textproduct: Central Illinois

KEY MESSAGES

- More fog will likely re-develop across central and southeast IL during tonight as a warm front approaches from the south. There is a 40-80% chance that visibilities will once again drop below 1 mile especially overnight and early Fri morning with some areas likely seeing a period of dense fog again.

- Expect an unseasonably warm and windy day with highs well into the 70s on Friday. A warm front lifting northward late tonight into mid Friday morning will bring a chance of showers and thunderstorms. A cold front will then trigger a broken line of thunderstorms late Friday evening and overnight Friday night. There is a Slight Risk (15-30% chance) of severe weather from highway 51 west, with the primary risk being damaging wind gusts. A marginal risk of severe storms is over eastern IL overnight Friday night into Saturday morning.

DISCUSSION

Issued at 215 PM CST Thu Mar 5 2026

The 20Z/2 pm surface map shows a weak frontal boundary in eastern IL just west of I-57 and east of St Louis extending from weak 1014 mb low pressure in nw IN. A few light showers were east of this boundary mainly in Champaign and Vermilion counties lifting ne. Aloft a weak short wave trof was over Lake MI into ne IL and nw IN. While a much stronger mid/upper level trof was over the western US from MT into southern CA. A few patches of light fog lingered over central IL with a few vsbys 1.5-3 miles but most vsbys were at or above 5 miles. A few peaks of sunshine were occurring through the low clouds blanketing central/se IL with more breaks in northern CWA. Temps ranged from upper 40s to mid 50s west of I-57 to the upper 50s/lower 60s in eastern IL, mildest in southeast IL.

Initial concern tonight will be the redeveloping of fog and how dense it will become and where that will set up. The latest CAMs are still showing more widespread fog redeveloping during this evening with redeveloping the fog this evening especially after 7-8 pm with HRRR and GLAMP most aggressive with dense fog development over more of CWA by late evening. Think we may eventually need another dense fog advisory tonight though may not last as long as last nights. The CAMs are still lifting the fog from south to north but a bit slower, diminishing in southern CWA late tonight/early Fri morning and lingering over northern CWA into mid Fri morning. Other issue tonight will be the warm front lifting NNE over CWA late tonight into mid Fri morning and likely having a scattered to broken band of convection with it. This could have pockets of brief moderate/heavy rains along with hail from 10-15Z especially northern CWA, and lifting north of CWA by late Fri morning per 18Z HRRR. Not much temperature drop tonight with lows in upper 40s north of I-72 and 54-58F in southeast IL.

Unseasonably mild day ahead on Friday with breezy SSW winds gusting 25-35 mph by Fri afternoon. HREF has 40-80% chance of greater than 35 mph wind gusts Fri afternoon between the IL river and I-70 and staying gusty around 30 mph or higher into Fri night. Highs Fri in the mid to upper 70s and warmest day for much of central IL since Nov 14-15th.

The strong mid/upper level trof digging over the Western US to eject a strong storm system ne from the central plains into the upper MS river valley and western Great Lakes Friday night while pushing a cold front eastward toward the IL river valley by sunrise Sat. Broken convection likely spreading eastward ahead of this front into the IL river valley by late Fri evening/early overnight Fri night and into eastern IL late Fri night and Sat morning. SPC day2 outlook has slight risk of severe from highway 51 west and marginal risk east Fri night. All severe elements at play Fri night over CWA, with far western CWA having risk of larger hail (larger than 2 inch) and higher winds. The 18Z HRRR has the line of storms strengthening late Sat morning as it moves into far se CWA before front clears that around around 18Z/noon on Saturday. So marginal severe risk continues in eastern IL Sat morning from Paris to Effingham southeast. Morning highs Sat in upper 50s/lower 60s over IL river valley and upper 60s to around 70F in eastern IL with breezy WNW winds behind the cold front causing temps to slip about 10F by 6-7 pm Sat.

Quiet weather returns to the region Sat night through daytime hours on Monday will IL in between storm tracks in southeast states and northern states near Canadian border. Cooler lows Sat night in the mid to upper 30s over central IL with areas se of I-70 near 40F. Sunday should be a nice day with a fair amount of sunshine and highs in the low to mid 60s. Breezy sw winds develop during Sunday afternoon over central IL especially north of I-72. Breezy sw winds bring warmer 70s back into the region on Monday with a fair amount of sunshine again.

A strong cutoff 500 mb low develops near the central Baja peninsulaof nw Mexico on Sat night and Sunday and move into central Texas by Wed morning. This will bring another strong storm system into the MO and IL on Tue and Tue night with showers likely and chance of thunderstorms from later Monday night into Tue night, lingering in southeast IL on Wed. SPC Day 6 outlook for Tue/Tue night has risk of severe storms just sw of IL and will this severe risk may be extended further ne into parts of IL Tue afternoon/Tue night. WPC Guidance has 1-2 inches of rain over CWA during this time frame and may aggravate river flooding conditions in southeast IL. Though much of central IL could use more rainfall especially nw IL (Knox and Stark counties) which only received less than a half inch of precipitation since Jan 9th.

07

AVIATION

(For the 00z TAFs through 00z Friday Evening) Issued at 537 PM CST Thu Mar 5 2026

IFR cigs will be prevalent this evening at all sites, through BMI and PIA will start with low MVFR for 3-4hrs. With a warm front lifting north tonight, conditions will decrease and become VLIFR later this evening and then last into the overnight hours. Precip is also expected which will reduce vis to less than 1sm at all sites at times. Scattered storms are also expected and have prob30 groups to cover that at each site for late tonight into tomorrow morning. Conditions begin to improve at all sites into the MVFR category, but PIA could still have some showers around as they will be closer to the low pressure area. Light and variable winds expected tonight then become southeast to south late tonight into tomorrow. Speeds will increase tomorrow with gusts of around 25kts expected.

Auten

ILX WATCHES/WARNINGS/ADVISORIES

None.