FXUS63 KILX 020701 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 201 AM CDT Wed Jul 2 2025 .KEY MESSAGES... - Heat and humidity will gradually increase into the weekend, with highs in the low 90s for Friday (July 4) and heat indices of 95 to 100 degrees. - Mostly dry conditions should prevail through at least Saturday morning, then occasional rain chances exist Saturday night into next week (20- 50%). && .DISCUSSION... Issued at 159 AM CDT Wed Jul 2 2025 Light winds and mostly clear skies are in place across central IL early Wed morning, save for a few isolated patches of mid-level clouds evident on NT Microphysics satellite imagery. The sfc pattern remains diffuse today, with broad, weak sfc high pressure over the Ozarks. As a result winds stay light today with a westerly component, although the exact wind direction will vary between NW and SW at times. Both fcst soundings and NAM Cu Rule output suggest scattered diurnal Cu today, with cloud bases around 4-6 kft. Temps today warm a few degrees relative to yesterday, with highs in the mid 80s. However, dewpoints remain in the mid 60s, keeping peak heat indices below 90 degrees. Overall, mostly dry conditions are anticipated through at least Friday (July 4th). A stray shower can't be ruled out near/north of the I-74 corridor on Thurs, due in part to the potential for convection to develop due to LLJ convergence across IA tonight into Thurs AM, as well as a subtle impulse rounding the ridge. This activity is more likely to be focused across northern IL, with just a 10% chance along/north of I-74 (which is below the threshold to warrant a mention in the official forecast). Upper level height rises begin on Thurs, and peak on Fri as the upper ridge axis shifts over IL (592 dam at 500 mb). As the sfc high shifts east of our area, southerly flow reestablishes and hot/humid conditions return for Fri/Sat, with heat indices of 95-100 degrees. Fortunately, this upper ridge does not appear to have the same staying power as the one that was associated with our previous heat event, as an upper low currently over California is expected to eject onto the Plains and lift towards the Upper Midwest over the weekend. Model consensus has improved with this system, bringing the timing into better focus. It now appears central IL will be dry for much of Sat, with PoPs first introduced across west-central IL during the evening (20-30%) as the cold front grows closer. The most likely timing for the front seems to be late Sat night into Sun, with the highest PoPs Sun afternoon (30-50%). Current forecast still keeps heat indices around 95-100 for Sun, though the potential for convection results in lower confidence in reaching these numbers compared to Fri/Sat. The question then becomes, does this front push completely south of our area...or does it stall out and increase the daily precip chances into next week? The upper ridge is expected to amplify and become anchored over the desert SW next week, placing IL in the path of any disturbances that round the ridge, so one way or another the pattern supports continued precip chances into next week. This is also reflected in the CPC 6-10 day outlook (valid July 7 - 11), which leans above normal for precip (40% chance). The potential for organized severe storms appears low. While ens guidance has a 40-60% chance of CAPEs over 2000 J/kg each day, the probability of deep layer shear over 30 knots is less than 15% well into next week. The greater concern may instead be locally heavy rainfall, given the weak flow patterns and a 50-70% chance for PWATs above the 90th percentile (1.7"). Erwin && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 1151 PM CDT Tue Jul 1 2025 VFR conditions expected through the period. Winds will be light, generally around or less than 5 kts with a westerly component. Some diurnal Cu is possible this afternoon, otherwise skies will be mostly clear. Erwin && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$