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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Monday, August 23, 2021

SPC Aug 23, 2021 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Mon Aug 23 2021 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MID MISSOURI AND UPPER MISSISSIPPI VALLEYS...AND INTO THE WESTERN UPPER GREAT LAKES AREA... ...SUMMARY... A few severe storms will be possible from the Mid Missouri Valley to the Upper Mississippi Valley Tuesday. ...Synopsis... Large-scale ridging will prevail over much of the country Tuesday, with broad anticyclonic flow aloft extending from the Desert Southwest, eastward across the central and southern Plains, and into nearly the entire eastern U.S./Gulf of Mexico. Farther north/northwest, a weak, northwestern U.S. mean trough will persist. In between these two features, several small-scale cyclonic disturbances will continue to eject east-northeastward across south-central Canada and the north-central U.S. within the belt of enhanced west-southwesterlies sandwiched between the northwestern trough and the southeastern ridge. At the surface, a weak front progged to extend from the Upper Great Lakes west-southwestward into the northern Plains will become baroclinically reinforced, as a mid-level short-wave trough emanating from the larger-scale troughing over the Northwest advances across southern portions of the Canadian Prairie. By the end of the period, this reinforced cold front should extend from the Upper Great Lakes southwestward to a secondary low over the central Plains. ...Upper Mississippi Valley/Upper Great Lakes/Mid Missouri Valley region... A complex/evolving scenario is evident across the north-central U.S. Tuesday, as an initial/weak short-wave trough crosses the upper Mississippi Valley region early in the period, and then shifts into Upper Great Lakes region during the afternoon and evening. The advance of this feature will be associated with potentially rather widespread, ongoing convection across a substantial portion of the region. This convection complicates the forecast -- both in terms of potential for airmass recovery, as well as locations of convective boundaries which may act to focus subsequent afternoon/evening convective redevelopment. Also complicating the forecast is the subsidence/capping -- especially across southern portions of the region -- due to the influence of background ridging. This capping should act to limit convective coverage in areas away from immediate, baroclinic boundaries. With all of that said, afternoon destabilization will likely be sufficient in some portions of the area to permit redevelopment of at least isolated storms -- possibly growing upscale with time into one or more clusters. Storm intensity/longevity should be aided by ample shear, afforded by 30 to 40 kt west-southwesterly mid-level flow. This suggests that at least a few severe storms will evolve, though uncertainty prevails with respect to location per current guidance -- both parameterized and convection-allowing models. Given these uncertainties, will maintain only MRGL categorical risk, but with potential for upgrade to slight risk in later outlooks, as possible corridors of more focused convective development can be ascertained. ..Goss.. 08/23/2021 Read more LIVE:
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