SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1231 AM CDT Thu Aug 05 2021 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHWESTERN US AND OVER THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Isolated damaging gusts and hail are possible with thunderstorms from central Oregon into the northern Rockies. A few strong storms may also produce wind/hail across the upper Mississippi Valley region. ...Northwestern US... Seasonally strong upper trough will eject across northern CA/western OR early in the period as 50kt 500mb speed max translates across northern CA into southwestern ID by 06/00Z. Significant mid-level cooling and substantial height falls, north of the jet, suggest large-scale support for organized convection. Forecast soundings suggest strong boundary-layer heating ahead of this feature east of the Cascades and surface parcels are expected to reach their convective temperatures by 22Z across eastern OR. Air mass is not particularly moist with PW values mostly in the .75-1-inch range. As a result, cloud bases will be around 3km AGL, which could enhance the prospect for gusty winds with stronger downdrafts. Transitory short wave should encourage convection to spread/develop east across ID into western MT during the late afternoon/evening. ...Upper MS Valley... Early-morning water-vapor imagery depicts a disjointed upper trough that extends across the eastern Dakotas into the southern High Plains. This feature is forecast to spread across MN/IA during the early afternoon and scattered convection may be noted ahead of this feature. However, strong post-trough boundary-layer heating is expected to aid buoyancy and the threat for isolated thunderstorm development along the surface trough by late afternoon. Forecast soundings suggest isolated thunderstorms may develop within a west-northwesterly flow regime characterized by MLCAPE around 1300 J/kg. Gusty winds and perhaps some hail could be noted with a few storms that form due to surface heating. ..Darrow/Moore.. 08/05/2021 Read more LIVE: spc.noaa.gov
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