Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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944 FXUS63 KLOT 082334 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 634 PM CDT Sat Jun 8 2024 .KEY MESSAGES... - A cold front will move through the area this afternoon and evening with a band of showers and a few thunderstorms. Widespread severe weather is not expected. - Breezy northwest winds and seasonable highs are expected on Sunday, followed by breezy northeast winds and seasonably cool conditions on Monday. - A gradual warming trend is expected from Tuesday onward with a return of above-average temperatures by the end of the week. && .DISCUSSION... Issued at 216 PM CDT Sat Jun 8 2024 Today and Tonight: Recent surface, radar, and satellite observations depict a low pressure system centered near Clinton, Iowa along a surface cold front extending from southern Wisconsin into eastern Iowa and central Missouri. A narrow tongue of low-level moisture characterized by surface dew points in the low to mid 60s continues to slide into northwestern Illinois ahead of the front and just to the south of subtle low-amplitude upper-level shortwave propagating within a seasonably strong upper-level jet across the central Great Lakes. Pockets of clearing across northern Illinois combined with increasing low-level moisture is allowing for the development of shallow low-level instability, with the most-recent RAP analysis indicating around 500 J/kg of MLCAPE (50-75 J/kg of which in the lowest 3 km). Over the next few hours, coverage of ongoing showers near the Wisconsin state line will increase and pivot southeastward over northern Illinois within the shallow but destabilizing boundary layer. A few thunderstorms remain possible amongst otherwise scattered showers within the southeastward-shifting zone. With strong low- to mid-level shear (thanks to a stark shift in wind direction along the front and a close proximity of the upper- level jet to our north), any sustained updrafts will have the opportunity to develop transient low- to mid-level rotation and become a low-topped supercell. As a result, we cannot rule out a report of a funnel cloud or even brief tornado this afternoon, particularly near the best overlap of low-level instability and near-surface vorticity along the front. Extrapolating the positioning of the low-level moisture axis and arrival timing of the front, such a threat for funnel clouds should materialize near I-80 between 3 and 6 PM. Now, this is not an environment that appears supportive of damaging tornadoes, and the most likely scenario is that a band of showers with an embedded lightning strikes moves through without any fuss. Nevertheless, move indoors if you see a funnel cloud or otherwise hear thunder. The axis of showers and embedded thunderstorms will move southeastward into northwestern Indiana this evening. Behind the front, an increase in northerly winds will cause waves on Lake Michigan to quickly build to 2-4 feet. While not an ideal beach day, be prepared for quickly changing conditions if out on the water. Overnight lows tonight will range from the low to mid 50s. Sunday and Monday As upper-level cyclonic flow gradually moves through the Great Lakes Sunday into Monday, several embedded short-wavelength troughs will move overhead. As a result, Sunday will be marked by seasonable temperatures in the mid to upper 70s and breezy northwest winds. Winds will turn onshore on Monday, leading to a seasonably chilly day with highs in the lower 60s lakeside to lower 70s inland. While our forecast is dry both days, it wouldn`t take much to squeeze out a few sprinkles during both afternoons as low-level lapse rates steepen and allow for appreciable depth to cumulus clouds. Also, onshore winds will cause choppy waves and dangerous swimming conditions across all Illinois and Indiana Lake Michigan beaches on Monday. Tuesday Onward: A gradual warming trend is expected Tuesday onward. Ensemble model guidance continues to advertise summer-like (and above-average) temperatures returning by the end of the week, following by increasing humidity levels (and chances for thunderstorms) sometime during the 3rd week of the month. Borchardt && .AVIATION /00Z TAFS THROUGH 06Z MONDAY/... Issued at 634 PM CDT Sat Jun 8 2024 Key Messages: - Rain ending early this evening with MVFR/IFR ceilings ending soon thereafter - Breezy northwesterly winds tomorrow afternoon The back edge of this afternoon`s rain is moving through the Chicago metro at the time of this writing, and this rain and its associated MVFR/IFR visibility reductions will cease prior to 01Z at ORD and MDW and 02Z at GYY. The back edge of the attendant MVFR/IFR stratus deck is lagging behind the back edge of the precipitation, but a return to VFR conditions is favored to occur approximately 1-3 hours after the rain has ended. Winds will go light tonight but should pick back up again after sunrise tomorrow. Initially, northwesterly gusts to around 20 kts can be expected tomorrow morning, but gusts closer to 30 kts are likely to become common during the afternoon as mixing heights rise markedly. Towards the end of the current TAF period, a southward-sagging cold front will produce a northerly wind shift, with winds likely to turn east of 360 degrees at ORD and MDW towards the end or just beyond the current end time of their 30-hour TAF period. Ogorek && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago