837 FXUS63 KLOT 020752 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 252 AM 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. - Cooler with rain on Wednesday, followed by additional periods of showers and perhaps some storms Thursday and Friday. && .DISCUSSION... Issued at 252 AM CDT Mon Jun 2 2025 Through Tuesday Night: Last light GOES true color RGB imagery nicely depicted the large area of smoke from Canadian wildfire blanketing most of the central portion of the country. The concentration of smoke aloft did decrease some Sunday, but satellite imagery shows what appears to be a much dense/higher concentration smoke in a roughly north-south axis near and west of the Mississippi River early Sunday evening. Mid level flow will continue to back to a more westerly direction today as mid-upper level ridge shifts eastward into the Midwest and western Great Lakes. This should shove that axis of denser smoke eastward and into our CWA today. Near surface smoke concentration output from the HRRR has been trending toward a lower near sfc smoke concentration today. In addition, the HRRR near sfc smoke forecasts upstream have generally shown a high bias based on visibility observations upstream. So while some near sfc smoke is possible this afternoon and tonight, it seems unlikely that the concentration would be enough to result in any significant visibility restrictions. The denser smoke concentration today will probably keep temps a couple/few degrees cooler than they otherwise would have been, but low to mid 80s still appear attainable. Strengthening southwesterly flow is expected in advance of an approaching upper trough and associated sfc cold front Tuesday. Southern stream shortwave is expected to phase with the large northern stream trough as they move eastward toward the region. Relatively warm mid level temperatures and subsequent weak mid level lapse rates should dampen instability out ahead of this front. By later Tuesday afternoon, a narrow axis of moisture will advect northward in advance of the front and lead to MLCAPE values near to maybe just above 500 J/kg into northwest IL. While there will be a notable increase in mid level flow associated with the southern stream shortwave trough, fairly unidirectional flow with strong low level jet should result in only about 30 kt of effective shear. Given the fairly strong low-mid level flow, cannot rule out a strong to marginally severe wind gust or two over our western CWA late Tuesday afternoon into Tuesday evening, the weak instability and poor low to mid level lapse rates suggest any threat of strong to severe gusts should be pretty limited. Showers and thunderstorms are expected to gradually spread eastward across our CWA Tuesday night, but what little boundary layer based instability we can muster up later Tuesday afternoon should largely be gone as we lose diurnal heating. Expect the thunderstorm coverage and intensity to gradually wane Tuesday night as this activity moves across the area. There`s a plausible scenario where the coverage of precipitation diminishes considerably too as the activity moves into eastern portions of our CWA Tuesday night. For now, didn`t make any changes to NBM pops (which are pretty aggressive) Tuesday night, since guidance is pretty insistent on widespread and fairly soaking rainfall across our CWA Tuesday night. - Izzi Wednesday through Sunday: The cold front associated with a 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 /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 1242 AM CDT Mon Jun 2 2025 Light S winds at TAF issuance will settle SSW from around sunrise through the remainder of the period. Speeds will increase to around 10 knots for much today and tonight. A few infrequent gusts to 20 knots can be expected late this afternoon, though smoke aloft should temper mixing enough to limit gustiness. Canadian wildfire smoke filtering over the area will remain apparent through at least tonight. Upstream satellite and surface obs over eastern Iowa suggest that a thicker ribbon of smoke will cross the terminals today, with daytime mixing bringing down some of the smoke toward the surface to produce hazy conditions this afternoon. Some haze may persist tonight as any smoke becomes trapped in the nocturnal inversion. As an added note, clouds in the current TAF are an approximation of the base of the main smoke layer, with little to no actual clouds expected over the area through the period. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago