SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0718 AM CDT Mon Oct 18 2021 Valid 181300Z - 191200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorms appears negligible across the U.S. today through tonight. ...Synopsis/Discussion... In mid/upper levels, high-amplitude troughs now over the West Coast States and northeastern CONUS/southeastern Canada will evolve into closed cyclones as they move eastward. The western 500-mb low -- now taking shape near northern parts of the CA/NV state line -- will move eastward across the Great Basin through today and into early tonight. By 12Z, the low should pivot slightly northeastward from east-central UT toward the Flaming Gorge area near the UT/WY/CO border confluence. Preceding height falls, difluence and DCVA/ cooling aloft, and midlevel moistening will spread across portions of the Great Basin and north-central Rockies today into this evening, supporting showers and isolated to widely scattered, mostly weak thunderstorms. With a dry and locally well-mixed diurnal boundary layer over lower elevations of northern UT, some of this activity may produce strong gusts. However, meager amounts of total moisture and low-level theta-e will limit overall thunderstorm coverage, and preclude an organized severe threat. Isolated thunder, with locally gusty winds, also is possible from high-based, low-CAPE convection atop the diurnal mixed layer in parts of far west TX this afternoon into early evening. This activity will be supported by subtle southwest-flow perturbations in midlevels, and weak large-scale scent beneath the left-exit region of a cyclonically curved subtropical-jet segment. Lack of greater low-level moisture/theta-e will be a major limiting factor. Elsewhere, the post-frontal air mass across the northern, central and eastern CONUS should remain too dry and/or stable to support thunderstorms. ..Edwards/Leitman.. 10/18/2021 Read more LIVE: spc.noaa.gov
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