966 FXUS63 KLOT 131123 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 623 AM CDT Fri Jun 13 2025 .KEY MESSAGES... - Scattered showers and possibly a couple of thunderstorms Today into Saturday, especially south of I-80. - Very warm and humid with occasional chances for showers and thunderstorms early to mid next week. && .DISCUSSION... Issued at 317 AM CDT Fri Jun 13 2025 Through Saturday: Early morning GOES vapor imagery depicts a closed mid-level low centered near Joplin MO, along with a weak surface low reflection. A broad region of modest low-level southerly flow was evident ahead of this feature across the lower and middle Mississippi River Valley, pulling deeper moisture up from the south as seen in 00Z RAOBs from Jackson MS and Little Rock AR. This moisture will continue to spread north into our region today, as the mid-level low lifts slowly east-northeast across MO. Regional radar imagery already indicates showers spreading northward into central IL at this hour, and these are expected to move into the WFO LOT forecast area a little later this morning. Not much in the way of lightning has been noted with this area of precipitation, as lapse rates are generally moist adiabatic throughout much of the column per the above referenced soundings. At the surface, a weak, nearly stationary frontal boundary was evident from roughly along a Moline-Bloomington-Lafayette line along the WFO ILX/LOT border area. This front is forecast to lift north as a warm front today in response to the low-level warm/moist advection ahead of the upper low, perhaps to around the I-80 corridor this afternoon. Shower coverage is expected to be highest across the southern half of the cwa, generally along and south of the frontal boundary and closer to better mid- level forcing associated with the mid-level wave. Despite the relatively weak lapse rates, a few isolated thunderstorms can`t be ruled out this afternoon and early evening, again mainly near and south of the warm front if enough sun can make its way through otherwise fairly extensive cloud cover. The mid-level low is progged to gradually weaken into an open wave later tonight into Saturday as it tracks across central/southern IL and IN. This will tend to maintain the focus for showers across the southern half of the forecast area into Saturday, while eventually shifting to the southeast Saturday afternoon as the mid-level wave shifts east. With slow cell movements and deep moisture (forecast p-wats approaching 2"), some localized rainfall amounts of an inch or more appear possible especially southeast of I-55. Easterly surface winds will continue to keep temperatures cooler near Lake Michigan both today and Saturday, with highs in the 60s likely along the immediate shore. Highs in the upper 70s to lower 80s are likely farther inland, with warmest readings likely toward northwest IL where less impact from thicker cloud cover and more widespread showers are expected. Mid-80s are likely across our western cwa by Saturday afternoon, as cloud cover decreases behind the departing disturbance. Ratzer Saturday Night through Thursday: As the upper level wave moves east and better height rises move over northern Illinois, Saturday night should be dry. Overnight lows will drop into the low 60s, with a few upper 50s closer to the Wisconsin border. Sunshine should filter through any clouds on Sunday to help warm up the area into the low to mid 80s during the day, though northeast winds will help keep the shoreline cooler in the upper 60s and low to mid 70s. Both EPS and GEFS models have pulled back on the precipitation chances on Sunday. Both have a shortwave aloft that forms over the Upper Mississippi Valley early Sunday, tracking it southeastward. However, they keep the track of the wave south and west of the forecast area. There will be lingering moisture around the region and with diurnal heating mid-level lapse rates will steepen in the afternoon, there could be enough instability to have some showers and an isolated rumble of thunder crop up (best chances east of Interstate 39). With such weak forcing, PoPs were trimmed back to just a slight (less than 25 percent) chance mention, though it is imagined there will be plenty of drier periods during the day. No changes were made to temps and PoPs that the NBM provided for Monday and Tuesday. High temperatures each day look to be in the 80s, and slowly creep into the upper 80s as winds turn southerly to allow for better warm air advection. Many of the shower and thunder chances on these two days will probably be diurnally driven, but with models showing a few weak waves passing over. PoPs increase to around 30 to 40 percent chance at this range. There remains a decent signal in the ensemble guidance for a stronger synoptic system and associated cold front to approach the region on Wednesday. This may be a period to watch for organized convection and a threat for strong to severe thunderstorms in the region. However, deterministic guidance is still flip-flopping on the details as the latest 00Z GFS pushes the surface low farther north and into Wisconsin, while the 00Z Euro now has it moving slower and passing right over northern Illinois. But at this range it is hard to have confidence in the exact outcome given the discrepancies. Nevertheless, if the Wednesday-Wednesday night timing comes to fruition, then Thursday would likely end up mainly dry and slightly cooler/less humid in the wake of the cold front passage. DK && .AVIATION /12Z TAFS THROUGH 18Z SATURDAY/... Issued at 623 AM CDT Fri Jun 13 2025 Key Aviation Messages for the current TAF period: - Chances for VFR showers today. - Potential for MVFR cigs overnight, with a slight chance for IFR cigs. Showers have blossomed out ahead of the warm front moving north prompting the inclusion of -SHRA on the first line of the TAFs for the Chicago terminals. Rainfall so far has been light with cloud bases over 5000 ft AGL. There will likely be a break in the rain after this first wave. Though given the amount of moisture aloft moving northward, VCSH was added starting at 14Z. The PROB30 was left in the TAF for the timing of when the expected steadier showers are expected at the terminals. Through much of the day, winds are expected to be at or less than 10 knots. Potentially a light southeasterly wind this morning, but it mostly be more easterly through the late morning/afternoon before eventually turning northeast Friday night. Guidance is starting to come into better agreement on MVFR cigs overnight. However, some models are still being bullish on the IFR threat. A FEW group below 1000 feet were kept in at this time given the lower confidence in IFR, though it was made SCT at GYY given the better chances that they could fall below to IFR tomorrow morning. Skies should return to VFR cigs Saturday morning, with current thinking around 15Z. DK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago