textproduct: Central Illinois

KEY MESSAGES

- A long-duration winter storm will impact the region in two waves spanning late Saturday morning through Sunday evening. Snow amounts appear fairly light through the day on Saturday, with only an inch or two of snow (highest south of I-70), however, more accumulating snow arrives late Saturday night into Sunday.

- There were no major forecast changes today. A Winter Storm Warning remains in effect from Cass to Vermilion County and southward, with 5-10" of total snow being the most likely outcome. The highest snow totals are expected near/south of I-70, and there is 10-30% chance for 12" of snow (or more). North of the Winter Storm Warning, 2-5" of total snow is possible.

- A Cold Weather Advisory remains in effect through midday Saturday. Wind chill values will range from 10 to 20 degrees below zero tonight into Saturday morning. Another Cold Weather Advisory may be needed Sunday night into Monday morning (60-80% chance).

DISCUSSION

Issued at 224 PM CST Fri Jan 23 2026

Climatologically, we are at the coldest point in the winter season in central/southeast Illinois, and this year, winter is not holding back. An expansive, robust 1048-mb sfc high pressure (normalized anomaly of 2-3 standard deviations) remains positioned over the Dakotas, with an Arctic air mass pushing south into the southern Plains/TN Valley. The Cold Weather Headlines verified this morning, with wind chill values of 25 to 35 below from Macomb to Bloomington and northward. While we should be past the most extreme wind chills, there will be little reprieve from the cold over the next week. Air temperatures remain in the single digits north of I-70 this afternoon.

In terms of the upcoming winter storm, the bottom line up front is that there has been little change in our thinking from the previous forecast. There is still expected to be two waves of snow, one primarily late Sat morning- early Sat evening, and another beginning after midnight Sun and continuing into Sun eve. The second of these waves still looks more robust. There will be a snowfall gradient across the ILX CWA with amounts decreasing as you move from southeast Illinois to the northwest. One of the primary challenges that exists with this forecast is pinning down where exactly this gradient sets up and how sharp it is.

While there were no major shifts in the forecast with this package, subtle shifts are still possible over the next 24 hours. The strength and location of the strong sfc high pressure to the north will ultimately impact where the baroclinic zone sets up. While sfc temps and the low-level warm nose will both be solidly south of our CWA, the temperature profile of the atmosphere will still impact the microphysics of this snow event. In some locations, fcst soundings show much of the thermal profile located within the dendritic growth zone (DGZ, which is -12 to -18 degC), which favors large dendrites and efficient snow rates. In other fcst soundings, typically those further south, closer to the baroclinic zone, the saturated layer is mostly warmer than the DGZ (in the -5 to -10 degC range), which favors column-shaped snowflakes that accumulate less efficiently. All of this is to say that despite the very cold air mass in place, we may not realize the high liquid-snow ratios in our forecast, which would cut down on the snow totals in the current deterministic forecast (which has 8+" south of I-70 for the entire event). The thermal profiles do appear more favorable heading into Sun, during which time the QPF amounts are also higher, which is why we anticipate greater snowfall amounts with that second wave.

Impacts appear fairly limited during the day on Saturday, with just a 30-50% chance of 1" of snow north of I-70 by 6 PM Sat. The stronger push of snow moves in after midnight Sun, and while the latest HREF (23.12z) only goes out through 12z/6am Sun it does suggest snow rates approaching 0.50"/hour south of I-70 late in the overnight hours. Rates of 0.25-0.50"/hour are expected within the Warning area north of I-70. These rates are likely to continue into the day on Sun. This is expected to lead to travel impacts within the Winter Storm Warning/Advisory areas from late Saturday night through much of the daytime hours on Sunday (with snow lingering in eastern IL into the evening). North winds gusting 20-25 mph on Sun combined with light snowflakes could lead to blowing/drifting, with any impacts maximized on east-west oriented roads.

Despite being within a day or two of the event, the uncertainties regarding the microphysics, baroclinic zone placement, and potential for a tight northern gradient do leave a good deal of uncertainty in the forecast. The highest end outcomes include over a foot of snow near/south of I-70 (10-30% chance of more), while the official forecast for the Winter Storm Warning is 5-10". There were internal discussions about expanding the Winter Weather Advisory to include Knox, Stark, and Marshall Counties, where 1-3" of snow is currently forecast, however, given the potential for a tight northern gradient we held off for now. There was not any consideration given to changing the Winter Storm Warning, the existing Warning appeared well positioned.

*** NEXT WEEK ***

As noted above, the extended forecast shows little in the way of relief from the cold, at least for the remainder of January. Ensemble guidance suggests high temps will generally be below 20 degF each day, with the exception of Tuesday (low/mid 20s). Additionally, snow cover may result in temps running cooler than guidance, especially on less windy, clear nights. With that in mind, did nudge the low temp forecast cooler Mon night and Tues night, resulting in lows near zero. Wind chill values may approach Cold Weather Advisory criteria at times, particularly Sun night-Mon morning (60-80% chance per LREF). After our weekend system departs, precip chances appear limited, at least during the first half of the upcoming work week. The extended outlooks from the CPC still favor below normal temps (60-90% chance) through next weekend.

Erwin

AVIATION

(For the 00z TAFs through 00z Saturday Evening) Issued at 548 PM CST Fri Jan 23 2026

VFR conditions will prevail at all TAF sites through the night and tomorrow morning. Then as snow arrives, conditions will become more MVFR, the IFR due to visibilities dropping to 1-2SM with light snow. High cigs to start, then becoming mid clouds around 12kft then lowering to 7-8kft during the late morning. Once snow arrives, cigs will drop to MVFR below 2kft. Winds will be less 10kts of less through the period with direction starting as northernly and then becoming northeast.

Auten

ILX WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory until noon CST Saturday for ILZ027>031- 036>038-040>057-061>063-066>068.

Winter Weather Advisory from 9 AM Saturday to midnight CST Sunday night for ILZ029-031-036>038-040-041.

Winter Storm Warning from 9 AM Saturday to midnight CST Sunday night for ILZ042>057-061>063-066>068-071>073.

Cold Weather Advisory until noon CST Saturday for ILZ071>073.