Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Sat Jun 27 2020 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF VIRGINIA AND THE CAROLINAS...AND VICINITY... ...SUMMARY... A few severe storms are expected across portions of the Northeast and Ohio Valley, and southward into the Carolinas and vicinity on Sunday. Isolated stronger storms and local severe potential is also expected from the Wyoming vicinity into the northern High Plains, and eastward to the Upper Mississippi Valley. ...Synopsis... An upper low over Quebec is forecast to shift slowly southward with time, while several disturbances rotate through the broader area of cyclonic flow aloft over the eastern quarter of the country. In the West, an upper low initially centered over the Pacific Northwest will dig slowly southeastward with time, with surrounding cyclonic flow to cover the western third of the country by the end of the period. At the surface, a cold front will advance southward across the Intermountain West, while lingering nearly in place across the northern High Plains. in the East, a weak front will move southeastward across New England and the Northeast through the period. ...The Northeast to the Carolinas vicinity... As upper troughing lingers across the Northeast Sunday, scattered afternoon showers and thunderstorms are forecast to develop across a large area, as at least weak diurnal destabilization occurs. Moderate northwesterly flow aloft should promote some storm organization along with fast cell motions, yielding local risk for gusty/damaging winds. Greatest risk appears likely to exist across parts of Virginia and the Carolinas vicinity. Here, models hint that a short-wave feature aloft -- embedded within the broader northwesterly cyclonic flow -- will move across the region during the afternoon. With a more unstable airmass expected to evolve as compared to areas farther north, storms will likely develop over the higher terrain and then move quickly east-southeastward -- possibly growing upscale into bands, locally. With moderate flow (30 to 40 kt) through a deep layer, potential for somewhat more widespread wind damage across this portion of the risk area warrants upgrade to 15% wind/SLGT risk -- focused during the afternoon and early evening hours. ...Wyoming vicinity into the northern High Plains/Dakotas... As the western upper low/trough digs southward, a surface cold front is forecast to linger in a north-northeast to south-southwest manner across the northern High Plains, while progressing southward on its western flank across the Great Basin. Isolated storms are expected to develop near the boundary during the afternoon, though modest instability expected across much of the area should limit storm intensity despite ample shear. Greater CAPE into the western Dakotas is expected, but capping should hinder overall convective coverage to a large degree. As such, 5%/MRGL risk for hail/wind potential still appears an appropriate forecast at this time. ...Mid Missouri and Upper Mississippi Valleys... Much uncertainty persists across the north-central portions of the country, with a short-wave mid-level disturbance progged to evolve across the Mid Missouri Valley vicinity and move northward with time. With a rather weak surface warm front expected to be lifting northward across the north-central U.S. with time, afternoon storm development is expected -- though models differ quite a bit with regards to the evolution of the upper disturbance, and as a result the surface warm front and possible/associated frontal wave. Thus, while risk for locally damaging winds and hail -- and even tornado potential -- could ultimately evolve, will introduce only 5% probability at this time due to ongoing/considerable uncertainty. ..Goss.. 06/27/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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