textproduct: Central Illinois

KEY MESSAGES

- Scattered showers will develop this morning, become more numerous through midday, and taper off from west to east tonight. Thunderstorms are also possible, especially this afternoon and evening. Rainfall amounts are likely to be around a half inch for most areas, but localized swaths of 1 to 3 inches are possible this afternoon and evening.

- Strong to severe thunderstorms are possible this afternoon and evening near and south of I-72. SPC has a Marginal (level 1 of 5) risk for severe weather, including a 5 percent damaging wind risk and 2 percent tornado risk.

- Wind gusts of 30 to 40 mph are likely Friday morning through afternoon. The stronger winds will be northwest of I-55.

- Much cooler weather will settle into the region Friday through the weekend potentially resulting in areas of frost both Saturday and Sunday mornings.

DISCUSSION

Issued at 229 AM CDT Thu Oct 15 2026

A cold front now well south of the area early this morning will lift northward as a surface low developing in the southern Plains lifts northeastward toward central IL. The front should lift through central IL during the afternoon hours, bringing 70 degree dewpoints to much of the area and SBCAPE values of 1000-1500 J/kg to around to I-72 corridor, coincident with 40-50 kt deep layer shear. 150-250 Storm Relative Helicity values are also forecast in this area, suggesting a few tornadoes will be possible. SPC has a Marginal Risk for Severe thunderstorms for a threat of locally damaging wind gusts and a few tornadoes possible. The cold front trailing the low should begin to push into west central IL by afternoon, and cross the remainder of central and southeast IL through the evening hours. High resolution models depict scattered showers developing mainly west of I-57 this morning as an initial upper level disturbance and low level moist-warm advection takes place. A small break is then depicted before another disturbance and the warm front approaches mid morning into early afternoon. While many high-res models decrease shower coverage during the afternoon hours, this is also the period where a few models depict a few supercells developing in the warm sector behind the warm front, with significant scatter among model solutions on when/where breaks or supercells will be developing. More consistency develops with clearing behind the cold front, as showers look to end west of I-55 by midnight, west of I-57 by 4 AM Friday, and throughout IL by 7 AM Friday. High resolution model ensembles depict average precipitation amounts of around a half inch, but also depict a few swaths of 1 to 3 inches. This rainfall will generally be beneficial with mostly dry conditions preceding the past few days, but 2 to 3 inch amounts could produce some locally excessive amounts and WPC indicates a Marginal Risk for excessive rainfall from around I-72 southward.

Behind tonight's strong cold front, a strong pressure gradient develops over the area for Friday, which should set up 15-20 mph northwest winds, with gusts 30-40 mph, with the higher values west of I-55. A potent upper level shortwave and 500 mb cold pocket of minus 25 C will promote scattered shower activity and cloud cover. Highs should only reach the mid 50s for a very cold/blustery feel compared with recent record warmth.

Friday night, high pressure will migrate eastward toward the Mississippi Valley, weakening the pressure gradient over especially western portions of central IL. With temperatures dropping into the mid 30s and the light winds, it appears areas of frost will develop west of I-57, but to the east enough wind should remain to keep temperatures in the upper 30s without frost. By Sunday morning, the high should migrate toward the mid-Atlantic coast, with winds already beginning to pick up from the south by morning. Nevertheless, mid-30s temperatures and frost potential looks to cover the entire area as the wind will likely be too little/too late to prevent it.

Southerly flow and a building ridge of high pressure will bring a warming trend starting Sunday, raising highs from upper 50s Saturday to upper 60s Sunday. Further warming through midweek should bring highs to mid to upper 70s by Wednesday. Dry conditions will continue Saturday through midweek under the influence of the surface high followed by upper ridge.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 545 AM CDT Thu Oct 15 2026

A warm front will lift toward the central IL terminals today, bringing lowering ceilings from predominant MVFR at 12Z to predominant IFR by 16Z-18Z as the front arrives. Showers and a few thunderstorms will accompany the warm frontal passage, especially near the I-72 terminals KSPI-KDEC-KCMI. Isolated thunderstorms will continue in the afternoon, followed by a cold front sweeping across the area in the evening, promoting additional showers and thunderstorms. Model guidance supports a slight upward trend in ceilings after the warm frontal passage, but cigs will likely remain MVFR to locally IFR until late in the forecast period or possibly after 12Z. At this time, have not included any VFR conditions through the forecast period. Winds E 7-10 kts initially, shifting to S-SE and increasing to 10-15 kts for the afternoon, then W-NW around 15 kts with gusts to 25 kts after 04Z-06Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.