SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CDT Fri Aug 06 2021 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN AND CENTRAL ROCKIES INTO THE NORTHERN PLAINS AND OVER THE MIDWEST... ...SUMMARY... Isolated severe storms are possible over parts of the central and northern Rockies into the northern High Plains this afternoon/evening. A couple strong to severe storms may also develop later today over parts of the Upper Mississippi Valley. ...Northern/Central Rockies to Northern Plains... Water-vapor imagery depicts a well-defined upper trough ejecting east-northeast across southeast OR/western NV. Notable height falls will develop ahead of this feature as it progresses to near the ID/WY border by 07/00z. Latest model guidance suggests a 50+kt 500mb jet will translate across northern UT into central WY by late afternoon and focused large-scale forcing for ascent appears likely within the exit region of this speed max. While PW values will remain somewhat dry across this region (~.75-1 inch), strong surface heating will contribute to destabilization and high-based convection should develop by 21z as surface parcels reach their convective temperatures. With cloud bases expected near 3km AGL, gusty winds with some potential for severe downbursts are possible. As the trough approaches the high Plains, LLJ should strengthen across western KS into extreme south-central SD. This may contribute to longevity of thunderstorm activity as it propagates east along a warm-advection corridor. Will maintain MRGL risk across this region due to somewhat meager moisture but there is some concern for organized wind-producing line segments given the strength of the upper trough. Will monitor this region for possible upgrade. ...Upper MS Valley... A weak mid-level disturbance is digging southeast across eastern SD toward northern IA early this morning. Convection continues ahead of this feature and should be ongoing at sunrise to start the period. A possible MCV, or certainly the remnants of this cluster, should propagate across eastern IA toward northern IL by late morning. Boundary-layer heating is expected to aid destabilization such that new updrafts, and possible thunderstorm clusters, develop and move east toward southern Lake MI/northern IN. Gusty winds and perhaps some threat for hail can be expected with this activity. ..Darrow/Lyons.. 08/06/2021 Read more LIVE: spc.noaa.gov
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