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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.

Monday, July 4, 2022

SPC Jul 4, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0244 PM CDT Mon Jul 04 2022 Valid 042000Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER MS VALLEY/SOUTHWEST GREAT LAKES AND MT TO THE WESTERN DAKOTAS... ...SUMMARY... A few tornadoes and scattered damaging gusts are possible through this evening centered on a portion of the Upper Mississippi Valley and southwest Great Lakes regions. Scattered large hail and isolated severe gusts are possible across parts of Montana into the western Dakotas from late afternoon through tonight. ...20z Update... The previous outlook remains on track. The only changes made with the 20z update were to expand the 2 percent tornado area across northeast ND into a small part of northwest MN given ongoing trends and reports of a funnel near Grand Forks ND. Otherwise, ongoing convection across southern WI/northern IL will pose a short term severe threat for another couple of hours. Reference MCDs 1356 and 1357 for more information on near term severe potential. Additional thunderstorms are expected to develop across portions of WI/MI later this afternoon/evening and may impact similar areas of northern IL into northern IN later this evening. Severe thunderstorms are also still expected to develop across parts of MT into the western Dakotas through this evening. For short term severe potential across parts of central MT, reference MCD 1358. ..Leitman.. 07/04/2022 .PREV DISCUSSION... /ISSUED 1127 AM CDT Mon Jul 04 2022/ ...Upper MS Valley and southwest Great Lakes... A non-severe MCS is ongoing from western WI to the IA/IL border area. While the northern portion will likely further decay, remnants of the southern portion may persist across northern IL into IN this afternoon. Weak mid-level lapse rates and just-in-time moisture return should limit more widespread intensification potential, but isolated damaging wind gusts will be possible into late afternoon as the boundary layer further destabilizes. In the wake of the MCS and its attendant convectively induced shortwave impulse, large-scale ascent should be suppressed to the northwest of the low-level warm theta-e advection regime that is expected to persist from the Mid-MO Valley to southern WI. While there is low confidence in timing of redevelopment, areal extent will likely be focused near the IA/MN/WI/IL border. The degree of boundary-layer destabilization is questionable and its plausible that redeveloping convection will remain slightly elevated atop it. In addition, convective mode should tend to evolve into a west/east-oriented cluster. But rather enlarged low-level hodograph curvature owing to the southwesterly jet and modest surface temperature-dew point spreads favor a conditional threat for a few tornadoes. Consolidation of clusters into a forward-propagating MCS is possible tonight across northern IL into northwest IN with scattered damaging winds becoming the primary threat until convection weakens overnight. ...MT to the Dakotas... Despite minor weak mid-level height rises, presence of 50s surface dew points banked up to the northern Rockies will foster scattered thunderstorm development by late afternoon off the higher terrain in MT. More isolated thunderstorms will likely initiate off the Black Hills and are possible in north-central/northeast ND near a weak surface low. A belt of enhanced mid-level southwesterlies to westerlies will be maintained downstream of the weakening closed low near northwest WA. This will foster 40-50 kt effective bulk shear supporting potential for several supercells with mid-level updraft rotation. Larger buoyancy should be confined to southern SD into southeast ND, more muted values from 750-1500 J/kg are expected to the northwest. This will likely be a limiting factor to greater intensities with significant hail and wind potential expected to be very isolated/conditional. Large hail should be the primary threat with more isolated swaths of severe wind gusts focused on eastern MT into southwest ND this evening/tonight. Read more CHECK UPDATE ZOOM GRAPHIC
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