic, Carolinas and GA by 12Z, extending southwestward over central/ southwestern peninsular FL. ...Southeastern CONUS... Ongoing lines of strong to severe thunderstorms near the Mississippi River should consolidate and sweep eastward across parts of the Mid South toward the Tennessee Valley region through midday -- in and near the 30% wind/"enhanced" area. This activity will pose a threat for severe gusts (some significant/65+ kt), a few embedded tornadoes, and isolated, marginally severe hail. See SPC tornado watch 10 and related mesoscale discussions for near-term coverage of this convective stage. Though peak intensity of the main thunderstorm line is likely to be in the next several hours, as it encounters the greatest warm-sector theta-e, some severe-wind and tornado threat may persist eastward across portions of AL/GA today and into the Carolinas this evening following very strong low-level warm/theta-e advection. Additional strong-severe thunderstorm development is possible over the warm sector throughout today into this evening, as convergence lines produce showers that can grow gradually deeper and upscale. Given the strength of the wind fields projected to spread over the warm sector and ahead of the main line, some of this activity may become supercellular, also with a tornado/damaging-wind/marginal-hail threat. Dewpoints generally reaching the 50s to mid 60s F just prior to cold frontal passage, and sufficient surface-based instability, should develop today in the warm sector to offset weak midlevel lapse rates and support 500-1500 J/kg MLCAPE -- more southward, and mainly south of I-20 in AL/GA and from the Piedmont eastward in SC/NC. Forecast soundings suggest hodographs will be straightening/losing size, but remaining very long, as the buoyant layer lowers closer to the surface and the main belt of convection approaches. Still, that supports effective SRH locally exceeding 400 J/kg, amidst 60-80-kt effective-shear magnitudes. The main limiting factor for areal severe potential will be lack of greater instability. Given the strength of ambient flow, a broad 15% wind area is maintained, with the understanding that localized pockets of denser wind/tornado potential may quickly evolve within. Farther north across northern TN/KY to southern VA, though MLCAPE will be weak, intense wind fields and associated convective momentum transfer still will support some potential for convective gusts to penetrate near-neutral stability layers and reach the surface. A broad area of 60-110-kt winds in the 850-700-mb layer will shift northeastward across parts of TN/KY and the southern Appalachians today. The severe potential in such scenarios is rather spotty and nebulous, and may extend well northward within cool surface air on an isolated basis. ..Edwards/Dean.. 01/12/2024 Read more View the full article Quote
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