Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Sat Jul 11 2020 Valid 121200Z - 131200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MISSISSIPPI VALLEY TO THE OHIO VALLEY AND CENTRAL APPALACHIANS...AS WELL AS OVER THE CENTRAL/SOUTHERN HIGH PLAINS... ...SUMMARY... Isolated severe thunderstorms will be possible on Sunday across portions of the southern U.S. into the Ohio Valley and central Appalachians vicinity, as well as across parts of the central and southern High Plains. Locally damaging winds and hail will be the main hazard with storms through Sunday evening. ...Lower MS Valley into the Ohio Valley and Central Appalachians Vicinity... Convection may be ongoing Sunday morning across portions of the Lower OH Valley toward AR. The impact this convection has on overall severe threat in the Day 2 period remains uncertain, as much uncertainty in convective evolution during the Day 1/Sat period remains. Nevertheless, an upper trough will be oriented north-to-south from Lake Erie toward the Southeast, with modest northwesterly deep layer flow persisting over the region. A weak surface low is forecast to migrate eastward from IL/IN early Sunday morning toward eastern KY by Sunday night, with a trailing cool front dropping southeast across the Midwest into the Mid-South/TN Valley vicinity. Deep layer flow will largely remain veered, leading to weak directional shear, but modestly increasing speeds with height should allow for sufficient effective shear to aid in clusters of semi-organized convection. A very moist boundary layer and strong heating will result in moderate instability, with MLCAPE values from around 1000-2000 J/kg (locally higher) and steepening low level lapse rates will enhance localized areas of damaging wind potential. Midlevel lapse rates will generally be less than 7 C/km across the region, but a few of the strongest cells could produce marginally severe hail, mainly from the lower OH Valley into the South. Depending where any MCVs or boundaries associated with convection in the Day 1 period become located by Sunday morning, a corridor or two of greater severe risk could materialize. However, uncertainty is still too high to introduce Slight risk probabilities at this time. ...Central/Southern High Plains Vicinity... An intense upper high will be centered over NM, with an associated ridge extending northward through the northern High Plains. Warm midlevel temperatures will result in capping for much of the period, limiting thunderstorm potential. However, an upper shortwave trough is forecast to shift east/southeast across the northern Rockies, bringing a belt of stronger west/northwesterly flow across the Rockies. Southeasterly low level flow will transport modest boundary layer moisture northward across the Plains, with upper 50s to low 60s F surface dewpoints forecast across much of the High Plains. An area of somewhat higher dewpoints is possible from the OK/TX Panhandle vicinity into parts of northeast NM and eastern CO. Thunderstorms are expected to develop during the afternoon over higher terrain, and spread eastward over lower elevations of eastern CO/northeast NM. This high-based convection could pose a threat for isolated damaging gusts in a narrow corridor east of the mountains into the evening hours where forecast guidance suggests increasing moisture and height falls associated with the approaching trough should erode the cap. This activity should quickly diminish with eastward extent during the evening hours as inhibition once again increases. ..Leitman.. 07/11/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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