815 FXUS63 KILX 031101 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 601 AM CDT Tue Jun 3 2025 .KEY MESSAGES... - Forecast temperatures today have trended lower due to widespread clouds, with highs in the mid to upper 80s. South-southwest winds will gust to 35 mph late morning through afternoon. - Periods of scattered thunderstorms this evening through Friday may generate localized heavy rain. The risk of flooding is low (5%), but nuisance ponding of water in poor drainage areas may occur. - There is a level 2 of 5 (slight) risk for severe weather west of the IL River this evening. The primary risk will be localized damaging thunderstorm winds. && .DISCUSSION... Issued at 115 AM CDT Tue Jun 3 2025 Ahead of an approaching upper level trough, thunderstorms will form along a cold front across KS, MO, and IA today, weakening as they arrive in west-central IL this evening. The cold front will lose some of its luster tonight into tomorrow as the stronger winds aloft lift into the Great Lakes, however outflows from ongoing convection and the marginally unstable airmass ahead of them should sustain scattered showers and storms through Wednesday. A pair of additional disturbances are expected to kick off more scattered storms Thursday into Friday, with the highest precipitation chances each day near and south of roughly the I-72 corridor. ***** SEASONABLY WARM AND BREEZY TODAY ***** Temperatures at 115am were in the mid 60s in east-central IL to low 70s in western IL, owing to differences in low level moisture with a plume of 60+ degree dewpoints observed near and west of the I-55 corridor. High clouds streaming into the region from convection well upstream across Nebraska should help limit radiational losses through dawn, though those same clouds will also filter sunshine and in a small way suppress surface heating today. Nonetheless, with the warm start to the day and south- southwesterly low level flow, temperatures should once again climb well into the 80s. The tightening surface pressure gradient ahead of the approaching cold front will result in seasonably strong south-southwest winds gusting to 35 mph beginning late morning. Soil moisture values are running quite low, around 20% water fraction by volume (wfv), however thinking is that risk for blowing dust is still fairly low due to (1) crusting of the surface soil from rain received last week and (2) emerged vegetation. ***** STORMY PERIODS THIS EVENING THROUGH FRIDAY ***** The storms upstream look to congeal into loosely organized clusters, feeding on 30-40 kt 0-6km bulk shear and 1500-2500 J/kg MLCAPE if you believe the RAP. This diurnally driven instability will quickly oxidize near and after sunset - around the time those storms are slated to reach the IL River Valley, which is largely why SPC's slight risk ends there. However, sufficient elevated instability (200-500 J/kg MUCAPE) rooted around 850mb will linger into the night across central IL so we'll maintain showers and a few rumbles of thunder. For most of us, the biggest impact of these storms will be to introduce a cooler, less humid, and briefly breezy airmass into the region during the evening, but, given the shear, organized linear storm segments mainly west of the IL River could pose a wind risk. In addition, some of the CAMs are hinting that a storm or two could develop earlier in the afternoon west of I-55, and any of these could pose a marginally severe wind risk from wet microbursts given the shallow inverted V on forecast soundings, steep low level lapse rates, and climatologically high PWATs (favors precip-loading) near 2". This should not be a widespread severe weather event, but wouldn't be surprised if a couple warnings end up being needed before the evening's over; time will tell. While wind shear will be weaker over the region tomorrow, surface heating, though filtered by clouds, should prove sufficient for some scattered thunderstorms forming on remnant outflows from tonight's convective activity during the late morning-afternoon. As is often the case with any possible thunderstorms this time of year, we have a level 1 of 5 (marginal) risk for severe weather mainly due to the low (but nonzero) risk for a marginally severe microburst given thermodynamics similar to today. For the vast majority of us, these showers and storms will provide nothing more than a beneficial rain. North of the frontal boundary, temperatures will run close to 10 degrees below climatological normal tomorrow as north-northeast winds bring chillier air down from Lake Michigan; forecast highs are only in the low 70s across our northern CWA. We elected to remove the key message this morning because of lower confidence, lack of significant air quality impacts, and also the fact that the smoke/haze will be an intermittent feature (with northerly flow) until the wildfires in the Southern Canadian Prairies are gone...but the HRRR and RAP suggest the hazy skies and possibly increased near- surface concentrations may return Wednesday into Thursday. Deterministic guidance suggests that a pair of additional shortwaves - one tomorrow afternoon and another on Friday - will spark additional rounds of convection. Between the GFS, CMC, and ECMWF, there remains disagreement on precise timing and placement of these subtle features, so confidence on any severe or flooding risk remains low. However, south of our resident stationary frontal boundary, instability and moisture should be sufficient to carry a nonzero and conditional risk for both severe weather (conditional upon shear and forcing) and localized hydrological (conditional on training of convection) issues. At this time, the risk looks to be highest (lowest) near and south (north) of the I-72 corridor. It would seem the pesky stationary boundary bedeviling us with these intermittent storm chances meanders far enough south to give most or all of central/southeast IL a repose from precip chances during the first portion of the upcoming weekend (PoPs fall to around 10%). However, there is some sign another shortwave dives down from the Northern Plains/Upper Midwest to renew storm chances late Sunday or early Monday. Of course, lots can change between now and then, but we maintain 30-40% precip chances with that wave Sunday-Monday. Bumgardner && .AVIATION... (For the 12z TAFs through 12z Wednesday Morning) Issued at 600 AM CDT Tue Jun 3 2025 VFR conditions will be predominant for most of the forecast period, however scattered showers and thunderstorms ahead of a cold front may impact the terminals at times this evening into tonight. PIA stands the highest chance (50%) of seeing lightning this evening, though chances were high enough (30%) at SPI, BMI, and DEC to include PROB30 groups there as well, though timing uncertainty is also higher at those airfields. The approaching cold front will result in an increasingly tight surface pressure gradient, so south-southwest winds will increase sharply mid to late morning, with gusts through the afternoon approaching 30 kt at times. Winds will ease behind the leading edge of the showers and storms tonight, while ceilings lower from northwest to southeast. HREF suggests a 50-70% chance for MVFR or lower ceilings at PIA by the end of the forecast period, with those probabilities spreading east thereafter. Bumgardner && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$