570 FXUS63 KLOT 100541 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1241 AM CDT Tue Jun 10 2025 .KEY MESSAGES... - Dry conditions are expected tonight through Wednesday, along with warming temperatures. - Shower and thunderstorm chances return Wednesday night and last through at least the weekend. - There is an emerging signal for hot and humid conditions to develop across the general region next week. && .DISCUSSION... Issued at 312 PM CDT Mon Jun 9 2025 Through Tuesday night: While an isolated thunderstorm did develop over Lake County, IL earlier before moving out over the lake, the surface cold front pushed through just a little too quickly for a more appreciable coverage of thunderstorms to be realized here, instead causing more widespread thunderstorm development to occur just to our east in northern Indiana and southwest Michigan. We`ll still have to keep an eye on the more agitated cumulus along and just behind the cold front in northwest Indiana over the next hour or two for any signs of deeper convective development, but the already low thunderstorm chances otherwise appear to be quickly dwindling. Isolated showers should still occur in northwest Indiana over the next one to two hours, and some spotty light showers closer to the core of the upper-level low over the region could sneak just south of the Wisconsin state line prior to fizzling closer to sunset, but otherwise, the remainder of the forecast area should remain dry into tonight. Dry conditions will then continue to prevail through Tuesday night as the upper-level trough departs to our northeast and the axis of a surface ridge slowly slides eastward across our longitude. The main sensible weather item of note tomorrow looks to be Canadian wildfire smoke yet again as northwesterly flow on the backside of the departing trough funnels another coherent plume of it in our direction. Upstream ASOS/AWOS observations in the eastern Dakotas show that some of this smoke is at ground-level, and the latest HRRR and RAP smoke models indicate that some near-surface smoke could be observed again here tomorrow as this smoke advects our way. The highest near- surface smoke concentrations are depicted during the afternoon as the top of the boundary layer expands into the 1 to 2 km AGL layer, where the greatest smoke concentrations will reside. It should be said, though, that both the HRRR and RAP smoke models were a bit overzealous with mixing higher smoke concentrations down to the surface on multiple occasions during our recent bouts of wildfire smoke, so confidence in their latest near-surface output isn`t particularly high at this time. Alongside our neighboring WFOs, have thus elected to hold off on introducing a formal smoke mention in the weather grids for now. However, we`ll need to monitor upstream observations closely tonight into tomorrow as the introduction of such a mention may eventually be needed. Did keep our sky cover percentages higher than they otherwise would be tomorrow with the expectation that skies should be quite hazy again from the smoke, though. The filtered sunshine should still nevertheless push temperatures tomorrow afternoon into the mid to upper 70s across the entirety of our forecast area, save for maybe northern portions of Porter County if surface winds over Lake Michigan can maintain a westerly or north-of-west direction into the afternoon. Ogorek Wednesday through Monday: On Wednesday, a semi-zonal upper-levevel ridge centered over the northern United States will extend eastward toward the Great Lakes as a surface high pressure system settles over the southeast. With experimental smoke model guidance indicating clearing mid-level concentrations giving cautious confidence to mostly sunny skies, increasing 850mb temperatures toward +18 to +19C should translate to highs in the mid to upper 80s areawide including up to the Lake Michigan shoreline. Return moisture flow around the perimeter of the surface high will lead to rising humidity levels as well, altogether making for a quintessential mid June day. Wednesday evening, pressure falls in the Plains south of a strengthening high pressure system in central Canada will support development of a low-level baroclinic zone from the northern Plains to the Great Lakes. Ensemble model guidance advertises a series of subtle upper-level ripples propagating atop the baroclinic zone Wednesday night through Friday, which will serve as the focus for episodic clusters of showers and thunderstorms (some of which could be strong to severe). At this point, ensemble model guidance favors the preferred axis of thunderstorm activity remaining just to our north in Wisconsin. However, convectively-invigorated baroclinic zones have a habit of ending up further south than models would suggest. Accordingly, will advertise nearly continuous chances (30 to 60%) for showers and storms from Wednesday night through at least Friday, keeping in mind many hours will be dry. Temperatures will be modulated by the eventual cadence and timing of individual thunderstorm clusters, though conceptually a general theme of cooler temperatures near the Wisconsin border and Lake Michigan shoreline with warmer temperatures near US-24 should prevail. Chances for showers and storms will continue into the weekend as a pesky upper-level low meandering through the southern Plains eventually lifts east-northeastward toward the Great Lakes. Exactly how, and when, the low arrives will be subject to refinement in later forecast packages as the overall regime is one that naturally carries lower than average forecast confidence. However, conceptually, would expect a couple days of cooler temperatures owing to more cloud cover and increased coverage of rain. Looking toward next week and beyond, there is an emerging signal within ensemble model guidance for hot and humid conditions to materialize in the general Midwest region (looking at the June 16-20 timeframe or so). With increasingly hot and humid conditions may come with increased threat for severe weather as well. (The EPS mean MUCAPE is already nearing 1500 J/kg in the June 18/19 timeframe, a remarkably strong signal for an environment supportive of severe storms for a 51-member ensemble 10 days out). Borchardt && .AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 1241 AM CDT Tue Jun 10 2025 Forecast concern for the terminals... - Breezy west winds Tuesday gusting into the lower 20 kt range. Overall quiet conditions are expected for the TAF period as a surface high will build into the region on Tuesday. However, there is an upper trough still pivoting across the Great Lakes tonight which may result in a period of SCT to BKN clouds between 09z and 15z as a plume of mid-level moisture moves in from WI. While there are some MVFR ceilings in eastern MN and northern WI with this moisture, recent satellite trends do show the ceilings rising and eroding a bit with southward extent as they encounter drier air. Thus have left TAFs VFR for now but will keep an eye on trends. Any ceilings that do manifest tonight will scatter into a 4500-5000 ft cumulus deck as diurnal mixing develops Tuesday morning and remain VFR through the end of the forecast period. As for winds, light west-southwest winds tonight will increasing and become more westerly on Tuesday with the aforementioned diurnal mixing. Gusts are expected to top out in the lower 20 kt range through mid-afternoon Tuesday before tapering through Tuesday evening. Light southwest winds will then close out the period. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago