FXUS63 KLOT 211106 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 606 AM CDT Sun Jun 21 2026 .KEY MESSAGES... - A storm system will bring widespread soaking rainfall and possibly a few storms to the area today into tonight. A conditional level 1/5 risk for severe weather is present for areas well south of I-80. - A corridor of locally heavier rainfall rates may occur somewhere in our area today and lead to flooding. The greatest chances for excessive rainfall are present near and south of I-88, where there is a level 2/4 risk for flooding. - A heightened risk for rip currents will exist at southern Lake Michigan beaches from this evening through Monday night. && .DISCUSSION... Issued at 342 AM CDT Sun Jun 21 2026 Through Tonight: GOES satellite and WSR-88D radar mosaic imagery this morning depict an expansive convective complex across the central Plains working its way towards the east and southeast. An MCV is evident in central Kansas at the time of this writing, displaced to the south of the parent shortwave that helped kickstart this convection yesterday afternoon as it ejected eastward out of the central Rockies. As this MCV, shortwave, and an associated surface low continue to progress eastward today, an expansive precipitation shield will spread over our forecast area from west to east from the mid-late morning through this afternoon, bringing a widespread soaking rainfall to the area that should last for several hours. This is an aspect of high confidence with our forecast. Two forecast aspects that remain of lower confidence, however, are the potential for flooding and thunderstorms in our area today as this system moves through the region. One feature that will play a key role in whether either of these threats are realized in our area today is a warm front that was analyzed to be present from near Kansas City to just north of Jackson, TN at 0800Z. This warm front will effectively serve as the northward terminus of where a threat for severe weather will be present today and will also help dictate how far north the threat for lightning and convectively-enhanced rainfall rates will trek. The latest CAM guidance, for what it's worth (which probably isn't a whole lot as it, unsurprisingly, does not have a good handle on the ongoing convection), generally favors the warm front lifting northward into central Illinois and Indiana this afternoon and possibly as far north as our southernmost tier of counties. These CAMs are modeling this outcome under the assumption that the ongoing central Plains MCS will slow down and/or decay through the remainder of the night and into the morning, affording the warm front enough time to lift this far north before having its progress stalled by the incoming convection and rain. While the MCS has notably weakened over the past few hours, the embedded MCV still appears to be well-defined and is generating new convective cells out ahead of it, and there is a reservoir of untapped 1000-2000 J/kg of MUCAPE out ahead of the complex in southern Missouri, so still have some doubts over whether this MCS will lose enough steam for the warm front to be able to make it as far north as the aforementioned CAM solutions are suggesting. Nevertheless, if the warm front were indeed to make it as far north as our southern CWA, then rich low-level moisture paired with strong low-level and effective shear values resulting from 50+ kt mid-level flow and backed surface winds near the warm front would yield a threat for low centroid supercell structures or bowing segments capable of producing tornadoes and damaging winds in our far southern counties today (in the area more or less delineated in SPC's Day 1 Convective Outlook). That said, the more likely scenario at this time is that the warm front and the attendant severe weather threat will remain south to potentially well south of our forecast area as a result of the incoming central Plains convection arriving at our longitude faster than indicated in CAM guidance and accordingly forcing the warm front to remain farther south than indicated in these models. Even if the warm front does not quite reach our area, there are still indications that a layer of meager elevated instability could claw as far north as the I-80 or I-88 corridor late this afternoon and evening and pose some lower-end threat for isolated lightning strikes in our area during this late day time frame while the main show remains to our south. Additionally, it still appears that the main synoptic surface low will track across our southern counties or just to our south across central Illinois and Indiana. Several models have been depicting notable frontogenetical forcing along the northern flank of the surface low inducing a band of precipitation featuring enhanced rainfall rates. Where this band of precipitation sets up and just how torrential the rainfall ends up being within it will depend on the exact strength and track of the surface low, which, due to the extensiveness of the upstream convection, remains extremely difficult to pin down at this time. In a scenario with a stronger surface low and associated deformation/f-gen band, rainfall rates could be efficient enough amidst 1.5-2" precipitable