textproduct: Central Illinois

KEY MESSAGES

- A pair of clipper system will skirt just to our north tonight and again Wednesday evening. Gusty winds are expected at times but little if any precip is expected. The greatest potential for any accumulating snow is 20-40 percent Tuesday evening near/north of I-74.

- An arctic air mass will bring a return of bitterly cold temperatures Thursday night through the weekend. Single digit highs and sub-zero lows will be possible for portions of central Illinois.

DISCUSSION

Issued at 147 AM CST Tue Jan 20 2026

This morning, an expansive surface ridge is in place centered over the mid Mississippi Valley and spanning much of the middle section of the country. Aloft, a broad upper trough centered over Hudson Bay continues to drive northwest flow across the Midwest with a series of low amplitude shortwaves bringing occasional precip chances to the Great Lakes and portions of the Midwest.

Rather benign weather conditions are expected today under the influence of the surface ridge, which slowly shifts to our east this morning, allowing for return flow to overspread central Illinois. This return flow will help temperatures rebound from the bitter cold, with highs reaching the upper 20s to lower 30s this afternoon. Meanwhile, a clipper system currently over southern BC/Alberta will track across Iowa late this evening, then northern Illinois overnight. Latest runs of the GEM, ECMWF, and NAM all suggest that snow with this wave will reach as far south as the I-74 corridor, while the GFS keeps it just to our north. NBM probabilities for accumulating snow (>0.1 in) are confined to areas north of a Galesburg to Peoria to El Paso line (10% contour), peaking around 20-40 percent across our northern tier of counties (Knox/Stark/Marshall). NAM forecast soundings at Lacon, IL, show the low levels struggling to saturate until around 12Z Wednesday, then quickly drying out in the mid-levels by 13Z, coinciding with the passage of the main H5 vort max and subsequent loss of forcing. Furthermore, a handful of the CAMs do show some light precipitation on a trailing surface cold front, which is not advertised by the regional/global models. Accompanying forecast soundings indicate some dry air below 700mb that will be difficult to overcome given the short duration of forcing, but we cannot entirely rule out some very light snow or flurries continuing later into the overnight and early morning hours Wednesday.

Another shortwave trough takes aim at the Great Lakes Wednesday evening. Precipitation chances with this system are expected to remain well to our north; however, we locally anticipate the warming trend to continue as southwest flow out ahead of the wave helps push temperatures into the mid 30s to mid 40s across central Illinois. Despite the low PoPs, central Illinois will still feel the effects of this system as gusty winds develop. The NBM indicates an 80 to greater than 90 percent chance of exceeding 30 mph wind gusts Wednesday, with probabilities generally 20-60 percent (highest over east-central IL) of exceeding 40 mph gusts.

A very strong 1050mb surface high will build from the Canadian Rockies into the central and northern Great Plains Thursday night into Friday. A bitterly cold air mass associated with this strong high will overspread central Illinois starting Thursday night, with air temperatures dipping below zero in spots by Friday morning. Widespread sub-zero temperatures are possible by Saturday morning (60 percent probability along/north of I-72 per NBM), which will contribute to wind chill values ranging from 10 below in the south to around 25 below in the north. Meanwhile, a wintry mix of snow and freezing rain will occur well to our south Friday along the baroclinic zone over portions of the Deep South. As the surface ridge retreats northeast across the Great Lakes late this weekend, precipitation may be able to spread north across central Illinois, potentially producing accumulating snow. There remains quite a bit of uncertainty on how far north this snow will occur. The latest run of the GFS keeps central Illinois dry through the weekend, while the Canadian and European deterministic runs do bring snow accumulations into central Illinois. The NBM 24-hour probability for an inch of snow remains low, only around 20% around the I-70 corridor and around 10% along the I-74 corridor. This period will require close monitoring as the event draws nearer.

Deubelbeiss

AVIATION

(For the 12z TAFs through 12z Wednesday Morning) Issued at 519 AM CST Tue Jan 20 2026

Light SW winds and VFR conditions are in place this morning under the influence of high pressure over the mid Mississippi Valley. As the ridge shift east, SSW winds will pick up above 10 kt around midday today. Winds will further pick up late this evening and overnight ahead of an approaching low that tracks across northern Illinois late tonight. Expect increasing mid clouds with MVFR ceilings and snow expected to stay just north of the terminals, but not far from SPI/BMI. A low level jet ahead of the low track will also result in low level wind shear with winds around 020 peaking between 50-55kt overnight.

Deubelbeiss

ILX WATCHES/WARNINGS/ADVISORIES

None.