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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.


Wednesday, June 28, 2023

SPC Jun 28, 2023 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0744 AM CDT Wed Jun 28 2023 Valid 281300Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FOR PARTS OF THE UPPER MS VALLEY AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Large hail, isolated damaging winds and a tornado or two will be possible this afternoon/evening across northwest Wisconsin/eastern Minnesota and across the Nebraska Panhandle and vicinity. ...Upper MS Valley this afternoon through late evening... Around the northern periphery of the midlevel high over TX, a shortwave trough (enhanced some by prior convection) will progress eastward over MN/WI through this evening. An associated/weak surface cold front will likewise move eastward across MN, while low-level moistening occurs from the southwest during the day beneath a lingering plume of steep midlevel lapse rates. MLCAPE will increase to 2500-3000 J/kg with sufficiently long/curved hodographs for a supercell threat later this afternoon/evening from eastern MN into northwestern WI, along and just ahead of the front. Large hail will be the main threat, though isolated wind damage and a tornado or two will also be possible. ...Central High Plains this afternoon into tonight... A surface cold front is moving slowly southward across northeast CO/northwest KS/southwest NE this morning. Low-level flow will veer to easterly during the afternoon, with boundary-layer dewpoints from the mid 50s to lower 60s F in the upslope regime. Subtle speed maxima aloft and surface heating in cloud breaks should allow weakening of convective inhibition by mid-late afternoon, when at least isolated thunderstorm development will be possible from southeast WY into the western NE Panhandle, and possibly northeast CO. Moderate buoyancy and long, relatively straight hodographs will favor supercells capable of producing isolated very large hail, along with some potential for strong-severe outflow gusts and a tornado or two. The persistence of the storms past late evening is uncertain. ...Northern/central IL and vicinity overnight... The moist boundary layer (dewpoints mid 70s) across OK will spread northeastward across MO and southern IA through tonight, beneath steep midlevel lapse rates of 8-9 C/km. Large CAPE is expected in this regime, though a warm elevated mixed layer will also tend to cap the boundary layer through the day. However, warm advection will increase tonight with corresponding strengthening of a west-southwesterly LLJ, and the chance for elevated thunderstorm development will increase overnight from eastern IA into IL. MUCAPE > 2500 J/kg, steep midlevel lapse rates and effective bulk shear > 50 kt will support the potential for elevated supercells to produce large hail, while DCAPE > 1000 J/kg suggest some potential for strong gusts to reach the ground. There is substantial uncertainty regarding the specific corridor of storm development overnight, so will maintain MRGL risk for now, but later updates will continue to monitor the northern/central IL area. ..Thompson/Mosier.. 06/28/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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