water values to cause flooding somewhere in or very near our forecast area. The latest flash flood guidance (FFG) values from the North Central River Forecast Center are generally around 1.5-2" for 3 hours and 2-2.5" inches for 6 hours, and while there are a few exceptions (e.g. lower values for our more heavily urbanized and flood- prone areas), those are generally the rainfall thresholds that we believe could start to cause some more notable hydrologic concerns to arise if they are exceeded with the specified time interval(s). Confidence in whether these thresholds will be exceeded in our forecast area today and where was too low to warrant the issuance of a Flood Watch with the overnight forecast package, but couldn't rule out the need for a short- fused Flood Watch issuance by the day shift if the forecast picture clears itself up more later this morning. Either way, area creeks, streams, and rivers will rise as a result of this rainfall, and it's not out of the question that some additional river flooding could occur somewhere in the near future as a result of today's rainfall. Monday through Saturday: Some shower activity from Sunday's storm system may linger around through Monday morning, but should clear our area by the early afternoon. During the afternoon, couldn't rule out diurnal cumulus growing deep enough to support a few spits of rain wherever surface convergence/confluence is maximized, but otherwise, expect a dry day on Monday with highs in the mid 60s (near Lake Michigan) to the mid 70s (well inland) as surface high pressure begins to build into the region. Buoyed by breezy onshore flow, high waves that will develop across southern Lake Michigan today will persist into Monday and continue to create a heightened threat of rip currents at area beaches through Monday night. Winds and waves will subside on Tuesday as the high pressure center passes close by, while daytime temperature readings will likely only be a touch milder compared to Monday. Late Tuesday night into Wednesday, global ensemble and deterministic guidance remains in good agreement that an upper- level trough will slide into the Upper Midwest, likely accompanied by a low pressure system at the surface. Moisture profiles should be plenty adequate to support rain showers across the region as this system passes by, and while lapse rates look to be lackluster on the whole, deterministic GFS and ECMWF soundings both depict CAPE profiles with equilibrium levels solidly above -20C that should be favorable for thunderstorms to occur in the area as well. Ensemble consistency breaks down over the latter half of the week into the weekend, but still broadly suggests that a few follow-up shortwave troughs could traverse the region in the days following Wednesday. Thus, additional showery and perhaps stormy periods could be seen going into the weekend, but confidence in the specific details of that potential remains low at this time. Confidence is higher in near to below normal temperatures persisting through the entirety of this upcoming week, though ensemble guidance does suggest that some warmer temperatures could be on the horizon just beyond the end time of our current 7-day forecast period. Ogorek && .AVIATION /12Z TAFS THROUGH 18Z MONDAY/... Issued at 606 AM CDT Sun Jun 21 2026 Key Messages: - Rain develops eastward across the terminal airspace late this morning through early afternoon. - Steadiest rain with periods of low MVFR to IFR CIGs and VSBYs expected late this afternoon into this evening. - Light and variable winds to start the day quickly settle east- southeastward by late morning, then turn breezy from the east- northeast late this afternoon and evening. Our next weather system will move into the area today. As it does, expect rain to overspread the area by midday/early afternoon. The more persistent and heavier rainfall is likely to impact the terminals late this afternoon into this evening. Lower MVFR VSBYs and low MVFR to IFR CIGS are likely to accompany some of the more persistent rain this evening. There is also a non-zero chance of a couple of isolated lightning strikes with this activity, though the better chances for this looks to be south of the terminals. Otherwise, he rain will gradually taper off late this evening and overnight. In spite of this, low cloud cover may persist through early Monday morning before improving. Light and variable winds early this morning will settle into an east-southeasterly direction later this morning as the system approaches. Winds will then turn breezy from the east, and eventually the northeast late in the day and this evening as the surface low tracks eastward across central IL and IN. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement from this evening through late Monday night for ILZ006-ILZ103. Beach Hazards Statement from this evening through late Monday night for ILZ104. IN...Beach Hazards Statement from this evening through late Monday night for INZ001-INZ002. LM...Small Craft Advisory from 4 PM this afternoon to 1 AM CDT Tuesday for the IL nearshore waters. Small Craft Advisory from 4 PM this afternoon to 4 AM CDT Tuesday for the IN nearshore waters. && $$ Visit us at weather.gov/chicago