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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.

Saturday, July 24, 2021

SPC Jul 24, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 0310 PM CDT Sat Jul 24 2021 Valid 242000Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON AND EVENING FROM NORTHERN ILLINOIS INTO LOWER MICHIGAN... CORRECTED FOR MCD REFERENCES IN OUTLOOK TEXT ...SUMMARY... A few severe thunderstorms with wind damage, isolated large hail, and a tornado or two are possible from northern Illinois into Lower Michigan late this afternoon into this evening. ...20Z Update... No change has been made to the Slight Risk. Scattered strong/severe thunderstorms are still expected late this afternoon into this evening from northern IL into Lower MI. See MCD 1340 and Severe Thunderstorm Watch 390 for more information regarding the threat in Lower Michigan, and MCD 1341 for more information regarding the threat across far southeast IA into northern IL. Isolated strong/severe storms are also possible across portions of the Southwest. The Marginal Risk has been expanded slightly to include portions of southwest UT and northwest NM, based on the position of ongoing strong convection that will move into portions of AZ/southern NV later this afternoon/evening. See MCD 1342 for more information regarding the threat in this region. ..Dean.. 07/24/2021 .PREV DISCUSSION... /ISSUED 1124 AM CDT Sat Jul 24 2021/ ...Lower MI... A well-defined shortwave trough over WI/Upper Mi will track rapidly eastward today across Lower MI. A moist and unstable air mass is in place over this region, along with relatively strong vertical shear. Thunderstorms (including a supercell or two) are expected to develop by mid-afternoon and track across the region, posing a risk of damaging wind gusts and isolated tornadoes. Please refer to MCD #1339 for further details. ...IL/IN... By mid-late afternoon, strong instability is expected to develop along the trailing cold front from southwest Lower MI into northern IL/IN. Scattered thunderstorms are expected to form along this axis, although models vary significantly regarding coverage and intensity. Those storms that do form will pose a risk of damaging wind gusts through the early evening. ...AZ/NV... Similar to yesterday, scattered afternoon thunderstorms will affect much of northern AZ and southern NV. A moist boundary layer coupled with strong heating through early afternoon will help to yield MLCAPE values around 1500 J/kg. Low-level shear is weak, but 25 knot mid-level winds will help organize westward-moving cold pools and result in the potential for gusty winds in some areas, along with hail in the higher elevations. Read more LIVE: spc.noaa.gov