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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.

Thursday, June 17, 2021

SPC Jun 17, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 AM CDT Thu Jun 17 2021 Valid 191200Z - 201200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE OHIO VALLEY INTO THE NORTHEAST...OVER PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND ALONG THE NORTHERN GULF COAST.... ...SUMMARY... Isolated severe storms are possible Saturday from the Ohio Valley into the Northeast, over parts of the central and northern Plains, and along the northern Gulf Coast. ...OH Valley into the Northeast... A shortwave trough is forecast to move across the Northeast on Saturday, with the strongest midlevel flow from MD northward. A cold front will push eastward across the Northeast, with pockets of favorable instability supporting a Marginal risk of hail or wind. Farther west, the front will become more east-west oriented across the OH Valley, where ample low-level moisture and instability will remain. Early day storms are possible from IN/OH into WV and PA, associated with the previous nights convection. Some of this activity could contain gusty winds, but a weakening trend is expected during the day. Daytime heating along with westerly 850 mb winds should allow for air mass recovery area-wide. Sporadic storms are possible along the length of the trailing front, and in association with a lee trough east of the Appalachians. Both hail and locally severe gusts will be possible. Predictability for these areas is low given model differences with wave/frontal speeds and precipitation depictions, but the large area of favorable deep-layer shear and sufficient instability should favor at least isolated severe storms across the entire region. ...Central and northern Plains... An upper trough is forecast to amplify over the northern Rockies/Plains on Saturday, with midlevel northwesterlies increasing to over 50 kt. Meanwhile, a lee trough will develop during the afternoon over the High Plains, with a cold front surging south overnight as a low shifts into eastern NE and the Dakotas. Strong heating and returning moisture will likely lead to several storms by 00Z from the Black Hills into northeast CO. Hail and localized severe gusts will be possible. Additional storms are forecast overnight into southern SD where warm advection will strengthen due to low-level jet response to the upper trough. Forecast soundings indicate plentiful elevated instability to support a hail threat. ...Southern LA/MS/AL... A developing tropical cyclone is forecast to affect portions of the northern Gulf Coast states on Saturday, although movement/predictability is a bit low. That said, ample tropical moisture is forecast to surge north along and east of the low, along with strong low-level shear. Wind speeds at 850 mb are forecast to exceed 50 kt, which will result in favorable hodographs for a tornado threat where MLCAPE is sufficient. ..Jewell.. 06/17/2021 Read more LIVE: spc.noaa.gov