textproduct: Central Illinois

KEY MESSAGES

- No major storm systems are expected to impact the region over the next week. As a result, the severe weather risk across central Illinois will remain low (less than a 5% chance) through next Thursday.

DISCUSSION

Issued at 325 AM CDT Fri May 22 2026

*** Showers Today and Tonight ***

A 1030mb high centered over Ontario/Quebec has been the dominating weather maker across central Illinois over the past couple of days...providing a cool/dry NE flow and keeping any precipitation at bay. As the high shifts further eastward and a short-wave trough noted on 07z/2am water vapor imagery over the Lower Mississippi River Valley pivots northeastward, showers will gradually develop and spread northward into parts of central Illinois later today into tonight. With a weak 1010mb surface low progged to track from Louisiana to southern Indiana by tonight, the richest deep-layer moisture will flow from the Gulf into the Ohio River Valley...remaining mostly E/SE of the KILX CWA. NAM precipitable water values rise from around 1.25 into the 1.50-1.75 range along/south of the I-70 corridor later today, signaling the location where the most persistent and heaviest rainfall will focus. 00z May 22 CAMs have generally shifted the greatest rainfall axis eastward and reduced amounts further west across central Illinois. Based on the 00z HRRR/NAM, have confined rain chances to locations along/south of I-70 through midday...then have pivoted slight chance PoPs (20%) as far NW as the I-55 corridor by late this afternoon. As the surface low lifts into Indiana, 20 PoPs will spread into the Illinois River Valley this evening...with 50-60 PoPs near the Indiana border. Showers will come to an end from west to east overnight...with storm total rainfall ranging from just trace amounts along/west of I-55 to around 0.25 in the Wabash River Valley.

*** Memorial Day Weekend Forecast ***

Once the initial system lifts into the eastern Great Lakes, short-wave ridging/synoptic subsidence in its wake will result in a mild and dry day on Saturday with highs topping out near seasonal normals in the middle to upper 70s.

The period of dry weather will be short-lived however, as another trough currently in the Northern Rockies tracks eastward and pushes a weak cold front into central Illinois Saturday night into Sunday. There is still some question as to how much deep-layer moisture will be able to return ahead of the system, so the synoptic models offer differing opinions of the amount/coverage of precip. The GFS and GEM are both fairly aggressive with rain amounts, but the ECMWF is considerably lighter. The 00z NBM featured a band of likely PoPs (60%) ahead of the front, but given model spread and uncertainty concerning moisture levels, have opted to lower PoPs a bit Saturday night/Sunday.

Once the front passes, a return to warm and dry weather is expected for Memorial Day with highs reaching the lower 80s.

*** Additional Rain Chances Next Week ***

After a dry day on Monday, the NBM spreads rain chances back into central Illinois from south to north beginning as early as Tuesday...then lingering through Thursday. The 00z models are all in good agreement concerning the general synoptic set-up next week, featuring a potential blocking pattern with strengthening upper ridging over the Upper Midwest and an upper low over the Lower Mississippi River Valley. While all models show showers/thunder gradually pivoting northward into at least parts of central Illinois, the exact northern extent remains in question as northerly flow between the ridge and another short-wave digging southward into New England sharpens. This may tend to suppress the southern wave and either keep its associated precip entirely to the south...or force the precip back southward as the week progresses. For now, the forecast is showery from Tuesday through Thursday...but this may change if current trends persist. Whether showers reach this far north or not, the lack of a strong system and overall weak instability/shear will prevent widespread severe weather development throughout the entire forecast period. As a result, the latest machine learning algorithms feature little to no chance (less than a 5% chance) for severe weather across central Illinois through at least next Thursday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 551 AM CDT Fri May 22 2026

Low VFR ceilings will prevail at the central Illinois terminals through the morning before MVFR ceilings gradually spread northward from southern Illinois this afternoon. The latest HRRR/RAP has delayed the lower clouds by a few hours and this has been reflected in the 12z TAFs. Have opted to lower ceilings to MVFR at KSPI/KDEC/KCMI by 17z, but have held off until 03z further northwest at KPIA. While the bulk of the showers associated with the system will remain across far E/SE Illinois into the Ohio River Valley, have continued VCSH at all sites except KPIA. Winds will initially be E/NE with gusts of 15-20kt, then will decrease to less than 10kt and back to NE tonight.

ILX WATCHES/WARNINGS/ADVISORIES

None.