458 FXUS63 KLOT 012328 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 628 PM CDT Sun Jun 1 2025 .KEY MESSAGES... - Hazy skies prevail through Monday from Canadian wildfire smoke. Patchy smoke possible near the surface Monday afternoon. - Above average temperatures expected Monday and Tuesday - A period of showers and storms expected late Tuesday through early Wednesday. - Much lower confidence, but a second round of showers and t-storms is possible late Wednesday into Thursday. && .DISCUSSION... Issued at 216 PM CDT Sun Jun 1 2025 Quiet conditions remain through the overnight, thanks to the high pressure in the region. Easterly winds will be light tonight before veering to the southwest on Monday. No precipitation expected until Tuesday night. An upper-level ridge over the Plains will slowly continue to move east toward the Great Lakes, keeping north to northwest flow aloft. This keeps the main impacts in the short term forecast centered on the smoke from the Canadian wildfires moving over the area (despite surface winds out of the southwest on Monday). Models are still suggesting that the higher concentration of smoke particles will move over northern Illinois tomorrow. Model soundings are suggesting diurnal mixing could be fairly deep tomorrow with a very weak inversion around 5000 feet. With better agreement in the near surface smoke models suggesting that mixing could bring at least some of the smoke down to the surface, it was decided to add patchy smoke to the forecast for all areas except Ford, Iroquois and the counties in northwest Indiana. Smoke getting to those areas will be monitored, but the plume might not reach there until later when it is a less favorable time of day for deeper boundary layer mixing. This will remain a lower confidence forecast given the uncertainty on how deep the mixing will be. Nevertheless, Hazy skies are expected to persist across the entire area during what would normally be a period with little cloud cover. Lastly, the Euro and the NBM are still keeping warm temperatures across the area, other models are starting to pick up on the fact that with hazy/smoky skies, max temperatures originally anticipated may not be realized. While temperatures are still currently expected to reach the 80s, depending on the smoke concentration, they may struggle to get to the mid to upper 80s. The upper-level flow pattern finally shifts westerly Monday night, then southwesterly Tuesday morning as the next upper- level low moves over the Hudson Bay extending over the northern Plains. There is higher confidence that this will effectively (finally) push the smoke east of the area. Although there is lower confidence in the exact timing of improvement in hazy sky conditions, an overall improving trend is anticipated through the day Tuesday. With smoke exiting the area, there is better chances for temperatures reaching into the upper 80s with a non-zero chance of a couple of 90 degree readings. An upper-level short wave trough over southern Colorado (embedded in the longer wave connected to the upper level low) will move toward the Great Lakes Tuesday night and Wednesday morning. A surface cold front extending from Lake Superior to Kansas will move eastward overnight providing ample forcing for showers and thunderstorms to develop. Lapse rates are looking fairly weak, and the system will be passing over during a less than favorable time. Given the lower instability, there is lower confidence in the severe risk on Tuesday though it cannot be completely ruled out. Especially for area west of the Fox Valley where it might arrive earlier in the afternoon. Models are still disagreeing on how quick this system exits. The GFS solutions keep this fairly progressive which would result in drier conditions around the Rockford Metro while showers continue around and southeast of Interstate 55 on Wednesday. Then the next upper-level short wave from over the Desert Southwest would arrive late Thursday night into Friday for another round of showers and storms. However, the Euro has a much slower progression suggesting it stalling and turning into a pseudo stationary front over the southeastern portions of the CWA, before the next short wave kicks it east and brings rain on Friday. This provides lower confidence in the overall trend and prevented making much adjustments to the PoPs that the NBM provided. Considering how dry the forecast has been as of recently, the main forecast note is the pattern is looking favorable for inclement weather from mid week and into the weekend. It is the timing of rainy versus dry periods that will need to be ironed out. Temperatures return to more seasonable values for the second half of the week and into the weekend. Shower chances cannot be completely ruled out next weekend, but current guidances favors more drier periods than wet. DK && .AVIATION /00Z TAFS THROUGH 06Z MONDAY/... Issued at 628 PM CDT Sun Jun 1 2025 Forecast concern for the terminals... - Increasing Canadian wildfire smoke aloft tonight which may result in periods of reduced visibility Monday. A weak surface high continues to reside over the Great Lakes which will maintain dry and generally VFR conditions through the period. That said, there is a lake breeze moving west across northern IL which will move through RFD between 130z and 02z this evening causing winds to turn east-southeast in its wake. Otherwise, expect light easterly winds to become more variable overnight before settling into a south-southwest direction Monday morning. Wind speeds will also increase on Monday as deeper mixing commences which should allow occasional mid to upper teen gusts to develop Monday afternoon. As gusts subside Monday evening, there is a chance that wind directions may briefly (an hour or two at most) become southeasterly but suspect the overall prevailing direction will be southwest. Finally, smoke from ongoing wildfires in Canada will remain overhead through the TAF period as well. The upper trough over the eastern CONUS that has been advecting the smoke into our area will gradually move eastward tonight into the day on Monday which will result in more westerly mid-level winds across Canada and the Upper Midwest. Therefore, suspect that the heavier concentrations of smoke (currently in the Dakotas and MN) will move more into WI with the plume of smoke in IA being more of our issue. While this plume will still result in hazy VFR skies, confidence in surface smoke concentration remains low. That said, have decided to maintain the SCT025 mention for the off chance a higher smoke concentration results in slightly lower ceilings in addition to some minor visibility reductions at the surface. Will continue to watch trends this evening and overnight and make adjustments as needed. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago