Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1159 PM CDT Thu Jul 23 2020 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY INTO SATURDAY NIGHT ACROSS PARTS OF THE UPPER MIDWEST...NORTHERN GREAT PLAINS...AND PARTS OF SOUTHERN TEXAS... ...SUMMARY... Strong thunderstorms may impact parts of the Upper Midwest and northern Great Plains Saturday into Saturday night, accompanied by at least some risk for severe weather. Meanwhile, developing Tropical Storm Hanna may be accompanied by potential for a couple of tornadoes as it makes landfall across parts of the middle and lower Texas coast. ...Synopsis... The stronger westerlies appear likely to remain confined to latitudes near and north of the Canadian/U.S. border vicinity, with modest amplification possible by late Saturday night across the northeastern Pacific into the Canadian Rockies. To the south of one significant downstream short wave trough, progressing across the Canadian Prairies and adjacent international border area, it appears that mid-level ridging will remain prominent along a major axis extending from the southern Rockies through much of the Ohio Valley. Within the tropical easterlies, to the south, developing Tropical Storm Hanna is currently forecast to make landfall across lower Texas coastal areas, to the south of Corpus Christi. ...Northern Great Plains into Upper Midwest/Great Lakes... Models indicate broad surface troughing across much of the northern Great Plains at the outset of the period, before a cold front associated with the significant short wave trough advances across much of the Dakotas and northwestern Minnesota by 12Z Sunday. It appears that there will be little coinciding eastward development of the surface troughing, but the northwestern periphery of surface ridging, extending west-northwestward from the Atlantic, may begin to weaken across the Upper Midwest into the upper Great Lakes region. This probably will commence as a less pronounced mid-level impulse preceding the primary wave accelerates east-northeast of the Red River Valley early in the period. There may be considerable remnant convection at the outset of the period associated with this lead wave, and it appears that stronger southerly/southwesterly 850 mb flow (30-40 kt) will be maintained across parts of the middle Missouri Valley toward the Upper Midwest through the period. Low-level moistening and daytime heating along the southern periphery of the mid-level impulse/associated convection may contribute to moderately large mixed-layer CAPE by Saturday afternoon. This probably will contribute to an environment conducive to vigorous convective development, with the potential for one or two upscale growing thunderstorm clusters through Saturday evening, particularly across parts of eastern Minnesota and northern Wisconsin into the upper peninsula of Michigan. It is possible that this could be accompanied by an organized severe wind threat. However, due to sizable spread still evident within the various model output, severe weather probabilities are being maintained at 5 percent. Otherwise, within the surface troughing to the west, ahead of the eastward advancing cold front, widely scattered to scattered strong thunderstorms are expected Saturday afternoon and evening. Modest westerly mid-level flow may contribute to sufficient shear to contribute to storm organization, but low-level wind fields appear likely to be rather weak. And some model output, including the latest NAM, suggest that CAPE, where lift is able to overcome mid-level inhibition, may be rather modest (around 1000-1500 J/kg). ...Middle/lower Texas coast... Tropical Storm Hanna may pose a risk for a couple of tornadoes as it makes landfall. However, this risk is still largely conditional as mesoscale developments which could impact this potential remain highly uncertain at this time. ..Kerr.. 07/24/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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