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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.

Wednesday, September 21, 2022

SPC Sep 21, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1253 AM CDT Wed Sep 21 2022 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WESTERN UTAH TO SOUTHERN IDAHO AND ACROSS THE UPPER OH RIVER VALLEY TO THE LOWER GREAT LAKES... ...SUMMARY... Scattered thunderstorms capable of severe hail, wind, and a few tornadoes, are expected this afternoon and evening across the Upper Ohio River Valley and the lower Great Lakes region. Isolated to scattered severe gusts are also possible across portions of the Great Basin this afternoon. ...Synopsis... An upper wave over the upper MS River Valley/western Great Lakes will gradually deepen over the next 24 hours amid continued cold air advection across the Midwest behind a southeastward moving cold front. Across the western CONUS, a closed low off the coast of northern CA will shift east into central OR, supporting a broad region of ascent across the Great Basin. ...Upper OH River Valley and Lower Great Lakes... The surface cold front, currently draped from central WI into the central Plains, will continue to migrate to the southeast as the synoptic surface low consolidates across southeast Canada through the day. Increasing southwesterly winds ahead of the front will advect rich boundary layer moisture (dewpoints in the upper 60s/low 70s) from IL/IN into OH and far western PA by early afternoon. Combined with modestly steepening mid-level lapse rates, buoyancy is currently expected to increase to around 2000 J/kg MLCAPE along/ahead of the front across IN/OH, decreasing with northeastern extent into NY/VT. The deepening of the synoptic wave will also support increasing flow in the 850-700 mb layer to near 30-45 knots and yield improving helicity in the lowest 1-2 km across northern OH to far western PA. Strong lift along the cold front combined with weak boundary-orthogonal storm motions should favor quick upscale growth from initially discrete cells/clusters capable of large hail to linear segments. The overall kinematic and thermodynamic environments will be supportive of an organized severe threat, including the potential for scattered damaging to severe gusts and a few brief, embedded tornadoes within linear segments. Increased wind probabilities were considered across northeast OH to western PA where latest CAMs show the best signal for an organized line; however, the potential for lingering morning convection along the warm front and poor run-to-run consistency in the spatial coverage of the threat limits confidence in the location/coverage of the best wind potential. ...Great Basin... Deep-layer flow is expected to increase through the day across UT into ID as the closed low moves east into the region. Ascent ahead of the wave coupled with increasing diffluence aloft should support a broad region of ascent with elongated hodographs featuring 0-6 km bulk shear values near 50-60 knots. Despite the dry conditions sampled by the 00 UTC SLC sounding, latest GOES precipitable water imagery shows a plume of higher PWAT values across the Four Corners region. The western periphery of this moisture will likely advect to the north/northwest as low to mid-level flow becomes more meridional, supporting increasing buoyancy through the late afternoon. However, the degree of destabilization remains somewhat uncertain with some spread in guidance noted. Regardless, the strong kinematics/lift should support organization of discrete/semi-discrete cells. Strong to severe gusts appear possible - especially if morning cloud cover remains limited and supports steep low-level lapse rates by the afternoon. ..Moore/Gleason/Weinman.. 09/21/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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