SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 PM CDT Tue Aug 17 2021 Valid 180100Z - 181200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF UPSTATE SOUTH CAROLINA AND WESTERN NORTH CAROLINA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF UTAH... ...SUMMARY... A few tornadoes will remain possible this evening into tonight across portions of the western Carolinas and southwestern Virginia. Locally severe wind gusts may affect parts of the Great Basin. ...Carolinas and Virginia... Tropical Depression Fred will continue northward and undergo an extra tropical transition across the central Appalachians tonight. As Fred's low-level circulation slowly fills, the accompanying mid-level speed max will move north across the western Carolinas and Virginia. Strong low-level shear (0-1 km SRH 150-300 m2/m2) remains in place as observed by 00Z regional soundings and VWPs. The favorable shear profiles and weak buoyancy should remain sufficient to support low-level mesocyclones and the potential for a few tornadoes this evening across the western Carolinas into southwest Virginia. Uncertainty remains high on the potential for tornadoes late tonight across western into central Virginia. Phased poorly with the diurnal cycle, already weak instability is forecast to diminish further overnight with northward extent. The strong shear and low-level moistening may compensate for this somewhat, but various forecast soundings across west-central Virginia show MUCAPE largely below 500 J/kg. A few mini-supercells may continue northward with a risk for a tornado or two closer to the center track of Fred where low-level shear should be the strongest. ...Great Basin... Within a relatively moist and unstable environment, scattered high-based storms ongoing across western Utah will likely continue eastward this evening ahead of a cold front and deepening shortwave trough. The cold front should sharpen as it moves to the south and east tonight, generating additional convection across central Utah. Despite the loss in diurnal heating, weak buoyancy will persist given increasing monsoon moisture and surface dewpoints near 55 F advecting northward into the Great Basin. Deep-layer shear will increase late this evening with the approach of the shortwave trough and associated 50-60 kt mid-level speed max. The ongoing storms and additional convective development should enhance already strong surface cold pools, likely supporting a few severe wind gusts across the Slight Risk area this evening before convection eventually weakens. ..Gleason.. 08/18/2021 Read more LIVE: spc.noaa.gov
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