textproduct: La Crosse

KEY MESSAGES

- Winter storm impacts the local area this afternoon through tonight with the threat for several inches of snow becoming more likely along and south of I-90. A Winter Storm Warning is in effect for portions of northeast IA where 5 to 7" of snow is likely. A Winter Weather Advisory is in effect for counties along and south of I-90 for snow accumulations of 2 to 6".

- Below normal temperatures persist throughout the next week with Tuesday being the "warmest" day with highs rising into the 30s.

- Additional snow chances continue into next work week. Rain will likely mix in with snow late Tuesday for areas south of I-94.

DISCUSSION

Issued at 335 AM CST Sat Dec 6 2025

Today - Tonight: Winter Storm Moves in this Afternoon, Highest Amounts in Northeast Iowa

Our winter storm that remains the main focus of this forecast cycle remains a challenging forecast as spatial disagreements between the global ensembles and Hi-res guidance persists with their 06z runs early this morning. Overall the conceptual model for this event is fairly well understood, quasi-zonal to northwesterly flow will pivot a 500mb shortwave, that is currently located over central MT, through the Great Plains throughout the morning and afternoon and eventually into the Upper Midwest. As this occurs, a surface low pressure center will deepen and progress eastward through Iowa during the evening hours. The million dollar question even just 12- 18 hours away from the snow moving into the region is where exactly this deepening surface low tracks and positions itself. Currently, the GEFS/EC group of solutions keep the surface low near the MO/NE/KS triple point with much of the heaviest snowfall just south of the local area. This is contrasted by much of the CAMs which, as shown in the 06.03z RAP, has the surface low positions in southeastern IA, roughly 50-100 miles further north. Additionally in this scenario, the hi-res guidance has a much more dynamic system with fairly strong 700-900mb frontogenesis across northeast IA where saturation in the dendritic growth zone primarily takes place. Consequently, the 06.00z HREF has a fairly decent footprint for 1"/hr snowfall rate probabilities in northeast IA over the course of the evening. Timing with this system is higher confidence with snow generally entering the local area from west to east during the late afternoon and exiting during the pre-dawn hours on Sunday.

Snowfall amounts will be dictated heavily by which scenario ultimately plays out in this GFS/EC vs hi-res CAMs showdown. In the first scenario, this would keep the heaviest totals south of the region with amounts likely in the 1-4" range near and south of I-90 and lower likelihood for 1"/hr rates with the strongest forcing further south of the area. In the hi-res CAMs solution, this would favor likely amounts of 6"+ across most of northeast IA and southwest WI where this strong frontogenetic footprint would be present. In either case, snow to liquid ratios will be on the slightly drier side, perhaps around 15:1 with somewhat limited DGZ residence shown in the RAP/HRRR in northeast IA. However, this is with the caveat that strong frontogenesis in the DGZ in the hi-res scenario could allow for increased ratios.

In any case, have opted to take a somewhat middle of the road approach in this forecast cycle. Have upgraded portions of northeast Iowa to a Winter Storm Warning for amounts of 5-7", where the 06.00z HREF has the highest probabilities for snowfall amounts of 6 inches or greater. Additionally confidence is higher that this is where amounts of at least 3-6" would be likely in either scenario. Elsewhere in northeast IA and southwest WI, have kept with a Winter Weather Advisory for amounts of 3-6" at this juncture. However, it needs to be understood that if the more aggressive hi-res solutions end up gaining higher confidence, this will likely warrant an upgrade to a Winter Storm Warning for other portions of northeast IA and southwest WI. The exact northern extent of this system also remains a key question due to the uncertainties on the position of the surface low. Currently, have opted to carry a Winter Weather Advisory up to along Interstate 90 with high probabilities for amounts in excess of 2" (70-100%) in the 06.00z HREF. Regardless, what is important to note as well is much of the snow will fall within a fairly short timeframe as the bulk of the accumulating snow will fall between 6pm to 3am across the local area. As a result, if you have any plans to travel during this timeframe, be extra cautious as snowfall rates will reduce visibility significantly and roadways will quickly become snow-covered and slippery.

Sunday: Colder with Clearing Skies

As we head into Sunday, subsidence on the backside of the upper- level trough that guided the aforementioned winter storm will aid in the development of surface high pressure into the region. This along with increased cold air advection will help clear our skies some and allow our temperatures to drop fairly respectably with median high temperatures in the NBM likely staying in the upper single digits to teens for much of the region. Overnight lows will likely fall into the single digits below zero across much of the region with minimum wind chills of around -5F to -15F. Certainly, a reminder that we have entered meteorological winter!

Next Week: Below Normal Temperatures with Additional Winter Systems Passing Through the Region

As we head into next week, the synoptic flow pattern really does not change at all with northwesterly to quasi-zonal upper-level flow in place with periodic shortwave perturbations sneaking into the region. Which will essentially result in a forecast consisting of below normal temperatures will periodic bouts of precipitation, in most instances snow. The only exception to this will be Tuesday night where additional precipitation types may be in play.

Monday evening and into the overnight features the first of these shortwaves which pushes north of the region bringing likely some light snow near and north of I-90. Overall amounts with this first wave appear on the minimal side with the grand ensemble (GEFS/EC/Canadian ensemble) only having medium probabilities (30-60%) for an inch or greater of accumulations north of I-94 with this. As we head into Tuesday, southerly surface flow ahead of an incoming secondary clipper system will allow us to "warm up" with the inter- quartile range in the NBM for highs on Tuesday ranging from the lower to upper 30s south of I-94, much of these warmer temperatures persisting into the evening and overnight ahead of the cold frontal passage associated with the surface low passage. As a result, seeing some indication that rain may be the predominate precipitation type at times south of I-94 as a fairly robust warm nose is present in the recent GFS soundings. If wetbulbing near the surface can be efficient, cannot rule out some freezing rain potential however the grand ensemble (GEFS/EC/Canadian ensemble) is not overly enthusiastic about this scenario with low probabilities (0-20%) for measurable ice accumulations. Regardless, this wave Tuesday evening and into early Wednesday appears to be the most messy but likely has the most dynamics going for it early in the week.

By the second half of the work week, the pattern remains steady state with additional shortwave perturbations across the global members that try to sneak their way in. With cold advection reestablishing well below normal temperatures for the local area, any of these shortwave perturbations would likely feature snow as the favored precipitation type. However, details regarding the strength or exact track of these clipper systems remains low at this time.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 527 AM CST Sat Dec 6 2025

MVFR stratus today and this afternoon followed by several hours of IFR due to snow are the primary concerns in the TAF period. Confidence is high enough to include several hours with IFR visibility at both RST/LSE but, with some uncertainty around start time, have preceded definite mentions with PROB30 groups. Snow should depart overnight with conditions eventually becoming VFR around 12z Sunday.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Winter Weather Advisory from 6 PM this evening to 6 AM CST Sunday for WIZ041>043-053>055-061. MN...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST Sunday for MNZ086-087-094-095. Winter Weather Advisory from 6 PM this evening to 6 AM CST Sunday for MNZ088-096. IA...Winter Storm Warning from 3 PM this afternoon to 6 AM CST Sunday for IAZ008-018-019-029. Winter Weather Advisory from 3 PM this afternoon to 6 AM CST Sunday for IAZ009-010. Winter Weather Advisory from 6 PM this evening to 6 AM CST Sunday for IAZ011-030.