SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1118 AM CST Fri Nov 20 2020 Valid 211200Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorms appears negligible across the U.S. Saturday through Saturday night. ...Synopsis... Models suggest that the most prominent branch of westerlies emanating from the Pacific may undergo amplification during this period. It appears that this will include a building mid-level ridge across the Canadian Rockies and northern U.S. intermountain region/Rockies, and a digging short wave trough across the northern Great Plains and middle Missouri Valley. The short wave trough may support weak frontal wave development along the leading edge of a reinforcing cold intrusion across the Ozark Plateau/lower Missouri Valley vicinity, where southerly return flow in the wake of a prior cold intrusion has allowed for weak to modest low-level moistening. However, substantive further Gulf moisture return appears unlikely, with only a very gradual continued boundary-layer moistening within easterly low-level flow to the south of remnant surface ridging across the Gulf Coast region. ...Four Corners region through the Ozarks vicinity... Ahead of the digging short wave trough, at least a couple of short wave perturbations are forecast to traverse the region within a belt of westerlies emanating from the southern mid-latitude/subtropical eastern Pacific. Associated forcing for ascent probably will contribute to areas of convective development. However, based on model forecast soundings, the extent to which this activity may become capable of producing lightning remains unclear. Low-level moisture return and warm advection are expected to remain focused across parts of the Ozark Plateau into the lower Missouri Valley, where relatively warm temperatures aloft/weak lapse rates may inhibit weak thunderstorm development until perhaps late Saturday evening/Saturday night. Upstream, very weak CAPE rooted at higher levels, aided by somewhat steeper mid-level lapse rates, mainly near/above the 700 mb level could become supportive of weak thunderstorm activity near the Oklahoma/Kansas border vicinity into southeastern Colorado. Otherwise, orographic forcing might contribute to an isolated weak thunderstorm or two across the mountains of southwestern Colorado late Saturday afternoon. ...Florida... Within gradually moistening easterly low-level flow, models suggest that areas of scattered showers may overspread the peninsula Saturday through Saturday night. As a mid-level high center shifts east of the south Atlantic Seaboard, weak cooling aloft may allow for increasing probabilities for thunderstorms by Saturday night, mainly near southeast coastal areas. ..Kerr.. 11/20/2020
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