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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.

Sunday, July 25, 2021

SPC Jul 25, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1230 AM CDT Sun Jul 25 2021 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY AND NORTHEAST AND OVER PORTIONS OF THE NORTHERN PLAINS... ...SUMMARY... Thunderstorms with isolated wind-damage potential are possible across parts of the Ohio valley and Northeast, and also across parts of the northern Plains, this afternoon and evening. ...OH Valley/Northeast... Great Lakes upper trough is forecast to move into QC/NY by the start of the day1 period before ejecting into New England later in the day. This feature is partly responsible for ongoing broken band of convection that currently extends from the lower Great Lakes-northern OH-central IN-northern MO. As large-scale forcing shifts away from this region, trailing frontal convection is expected to gradually wane such that only isolated showers/thunderstorms may be ongoing along the wind shift at sunrise. Latest short-range model guidance and HREF are not particularly aggressive with convection across the OH Valley/Northeast during the day as negligible large-scale forcing will be noted across this region. Even so, boundary-layer heating could contribute to a few robust updrafts that will be modestly sheared within northwesterly flow. Gusty winds are the primary threat if this activity materializes. ...Northern Plains... Broad upper ridging will remain centered over the northern Rockies which will maintain northwesterly flow across the northern Plains today. This flow regime will prove favorable for displacing a lee surface cyclone off the higher terrain into northern SD which will result in intense boundary-layer heating across this region. Forecast soundings suggest temperatures will soar to, or slightly above, 100F, effectively removing inhibition within an air mass that will be adequately moist for sustaining deep convection. Although PW values will range between 1-1.3 inches, cloud bases will be very high across the initiating zone (600mb) with surface temperature-dew point spreads around 50F. Any storms that form in this environment could produce locally damaging wind gusts. Southwesterly LLJ is forecast to strengthen across SD during the evening and this may contribute to additional activity toward the SD/MN border during the early evening. ..Darrow/Bentley.. 07/25/2021 Read more LIVE: spc.noaa.gov