388 FXUS63 KLOT 301803 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1203 PM CST Tue Dec 30 2025 .KEY MESSAGES... - Light snow likely afternoon into this evening. Most accumulations (coating to an inch) focused roughly northeast of a Rockford to Rensselaer line. - A period of snow again Wednesday afternoon. && .UPDATE... Issued at 1020 AM CST Tue Dec 30 2025 Just a quick update to speed up the arrival time of light snow by a few hours based on upstream observations and latest model guidance as snow is breaking through an incipient dry layer, with light activity likely to begin near Rockford/I-39 over the next hour or two. This initial activity looks pretty light given very modest overall ascent with the main wave still well to our northwest--currently pushing into NW Minnesota at this hour. Nonetheless, upstream observations suggest visibility reductions under 2-3 miles will be possible into this afternoon as deeper top-down saturation works its way through the northern half of the forecast area. The main activity and bulk of accumulating snowfall (coating to locally north of an inch) still looks like it'll focus during the 5 PM to midnight timeframe, favoring the northeast half of the CWA, and likely limited to a roughly 3-4 hour period at any given point. Based on the incoming morning guidance, have also expanded PoPs and some light accums a bit farther south across our NW Indiana counties. Carlaw && .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 /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1203 PM CST Tue Dec 30 2025 A period of SN across southern Wisconsin and northwest Illinois will spread across all sites this afternoon, with MVFR visibility possible at the Chicago sites and IFR visibility possible at RFD. This area of SN will briefly diminish toward sunset before a more potent area of SN spreads across the area this evening. IFR visibility is expected to prevail in the 00-04Z window for ORD/MDW, with the expected drier and smaller snowflakes lowering visibility into LIFR levels at times roughly in the 01-03Z window. SN intensity will quickly wane late this evening, with a low (<20 percent) chance that FZDZ mixes with the SN for an hour or two before ending. MVFR ceilings with perhaps some scattering are then expected overnight through Wednesday morning. Another period of SN is forecast Wednesday afternoon into early evening as a strong jet streak shifts southeastward across the area. While SN is expected to prevail for much of the period, it will likely exhibit a streaky presentation on radar and result in varying visibility from IFR to VFR levels. Otherwise, W/WSW winds around 10 knots will back SW and gust to around 20 knots during the SN this evening. Winds will then settle WNW around 10 knots overnight into the morning before veering NW and gusting over 20 knots during the afternoon. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST this afternoon for the IN nearshore waters. && $$ Visit us at weather.gov/chicago