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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.


Thursday, August 26, 2021

SPC Aug 26, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Thu Aug 26 2021 Valid 261630Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST SOUTH DAKOTA THROUGH SOUTHERN MINNESOTA AND NORTHERN IOWA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER MISSISSIPPI VALLEY INTO THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Severe thunderstorms capable of damaging wind gusts are likely across parts of southern Minnesota into Iowa as well as the central Plains. Severe thunderstorms will also be possible during the late afternoon and evening across parts of the northern High Plains. ...Upper Mississippi Valley through Central Plains regions... Organized linear MCS near the SD/MN border as of late morning is expected to continue east southeast into southern MN this afternoon, though a recent weakening trend has been observed. Updrafts within the line remain elevated above the surface. However, a southwesterly low-level jet will maintain moist and unstable inflow in the 850 mb layer where updraft bases are probably rooted. This MCS has organized a strong cold pool which, in addition to the low-level jet and an apparent MCV on the northern end, should help to sustain activity next few hours. See swomcd 168 for more details. Farther south the MCS across northern IA continues to weaken. However, some re-intensification is possible as the downstream atmosphere destabilizes. Farther upstream, additional storms are expected to develop across the High Plains and intensify as they spread east into the destabilizing boundary layer. Other storms may develop along the outflow boundary that may eventually stall over southern SD. One ore more MCS clusters may eventually evolve from these storms especially as the low-level jet strengthens during the evening and overnight. Activity will subsequently spread east into the upper MS Valley region where ENH risk has been maintained for the possibility of this scenario. ...Central MT this afternoon/evening... There will be a window of opportunity for a few severe storms with damaging winds and large hail in association with surface heating and residual boundary-layer dewpoints in the 50s along a stalled front across central MT. The phasing of the diurnal heating cycle and the approach of a midlevel trough from ID should support widely scattered thunderstorms by late afternoon, some of which could be supercells given moderate buoyancy and sufficiently long hodographs with effective bulk shear of 30-40 kt. Activity should weaken by mid evening as the boundary layer stabilizes. ...Northern ME this afternoon/evening... In association with a shortwave trough moving eastward from James Bay, a surface cold front will approach northern ME this evening from QC. Buoyancy and deep-layer vertical shear will be sufficient for organized/supercell storms ahead of the front across northern ME, but the stronger forcing for ascent will pass to the north, leaving storm coverage in question. Any storms that do form this afternoon/evening will be capable of producing damaging winds and/or large hail. ..Dial/Lyons.. 08/26/2021 Read more LIVE:
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CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)