textproduct: La Crosse

KEY MESSAGES

- Areas of fog will persist this evening and into the overnight with locations west of the Mississippi River likely (60-90% chance) seeing visibilities of 1/4 mile or less at times overnight.

- Above normal temperatures persist for the middle of this week with highs ranging from the middle 30s to upper 40s.

- First of two systems moves into the region Thursday and into early Friday with rain transitioning to snow, however minimal snowfall accumulations are currently expected.

- A secondary winter system moves into the region late Friday night and into Saturday with accumulating snowfall likely. There are medium probabilities (30-60% chance) for snow accumulations of 3 inches or greater on Saturday.

DISCUSSION

Issued at 147 PM CST Tue Jan 6 2026

Rest of Today - Wednesday: Fog This Afternoon into Tonight, Continued Above Normal Temperatures

GOES-19 water vapor imagery shows two week shortwaves moving east of the local area this afternoon which were responsible for the freezing rain across portions of north-central WI this morning and early afternoon. In the wake of these waves, weak subsidence, light winds and saturated/snow-covered ground will enable fog formation throughout the remainder of the day with the 06.12z HREF having fairly high probabilities for 1/4-mile visibilities west of the Mississippi River. As a result, may need to have a Dense Fog Advisory into the evening and overnight if observational trends continue to support areas of dense fog in this region into the overnight.

Wednesday will feature quasi-zonal with broad upper-level ridging being the main synoptic mechanism dictating our conditions. As a result, this in combination with ongoing low-level warm advection will allow temperatures to rise well above normal for the middle portion of this week. Currently, the NBM has median high temperatures ranging from the upper 30s to middle 40s for much of the area on Wednesday with the inter-quartile spread ranging from the middle 30s to upper 40s. Needless to say, Wednesday will likely trend 15 to 20 degrees above normal for most places with the 06.00z Extreme Forecast Index having high probabilities (60-90% chance) for exceeding ECMWF M-Climate reanalysis.

Thursday - Saturday: Active Pattern, Snow Potential for Saturday

Things begin to turn more active by the time Thursday rolls around as a weak shortwave pivots towards the region on the western periphery of the aforementioned ridge which will be centered over the eastern CONUS by Thursday. As this wave pushes into the local area, a fairly decent surface low pressure center is progged to develop with this system into the afternoon and evening on Thursday. However, given the fairly warm antecedent airmass and minimal upstream support with any uppper-level wave or low with this shortwave, rain currently appears to be the favored precipitation at onset on Thursday. Additionally, this is supported with 850mb temperatures generally remaining near to slightly above freezing throughout the day Thursday and into Friday. That being said, a weak cold frontal passage is progged by deterministic guidance to push through the area overnight Thursday which may be just enough to switch us over to snow for a period (albeit likely a very wet snow given a 0C isothermal layer from 950 to 850mb in the 06.12z GFS) before a lull in precipitation likely ensues during the daytime hours on Friday. Either way, probabilities for measurable snowfall Thursday and into day on Friday look to be on the lower-end (10-30% chance) in the grand ensemble (GEFS/EC/Canadian ensemble) across the local area. So currently not seeing any signal for an overly impactful system with this first wave on Thursday and into Friday.

It is important to understand that this is just the first wave that moves through the area late this week as a secondary system will be worth watching late Friday and into Saturday that follows a similar trajectory to the previous system as it ejects from the southern Rockies and towards the Midwest late Friday. As it approaches the region, much of the deterministic and ensemble guidance has it phasing with a larger, southern Canadian trough that pushes into the Northern Plains. Overall cluster analysis of the grand ensemble (GEFS/EC/Canadian ensemble) paints two general scenarios, one where this system does phase with this up-stream trough (roughly 77% of members in the grand ensemble) and one where these do not phase (roughly 23% of members in the grand ensemble). Still a lot of questions synoptically with this system as with the phasing upper- level waves scenario comes a rapidly intensifying 300mb jet streak in the exit region of the amplified trough across the Midwest and Great Lakes shown in deterministic guidance. Exactly, how quickly this strengthening takes place will be key for how rapidly surface cyclogenesis takes place and thus impacting how the deformation zone in the local area manifests. Regardless, with the injection of cold air from the Canadian wave, thermal profiles respond accordingly in the 06.12z GFS soundings which favor an all snow scenario for Saturday.

In the scenario where these waves do phase, there is fairly respectable probabilities (30-60% chance) in this ensemble group for amounts of 3 inches or greater as opposed to the non-phasing scenario with very low probabilities (0-20% chance) for similar amounts. Looking explicitly at the EC ensemble, the vast majority of members (roughly 90%) have measurable snow into Saturday. However, given that the 06.00z Extreme Forecast Index has a 0 shift of tails for Saturday across the local area, this is suggesting some higher-end members of which the EC ensemble has a few members that show amounts in the 8-12"+ range. This higher end scenario would likely be contingent on a faster evolving surface low. Regardless, this developing surface feature would translate northeastward later into Saturday and thus leaving us precipitation free by the daytime hours on Sunday.

The bottom line with this period is it looks like two systems will impact the region, the first being a rain to snow transition favoring minimal accumulations on Thursday and early Friday. The second having some larger spread in potential snowfall amounts at this point but has more favorable dynamics and would suggest an all snow solution for Saturday. Definitely will be a period to pay attention to in the coming days as forecast details will continue to be refined.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1148 AM CST Tue Jan 6 2026

The recent rainfall and impending fog bank just west of the local forecast area from northern Iowa into southern Minnesota threatens LIFR-IFR impacts through most of the 06.18Z TAF period. While limited lifting is possible this evening, extent appears minimal, potentially mostly limited to River Valleys. Therefore, have continued impacts until erosion of low level moisture Wednesday morning. Will require further assessment in coming TAF issuances.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Winter Weather Advisory until 3 PM CST this afternoon for WIZ017. MN...Dense Fog Advisory until 3 PM CST this afternoon for MNZ086- 094. IA...Dense Fog Advisory until 3 PM CST this afternoon for IAZ008>010-018-019-029.