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Monday, September 20, 2021

SPC Sep 20, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0208 AM CDT Mon Sep 20 2021 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING ACROSS MUCH OF CENTRAL AND SOUTHEASTERN OHIO...PARTS OF WESTERN PENNSYLVANIA...EASTERN KENTUCKY...MUCH OF WEST VIRGINIA...SOUTHWESTERN VIRGINIA...AND NORTHEASTERN TENNESSEE... ...SUMMARY... Strong thunderstorms may impact a corridor from parts of the Cumberland into Allegheny Plateau vicinity Wednesday afternoon and evening, and perhaps pose a risk for a couple of tornadoes and damaging wind gusts. ...Discussion... Models suggest that the westerlies may begin to undergo amplification across the northern mid-latitude eastern Pacific into western North America during this period, with large-scale mid-level ridging building inland across the British Columbia coast and downstream troughing digging to the lee of the Canadian Rockies. However, a blocked regime over the mid-latitude Atlantic will continue to impact flow across much of the United States. It appears that elongated large-scale mid-level troughing over the middle and lower Mississippi Valley at the outset of the period will only slowly shift eastward Wednesday through Wednesday night. It may broaden considerably, with models generally indicating that one significant short wave perturbation will contribute to a deepening embedded lower/mid tropospheric cyclone. Spread among the various models remains large, however, with this taking place anywhere from the lower Ohio Valley into the lower Great Lakes region. It appears that this may be accompanied by modest surface cyclogenesis along a slowing cold front. Of primary concern is the potential for this to be accompanied by enlarging, clockwise-curved low-level hodographs in a warm sector with surface dew points in the mid 60s to near 70F. Although lower/mid tropospheric lapse rates may not become particularly steep, the environment might still become conducive to organized convection, including low-topped supercells, with the potential to produce a couple of tornadoes and damaging wind gusts. This seems most likely to become focused in relatively close proximity to the low, during a period of more substantive deepening late Wednesday afternoon and evening, probably somewhere west of the Allegheny Front. ..Kerr.. 09/20/2021 Read more LIVE: spc.noaa.gov
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