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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 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1248 AM CDT Sat Sep 17 2022 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER MISSISSIPPI VALLEY INTO THE MID MISSOURI VALLEY... ...SUMMARY... Isolated severe thunderstorms are expected Saturday across the upper Mississippi Valley region, south into the Mid Missouri Valley. All hazards are possible across the north with primarily hail/wind into the Missouri Valley. ...Discussion... A notable short-wave trough is currently ejecting across the northern High Plains and should advance into the eastern Dakotas by 18z, before shifting into the upper Great Lakes/northwestern ON by daybreak Sunday. A weak surface low is forecast to evolve along the lee trough in response to this feature, then track into northeast SD by 18z. Some deepening is expected, which should result in a sharpening baroclinic zone across central MN by peak heating. Latest model guidance suggests strong surface heating should occur across eastern SD into west-central MN immediately ahead of the surface low/front. Resultant thermodynamic profiles could yield SBCAPE in excess of 2500 J/kg where dew points hold in the mid 60s. Additionally, forecast shear favors supercells as the approaching short wave is expected to contribute to strengthening wind profiles. NAM 20z sounding for AXN exhibits 40kt surface-6km bulk shear, veering winds with height and 2800 J/kg SBCAPE. Convection is expected to develop near the ND/SD/MN border ahead of the surface low, possibly as early as 19-20z. This activity should track northeast along a warm front that will advance north ahead of the short wave. All hazards are possible with these supercells, including the risk for a few tornadoes. Convection should spread toward the upper Great Lakes late in the period. Farther south, a weakening corridor of convection is spreading across the central Plains ahead of a disturbance at 0530z. LLJ is currently strengthening across KS into southern NE early this morning, and this should aid continued eastward propagation into the beginning of the day1 period. This activity is not forecast to completely dissipate, and some early-day hail/wind threat appears possible as LLJ veers into western IA and strengthens. It's not entirely clear how concentrated this activity will be, as some uncertainty exists regarding downstream heating and the influence of convective debris/precipitation. Additionally, timing of the early-day disturbance is not particularly favorable for supporting renewed convection along the primary surface boundary that should remain draped across southeast NE into northern KS. Even so, strong surface heating in the wake of this activity, along with convective outflow, may result in secondary development later in the afternoon. While the early convection will likely be multicell clusters, some risk for supercells appears possible where isolated convection could evolve along the trailing boundary. Hail/wind are the primary risks with this activity. ..Darrow/Karstens.. 09/17/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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