textproduct: La Crosse

KEY MESSAGES

- Widespread dangerous cold returns Thursday with -25F to -40F wind chills possible Thursday night through Sunday morning.

- Snowfall tonight and Wednesday afternoon/evening. Higher accumulations expected Tuesday night with a swath of 1"-2" south of I-90 and a narrow axis topping 3" within this swath, currently favored to occur south of US Highway 18.

- Wednesday afternoon/evening brings minor (1" or less) snow amounts but potential for gusty winds and greatly reduced visibility as snow falls.

DISCUSSION

Issued at 314 AM CST Tue Jan 20 2026

Dangerous cold Thursday night through Sunday morning

Cyclonic flow over eastern North America continues over the next 7 days will lead to below average temperatures. The approach of an upper low Thursday/Friday will lead to a reinforcing surge of cold air spilling into the CWA starting Thursday afternoon. Thursday night into Sunday morning appear very likely to feature dangerously cold conditions with wind chills under -25. Similar to what has been stated with the past few forecast updates, timing of the coldest morning is still uncertain as the coldest air temperature morning (Saturday) appears likely to feature very light winds. 20.00z LREF and 2 of the ensembles (ECENS/GEFS) that make up the broader ensemble point toward Friday morning with a 60-95% chance to see wind chills at least 35 below while CMC ensemble also keeps similar probabilities both Friday and Saturday mornings. Given these probabilities, am growing increasingly confident in warning-level conditions (10 minutes to frostbite) Friday morning. As for Saturday and Sunday mornings, uncertainty is a bit higher given reduced contribution from wind, but advisory-level (30 minutes to frostbite) impacts do appear probable (65-90% and 30-60%, respectively per 20.00z LREF). Should these trends hold, will strongly consider a longer lead time Watch in the next few forecast cycles.

2 rounds of snow tonight and Wednesday afternoon/evening

Two disturbances in the northwesterly flow aloft look to swing southeast out of Canada. First wave arrives tonight which should lead to a swath of snow mainly south of I-90 where broad lifting due to QG ascent occurs within the DGZ. Given presence of 925/850mb frontogenesis, expect a narrow axis within this swath with totals of 3"+. Progged location of the swath of snow has shifted southward considerably over the past 4 runs of the operational NAM/GFS bringing it in line with operational CMC/EC. Short range ensembles show a similar pattern with a jog southward seen in 20.00z HREF. Have therefore focused highest PoPs and snow amounts in NE IA and far SW WI, cutting both downward farther north. As for amounts, with much of the snow producing layer likely in the DGZ, should get snow to liquid ratios close to 20:1 Adjusting 20.00z HREF probabilities for this, the chance to exceed 3" is around 60% for some areas south of Highway 18 in NE IA and far SW WI. While uncertainty is higher than would be optimal given recent shift in placement of the snow band in guidance, given these probabilities and inter-office collaboration concerns, have issued a Winter Weather Advisory for Fayette, Clayton, and Grant Counties. The good news is that impacts should be at the low end for an Advisory due to light winds and highest snow rates occurring after 6 PM.

Second round of snow presents a different set of potential impacts. With a bit stronger of an upper wave and thus cooler temperatures aloft, potential for a pocket of surface-based instability to develop exists. Within this potentially unstable boundary layer, progged winds ramp up to around 40 knots at 850mb. Thus, while snow amounts look to be minor (1" or less) as the period of snowfall looks to be even shorter compared to Tuesday, could have moderate to short lived high impacts on driving conditions due to potential for a short burst of snow, strong gusts, and greatly reduced visibility.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1116 AM CST Tue Jan 20 2026

VFR conditions currently present across the region with southwesterly winds in the 5 to 12 kt range. An area of snow is expected to move in from the west this evening, impacting the terminals through the overnight hours. While the heaviest snow should remain south of the terminals, MVFR CIGs and MVFR to IFR visibilities should still materialize at both KLSE and KRST. The area of snow is expected to quickly move to the east with only light flurries possible after 08Z. MVFR CIGs will likely linger until daybreak before scattering out to VFR. Winds will generally stay out of the south to southwest through the period with speeds below 12 kts.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Winter Weather Advisory from 6 PM this evening to 6 AM CST Wednesday for WIZ061. MN...None. IA...Winter Weather Advisory from 6 PM this evening to 6 AM CST Wednesday for IAZ029-030.