948 FXUS63 KLOT 300844 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 244 AM CST Tue Dec 30 2025 .KEY MESSAGES... - Light snow likely late this afternoon/early this evening, mainly northeast of a Rockford to Rensselaer line. - A period of snow again Wednesday afternoon. && .DISCUSSION... Issued at 244 AM CST Tue Dec 30 2025 Northwest flow aloft in the wake of the big weekend storm system should remain in place the rest of the week. A series of low amplitude shortwave troughs are likely to ripple through the northwest flow at fairly regular intervals. The first wave, has crossed the Canadian border into the northern Plains early this morning and will rapidly move southeast toward reaching the mid-Mississippi Valley later this afternoon. Air mass in advance of this system is dry, but top- down saturation is likely to result in snow developing southeastward mid-late afternoon along the I-90 corridor. Not only is moisture limited, but time/height X-sections depict a short window (2-4 hours) with deep ascent and column saturated enough for precip to reach the ground. Within a few hours of snow reaching the ground, ascent is progged to weaken and mid levels will begin to dry out. This should result in snow ending or transitioning to a light snizzle by mid-late evening. Overall, looks like a low QPF event with fairly modest snow:liquid ratios given the expected mostly smaller flake size. Accumulations looks to be generally an inch or less, but with temps well below freezing and snow likely hitting during or toward the end of the evening commute, there could still be travel impacts. Temperatures will remain cold today, likely struggling to reach 20 degrees during the daytime near the Wisconsin border and only climbing into the lower 20 south of I-80 today. Temps tonight will likely slowly rise reaching the mid to upper 20s by daybreak Wednesday. Clipper number 2 will be right on the heels of today's system. Snow looks to start earlier in the day tomorrow than today and could fall with a bit more gusto than today's snow. Stronger and deeper ascent, aided by fairly strong divergence in the left exit region of a 130kt+ 250mb jet streak could provide for a period of some slightly beefier snowfall during the afternoon. Still, with moisture still pretty limited and only a 3-5 hour window of accumulating snow expected, it looks like the hardest hit areas could end up with an inch or two of snow by the time the snow ends Wed evening. It looks fairly windy during the snow Wednesday, but not as windy nor as cold as it was during Sunday night's snow. Quick shot of seasonably cold air is expected Wednesday night into Thursday. As winds veer to more northerly direction and prior to column really drying out, there could be a short window of some lake effect snow into northeast Porter County Wed evening, which could bump totals there up a bit. There are indications that we could temporarily transition to more of a zonal flow pattern over the weekend. This would allow for some moderation in temps and with dry conditions. - Izzi && .AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 1107 PM CST Mon Dec 29 2025 Key Aviation Messages for the current TAF period: - Period of IFR snow late afternoon/evening tomorrow Mid-high level cloudiness will quickly increase Tuesday morning in advance of the next fast moving weather system expected to impact the area tomorrow. Confidence in a period of light snow has increased enough to go with a period of prevailing IFR snow very late afternoon into the early-mid evening. Snow is expected to end by mid-late evening with MVFR CIGS likely to through the remainder of the night. - Izzi && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 3 AM CST early this morning for the IL nearshore waters. Small Craft Advisory until 3 PM CST this afternoon for the IN nearshore waters. && $$ Visit us at weather.gov/chicago