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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.

Monday, June 28, 2021

SPC Jun 28, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0216 AM CDT Mon Jun 28 2021 Valid 301200Z - 011200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE UPPER OH VALLEY INTO THE NORTHEAST STATES... ...SUMMARY... Isolated severe thunderstorms are possible Wednesday afternoon and evening from the Upper Ohio Valley into Northeast States. ...Synopsis... Subtropical ridging is forecast to persist across the southern Plains and Southeast States on Wednesday, while a weak upper flow regime continues over the Southwest and Great Basin. Upper ridging centered of southern Alberta early Wednesday is expected to gradually shift eastward throughout the day as a compact shortwave trough traverses its western periphery over British Columbia. Lastly, a series of shortwave troughs will likely progress through the base of an upper trough extending from the Hudson Bay into the Upper Midwest early Wednesday. Evolution of these shortwaves coupled with the eastern moving upper ridge will likely result in an overall eastward progression of the upper trough, with some deepening also possible. ...Upper OH Valley into the Northeast States... Stronger mid-level flow through the base of the upper trough mentioned in the synopsis will gradually shift southward into more of the Upper OH Valley and Northeast as the upper trough deepens. This stronger flow aloft will overlie a very moist and at least moderately unstable air mass, characterized by upper 60 to low 70 dewpoints. This air mass is expected to destabilize amid daytime heating, with low-level convergence and increasing large-scale forcing for ascent attendant to an approaching shortwave trough both contributing to widespread thunderstorm development. A predominantly multicellular storm mode is anticipated, but a few more organized line segments are possible, with an attendant threat for damaging wind gusts. Some isolated hail is also possible, particularly in areas where diurnal heating and resulting instability are strongest. Veered low-level flow and a mostly linear storm mode should keep the tornado potential low. Uncertainties regarding the effects of antecedent showers and thunderstorms as well as some run-to-run variability within the guidance merits only including 5% severe probabilities with this outlook. Higher probabilities may be needed in later outlooks if current trends within the guidance continue. ..Mosier.. 06/28/2021 Read more LIVE: