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Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

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.

Saturday, September 17, 2022

SPC Sep 17, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0250 PM CDT Sat Sep 17 2022 Valid 172000Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NORTHERN MINNESOTA...AND ACROSS PARTS OF THE MID MISSOURI VALLEY AREA... ...SUMMARY... Scattered severe hail, isolated damaging winds, and a tornado remain possible across a portion of northern Minnesota during the late afternoon to early evening. Scattered large hail, damaging winds, and a brief tornado are also possible this evening across a portion of the Mid-Missouri Valley. ...Discussion... Though severe weather has yet to evolve in earnest, gradual afternoon destabilization that is underway still appears likely to result in development of late afternoon/early evening convection -- some of which may pose an all-hazards severe risk, consistent with prior outlook areas and reasoning. As such, no appreciable changes appear necessary at this time. ..Goss.. 09/17/2022 .PREV DISCUSSION... /ISSUED 1127 AM CDT Sat Sep 17 2022/ ...Central to northern MN... A low-amplitude shortwave trough approaching the Upper Red River Valley will move across northern MN into northwest ON by this evening. Partial cloud breaks are evident ahead of this wave mixed with patches of persistent but thinning low-level stratus. The 12Z NAM appears overdone with MLCAPE magnitude given its depiction of mean mixing ratios from 14-15 g/kg later today when upstream 12Z observed soundings sampled only 12-13 g/kg at most. With the EML plume and attendant steep mid-level lapse rates also displaced south of this region, MLCAPE will probably only peak towards 1500 J/kg. Surface-based thunderstorm development will likely be focused in a confined corridor near the evolving frontal wave, currently over northeast SD, as it tracks east-northeast into northern MN. 12Z guidance has generally trended toward a weaker depiction of low-level mass response relative to the 00Z ECMWF, suggesting low-level hodograph curvature may remain small except along the surface warm front. Favorable elongation of the mid to upper hodograph given speed shear with height amid southwest flow should support a few discrete supercells. Severe hail will probably be the primary hazard in coverage, but a couple tornadoes are possible if activity can remain rooted where SRH is enhanced along the west/east-oriented warm front. These threats will likely diminish into late evening as activity spreads towards northeast MN. ...IA to central KS... A weakening MCS persists across southern IA and northwest MO with large-scale outflow analyzed from the I-70 corridor in northeast KS arcing to the northwest in central NE. Air mass recovery will occur across the Mid-MO Valley into this evening, but will clearly be impacted by this morning's activity, which renders uncertainty in just how intense redevelopment this evening will truly be. A hot air mass will be prevalent from the southern High Plains into central KS. Isolated high-based thunderstorms will probably develop along the dryline to triple-point intersection with a threat for isolated severe gusts and hail. More prevalent convective redevelopment will occur atop the residual outflow/differential heating zone this evening as a southwesterly low-level jet intensifies. Forecast soundings differ, but given the presence of the upstream EML and limited time for intense boundary-layer heating it appears most probable that convection will be rooted from elevated parcels, especially with time after dusk. This renders low confidence in a greater tornado threat despite low-level hodographs becoming highly enlarged. With weak changes in magnitude in winds with height above 700 mb, a cluster convective mode should dominate. This should subdue the large hail threat and the weak low-level lapse rates deeper into IA should limit the overall severe wind threat with northeast extent as well. Still with upscale growth into a slow-moving MCS and embedded organized updrafts probable this evening, will maintain a cat 2 severe risk delineation. Read more CHECK UPDATE ZOOM GRAPHIC
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