textproduct: Central Illinois

KEY MESSAGES

- A wintry mix is expected tonight into Sunday morning. Snow accumulations of 1-3" are most likely north of a Galesburg to Pontiac line. Further south, a glaze of ice is possible. This includes areas from Galesburg and Pontiac south to a Beardstown to Mattoon line. A winter weather advisory is in effect for these areas.

- The pattern remains unsettled, with two additional disturbances during the middle of the week. The first is expected to produce primarily rain Tues night-Wed (30-50% chance), then the second could produce light snow Wed night-Thurs (30-40% chance).

- Temperatures moderate by mid-week, with highs reaching the 40s. Below normal temperatures return late in the work week.

UPDATE

Issued at 902 PM CST Sat Dec 6 2025

Challenging update as air temps are starting to slowly rise this evening at some sites, especially in the west. Areas in the east have not bottomed out yet, but believe these areas will see slowly rising temps overnight as well. More temps at or above 32F would prevent more freezing rain/drizzle. However, snow still appears likely in the north overnight.

Speaking of precip. Even though radar is showing some returns over area northwest of the IL river, surface reports of precip in those locations has not occurred yet. Model soundings at ILX and DVN do show some dry air that needs to be overcome before precip starts reaching the ground. Observations show lowest cigs in the northwest of around 6kft with sites further east of 10kft or higher. So, observations indicate there is still quite of bit of dry air to overcome.

Based on these observation and HiRes model solutions, believe precip will still not for several more hours, like just before or around midnight in the north and west, with after midnight in the northeast. Temps in the north are still below freezing, so think the winter weather advisory is still valid for now.

Overall the current forecast looks fine, but will try to spruce up the hourly temps and pops for the remainder of the night. Update should be out shortly.

Auten

DISCUSSION

Issued at 118 PM CST Sat Dec 6 2025

*** THROUGH SUNDAY ***

Temperatures this afternoon exceeded expectations, at least across the southern half of the CWA, as a period of mostly clear skies allowed temps to climb into the mid/upper 30s. This has led to some snowmelt, with melting visually evident in satellite imagery near I-70, and reduction in the snow depth further north. Snow depth at NWS Lincoln was down to 3" at midday, compared to 4" over the last several days.

A clipper system, in the form of a sfc low currently over Nebraska, remains on track to bring a wintry mix to the area tonight into Sunday morning. The biggest change this forecast cycle was a tightening of the QPF gradient, with a continued slight northward trend in the track of the low. This slight northward shift also increases the potential fog advection fog tonight (more on that below).

The precipitation type forecast remains complex with this system. As precip pushes in from west to east tonight, the temp profile appears just cold enough to favor snow, but some fcst soundings quickly develop a weak warm level warm nose which could lead to freezing rain or just rain mixing in. Latest guidance focuses the snow accums mainly near/north of a Galesburg to Pontiac line (1-3", increasing to higher amounts as you approach I-80 corridor). With southward extent, snow probs drop sharply, with the latest NBM having a 30% chance of 1" at Peoria and just a 10% chance in Bloomington-Normal.

There is also concern for a period of freezing drizzle as the column desaturates from top down, leading to a loss of cloud ice. Sfc temps near freezing further complicate determining whether drizzle or freezing drizzle will occur. Latest high-res guidance continued to trend slightly warmer from previous forecasts, suggesting temps a few degrees above freezing. I share the previous forecasters line of thinking that the snow cover and frozen ground will hold temps near or just below freezing, but the trend toward warmer conditions in the models and the overperformance of temperatures today decreases confidence in that assessment. Given the shifts north and the tightening of the QPF gradient, am least confident in ice occurring in the southeastern portions of the winter weather advisory (Coles to Edgar County and south). Those areas may wind up seeing little to no wintry impacts out of this system. Elsewhere within the advisory area, a glaze of ice still appears likely, which will result in very slippery conditions.

Precip should largely diminish into the late morning/afternoon, although some lingering drizzle or flurries are possible immediately behind the cold front (mainly across SE IL). Drizzle will likely occur at first, then transition to flurries as CAA results in the saturated low-level layer cooling enough for cloud ice to return.

