Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Thu Jun 25 2020 Valid 261200Z - 271200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER GREAT LAKES REGION SOUTHWESTWARD TO THE MIDDLE MISSOURI VALLEY... ...SUMMARY... Scattered posing a risk for damaging winds and hail are expected from the central Plains east-northeastward across the Midwest to the Great Lakes Friday afternoon and evening. ...Synopsis... Gradual evolution of quasi-zonal flow aloft will occur Friday, as eastern U.S. troughing shifts offshore. A positively tilted, low-amplitude short-wave trough within the westerlies will cross the central portion of the country through the period. At the surface, a cold front initially stretching from Minnesota to western Kansas will become elongated in a more northeast-to-southwest manner, as front moves eastward across the Great Lakes region, while lingering over Kansas. Meanwhile, a second cold front is forecast to work its way inland/across the Pacific Northwest, ahead of a mid-level short-wave trough digging southeastward out of the Gulf of Alaska. ...Mid MO/Mid MS Valleys to the Great Lakes... Scattered thunderstorms are forecast to be ongoing across portions of the upper Mississippi Valley/Upper Great Lakes region area at the start of the period, ahead of the advancing cold front. As diurnal heating drives afternoon destabilization, new storm development is expected near the advancing cold front, first over the Wisconsin vicinity and then stretching southwestward along the cold front into Kansas. Flow aloft through the lower and middle troposphere across the region will be sufficient for organized storms -- likely evolving locally into fast/eastward-moving bands. Along with hail potential, damaging winds will likely to be the favored severe risk. Depending upon degree of destabilization which can occur across the Great Lakes area in the wake of early-period convection, a more organized/bowing-type wind risk could evolve, which could require higher wind probability/greater categorical risk in later forecasts. Convection should continue through the overnight hours -- spreading as far east as parts of Pennsylvania and New York, but with severe risk likely waning gradually as the airmass stabilizes with time. ...Central and southern High Plains... Isolated to widely scattered, late afternoon/early evening thunderstorm development is expected over the Front Range, as low-level easterly upslope flow evolves north of the cold front becoming more west-to-east oriented across Kansas through the day. Moderate westerly flow aloft atop low-level southerlies will likely result in sufficient shear organized/rotating updrafts. A deep mixed layer which will evolve through the afternoon over the High Plains suggests that storms moving off the higher terrain will be capable of locally strong wind gusts. An isolated landspout-type tornado also cannot be ruled out, though potential for greater tornado risk should remain limited by a dry/deep boundary layer. At this time, will maintain only marginal/level 1 categorical risk, due to anticipated storm coverage being sparse. Risk may be upgraded to slight risk in future outlooks if a bit more widespread development becomes more likely. Evening development of a southerly low-level jet could permit some upscale growth as storms move southward/southeastward during the evening, with some wind risk possibly lingering locally through the evening hours. ...East Texas and the Arklatex vicinity... Model forecasts of a weak upper low drifting northward across East Texas will likely support an increase in afternoon storm development across the Texas/Arkansas/Louisiana vicinities. Slightly enhanced southerly low-level flow ahead of the low may promote rather fast northward storm motion, possibly resulting in a stronger wind gust or two. However, risk appears too low to warrant inclusion of a risk are at this time. ..Goss.. 06/25/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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