160 FXUS63 KLOT 022040 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 340 PM CDT Mon Jun 2 2025 .KEY MESSAGES... - Smoke (mostly aloft) will filter sunshine until cloudiness rolls in Tuesday. - Showers and thunderstorms will likely overspread the area from west to east late Tuesday afternoon into Tuesday evening. A couple of strong to marginally severe storms could affect locations near and west of the I-39 corridor. - Cooler with rain on Wednesday, followed by additional periods of showers and perhaps some storms Thursday and Friday. && .DISCUSSION... Issued at 340 PM CDT Mon Jun 2 2025 Through Tuesday Night: A mix of cirrus and Canadian wildfire smoke is evident over the region this afternoon on GOES visible satellite imagery. Fortunately, the overall lack of visibility reductions in regional METAR observations has suggested that the smoke has largely remained suspended aloft, though HRRR-Smoke cross- sections indicate that the bottom of the thick smoke layer is situated roughly at 1 km AGL and that light smoke concentrations could still be brought down to ground level while mixing heights are at their peak this afternoon. The latest HRRR, RAP, and Canadian smoke model runs all favor smoke persisting aloft through tomorrow morning across our whole forecast area before focusing across the southeastern half of our CWA tomorrow afternoon, where there will be another chance for some light smoke concentrations to get mixed down to ground level again. Tonight into tomorrow, a northeastward-drifting southern stream shortwave trough will become sheared out and get absorbed into a much broader positively-tilted northern stream longwave trough as the troughs pass over the Great Plains. As this occurs, convection that has blossomed this afternoon along an elongated frontal zone spanning from Texas northeastward into Ontario will expand its spatial footprint and persist through the night into tomorrow as the frontal zone slowly inches eastward. This frontal zone should remain far enough to the west for most of our forecast area to remain dry during the daytime on Tuesday. One thing to keep an eye on though will be how quickly a band of convection tracking across Kansas and Oklahoma decays as it encounters increasingly depleted instability with northeastward extent. Most of the latest model guidance supports at least isolated showers surviving into our northwestern CWA before fading away, so have maintained slight chance and chance PoPs there for the afternoon. Otherwise, strengthening southwesterly wind fields ahead of the frontal zone will result in wind gusts exceeding 30 mph during the afternoon. The warm air advection off of these winds coupled with filtered sunshine will afford us another warm day with high temperatures in the 80s, warmest across the southeastern half of our forecast area, where cloud cover should be less opaque and expansive compared to points farther northwest. Closer to the cold front, new thunderstorm development is expected during the daytime on Tuesday as the pre-frontal air mass destabilizes. Deep-layer shear vectors will be oriented roughly parallel to the initiating frontal boundary, which should cause the deeper frontal convection to grow upscale relatively quickly. However, subpar lapse rates and only a modest overall degree of instability (especially if the decaying morning convection gunks the environment up a good bit to our west and southwest) puts into question how strong the thunderstorms developing in northern Missouri and southern/eastern Iowa will become and how far northeast they will be able to sustain an appreciable intensity. That said, low to mid-level wind fields will be fairly strong, so if any robust storms that develop in northern Missouri or southeastern Iowa manage to make it into our forecast area before losing steam, then they could produce strong to damaging wind gusts tomorrow evening. This would especially be the case within any organized bowing structures that materialize. The best overall chances for severe weather should remain to our west and southwest, but within our forecast area, areas near and west of the I-39 corridor would be most likely to be affected by any stronger storms that manage to make it up here. By the late evening, diminishing boundary layer instability and increasing convective inhibition should kill off any remaining stronger convection, though a band of showers (perhaps with some embedded lightning) should persist across northwestern portions of our forecast area through the night. Ogorek Wednesday through Monday: The cold front associated with the longwave trough over northern Manitoba today will drift southeastward across the forecast area Tuesday night into Wednesday morning, bringing primarily anafrontal showers/rain across the area under modest forcing with the right entrance of a mid to upper-level jet. This pattern resembles early fall more than early summer, with max temps for the calendar day Wednesday for at least some of the area occurring prior to sunrise ahead of the front. Wherever the rain band is more prominent during the day, temps should hold in the 60s (50s near the lake). A trough over the northern Rockies midweek is progged to either pickup or partially shear an upper-level low currently over the desert southwest. Given the distance between the two features, guidance non-suriprsingly varies with the broader mid-level pattern across the central CONUS Thursday into Friday. The consensus is for most of the energy from the southwest low to result in cyclogenesis along the stalled front across Missouri and southern IL/IN late Thursday, resulting in a renewed chance of rain or periods of showers with some storms Thursday night into Friday. Behind Friday`s potential precip, the front should finally clear the area well to the southeast. A sprawling high pressure across the western Great Lakes this weekend should produce seasonable conditions and dry weather Saturday and possibly through Sunday. Kluber && .AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 1227 PM CDT Mon Jun 2 2025 SSW winds are expected through the period, backing to more of S direction overnight for a time. Speeds will settle around 10 knots and persist through tonight. A few infrequent gusts to 20 knots can be expected this afternoon, though smoke aloft should temper mixing enough to limit gustiness. Winds will then increase with gusts in excess of 25 knots by late Tuesday morning, and approaching or exceeding 30 knots with medium confidence Tuesday afternoon. Canadian wildfire smoke filtering over the area will remain apparent through at least tonight. Some haze this afternoon, though likely above 6SM visibility (and thus no inclusion in the TAF), could persist tonight as any smoke becomes trapped in the nocturnal inversion. Any shower or isolated thunderstorm activity will remain confined NW of the ORD/MDW terminals through Tuesday afternoon. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory from 10 AM to 10 PM CDT Tuesday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago