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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, August 28, 2021

SPC Aug 28, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1216 PM CDT Sat Aug 28 2021 Valid 291200Z - 301200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL GULF COAST... ...SUMMARY... Isolated strong to severe storms are possible across portion of the Upper Great Lakes Sunday. Additionally, tornadoes may occur within the right-front quadrant of Hurricane Ida over the central Gulf Coast. ...Hurricane Ida... The National Hurricane Center is forecasting landfall of what is expected to be major Hurricane Ida Sunday afternoon or evening along the southeast or south-central coast of Louisiana. The outer bands of Ida will likely be impacting immediate coastal areas of southeast LA/MS/AL Sunday morning. Impacts will increase across southeast LA into southern MS/AL and the FL Panhandle through the period as Ida tracks toward the northwest. Low-level wind fields are expected to be quite strong with Ida, resulting in strong low-level shear favorable for rotating cells within the right front quadrant of the hurricane. Forecast dewpoints across the region have increased somewhat from yesterday, with surface dewpoints generally in the 73-76 F being common, though mid-to-upper 70s F dewpoints are already in place. Small deviations is surface dewpoints can have large impacts on tornado potential in tropical cyclones via changes in low level instability. At this time, at least pockets of greater surface-3km MLCAPE (100-175 J/kg) are forecast, which would support an increasing threat for tropical cyclone tornado activity. As the forecast track/intensity for Ida has not changed much since the previous outlook, tropical cyclone tornado analogs also remain unchanged. A few previous storms matching the track, speed, and/or strength well are Katrina (2005), Gustav (2008) and Ike (2008). Each one of these storms produced numerous tornadoes, with Katrina producing the most at 59. These historical analogs and favorable environment merits maintaining 5% tornado probabilities throughout much the right-front quadrant, with 2% probabilities (and 5% thunderstorm wind gust probabilities) across more of the Lower MS Valley and Southeast. ...Upper Great Lakes/Ohio Valley... Thunderstorms are expected to develop early Sunday afternoon along and ahead of a cold front associated with a shortwave trough moving across the upper Great Lakes/Ontario. Vertical shear will be weaker with southward extent into the Ohio Valley, resulting in a mainly multicellular storm mode. However, moderate instability will be in place and an isolated instance or two of hail and/or a couple of damaging wind gusts could still occur. Better vertical shear is anticipated across the Upper Great Lakes region, with an attendant increase in the potential for a few stronger, more organized storms. Deep-layer flow will generally be unidirectional and parallel to the cold front, resulting in mainly thunderstorm clusters/line segments. Isolated hail and damaging wind gusts will be possible with this activity from northeast IL through Lower MI. ..Leitman.. 08/28/2021 Read more LIVE: spc.noaa.gov