SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1237 AM CDT Wed Sep 22 2021 Valid 221200Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER OHIO VALLEY AND CENTRAL APPALACHIANS... ...SUMMARY... Scattered strong to severe storms will spread across portions of the Ohio Valley and central Appalachians. Damaging winds are the primary threat, though a few tornadoes could be noted. ...OH Valley/Central Appalachians... Early-morning water-vapor imagery depicts a well-defined mid-level short-wave trough digging into the lower MO Valley. This feature is forecast to track across the lower OH Valley during the day as an 80kt 500mb speed max translates across the TN Valley into northern KY by 18z. During the latter half of the period, this feature should deepen with a closed low advancing into northwest OH. Strong mid-level 12hr height falls will precede this upper trough with wind profiles/shear expected to increase markedly across eastern OH into western PA. Latest NAM guidance suggests partial clearing will allow strong boundary-layer heating along a corridor extending from western VA into eastern OH/western PA. This will result in steepening low-level lapse rates (7 C/km) immediately ahead of the front. Forecast soundings by early afternoon across eastern OH exhibit MLCAPE in excess of 1000 J/kg and lifted parcels should easily convect, both along the advancing front and ahead of the boundary. While supercells are expected, especially with more discrete updrafts ahead of the wind shift, strong lift should contribute to a forced squall line that will advance across the upper OH Valley in response to the strong short wave. While damaging winds will be the primary concern, low-level SRH and bulk shear favor some tornado potential. Greatest risk for tornadoes will be during the afternoon into early evening hours when the boundary layer will be most buoyant, primarily over eastern OH/western PA. ..Darrow/Moore.. 09/22/2021 Read more LIVE: spc.noaa.gov
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