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Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

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.

Saturday, August 27, 2022

SPC Aug 27, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Sat Aug 27 2022 Valid 272000Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF IOWA...SOUTHEASTERN MINNESOTA...AND FAR WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorm potential appears most concentrated today over parts of Iowa, southeastern Minnesota, and far western Wisconsin. ...20Z Update... The only substantial change to the outlook with this update was to trim the northeastern extent of the Slight Risk across western WI. Cloud cover has remained entrenched most of this area through the day, which has limited destabilization and reduced severe chances through this evening. Otherwise, convection is still expected to gradually increase in coverage and intensity across parts of IA into southern MN this afternoon and evening. Reference Mesoscale Discussion 1728 for more information on the short-term severe threat across these areas. ..Gleason.. 08/27/2022 .PREV DISCUSSION... /ISSUED 1126 AM CDT Sat Aug 27 2022/ ...IA/MN/WI this afternoon/evening... A midlevel shortwave trough over the central NE/KS border will continue moving northeastward to western IA by this evening and the upper MS Valley overnight. Clouds and ongoing convection within a deep moisture plume over the central Plains will likewise spread northeastward through the day. Surface heating to the east of the thicker cloud band and relatively steep low-midlevel lapse rates will contribute to MLCAPE of 1500-2500 J/kg, and the likelihood of additional thunderstorm development this afternoon in the zone of differential heating from IA into southern MN (along and south of a warm front). Vertical shear profiles are forecast to be a bit disjointed with substantially backed/weaker flow in the mid levels across IA this afternoon. Low-level shear/clockwise hodograph curvature will be larger this afternoon/evening closer to the warm front across southeast MN/western WI, with a similar weakness in the midlevel flow. Thus, the environment favors a mixed/messy storm mode with clusters and some transient rotating updrafts, with a primary threat for damaging winds and isolated large hail given the moderately large buoyancy/precipitation loading and sufficiently steep low-midlevel lapse rates (DCAPE near 1000 J/kg). ...TX Panhandle into KS this afternoon/evening... Along the southern fringe of the residual monsoonal moisture plume and the ejecting midlevel trough over northern KS, differential heating and weak convergence along a lee trough will support scattered thunderstorm development later this afternoon. Midlevel lapse rates will not be steep, but surface heating/mixing will steepen low-level lapse rates, and westerly flow aloft will contribute to modest effective bulk shear of 25-30 kt. Somewhat organized cells/clusters will be capable of producing isolated strong-severe outflow gusts and marginally severe hail from mid afternoon into this evening. ...Southern MT and vicinity this afternoon/evening... Within the primary jet, an embedded speed max/shortwave trough over southern BC and WA will progress eastward to MT later this afternoon into tonight. An associated cold front will move into central MT by this evening, with strong surface heating and deep mixing in advance of the front. Some high-based convection is expected to form over the higher terrain of southern MT later this afternoon, and storms will spread eastward into this evening. Though low-level moisture and buoyancy will be limited, deep inverted-v profiles will support isolated strong-severe outflow gusts. Read more CHECK UPDATE ZOOM GRAPHIC
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