textproduct: Central Illinois

KEY MESSAGES

- Above normal temperatures are likely to persist into mid-June, with highs in the 80s over the next week.

- There is a 30-50% chance for showers and storms Sunday night into Monday, with chances highest west of the Illinois River. Otherwise, mostly dry conditions are expected through much of next week.

DISCUSSION

Issued at 245 AM CDT Sat May 30 2026

The upper pattern remains amplified, with an Omega block in place in the form of upper lows over the western US and New England and a ridge axis extending from the Midwest well into central Canada. Sfc high pressure over Ontario will expand southward today. Between this sfc high and lee cyclogenesis in response to the western US trough, winds will maintain an easterly component across central IL and limit moisture advection. Still, a few showers can't be ruled out this afternoon as well as overnight along a stalled frontal boundary/moisture gradient over western IL. The latest CAMs keep most of this activity just west of the ILX CWA, but there's enough signal to maintain low PoPs (15-20%) west of a Galesburg- to- Springfield line. Precip activity will struggle to make it any further east due to the diminishing moisture content. The instability and wind shear values are both marginal at best, with MUCAPE less than 800 J/kg and deep layer shear less than 25 kts, thus severe storms are not expected.

The NBM has been too cool with the high temp forecast over the last several days, and despite cloud cover yesterday was no exception. Even with clouds present again today, opted to nudge highs a few degrees warmer than the NBM as the easterly flow promotes dry low- levels. Temps often overperform guidance on these dry days, especially early in the planting season when evapotranspiration is minimal and the sun's energy is primarily focused into sensible heat flux. Our latest forecast has highs in the mid 80s, but I wouldn't be surprised if saw readings creep into the upper 80s once again.

The influence of the sfc high pressure to our northeast weakens into Sun night, opening the door for precip to nudge east into our area as additional weak disturbances emanate around the western US trough. Exactly how far east any rain manages to make it remains low confidence, but for now the latest model blend delivered 20-50% PoPs east of I-57 Sunday night, highest with westward extent, which seemed reasonable. Scattered storms could linger into Monday. A modest uptick in the wind shear and an eastward pivot in the instability axis could promote a few strong storms, mainly southwest of a Macomb-to-Springfield line. Hail and wind would be the main concerns with any such storms.

Into early next week, the upper ridge strengths and yet another renewed push of sfc high pressure occurs over the Great Lakes. The associated height rises/subsidence should keep the region dry Tues- Wed (and likely into Thurs as well). Temps remain above normal, with the latest NBM depicting highs in the low to mid 80s. Given the recent cool bias and ample sunshine expected mid- week, suspect that we will continue to outperform the NBM forecast. The NBM 90th percentile (10% chance of higher values) has high temps in the mid to upper 80s (or perhaps low 90s by Thurs), and these values may wind up being closer to reality than the current forecast.

Dewpoints remain low during the mid-week period, especially in the scenarios where we overperform on temps. The latest blend has afternoon dewpoints around 50F on Tues-Wed. However, that may change by late next week, as models depict an expansive sfc high finally shifting east of our area, rather than being positioned to the north, which would introduce southerly flow and increasing humidity. Above normal temps appear likely to continue into the extended forecast, with the CPC highlighting the entire state of IL as having a slight risk of extreme heat, valid from next Saturday (June 6) into the second week of June.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 537 AM CDT Sat May 30 2026

No meaningful changes were necessary with this TAF update. VFR conditions are set to prevail through the period, with broken high level cloud cover. Easterly winds will increase to around 10-15 kts by mid-morning, with some weakening possible towards the very end of the period.

ILX WATCHES/WARNINGS/ADVISORIES

None.