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Tuesday, October 26, 2021

SPC Oct 26, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Tue Oct 26 2021 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF KANSAS...OKLAHOMA...AND TEXAS... ...SUMMARY... Scattered severe thunderstorms associated with large hail, wind damage and isolated tornadoes are expected across portions of Kansas, Oklahoma, and northern/central Texas late this afternoon through the evening into the overnight. ...Central/Southern Plains... Within an amplified large-scale flow regime, an upper trough centered over the Great Basin and Lower Colorado River Valley early today will further amplify and continue eastward while enhancing a meridional flow regime into the central/southern Plains. Lee-side surface cyclogenesis will steadily occur today from northeast Colorado into western/northern Kansas tonight. To the east of a sharpening dryline and upstream cold front, a seasonally moist air mass will steadily develop northward with upper 50s/near 60 F surface dewpoints expected as far north as the Kansas/southwest Nebraska border vicinity by evening, with prevalent mid 60s F dewpoints likely across the western half of Oklahoma/southwest Kansas and all of west-central/north Texas. Initially warm temperatures aloft and residual capping will likely inhibit deep convective development through the diurnal heating cycle. Nonetheless, owing to ample post-dryline mixing and modest confluence/convergence near the dryline, initial surface-based deep convective development could occur as early as around 23Z-00Z (6pm-7pm CDT). This is most probable near the eastern Texas Panhandle/western Oklahoma border vicinity as well as southwest/west-central Kansas, and is a bit earlier (hour or two) and farther west than pre-dawn HRRR runs. Scattered severe storms will become more probable/certain after sunset through the late evening hours as the Pacific cold front overtakes the dryline and more appreciable forcing for ascent arrives into the region. Near/east of the dryline, seasonally moist boundary layer beneath a pronounced elevated mixed layer will support a corridor of upwards of 1500-2000 J/kg MLCAPE across far western Oklahoma into southwest/west-central Kansas by early evening. Under the influence of meridional flow, strong deep-layer southwesterly winds and 40+ kt effective shear will support some initial supercells capable of large hail and a tornado risk with the late afternoon/early evening development. Portions of west/northwest Oklahoma into southwest Kansas will continue to be re-evaluated today for the possibility of somewhat higher (10 percent) tornado probabilities. Storm mergers should quickly occur into mid/late evening with a transition to more of a quasi-linear convective mode, with veer-back-veer wind profiles noted in forecast soundings vertically between 1-3 km AGL. Damaging wind potential is likely to increase accordingly during the evening with the linear transition, although some potential for a few tornadoes will continue with a mixed/quasi-linear convective mode owing to the strength of the low-level winds, along with relatively minimal nocturnal boundary layer inhibition. Strong to severe storms are likely to continue, at least on isolated basis, well into/through the overnight hours, with a line of storms likely to reach east/southeast Oklahoma and the I-35 corridor of Texas by the early morning hours (~09Z-11Z) of Wednesday. ..Guyer/Kerr.. 10/26/2021 Read more LIVE: spc.noaa.gov
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