SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0725 AM CDT Sun Oct 31 2021 Valid 311300Z - 011200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No severe thunderstorms are expected across the continental United States today and tonight. ...Synopsis/Discussion... In mid/upper levels, largely zonal flow will characterize the southern stream from CA across the southern/central Plains to the Southeast, with only minor embedded shortwave perturbations. In the northern stream, a synoptic-scale trough is located from western Hudson Bay south-southwestward across portions of MN and the Dakotas, and is forecast to develop a closed 500-mb cyclone centered over northern ON today. By 12Z tomorrow, the low should reach southern James Bay, while a trailing shortwave trough digs south- southeastward from SK to eastern MT and the western Dakotas. In response to those developments, the longstanding eastern CONUS cyclone is devolving into an open-wave trough over the lower Great Lakes and northern Mid-Atlantic. This feature will continue to weaken as it accelerates northeastward through New England and southern QC, amidst broader-scale height falls that precede the northern-stream cyclone. Any remaining lightning potential with the associated, weakening low-level warm-advection plume appears to be too isolated and brief over land to warrant continuation of the prior day's New England thunder outlook into this period. Meanwhile, as a progressive synoptic trough/cyclone over the open northeastern Pacific moves eastward, a smaller cyclone now over coastal OR will become an open-wave trough over OR today, shifting/ extending eastward to southern ID overnight. The remnant vorticity banner should detach from the cyclonic height field preceding the northeastern Pacific synoptic wave, and move slowly through a larger-scale mean ridge over ID starting near the end of the period and through day 2. To its east, under strongly difluent flow aloft, the combination of favorable boundary-layer diurnal heating and marginal low/middle-level moisture will enable 100-300 J/kg MLCAPE, and MUCAPE around 500 J/kg, with weak inhibition from mid/late afternoon into mid-evening. Isolated weak thunderstorms will be possible from portions of southern ID/northern UT to parts of southern WY and northwestern CO. ..Edwards.. 10/31/2021 Read more LIVE: spc.noaa.gov
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