textproduct: Central Illinois

KEY MESSAGES

- Expect an abrupt return to winter tonight, with wind chills dropping below 0 by early Monday morning. A dusting of snow is possible mainly north of I-72, and could result in some slick spots on roads.

- Strong winds will blow from the west-northwest tonight. Expect frequent gusts to 45+ mph, with a 20-30% chance for a sporadic gust or two to 55 mph (highest chances north of I-70). This will result in difficult driving conditions for high profile vehicles, and may cause a few localized power outages due to downed tree branches.

UPDATE

Issued at 907 PM CST Sun Dec 28 2025

Updated/increased PoPs for this evening with a shortwave feature clipping parts of central IL, mainly north of I-72. Not expecting anything more than a wind-blown dusting of snow, but there could be some slick spots on roadways as some melting and re-freezing takes place as temperatures plunge further overnight. Temperatures in the snow started out in the 20s, but we'll continue to see temperatures dip into the teens overnight. In addition, another trailing shortwave looks to pass through northern IL Monday morning, perhaps extending light snow into parts of central IL, mainly I-74 northward. Again, this only looks to be a light wind- blown dusting. Otherwise, widespread 40 to 50 mph gusts have developed across central and southeast IL, and should continue into Monday morning before gradually weakening during the day. A wind Advisory remains in effect until 3 PM Monday.

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DISCUSSION

Issued at 113 PM CST Sun Dec 28 2025

***** STRONG STORMS THIS AFTERNOON *****

CAMs remain in agreement that a hslc line of storms will form along a cold front early this afternoon between roughly the IL River and I- 55. As these storms move into a strongly sheared and increasingly unstable airmass to the east (sfc dewpoints are already in the low- mid 60s), they are forecast to intensify, posing a risk for mainly scattered damaging wind gusts of 60+ mph. However, with low LCLs, 1000-2000 J/kg of SBCAPE, and 50-65 kt 0-6km bulk shear, both the HRRR and RRFS advertise sig tor parameter values climbing to 2 to 4 east of a roughly Taylorville to Bloomington line. 0-3km CAPE over 150 J/kg and and 30-40 kt shear would favor a QLCS tornado risk with any bowing segments that maximize the line-normal component of this shear, but the HRRR, ARW, and each REFS member suggest there may be some hybrid/supercell characteristics as well. Needless to say, the SPC level 2 of 5 (slight) risk for severe weather and 5% tornado risk seem justified by what we're seeing; we anticipate needing a line of severe thunderstorm warnings with one/more embedded tornado warnings this afternoon. Timing would be roughly 1-2pm near/west of I-55 to 7pm along the IL/IN state line. In addition, storm motion will be fast at 50-65 mph, so be sure to have multiple ways to receive warnings and a plan for quickly taking shelter if necessary.

***** TURNING WINDY AND SHARPLY COLDER *****

Behind the cold front, the rapid pressure rises will result in an abrupt uptick in (non-thunderstorm) winds out of the west-northwest. This effect will be most pronounced in areas near and east of roughly I-55, since the front will be strengthening as it moves through. Simultaneously, the sfc low will rapidly deepen (~20 mb in 15 hours) in the left exit region of the curved 125-140 kt 500mb jet streak, where differential positive vorticity advection will be maximized (from both shear and curvature). This will result in a sharp pressure gradient across the area. Unsurprisingly, forecast soundings from various CAMs suggest mean PBL winds reach 35 to 40 kt late this evening, with winds at the top of the mixed layer around 45 kt; the NAMNest even suggests a few hours where the max wind at the top of the PBL reaches 50+ kt across our north. Consequently, we suspect winds will be sustained at 30-35+ mph with frequent gusts to 45+ overnight area-wide. In our north, sustained winds may approach 40 mph for a couple hours with a gust or two to 55+ mph tonight. The HREF suggests less than a 10% chance of these 55 mph gusts, but we lean more towards the REFS which advertises those probabilities at 20-40% given the strong cold advection (and subsident) regime with rapid pressure rises. The Wind Advisory remains in effect from 3pm this afternoon through 3pm tomorrow area-wide.

In addition to the wind this evening, a brief burst of snow with moisture wrapping around the low could give our area a quick dusting to an inch of accumulation. This seems most likely between 6pm and midnight north of roughly I-72 (I-74 east of Champaign). Additional snow showers may (20-40% chance) continue along the I-74 corridor into tomorrow morning, with lighter activity (we called it "flurries" in the forecast) further south. With the rapid drop in temperatures this evening, possibly resulting in a flash freeze (though this will depend on how much evaporates due to the strong winds), and the proceeding snow, we may wind up with some slick spots on untreated roadways and sidewalks. Temperatures (wind chills) will drop 25-30+ (35-45) degF in an hour behind the cold front this evening, followed by a more gradual drop overnight with lows in the teens (and wind chills between 0 and minus 10) by sunrise Monday morning. Wind chills are unlikely (20-30% chance) to rise out of the single digits on Monday.

Tuesday into Wednesday, global models and their respective ensembles are in general agreement that ridging in the Plains will attempt to nudge its way into the Midwest, but uncertainty increases in the forecast Thursday (New Year's Day) and beyond as another push of arctic air across the Great Lakes attempts to spill southward into our neck of the woods. It also appears a clipper system will impact some portion of the Midwest/Lower Great Lakes Regions Wednesday night into Thursday, but probabilities for measurable snowfall are highest to our north - only running 15-30% (highest along the I-74 corridor) in our area.

Bumgardner

AVIATION

(For the 00z TAFs through 00z Monday Evening) Issued at 505 PM CST Sun Dec 28 2025

A rapidly deepening low pressure system will lift from northeast IL across Lower Michigan and into Lake Superior tonight. The tight pressure gradient will result in increasingly strong winds blowing out of the west-northwest this evening into tonight, with sustained speeds around 25-30 kt and gusts over 40 kt at times. Ceilings should be mainly MVFR throughout the overnight period, however flight conditions may briefly enter the IFR category due to reduced visibilities in a wave of snow translating west to east across the airfields between 01z and 05z (7-11pm) this evening. As the surface low lifts away to the northeast, the gradient will gradually relax and MVFR ceilings may (50-70% chance) break up late Monday morning into early afternoon.

Bumgardner

ILX WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 3 PM CST Monday for ILZ027>031-036>038- 040>057-061>063-066>068-071>073.