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Weather conditions on bar directly above are near Lakefront. Tabs under Moon Phases refer to O'Hare (official).

Archives for SPC Convective outlook are updated daily with a live map a the beginning of the article. Touch or click map to get possible update, and follow link at end of article for referral to NOAA/NWS Storm Prediction Center. Archives for Chicago's hourly weather data were updated 24-48 hours after end of each day prior to Dec. 2020.

Thursday, August 26, 2021

SPC Aug 26, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 26 2021 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR NORTHERN IA AND SOUTHERN MN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF THE NORTHERN HIGH PLAINS INTO MT... ...SUMMARY... Severe thunderstorms capable of damaging wind gusts are likely across parts of southern Minnesota into Iowa. Severe thunderstorms will also be possible during the late afternoon and evening across parts of the northern High Plains. ...Southern MN/northern IA and vicinity through tonight... Weak lee cyclogenesis is expected today across the central High Plains, along the southeast periphery of a midlevel trough over the northern Rockies. East of the lee cyclone and later today, a surface front will move slowly northward across NE/IA. However, uncertainty in the forecast stems from the influence of the morning western IA storms on the location of the front by early afternoon, and whether or not destabilization will occur quickly enough from south to north to allow the ongoing storm cluster in northern SD to intensify by early-mid afternoon. To the south of the ongoing convection and the front, a reservoir of low-mid 70s boundary-layer dewpoints beneath the eastern extent of a steep midlevel lapse rate plume, will combine with daytime heating and result in MLCAPE values in excess of 3000 J/kg. The warm front will also lie along the southern fringe of the 30+ kt midlevel flow, where vertical shear will be favorable for both supercells and organized storm clusters. Assuming sufficient recovery occurs by this afternoon, intensification of the SD storms is expected in the vicinity of southern MN, or possibly new storm clusters may form along the outflow-reinforced front. In either case, the threat for damaging winds will increase across southern MN and northern IA through the afternoon/evening, and the stronger embedded supercells may also produce isolated large hail and a tornado or two. Farther west, a few additional storm clusters will be possible along the front this evening into tonight from northern NE into southern SD, where occasional damaging gusts and/or large hail will be possible. ...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 scattered thunderstorms, some of which could be supercells given moderate buoyancy and sufficiently long hodographs with effective bulk shear of 30-40 kt. ...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. ..Thompson/Gleason.. 08/26/2021 Read more LIVE: spc.noaa.gov