635 FXUS63 KLOT 120146 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 846 PM CDT Wed Jun 11 2025 .KEY MESSAGES... - Thursday will be very warm and more humid inland of Lake Michigan, though it will be much cooler near the lake. - Shower and thunderstorm chances will continue to remain muted locally. && .UPDATE... Issued at 846 PM CDT Wed Jun 11 2025 We find a complex of strong to severe thunderstorms pushing across northeast and east-central IA this evening. These storms formed beneath an upper shortwave and along a quasi-stationary front oriented west-east across north-central IA and right along the IL/WI state line. This activity had been expanding southward into the open warm sector with the help of some outflow forcing, but this trend has really slowed down as of late. A number of convective-allowing models had been resolving such a trend, and a large majority of them suggest that the southern extent of the activity will actually retreat back north as diurnal cooling depletes instability and high pressure to our south further impedes on the better thunder environment closer to and east of the Mississippi. So while recent radar trends appear to be tracking storms right toward far northern IL, there is support for this activity to just miss our CWA to the north later this evening. Satellite trends also show storm- tops steadily coming down. But that`s not to say that it can`t happen; we`ll have to keep a close eye on how the activity trends as it nears the river. If storms do maintain themselves across our northern- most counties, they could feature some small hail and strong gusts of wind, but parameters on CAM soundings even across far southern WI do not look very supportive of severe convection later this evening. Timing on any activity across our north would be late this evening stretching into the early part of the overnight. All in all, the forecast in the short term is in solid shape with no noteworthy changes made. Doom && .DISCUSSION... Issued at 253 PM CDT Wed Jun 11 2025 Through Thursday: A weak west to east oriented cold frontal boundary will gradually sag southward from southern Wisconsin tonight, reaching down to about the I-80 corridor by early Thursday. Meanwhile, a mid-level impulse over southwest MN this afternoon will push east- southeastward into central lower Michigan later tonight. The shortwave trajectory and very dry air below 600 mb with moisture profiles not expected to improve much if any (prohibitive MUCIN) are expected to result in convection remaining focused north of far northern Illinois tonight. With that said, still can`t completely rule out a weakening shower/thunderstorm sneaking into the IL/WI state line area later this evening (~20% chance). Outflow from storms to the north over Wisconsin and over the lake may result in a temporary push of breezy northeast winds into northeast IL north of the sagging frontal boundary. Overnight lows will be seasonably warm, in the lower to mid 60s (locally upper 60s in/near Chicago). The aforementioned cold front will be enhanced some by the still cool Lake Michigan waters on Thursday. As such, high temperatures will be ~20F+ cooler along the lakeshore tomorrow versus today`s highs, paired with northeast winds in the 10-20 mph range. It will be another very warm day inland though with highs in the mid to upper 80s, along with increased humidity levels (dew points into the 60s). A split mid-level flow regime, along with very weak flow aloft locally and 700-500 mb RH remaining below 30%, will translate to primarily dry conditions for most of the area on Thursday. The possible minor exception to this will be near the backdoor cold front as it pushes inland through the afternoon paired with dew points pooled as high as the mid 60s near the boundary. Once capping erodes from afternoon heating, can`t rule out a few isolated t-storms (~20% chance) across interior northern/north central IL. Aside from this small but not-zero convective chance, temperatures will steadily cool behind the backdoor front into Thursday evening, particularly closer to the lake. Any isolated slow moving showers/storms out over the western 1/3 or 1/4 of the CWA Thursday evening will dissipate. Then overnight, some isolated showers may push into the far southern CWA on the northeastern fringes of closed mid-upper level low pressure over Missouri. Mid-level overcast will keep overnight temps propped up again, with most spots in the low-mid 60s by early Friday, except upper 50s in far northeast IL farther north of the front. Castro Thursday Night through Wednesday: Upper low currently over the southern Plains is still progged to weak to an open wave as it tracks slowly toward the northeast toward the mid Mississippi and lower Ohio Valley later this week. Scattered showers and perhaps a couple of isolated thunderstorms will accompany this weakening wave as it moves north, with the primary question being how far north this activity will get Friday into Saturday. For now, opted to maintain the NBM pops for Friday through Saturday, though given latest guidance trends those may be too aggressive with much of that time period possibly ending up rain free, particularly northern CWA. In the wake of that decaying southern stream upper low and a weak northern stream shortwave trough, Canadian high pressure looks to build into the western Great Lakes for the second half of the weekend with dry conditions expected. Peering ahead into next week, it looks as though a fairly zonal flow will set up through at least the first half of the week with the potential for subtle shortwaves to ripple through and possibly become convectively enhanced. Unfortunately, timing any of those lower amplitude or convectively enhanced features isn`t currently possible at this distance, so maintaining some pops each day is best course of action at this point. Weak frontal boundary is expected to be in the area Thursday night and Friday, with lake enhancement likely keeping the effective boundary south and west of the southern tip of Lake Michigan. Biggest temp gradient with this boundary should be near the lake where marine layer will keep temps cooler. This boundary should push south of the area later Friday night into Saturday with drier and slightly cooler Canadian air mass spreading into the area in its wake. Low confidence on which side of the boundary our area will be on through the first half of next week with some potential for convection to push the boundary farther south than progged. - Izzi && .AVIATION /00Z TAFS THROUGH 06Z FRIDAY/... Issued at 629 PM CDT Wed Jun 11 2025 The main avn weather concerns for the 00Z TAF period include: * A slight chance for a shower or thunderstorm late this evening, primarily at RFD. SW winds will subside to below 10 kt early this evening before turning to a NE direction late tonight, likely going variable at around 5 kt for a few hour period in the process. Expect ENE winds near 10 kt gusting into the teens kt during the afternoon on Thursday before subsiding by mid-evening. Meanwhile, a complex of showers and thunderstorms will move across lower WI late this evening. While a majority of this activity is expected to pass north of the TAF sites, it`s possible that a passing storm clips the airfields, particularly RFD. Chances are too low to include any mention in the TAFs, however. If this were to occur, timing looks like late this evening near RFD and around, if not shortly prior to, 06Z should a storm move over the Chicago sites. VFR is anticipated throughout the period. Doom && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago