
Widespread life-threatening flash and urban flooding continues in south-central Texas, with considerable flooding impacts possible across central Texas. Wildfire smoke is impacting air quality across much of the Great Lakes region into southern New England and the Mid-Atlantic. Monsoonal thunderstorms may produce isolated to scattered flash flooding across the Southwest into the Great Basin. Read More >
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| 537 FXUS63 KLOT 181114 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 614 AM CDT Sat Jul 18 2026 .KEY MESSAGES... - Hot and humid conditions continue today. - Scattered thunderstorms are expected to develop along a cold front this afternoon and evening, some of which could be strong to severe. Highest thunderstorm chances exist near and south of I-80. - Wildfire smoke may return to the area in the wake of the cold front late Saturday and continue into Sunday. && .DISCUSSION... Issued at 316 AM CDT Sat Jul 18 2026 Early this morning, conditions are quiet locally with mostly clear skies and mild temperatures in the 70s. A few isolated showers had previously been festering around the area, but those cleared out shortly after midnight. Meanwhile, an MCS is tracking south-southeastward across western WI, in the vicinity of La Crosse as of around 3 AM. This formed late last evening along a cold front that will be dropping into our area from the north later this morning. Latest radar and satellite trends would suggest that this feature should largely miss our area to the west this morning with the track of the thunder and heavier shower coverage trending toward the Mississippi Valley and areas immediately west of our CWA. A line of light showers extends east from the core of the system and is more on track to reach our local area, but it`s tough to get a handle on exact trends and model guidance isn`t offering much help. The most we should expect out of this complex within our area is perhaps a few showers and maybe an embedded thunderstorm across our northern and especially northwestern CWA shortly after dawn, although there`s a good chance this leaves us alone altogether. This complex, if it even makes it into northern IL, will precede the effective cold front by a couple of hours which looks to cross the WI state line closer to mid-morning. This front will be the trigger for potential severe weather later today as it drops south across our CWA through the afternoon. There`s excellent agreement on the timing of the frontal passage, but not so much on thunder coverage. As the front moves across the northern CWA mid-late morning, the environment looks to be capped to ML-based convection. A few camps are resolving some isolated elevated convection during the morning across our north, but most guidance keeps this period dry. Should elevated thunderstorms develop during the morning, it`s possible that some stronger wind gusts could punch through to the surface. Thunder chances will build into the afternoon as the environment continues to destabilize ahead of the front. The cap is expected to break sometime around late morning/early afternoon and storms are expected to blossom along the front as it does. There is good agreement on this happening as the front is roughly between the I-90 and I-80 corridors, so unfortunately Chicago and core of the metro area reside in this area of highest uncertainty with the option to stay dry or to see densely scattered, potentially strong thunderstorms build overhead. Confidence in an uncapped environment and, in turn, thunderstorms becomes rather high as the front moves south of I-80. The line will then exit our area to the south near the start of the evening. Effective shear will be meager this afternoon, on the order of 20 to 25 kt. But over 3,000 Joules of MLCAPE ahead of the front with deep layer moisture and tall ELs will promote deep, robust updrafts capable of producing damaging downburst winds and perhaps small to marginally severe hail. Low level hodographs do not look very supportive of a tornado threat. And while coverage looks pretty tightly confined to the front with the storm threat only lasting as many as a couple of hours over any given area, slower storm motions (toward the south at around 20 to 25 mph) and well over 2" of PWAT will allow for periods of very heavy rainfall and perhaps some localized flooding. Just about all latest CAM guidance depicts pockets of 1 to 2" of QPF over the course of a couple of hours, largely south of I-80, which would likely lead to some ponding or nuisance flooding in spots. In the newest Day 1 Outlook, SPC expanded the wind-driven Slight Risk westward to include all areas roughly along and south of I-80 with a marginal risk up to the WI state line. The smokey conditions and air quality have greatly improved since 24 hours ago. However, north and northwesterly flow in the wake of the cold front will introduce another plume of smoke to the region late tonight into Sunday. Luckily, the latest HRRR and RRFS smoke forecasts anticipate smoke concentrations far less than what we saw on Thursday and early yesterday. Nonetheless, look for more haze and impacted air quality again on Sunday. Relative high pressure will slide into the upper Midwest for Sunday and should provide mostly sunny skies to round out the weekend, with the possible exception of a filter of haze. After seeing upper 80s and lower 90s again today with heat indices pushing 100F, more comfortable conditions are expected for Sunday with high temperatures in the lower and middle 80s and lower humidity. Additionally, high waves and dangerous currents are expected to develop on southern Lake Michigan late today and into early Sunday. Accordingly, issued a Beach Hazards Statement around the area for dangerous swimming conditions from this evening into mid-morning Sunday with conditions looking to ease through the rest of the day. Attention then turns to the Monday and Monday night period with the potential for additional severe convection around the region. A shortwave impulse scooting across the Plains will phase with a strengthening upper trough swinging into the upper Midwest and a surface cold front is expected to pass through the area. A lot of uncertainty revolves around this system with a number of medium range camps even resolving two separate cold frontal passages: one during the daytime and a second late Monday night. For that reason, we could be looking at multiple rounds of thunderstorms, although some models only want to convect along one front and not the other. Despite the traditionally less favorable time of day, the latter potential harbors the seemingly greater severe threat as it will be more strongly forced by features aloft and working with a much better shear profile than during the daytime. But for now, there`s too much uncertainty to say much else, so stay tuned as the picture comes into focus over the next couple of days. SPC has introduced a Day 3 Slight Risk to our northwestern CWA and a Marginal Risk elsewhere for Monday. Doom && .AVIATION /12Z TAFS THROUGH 18Z SUNDAY/... Issued at 614 AM CDT Sat Jul 18 2026 West-southwest winds will increase in magnitude over the next few hours with frequent gusts in the lower 20 kt range by mid- morning. Meanwhile, a cold front will move southward across the terminals from mid-morning through early afternoon shifting winds from west-southwest to northwest. A backdoor cold front coming off Lake Michigan will then turn winds northeasterly, first at GYY/ORD/MDW and then DPA/RFD. Have already noted thunderstorms developing along the approaching cold front in northern Iowa within a narrow axis of relatively steeper lapse rates. It is possible these initial thunderstorms weaken in a few hours as the low-level jet similarly weakens, but also can easily envision coverage simply increasing with time as the front interacts with the warming boundary later. When taken altogether, will continue to advertise a window for thunderstorms at all terminals today favoring RFD between 15-17Z, DPA/ORD/MDW between 17-20Z, and GYY in the 19-22Z window. Winds in and around thunderstorms may be erratic with gusts above 30kt. A brief period (2-3 hours) of MVFR cigs may follow the front and thunderstorms today before gradual clearing this evening. HRRR- smoke guidance suggests wildfire smoke will once again spread into the area this evening and stagnate through much of tomorrow. Compared to the smoke event a few days ago, smoke concentrations this evening onward appear lower with associated less drastic visibility drops So, will maintain the inherited 5SM visibility in smoke and let upstream observations inform changes in future TAF packages. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Air Quality Alert until midnight CDT tonight for ILZ005-ILZ006- ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106- ILZ107-ILZ108. Beach Hazards Statement from this evening through Sunday morning for ILZ006-ILZ103-ILZ104. IN...Beach Hazards Statement from this evening through Sunday morning for INZ001-INZ002. Air Quality Alert until midnight CDT Monday night for INZ001- INZ002-INZ010-INZ011. Air Quality Alert from 1 AM Sunday to 1 AM EDT Tuesday for INZ019. LM...Small Craft Advisory from 7 PM this evening to 4 AM CDT Sunday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago |
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