SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Fri Jul 23 2021 Valid 231200Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Severe thunderstorms are possible from North Dakota eastward across northern Minnesota into northwestern Wisconsin, mainly Friday afternoon and evening. Damaging wind gusts and large hail are expected to be the primary severe threats. ...Northern Plains/Upper Mississippi Valley... Upper ridge over the northern Plains will flatten during the day1 period as a weak impulse tracks across the Dakotas into MN early. Later in the period, more substantial height falls will be noted ahead of a digging short-wave trough as it moves across MB/western ON into northern MN/WI during the overnight hours. The early-day impulse is currently related to decaying convection across the western Dakotas. Remnants of this feature will translate into central MN during the afternoon, and as surface temperatures soar into the mid 90s a few strong thunderstorms could develop as surface parcels reach their convective temperatures. However, more substantial low-level convergence will be noted upstream along a cold front that should progress to a position from southeast MB-central ND by 24/00z. The combination of intense surface heating ahead of this boundary, and focused low-level convergence, should result in favorable conditions for scattered thunderstorm development. Increasing deep-layer flow/shear suggest this activity could organize with subsequent southeast propagation expected during the evening hours. Damaging winds and hail are the main threats with this activity. Isolated high-based thunderstorms may also develop along a prefrontal surface trough extending across central SD into extreme northwest NE. Seasonally high PW values with weaker flow aloft suggest gusty winds will be the primary concern. ...AZ/NM... Extensive clouds/precipitation will spread across the lower southwestern deserts early in the day1 period. This should lessen buoyancy/instability due to significantly cooler afternoon temperatures. However, weak upper low currently near MAF is forecast to drift northwest into NM and large-scale support and flow aloft may become a bit more favorable for some organization with convection across portions of northern NM into northern AZ. Will maintain MRGL risk across this region for isolated damaging winds and marginally severe hail. ..Darrow/Bentley.. 07/23/2021 Read more LIVE: spc.noaa.gov
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