textproduct: La Crosse

KEY MESSAGES

- Fog forms again this evening/tonight and could become dense for portions of the area. Visibility could be reduce to less than a mile at times.

- Sunday-Sunday night winter storms inching closer to the local region, bringing a higher threat for associated impacts: a few inches of snow, winds gusting 40+ mph (60-70% chances), and dropping temps that could freeze wet surfaces, lead to below zero wind chills. Winter Weather headlines for portions of the area are likely.

DISCUSSION

Issued at 135 PM CST Fri Dec 26 2025

> TONIGHT-SAT MORNING: Fog potential

With light winds...abundant low level moisture and strong inversion over the much of the area today...fog will form again this evening and tonight. Latest hi-resolution guidance suggest visibility will be less than a mile...potentially to a quarter mile or less...at times. Feel we will need another dense fog advisory for portions of the area. However the caveat is how much dry air near the surface would cause for a brief time period for dense fog...as southerly winds increase late tonight/Saturday morning and could erode fog quicker.

> WINTER STORM SUN/SUN NIGHT: trending stronger and tracking closer to the local area. Related likely impacts also increase: some accumulating snows, strong winds, falling temps. Winter Weather Headlines are likely for portions of the area.

The GEFS and EPS continue to drop a PAC NW shortwave trough southeast across the central plains Sun, driving it across the OH River Valley to the eastern great lakes by Mon morning.

Definite strengthening trend in the ensemble systems over the past 24-36 hours, showing a slowing, shift west/northwest of the associated sfc low track, with an uptick in strength. Further, both the GEFS and EPS have a majority of their members suggesting an even slower system, tad stronger is more likely than what the means depict. Considering how the long range guidance has been moving, this trend bears holds some weight.

What this shift in storm track/system strength means locally is the deformation region west/northwest of the low lays out over portions of the forecast area, more QPF/snow suggested, and lingers longer (enhancing potential accumulations). Associated winds are stronger, with a local peak more Sun night through Mon.

- PRECIPITATION: areas of drizzle/light rain likely ongoing from Sat night across much of the area. A stronger focus develops along the system's cold front-northeast of the sfc low during the day Sunday, likely stretching from southern IA into southern WI. This will be rain and could brush parts of northeast IA/southwest WI.

Just northwest of there the deformation region of the system should start to blossom with precipitation in the afternoon, lifting northeast Sun night but continuing to drop light pcpn into Monday morning across northern parts of WI. Initially rain, this will transition to a rain-snow mix then just snow from northwest to the southeast as cold air funnels in from Canada. There is a small window (few hours) where freezing drizzle/rain could be realized Sun afternoon as temps cool below freezing but cloud depth isn't deep enough to support ice. GEFS sits at 10% for these chances, mostly over parts of SE MN/NE IA. Low end chances, but think worth keeping a close eye on.

For snow, time and residence suggest highest totals north of I-90, I- 94. Latest outlay drops 2 to 4" north of 1-94 with 1 to 3" south of there. Expect some adjustments to these amounts with the storm track having a large bearing on how much falls where, along with how quickly pcpn can transition to just snow.

- WINDS: tightening pressure gradient Sunday, not slackening until later Mon evening. Low level jet noses in Sun night, and while the mixed layer is only slated to be around 2.5 kft, there is 40+ kts of wind at the top of that layer - and unidirectional winds through the layer will work to bring a lot of that down to the surface.

The EPS has 60-70% chances for 40 mph gusts Sunday night across most of SE MN/NE IA with 10 to 20% chances to push past 45 mph.

With initial rain, rain snow mix...fairly wet snow will be hard to move. But snow ratios will increase overnight Sunday, and a lighter, more easy to move snow is more likely. Blowing, drifting snow could become a concern where an inch plus falls.

- TEMPS: slug of cold Canadian air to flow in post the storm system with latest deterministic runs of the GFS and EC dropping 850 mb temps from around +7 C at 12z Sun to -4 C by 00z Sun evening. High temps still trending to occur at 12:01 AM for many. With strong winds on tap for the night time hours, wind chills are expected to drop into the single digits/teens below zero.

A raw end to the holiday weekend.

In addition, with a wintry mix changing over to snow, relatively warm roads will quickly chill...and what may have been wet will become icy/snow cover and slick. Another potential travel hazard.

> NEXT WEEK: colder start to the week with a smattering of snow chances.

Change in the favored weather pattern with the EPS and GEFS leaning into more troughing as we push through the first half of the new week. Ample cold, Canadian flows southward in this scenario. 75% of the GEFS and EPS members suggest highs wouldn't warm out of the teens for most Wed-Fri.

A few bits of shortwave energy could/would drop across a northwest hanging ridge, into the trough, bringing the region some snow chances here and there. General consensus in a bulk of the GEFS and EPS members to spin a feature across northern portions of the region Tue, with another taking a bit more southern track on Wed. Both could bring light snow.

Heading into the weekend the WPC clusters all point to the west coast ridge building across the central plains, gradually leaning over the local area. Not as stout of a ridge as it is currently, with differences between the clusters on ridge axis/strength. Not a lot of confidence in how this plays out, but if current clusters play, some moderation in temps for next weekend would result.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 525 PM CST Fri Dec 26 2025

IFR to LIFR conditions currently present across the region. Both visibilities and CIGs are expected to continue to degrade through the evening with all sites across the area likely dropping to LIFR for both elements. Dense fog has already developed across portions of SE Minnesota and NE Iowa and this is expected to expand eastward over the coming hours. Improvement in conditions is not anticipated until after 15Z with gradually improving visibilities by late morning/early afternoon. CIGs are expected to lift to MVFR and potentially VFR along and east of the river by tomorrow afternoon (including the KLSE terminal) but KRST will remain in the IFR/LIFR range through the remainder of the period. Conditions should again deteriorate to areawide IFR/LIFR tomorrow evening.

Generally light and variable winds this evening will become more south/southeasterly through the overnight hours. Speeds will start to increase closer to daybreak into the 10-15kt range. KRST could see some higher gusts by late morning to between 20-25 kts before coming down around sunset.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...Dense Fog Advisory until noon CST Saturday for MNZ086-087-094- 095. IA...Dense Fog Advisory until noon CST Saturday for IAZ008-009-018- 019.