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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.

Thursday, July 22, 2021

SPC Jul 22, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Thu Jul 22 2021 Valid 222000Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL INTO NORTHEAST MONTANA... ...SUMMARY... Thunderstorms capable of severe wind gusts are possible late this afternoon into early tonight from parts of central into northeast Montana. Other isolated strong storms may occur over parts of Arizona, and over portions of Florida/Georgia. ...20Z Update... The only substantial change to the outlook was to extend 5% wind probabilities a little further east across western ND and northwest SD, based on the expected eastward progression of storms currently developing across eastern MT. Localized severe wind gusts still appear possible from eastern MT into the western Dakotas, as storms move through a hot and well-mixed environment, though marginal deep-layer shear and weak low-level flow are expected to generally limit storm organization and coverage of the threat. Further west, strong storms are still expected to develop across portions of central MT late this afternoon and move northeastward this evening, accompanied by a potentially more organized severe wind risk. See MCD 1326 for more information. ..Dean.. 07/22/2021 .PREV DISCUSSION... /ISSUED 1058 AM CDT Thu Jul 22 2021/ ...MT... A large upper ridge is centered over the central Rockies today, with relatively strong southwesterly flow aloft extending from the Pacific Northwest region into ID/MT. Visible satellite imagery shows mostly clear skies over central MT, where dewpoints are in the 50s. Temperatures should warm rapidly into the 90s over this region, resulting in very steep low-level lapse rates and inverted-v thermodynamic profiles. Thunderstorms will develop this afternoon over the mountains of southwest MT and move quickly northeastward into the adjacent plains. Given the fast steering flow and favorable lapse-rates, these storms will pose a risk of damaging wind gusts through the afternoon and evening. ...AZ... Similar to yesterday, thunderstorms are expected to develop this afternoon over the mountains of western NM and eastern AZ. Easterly mid-level winds will help these storms move off the higher terrain into the lower deserts this evening. Ample low-level moisture will aid in a few intense cells capable of locally gusty/damaging winds. ...FL... A narrow corridor of stronger northwesterly mid-level winds is evident in morning model data over southern GA and northern FL. This is coincident with a very moist boundary layer with dewpoints in the mid 70s and precipitable water values over 2 inches. Strong heating will yield afternoon MLCAPE values over 2500 J/kg and the development of scattered thunderstorms. The strongest cells will be capable of wet microbursts and perhaps small hail. Read more LIVE: