809 FXUS63 KLOT 141115 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 615 AM CDT Sat Jun 14 2025 .KEY MESSAGES... - Chance for showers this morning, mainly southeast of a Livingston County to Jasper County line - Temperatures will increase this weekend and into next week, accompanied by increasing shower/storm chances by midweek. - Severe weather is possible next week, particularly Wednesday, with multiple rounds of thunderstorms possible Monday through Wednesday night. && .DISCUSSION... Issued at 302 AM CDT Sat Jun 14 2025 Through Sunday: KLOT radar is showing diminishing shower coverage over the southeastern portions of the forecast area. These showers are situated along and just north of a quasi-stationary boundary from St. Louis, MO to Lafayette, IN. This boundary is associated with an upper level low sitting over eastern Missouri/southwestern Illinois. Over the next 6 to 12 hours, this low is expected to weaken as it slowly moves east over southern Illinois. Its gradual movement will help nudge the surface boundary southeast of the forecast area through the morning. Showers are expected to linger through the morning and into the early afternoon mainly along and southeast of a Livingston County to Jasper County line. Weak forcing should help keep rain rates low, though with over two inches of precipitable water there remains a chance for a downpour to focus over an area that received rainfall last night which result in ponding in flood prone areas. Lastly, model soundings do show an a sliver of instability late this morning and into the afternoon. However, those soundings are fairly capped and not expected to break that cap until the showers move southeast of the area. Perhaps an isolated thunderstorm or two develops, but the better instability will be to the south along the boundary as it slinks away from the forecast area through the day. An upper level high will strengthen over New Mexico and build a ridge into the Plains today. Drier air and increasing subsidence moving into the forecast area ahead of the ridge is expected to reduce cloud cover this afternoon, at least to the west. Temperature are expected to reach he lower 80s for areas west of the Fox Valley which should receive more sunshine. However, as cloud cover is expected to linger for much of the day closer to the lake and over northwestern Indiana, that (and northeast winds over the lake) should help cap high temperatures for those areas in the mid to upper 70s. Cloud cover will continue to erode tonight as dry conditions prevail and low temperatures in the upper 50s/low 60s are expected. As a weak upper level pattern remains, most of Sunday should stay dry. Clearer skies should allow for more of the forecast area to warm up solidly into the 80s, though northeast winds off of the lake will help keep the lake shoreline in the 70s. Models keep suggesting a very weak upper level short wave that develops and moves down the ridge from southeastern Minnesota to southern Wisconsin. Combine that with diurnal heating and there is a slight (less than 25 percent) chance for some showers and thunderstorms on Sunday afternoon in northwest Illinois and along the Wisconsin stateline. There is better confidence for the showers and storms to be northwest of the Rockford Metro area, but whether or not it materializes will depend on the movement of that wave and how close to the forecast area it gets before the sunsets and a less favorable time of day for storms. DK Sunday Night through Friday: Guidance remains in good agreement in depicting a more zonal flow pattern in the mid-upper levels to start next week. Surface high pressure stretching from the Great Lakes through New England drifts slowly to the east Sunday night into Monday, while warm, moist southerly return flow develops off of the western Gulf into the Plains and upper Midwest/Mississippi Valley. Models depict several low-amplitude short wave disturbances tracking eastward across the region along the southern periphery of stronger jet winds, which should modulate diurnal thunderstorm initiation across the upper Midwest and development of a few MCSs, which could affect our forecast area. Various models show quite a bit of differences in details with these low-amplitude waves, not surprisingly, leading to fairly low confidence in exact timing and placement of them and any organized convective complexes they produce. Global ensembles continue to indicate a more amplified mid- level short wave tracking across the central and northern Rockies and onto the Plains late Tuesday and into the Midwest Wednesday/Wednesday night. While some differences remain with the timing and strength of this feature, the general trends support an area of surface low pressure lifting northeast across the upper Midwest Wednesday with attendant synoptic increases in low-level warm sector theta-E, instability and vertical wind profiles. This pattern appears supportive of heightened severe thunderstorm potential within the region on Wednesday, which will continue to be monitored for a possible severe weather threat in or close to the WFO LOT forecast area. Ridging in the wake of the more amplified mid-week system may ease the periodic shower and thunderstorm threat for at least a portion of the latter half of the week, though there is some indication that the main upper ridge axis will set up to our west keeping us along the southern periphery of additional shower/thunderstorm threats across the upper Midwest. Temperatures are forecast to warm into the mid-upper 80s early next week, with 90 not out of reach especially Tuesday and Wednesday. This will be dependent on thunderstorm trends and affects of any outflow boundaries, however, lending somewhat lower confidence to current forecast highs. Humidity levels will be on the rise through mid-week as well. Ratzer && .AVIATION /12Z TAFS THROUGH 18Z SUNDAY/... Issued at 615 AM CDT Sat Jun 14 2025 Key aviation messages for the 12Z TAFs: - Period of IFR/patchy LIFR early, improving through MVFR to VFR through midday. Weak surface low pressure continues to track slowly east- northeast across downstate IL this morning. To the north of the low, relatively cool, moist low-level northeast flow persists across the terminals. This has resulted in development of fairly widespread IFR stratus ceilings and MVFR visibilities in light fog across northeast IL. There have also been some patchy LIFR conditions, currently at KDPA and K06C (Schaumburg IL) as well as along the immediate Lake Michigan shore. Model guidance has captured these trends reasonably well overnight, and indicate that we`ll see gradual improvement to low-MVFR by mid-morning and eventually scatter to VFR by midday. VFR conditions should then prevail for the remainder of the forecast period. Surface winds are expected to remain northeast at around 10 kts through the day, diminishing and becoming somewhat light and variable tonight. Winds then are expected to become east- northeast after sunrise Sunday morning. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago