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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.


Friday, July 28, 2023

SPC Jul 28, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1247 AM CDT Fri Jul 28 2023 Valid 281200Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PRIMARILY OVER IOWA...NORTHERN ILLINOIS...SOUTHERN WISCONSIN AND PARTS OF SURROUNDING STATES... ...SUMMARY... Severe storms are most probable from southeast South Dakota across Iowa, northern Illinois and southern Wisconsin this afternoon and evening, with corridors of damaging wind and large hail. Other scattered strong to severe storms are expected from Ohio into Virginia, and across the northern High Plains. ...Synopsis... Moderate northwest flow aloft will exist over the northern Plains into the upper Great Lakes and across much of the Midwest, with an upper high across the Four Corners region. A stalled front will stretch roughly from the SD/NE border eastward toward WI/IL, with a very moist and unstable air mass along and south of it. Midlevel height falls are forecast across the upper MS Valley and Great Lakes late in the day, with a substantial area of thunderstorms moving east/southeast across much of the Midwest. Elsewhere, the base of an upper trough will skirt northern New England, enhancing deep-layer shear and providing cooling aloft to support scattered storms across ME, perhaps with marginally severe hail. ...Midwest... A few showers or storms may remain over parts of WI and lower MI during the morning, as unstable air interacts with an outflow boundary from the overnight convection. To the south, an expansive area of unstable air with 70s F dewpoints will remain from the middle MO Valley eastward across much of the Midwest. Heating will lead to strong instability from eastern SD and NE to the OH River, with a belt of stronger flow aloft near the elongated stationary front. Heating will be strongest across NE, IA and IL, and this warming air mass will shift northeastward through the afternoon and interact with the boundary. While model differences do exist, the general idea is for storms to form anywhere from central SD into southern WI by mid/late afternoon, eventually merging into one or more MCSs. The high degree of convective feedback in the forecast wind fields suggest a fairly significant swath of damaging winds may develop from IA into northern IL and surrounding areas. In addition, isolated very large hail will be possible as deep-layer shear will be favorable along the stationary front. ...Southern MT into the northern High Plains... Upper ridging will occur over the northern Rockies today, with veering surface winds from northeast to easterly, aiding westward transport of moisture. Meanwhile, strong heating beneath cool midlevel temperatures will lead to steep lapse rates, and effective shear will be near 50 kt. As such, storms forming over the high terrain of southwest MT and extending southeastward across WY may produce marginal hail during the late afternoon and early evening. ...VA into MD... Strong heating will occur today, with a weak lee trough developing. Convergence and an uncapped air mass will lead to scattered storms over western into central VA, with inverted-v profiles and MLCAPE over 2500 J/kg favoring locally strong downbursts. ...Northern ME southwestward toward far northern NY... Scattered storms are likely to develop over southern Quebec during the afternoon along a front and in association with a progressive shortwave trough. This wave will lengthen hodographs with 40-50 kt effective shear extending southward into New England, and provide cooling aloft which will steepen midlevel lapse rates. Sufficient MLCAPE around 1000 J/kg may favor a supercell or two producing severe hail. ..Jewell/Bentley.. 07/28/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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