SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CDT Sat Aug 28 2021 Valid 281630Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST SD...CENTRAL AND SOUTHERN MN...NORTHERN WI...AND WESTERN UPPER MI... ...SUMMARY... Multiple rounds of severe thunderstorms are expected through this evening from southeast South Dakota across southern/central Minnesota into northern Wisconsin. The most intense storms will be capable of significant damaging wind gusts in excess of 75 mph, a few tornadoes, and large hail. ...Upper Midwest to NE... Ongoing cluster across central MN is expected to track east along the primary baroclinic zone through east-central MN through northwest WI. The airmass ahead of this MCS will continue to destabilize amid ample MUCAPE (around 3000 J/kg) sampled by the 12Z MPX sounding. With a leading mid-level jet and further cold pool development, this cluster should persist with compact bowing structures yielding severe wind gusts as the primary hazard (a few which should be significant). Damaging winds should remain spatially confined in latitudinal extent, but an elongated west-east swath appears probable. A couple QLCS tornadoes will also be possible, especially as mature bow stage in the northwest WI vicinity this afternoon. A separate round of severe thunderstorms is expected towards late afternoon, initially centered on southeast SD. This activity will likely expand east along the trailing outflow from the leading MCS across southern MN and southwest along the surface cold front into central NE. The stronger vertical shear will be confined to along and north of the baroclinic zone, with a mix of supercells and bowing segments probable over southeast SD and southern MN. All severe hazards will be possible but a transition to primarily damaging winds will occur during the evening as convection grows upscale into multiple bands/clusters and a broader MCS evolves east-southeast. Overall intensity will wane towards late evening as instability diminishes and outflows become farther separated from the stronger vertical shear. ...North-central Gulf Coast... Hurricane Ida is expected to strengthen today over a deep/warm Loop Current eddy and continue northwestward between the southeast Atlantic coast midlevel ridge and a weak midlevel low over the northwest Gulf. Ida is forecast to reach the southeast LA coast as a major hurricane Sunday afternoon/evening (see latest NHC advisories for details). The outer northeast quadrant of the hurricane will approach a portion of the north-central Gulf Coast late in the period, when strengthening wind profiles will begin to support the threat of supercells and a brief tornado or two early Sunday morning. ...South central PA to northwest VA... Thunderstorm coverage should be lower today compared to yesterday, in the wake of an MCV now moving off the DE coast. However, boundary-layer dewpoints remain in the 68-72 F range to the southwest of a weak backdoor front, and surface heating over the higher terrain of the Alleghenies and Blue Ridge should support thunderstorm development by mid afternoon. Thermodynamic profiles are fairly similar to previous days with MLCAPE of 1500-2500 J/kg and DCAPE of 750-1000 J/kg, which could be sufficient to support isolated downbursts capable of producing localized tree damage. ..Grams/Karstens.. 08/28/2021 Read more LIVE: spc.noaa.gov
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