SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Sat Aug 07 2021 Valid 071200Z - 081200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL PLAINS TO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered severe storms capable of producing mainly large hail and damaging winds gusts will be possible today from parts of the northern/central Plains into the upper Mississippi Valley. ...Synopsis... A mid-level short-wave trough is forecast to shift out of the Rockies and into the central and northern Plains today, ahead of a stronger trough digging southeastward across western Canada toward the northwestern U.S. through the period. Meanwhile in the East, weak mid-level troughing is expected to cross the Appalachians and move into the East Coast states. At the surface, a cold front will shift into/across the northwestern states ahead of the aforementioned/digging upper trough. Over the Plains, a more ill-defined surface pattern is progged -- in part due to widespread convection and associated boundary interaction. Generally, a weak synoptic baroclinic zone will extend from the upper Mississippi Valley to the southern High Plains -- lingering through the period. Elsewhere, high pressure will prevail east of the Mississippi, though a very weak surface low/trough will affect the Carolinas area, in conjunction with the advance of the weak upper system. ...Central Plains and vicinity eastward across the upper Mississippi Valley... Complex convective evolution is expected across central portions of the country today, with multiple areas of storm development/growth expected. Storms will likely be ongoing at the start of the period over southern Minnesota/northern Iowa vicinity, and in a more isolated manner westward into the Dakotas, and southwestward into Kansas. Through the day, as heating contributes to widespread moderate destabilization, the Minnesota storm cluster will likely shift into Wisconsin, followed by several areas of new storm initiation westward and southwestward along the weak surface front, as the upper short-wave trough advances into the Plains during the afternoon. With a belt of enhanced (35-45 kt) low- to mid-level southwesterly flow preceding the trough, aligned from the central High Plains/Texas Panhandle northeastward to the upper Mississippi Valley, sufficient shear for storm organization will exist. Large hail will be possible with stronger updrafts, especially during the afternoon as convection remains more cellular in some areas. However, the more substantial severe risk will likely be in the form of locally damaging winds, as storms grow upscale into one or more clusters during the evening -- within a zone extending from northern Kansas/Nebraska to the upper Mississippi Valley region. More isolated/higher-based storms -- capable of producing locally strong wind gusts -- are expected farther southwestward from western Kansas into the Texas Panhandle during the afternoon and early evening hours. ...Eastern North Carolina/southeastern Virginia area... Widespread -- but generally sub-severe -- convection is forecast across the North Carolina/Virginia vicinity today, ahead of the weak/advancing upper trough. With resultant weak lapse rates aloft, CAPE should remain limited, tempering storm intensity. Additional, modest shear likewise suggests largely sub-severe storms. However, a locally stronger gust or two cannot be ruled out, and thus will maintain 5% wind/MRGL risk across this area. ..Goss/Lyons.. 08/07/2021 Read more LIVE: spc.noaa.gov
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