####018005905#### FXUS63 KLOT 040922 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 322 AM CST Thu Dec 4 2025 .KEY MESSAGES... - Brief period of very cold weather through tonight. - Series of clippers to bring periodic light snow chances to the region through the period. Confidence is not particularly high with tracks/timing of these features. && .DISCUSSION... Issued at 322 AM CST Thu Dec 4 2025 Arctic high pressure (1035mb at Yankton SD at midnight) is building east-southeast across the Corn Belt early this morning, in the wake of the sharp cold front which pushed through the area Wednesday afternoon/evening. Temperatures continue to steadily fall as northwest winds on the eastern periphery of the high provide persistent low-level cold advection. Temperatures are expected to dip into the negative single digits in spots west of Chicago through/shortly after sunrise and the positive single digits and low teens farther east. Coldest wind chills are still expected to be around -15F early this morning, as temps continue to fall but winds gradually diminish. The surface ridge is progged to drift east across the forecast area this afternoon under mostly sunny skies, further reducing wind speeds. With a substantial early-season snow pack and shallow mixing, temps will be slow to recover from this morning's lows, though sunshine should help. Guidance depicts a large range in forecast highs for today, from the low-mid teens to the low- mid-20s for afternoon highs for afternoon highs, and have blended this to be a little warmer than our previous forecast. With the surface ridge across the area early this evening, we'll see a quick drop in temps after sunset given the light winds, mainly clear skies and the snow pack. Will likely see readings drop into the negative single digits in places during the evening, then become steady/slowly rise overnight as warm advection develops (especially aloft) as winds turn south and increase on the back side of the now-departing surface ridge. Wind chills will likely bottom out around -15F (or even a bit colder) during the night with increasing south winds offsetting the slow rise in temps. Some guidance trends suggest the potential for some low-stratus development after midnight as warm/moist advection flow increases above the shallow boundary layer. Temperatures are expected to reach the upper 20s and ending this short bout of very cold arctic weather. The first in what appears to be a series of clipper-type systems is forecast to propagate southeast across the northern Plains and upper Mississippi Valley Friday afternoon/evening. 12/18Z guidance from Wednesday had waffled a bit on the track and precip footprint with this system, though 00Z guidance is in general agreement in bringing the positive-tilt mid-level wave across the area Friday night with the primary surface low passing north of the area. Forecast soundings depict rather dry moisture profiles which mainly saturate in the mid-levels briefly Friday evening. Ascent is not particularly strong and the DGZ depth not impressive, suggesting the potential for a period of mainly light snow, with QPF and ensemble precip probs also notably low south of the IL/WI border. Have maintained 30-40% pops generally north of I-80 for this - highest toward the WI state line and north of it. Guidance remains in decent agreement with another mid-level wave tracking east-southeast across the central/northern Plains on a slightly farther south track Saturday, which looks to have a better potential for producing some light snow across parts of the forecast area Saturday night into Sunday, albeit in a weakening phase. The clipper parade continues onward into next week, with ensembles continuing to highlight systems Monday night into Tuesday, and again Tuesday night into Wednesday. There continues to be ensemble support for a deeper surface low to track north of the area in the Wednesday time-frame, potentially producing warm enough thermal profiles in which mixed precipitation could be an issue over our cold snow pack. Snow cover should remain largely in place, given cooler than average temperatures expected through the period. Ratzer && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 1104 PM CST Wed Dec 3 2025 In the wake of an arctic cold front that crossed the area early last evening, NW winds gusting to around 20 knots will gradually diminish through the morning. Winds will then back SW under 10 knots mid afternoon as a surface high pressure shifts across northern Illinois. SW winds are then expected to persist through tonight. VFR conditions are favored through the period, though clear skies (at least initially) Thursday night and weak low-level warm air/moisture advection may result in developing BR/MIFG. Kluber && .CLIMATE... Issued at 542 PM CST Tue Dec 2 2025 Updated at 250 PM CST Tue Dec 2 2025 Here are the current record low temperatures for Thursday into Friday this week: Chicago Cold High Low Thursday 12/4 13 (1991) 0 (1893) Friday 12/5 4 (2005) Rockford Cold High Low Thursday 12/4 7 (1991) -4 (1991) Friday 12/5 -5 (2005) - Izzi && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 9 AM CST this morning for Winthrop Harbor IL to Gary IN. Small Craft Advisory until 3 PM CST this afternoon for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN. && $$ Visit us at weather.gov/chicago