SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Mon Apr 21 2025 Valid 212000Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER OHIO VALLEY AND LOWER GREAT LAKES...AND PORTIONS OF THE SOUTHEAST... ...SUMMARY... Isolated strong to severe thunderstorms are possible today across the upper Ohio Valley/lower Great Lakes and parts of the Southeast. Damaging winds and marginally severe hail are the primary risks. ...20Z Update... The Marginal risk in the Lower Great Lakes was trimmed behind the eastward-moving frontal band of convection. Elsewhere, the forecast remains on track and minimal changes were made with this update. For details on the near-term severe risk, reference MCDs #512 and #513. ..Weinman.. 04/21/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Mon Apr 21 2025/ ...Upper OH Valley... Morning surface analysis and satellite imagery show a cold front sweeping eastward across OH. Considerable cloud cover is present ahead of the front, but a narrow corridor of heating immediately ahead of the front will allow a period of heating - promoting scattered thunderstorms. Low-level moisture is limited with dewpoints only in the 50s, and forecast soundings show CAPE values generally below 1000 J/kg. Nevertheless, strong low and mid-level winds and considerable vertical shear will promote a risk of a few organized/severe storms capable of damaging wind gusts and perhaps a tornado or two. Refer to upcoming MCD #511 for further details. ...LA/MS/AL/GA/TN... The aforementioned surface cold front extends southeastward across west TN. A relatively moist air mass is present ahead of the front from southeast LA into parts of MS/AL and middle/east TN, although considerable cloud cover will limit heating. Most 12z models suggest scattered thunderstorms will form in this zone during the late afternoon and evening, with sufficient CAPE for a few robust updrafts. Low and mid level winds are not particularly strong, and large scale forcing is weak. This should limit the overall organization and severity of storms, but a few cells may produce gusty winds and hail. ...SD... Water vapor imagery shows a mid-level shortwave trough over WY approaching SD. Forcing ahead of this feature will likely lead to scattered high-based showers and thunderstorms across eastern WY and western/central SD this afternoon and evening. There is some chance that a storm or two could produce locally damaging wind gusts.