textproduct: La Crosse

KEY MESSAGES

- Moderate confidence in snow squall potential through the day Thursday. While confidence is high for plummeting temperatures and flash freeze, wavering confidence in exact timing limits overall confidence.

- Increased south winds near 40 mph tonight further increase out of the west Thursday, from 40 to 50 mph west of the Mississippi River Valley where a Wind Advisory is in effect from 12PM to 6PM.

DISCUSSION

Issued at 122 PM CST Wed Dec 17 2025

Precipitation Chances Increase Tonight:

An upper level trough progressing east over the Rocky Mountain West advects through the Plains tonight, driving local weather impacts tonight through Thursday. Amplified quasigeostrophic forcing sustains the strong surface low (978mb), seen reforming along the parent low's triple point. HREF/LREF confidence for <985mb MSLP traversing the Missouri River Valley from North Dakota into Minnesota near 18.06Z. Above freezing temperatures result in liquid precipitation type initially tonight through Thursday morning with initial frontal passage.

After the initial low level front progresses across the forecast area Thursday morning, subsequent deepening of the mid level extratropical cyclone intensifies potential local impacts through Thursday. Amplification in prefrontal low level return flow tied to initial phasing of the trough tonight increases low level moisture, providing additional wraparound moisture for snowfall impacts through Thursday.

Thursday Snow Squall & Flash Freeze Impact Potential:

A break in precipitation Thursday morning from a slot of dry air after the morning frontal passage and before subsequent reorganization of the extratropical cyclone. Top-down cooling brings surface temperatures near freezing from northwest to southeast through the late morning into the early afternoon as subsequent snowfall chances increase into the early afternoon while also limiting freezing rain chances.

The polar cold front will be quite strong with a tight low level theta e gradient and intense low level frontogenesis. A stronger inter/intra ensemble solution to the surface low increases accompanying isallobaric winds and accompanying snow squall concerns. While current confidence for required parameters such as instability, frontogenesis, flash freezing, and a thick DGZ residence align, exact timing between high resolution models leaves some uncertainty. Earliest solution in the HRRR & RAP models quickly advect a line of snow east by the early afternoon with the Fv3 initiating snowfall along our western periphery during that time. This earlier solution would reduce impacts due to the warmer temperatures limiting DGZ growth.

Increased messaging for snow squall concerns given the signal but will need to continue to monitor.

Increased Winds Tonight & Thursday:

Low level confluence tightens the pressure gradient and increases south winds tonight with gusts near 40 mph at times primarily west of the Mississippi River Valley with frontal passage.

Subsequent increasing west winds accompany the strong low level CAA and strong extratropical cyclone Thursday through Thursday night with overall forecast confidence for 40-50 mph gusts west of the Mississippi River Valley and 30-40 mph elsewhere.

Temperatures Through The Weekend:

The colder airmass through Thursday ushers another bout of below zero apparent temperatures Thursday night into Friday morning and single digit apparent daytime highs Friday. Subsequent upstream cyclogenesis through the end of the week tracks in the wake of midweek cyclogenesis, affecting confidence in local temperatures through the weekend as the local forecast area is placed between potential low level return flow and a canadian polar airmass.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1119 PM CST Wed Dec 17 2025

VFR conditions currently present across the region ahead of the upcoming winter system. CIGs are expected to deteriorate shortly after 06Z to the MVFR/IFR range areawide as precipitation moves into the area. Precipitation is not expected to be very heavy but should be enough to create some MVFR visibility reductions. This should stay in the form of rain for the terminals through the overnight hours, though a low chance (less than 20%) exists for a brief rain/snow mix around daybreak. Rain begins to move out late Thursday morning with a few hours of dry conditions before chances for light snow move into the area for the afternoon and evening time frame. Confidence is still a bit too low to create prevailing groups for the snow at this point so have continued with the PROB30s for now but this may need to be adjusted in future updates.

Southerly winds will remain gusty overnight, quickly shifting to the west/northwest as the aforementioned cold front pushes through the region. Sustained winds by late tomorrow afternoon will be between 20-30 kts with gusts to around 40 kts possible, especially west of the Mississippi River. Wind speeds look to stay elevated through the end of the period, only starting to come down after 06Z Friday.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...Wind Advisory from noon to 9 PM CST Thursday for MNZ086-087- 094-095. IA...Wind Advisory from noon to 9 PM CST Thursday for IAZ008-009- 018-019.