textproduct: Central Illinois

KEY MESSAGES

- A long-duration winter storm has begun, with impacts likely to ramp up overnight into Sunday. A northward shift in guidance resulted in a slight uptick in forecast snow totals, with most areas in the Winter Storm Warning expected to see 6-11 inches of snow. The highest snow amounts are still expected south of I-70. Snow amounts will decrease to the northwest, with 1-4" of snow northwest of the IL River.

- Northerly winds gusting to around 25 mph on Sunday could lead to blowing and drifting snow, especially on east-west oriented roads.

- Wind chills will be 'warmer' tonight, between 0 and 10 degrees below zero. Colder conditions return Sunday night into Monday, with wind chills of 15 below likely (60-80% chance). A Cold Weather Advisory has been issued for Sunday night through midday Monday.

UPDATE

Issued at 922 PM CST Sat Jan 24 2026

Last couple of hours, radar has been showing an enhanced band of snow over northwest parts of our CWA...in Knox county. Some HiRes models did show a fgen band over the area with slightly higher snowfall amounts. Guidance does suggest this will continue for several more hours tonight. Believe snowfall amounts and impacts warrant including Knox and Stark counties in the Winter Weather Advisory. So have already updated the grids for that inclusion and forecast should already be out reflecting that.

Auten

DISCUSSION

Issued at 240 PM CST Sat Jan 24 2026

*** LONG DURATION WINTER STORM ONGOING ***

A historic winter storm is unfolding across a large swath of the US through this weekend, with over 180 million people currently under winter precipitation-related warnings or advisories. A strong but weakening sfc high pressure remains positioned near the Great Lakes, resulting in continued northeasterly winds across central IL. Sfc temps are generally in the single digits above zero across the ILX CWA this afternoon, and the sfc freezing line is well to the south (across the far southern Plains/deep south). The frontal zone then slopes northward with height, with the 850mb freezing line analyzed from SW TX to near Little Rock, AR, into TN. An upper low near Baja California is beginning to lift northeastward, and this will provide better forcing locally as we proceed into late tonight/Sun. This upper low bring additional moisture overrunning the frontal zone, not only from the Gulf but from an atmospheric river over the eastern Pacific.

Light snow has overspread much of the ILX CWA as of 20z/2pm, with sfc obs reporting visibility between 1 and 2 miles in most locations. Any accumulations to this point have been minimal. The HREF continues to suggest that snow rates will remain below a quarter inch per hour through the daytime hours today.

Much of the expectations regarding the evolution of this system, including timing of impacts, snow rates, and a NW to SE gradient in snow totals (with amounts increasing to the SE) remain on track. The deterministic 12z guidance suite did wobble back northward. However, we've seen many of these north-south wobbles over the last several guidance cycles, and would caution against becoming too caught up on the run-to-run changes of the deterministic models. Unfortunately, life in the snow gradient zone means that small changes in the precip placement translate to noticeable changes to the model snow projections, and the latest northward shift resulted in a few inch increase to the median snow amounts across the Winter Storm Warning area.

We still feel that our messaging for this system is on track, with 5-11" being the most likely outcome for counties in the Winter Storm Warning, and we still expect a fairly sharp drop off in snow amounts on the northern side of the system. The latest probabilistic NBM has a sharp decrease in probability of 6-8" of snow north of a Jacksonville to Rantoul line, greater than 50-70% to the south, quickly dropping to just a 20-30% chance in locations north/west of Lincoln. No changes were made to the Winter Storm Warning or Winter Weather Advisory with this forecast package.

To this point, I have not seen any overwhelming signals for strong mesoscale forcing, such as fgen banding or a cross-hair signature in the fcst cross sections. The main takeaway here is that snow rates should stay in check (less than 1" per hour for much of the event). The potential exception is south of I-70, where some CAMs (HRRR/NAM Nest) indicate enough QPF during the 06-18z time frame to support snow rates exceeding 1" per hour at times. This corridor of higher QPF is very close to the southeastern portion of the ILX CWA, and may wind up staying just south of our area. This will need to be monitored as additional models come in.

Much of the discussion/concerns about the microphysics of this event persist today. To quickly recap, much of the forecast temperature profile across the Winter Storm Warning area is warmer than the dendritic growth zone (DGZ), favoring column-shaped snowflakes that accumulate less efficiently. Further north, where the temp profile is in the DGZ, the ascent is much weaker and therefore may also struggle to realize high snow-liquid ratios. If this event were to underperform expectations, I believe the most likely culprit would be snow-liquid ratios (SLRs) being lower than the forecast values of 18:1 or 20:1. Some adjustments were made this forecast package to start trending the SLRs lower, but the increase in QPF caused by the northward shift in guidance offset these changes, and resulted in similar or higher snow totals from the previous forecast. With this concept in mind, will caution that deterministic snow maps using the Kuchera ratio appear to be using 18:1 or greater across a large portion of the ILX CWA for this event. If our concerns about the SLRs are accurate, these snow maps will have inflated totals, and that's before considering other effects like snow compaction.

Northerly winds increase on Sunday, with gusts of 20-25 mph, which could lead to some blowing/drifting of snow, especially on east- west roads. Expect moderate travel impacts within the Winter Storm Warning area through Sunday evening, with a greater than 60% chance of major travel impacts along and south of I-70. Impacts become more likely late this evening into Sunday morning.

*** CONTINUED COLD WEATHER ***

The synoptic pattern will continue to feature troughing over the eastern US and ridging over the western US during the upcoming work week, which will allow below normal temps to persist. Temps aren't quite as cold tonight as previous nights. Minimum wind chill values still won't be pleasant, in the 0 to 10 below range, but this is warmer than Cold Weather Advisory criteria.

For Sun night into Mon, low temps fall back below zero and wind speeds increase as a pressure gradient exists between the departing low and a sfc high over the Plains. There is high confidence that wind chills drop at least 15 degrees below zero overnight into Monday morning, so a Cold Weather Advisory was issued for this period.

As the sfc high shifts southeast of the region and a sfc low passes by to the north, we see a brief 'warm up' on Tues, with highs forecast to climb into the 20s. That will be the warmest day through at least Saturday. One thing to keep an eye on this week is with a snow cover looking likely, if we get a cool, calm night, temperatures will likely tank well below the forecast guidance. For now, both Sunday and Monday night look windy, so did not make any aggressive temperature edits at this time. Low temps are forecast to be in the single digits (either above or below zero) through the week, which is anywhere from 10-20 degrees colder than normal.

Erwin

AVIATION

(For the 06z TAFs through 06z Sunday Night) Issued at 1111 PM CST Sat Jan 24 2026

IFR conditions will prevail at all sites due to vis being below 3sm with snow through most of the TAF period. Some vis improvement to 4sm will be seen at all sites Sunday afternoon. Cigs will be below 3kft through the TAF period at all sites with below 3kft during the overnight and morning hours, but then become VFR levels in the afternoon. Not expecting cigs below 1kft due to northeast winds, which tend to dry out the lower layers. Winds will be northeast to start and then become more northerly tomorrow and tomorrow afternoon. Will also see gusts to just over 20kts tomorrow and tomorrow afternoon.

Auten

ILX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 6 PM CST Sunday for ILZ027>031- 036>038-040-041.

Cold Weather Advisory from midnight Sunday night to noon CST Monday for ILZ027>031-036>038-040>057-061>063-066>068-071>073.

Winter Storm Warning until 9 PM CST Sunday for ILZ042>057- 061>063-066>068-071>073.