SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0127 PM CST Wed Nov 25 2020 Valid 252000Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH LATE EVENING FROM SOUTHEAST LA INTO PARTS OF AL AND NORTHWEST GA...AND ACROSS THE LOWER OH VALLEY... ...SUMMARY... Isolated damaging winds and a tornado or two will be possible through late evening from southeast Louisiana to central Alabama and northwest Georgia, and across the lower Ohio Valley. ...20z Update... The ongoing forecast remains on track. Only minor changes have been made on the western edges of the OH Valley and southeast LA/AL/northwest GA Marginal risk areas. These adjustments have been made based on the current location of the cold front and surface low. A few strong gusts and possibly a brief spin-up remain possible through this evening. ..Leitman.. 11/25/2020 .PREV DISCUSSION... /ISSUED 1027 AM CST Wed Nov 25 2020/ ...Lower OH Valley this afternoon/evening... A midlevel shortwave trough over MO will continue east-northeastward to the upper OH Valley overnight. A surface cyclone near Saint Louis will likewise move east-northeastward toward Lake Erie, and both the midlevel trough and cyclone are expected to weaken gradually by tonight. A narrow zone of surface heating/destabilization and boundary-layer dewpoints in the upper 50s is expected this afternoon from southern IL into southwestern IN and western KY, southeast of the surface cyclone. Though surface-based buoyancy will remain weak, vertical shear will be favorable for a low-end threat of low-topped supercells or short line segments capable of producing isolated damaging winds and perhaps a tornado. ...Southeast LA to central AL/northwest GA through late evening... Farther south, a pre-frontal squall line is moving eastward across southeast LA, central MS, and northwestern AL. The influence of this ongoing convection will likely limit the potential for destabilization this afternoon, immediately to its north into TN. The ongoing convective band will shift slowly eastward, with some low-level moistening/destabilization possible into central AL. Deep-layer and low-level vertical shear/SRH will tend to weaken through the day from southwest-to-northeast as the primary synoptic wave passes to the north over the OH Valley. Still, some low-end potential will remain for line segments and embedded supercells capable of producing isolated damaging winds and a tornado or two.
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