There is potential for advection fog tonight into Sun morning. The northward shift in the low track has also resulted in greater low-level moisture advection, with latest HREF mean indicating dewpoints of 33 or 34 degF advecting into eastern IL overnight (up a few degrees from previous cycle). With the existing snow pack and frozen ground, this could support fog development, including dense fog, despite plenty of mid/upper level cloud cover overnight. Areas across SW MO, SE KS, and OK experienced dense fog Sat AM, although there was less mid/upper clouds in those areas this morning than is forecast here overnight, so its not a perfect comparison. The HRRR, RAP, and NAM suite all suggest dense fog development east of I-55, while other guidance sources have little to no fog, so this seems like an all or nothing scenario where there is widespread dense fog east of I-55, or little to no fog. The latest HREF currently has a 30-50% chance of vis below 1 mile east of I-55, although as previous shifts noted, the modeled sfc temps may be a tad too warm due to the existing snowpack.

Following the cold frontal passage on Sunday, bitter cold air returns by Sunday night, with single digit lows north of a Macomb- Bloomington line, teens along the I-72/Danville corridor, and 20s near/south of I-70. Wind chills could fall a few degrees below zero.

*** MONDAY - FRIDAY ***

As ridging remains anchored out west, a broad northwest flow regime and baroclinic zone will exist from the Pacific NW to the Ohio Valley, resulting in continued clipper systems passing by throughout the week. The next such system is tracking such that moderating temps are forecast mid-week (highs in the 40s Tues- Wed). This will favor rain as the primary p-type Tues night into Wed, although a rain-snow mix can't be ruled out during the nighttime hours, especially north of I-74 where it will be coolest. Another weak clipper will follow quickly behind this one, and could offer a chance for snow Wed night-Thurs. Currently, snow accums from this system appear minor, with a 30-50% chance of a dusting but less than a 20% chance of 1".

The latest guidance has trended towards a deep cut-off low digging into the Midwest by late in the week, bringing a strong cold front through and ushering bitter cold air back into the region. Will note that this has not yet been a consistent feature from run-to- run, but it certainly bears monitoring. If the latest guidance is to be believed, high temps may struggle to reach 20 degF on Fri- Sat, which could be near record cold high temps in some locations. The LREF has a 30-50% chance of wind chills meeting advisory criteria (colder than 15 degrees below zero) north of I-72 Friday night into Saturday. While the exact intensity of the cold remains in question, the CPC 6-10 day and 8-14 day (valid through Dec 19) outlooks both favor colder than normal temperatures across Illinois, so our cold start to meteorological winter appears set to continue.

Erwin

AVIATION

(For the 06z TAFs through 06z Sunday Night) Issued at 1112 PM CST Sat Dec 6 2025

Challenging aviation forecast for all sites next 24hrs. VFR conditions will start all sites, but MVFR cigs will arrive as a mix of fzdz and snow arrives at most sites. SPI is the only site that will see only rain through the period when precip is expected. BMI and PIA will have winter mix of snow, sleet, and freezing rain overnight, but should transition to a mix of rain and snow toward morning. DEC and CMI will also see winter mix or fzdz/sn, but change to ra/sn mix toward morning, followed by drizzle and snow mix in the morning. IFR cigs/conditions will also arrive over night with the precip from the west. However, very low cigs and vis have begun to advect northward from the south and will affect DEC, CMI and BMI prior to the precip and during the precip. Once precip ends tomorrow late morning, IFR & LIFR cigs will continue tomorrow afternoon, but as the front moves through, clouds will scatter out at PIA and BMI. Scattering out of clouds is possible at SPI, DEC, and CMI, but confidence is low and would prefer to be somewhat pessimistic. So, will go with broken MVFR clouds around 2.5kft for the evening hours.

Winds will be southeast at 10kts or less through the night and tomorrow morning, but when the boundary moves through, winds will become northerly and be breezy with gusts around 20kft for late morning through afternoon at all sites. Wind speeds will decrease during the evening hours.

Auten

ILX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 6 AM CST Sunday for ILZ027>031- 036>038-040>048-053>057-063.