textproduct: La Crosse

KEY MESSAGES

- This afternoon into Wednesday morning brings multiple winter weather hazards to the region. Heavy snow is expected north of I-94 this evening with up to 6 inches falling in 4-6 hours. South/west of I-94, a period of light freezing rain and cold rain is expected this evening followed by a short break until, between midnight and 6 AM Wednesday, strong winds and a brief burst of intense snow showers is expected. Along I-94, largely snow will occur but a glaze of ice may also occur as well.

- Very cold temperatures for the end of the week. Highs will struggle to climb out of the single digits Friday and Saturday. Morning wind chills of -25 or lower possible.

DISCUSSION

Issued at 357 AM CST Tue Dec 9 2025

Winter storm this afternoon into Wednesday morning

08z WV satellite shows a shortwave over western British Columbia with a broad upper jet on the equatorward side of this feature extending over WA/OR east to ND/SD. Surface lee cyclogenesis has begun in southern Alberta as a result. Across our CWA, patchy FZDZ has occurred overnight ahead of an exiting shortwave. Wind field across the northern Plains and Upper Midwest has begun responding to the deepening surface low in southern Alberta, becoming southwesterly, advecting in warmer air, as evidenced by slowly rising temperatures overnight.

This afternoon into tonight, surface cyclone deepens as it races southeast toward our CWA which looks to become under the left exit region of the upper jet. Low level wind fields ramp up in response, with warm advection continuing. As the upper wave approaches, widespread precip will develop.

North of I-94, confidence is high that precip will fall as all snow around 5 to 10 PM this evening with snow rates above 1" per hour expected given strong forcing from the upper wave and an axis of 700/850mb frontogenesis developing on the northern periphery of the warm advection. While totals may not quite reach 6" (only about a 30% chance per 09.00z LREF/HREF/NBM), expected impacts from the high snow rate are sufficient to continue the Winter Storm Warning.

For areas south/west of I-94, progged soundings suggest warm advection will have been sufficient enough for a warm nose to develop, leading to a period of freezing rain. While this freezing rain should end after a couple of hours as surface temperatures continue to climb, cold pavement temps and widespread snow cover may lead to additional droplets continuing to freeze even as 2m temperatures reach above freezing. Thus, a light glaze of ice to a few hundreths in accumulation is expected. Have therefore expanded the ongoing Winter Weather Advisory to cover the remainder of the CWA.

For areas right along I-94, uncertainty in the exact source of impacts - snow and/or freezing rain - remains stubbornly high. Global models, as evidenced by the 09.00z LREF, are a bit farther south with their axis of high probability to reach 3" of snow compared to high resolution ensembles, as evidenced by the 09.00z HREF and particularly the 09.00z REFS. For example, 09.00z LREF shades potential for 3" of snow close to La Crosse while the HREF keeps 60% probabilities close to I-94. Overall run to run trend in LREF has been toward the north, however, so continue to think cutoff of appreciable snow impacts will reside around or just south/west of I-94. As for ice, areas along I-94 are favored to only receive a light glaze as warm advection looks to end before an appreciable warm nose develops.

Moving ahead to the overnight hours, 09.00z NAM/RAP soundings suggest the presence of strong near surface lapse rates with saturation at the top of this conditionally unstable boundary layer immediately following the passage of the surface cold front. Therefore, there will be potential for a short burst of intense snow showers following the passage of the cold front. Progged low level lapse rates are steepest in areas west of the Mississippi, so will need to watch this area closest.

Finally, surface winds will be on the increase overnight outside of the aforementioned snow showers as a 55 knot 850mb jet overspreads NE IA, far SW WI, and parts of SE MN in the presence of strong CAA aloft. 09.00z HREF wind probabilities suggest a 50 percent chance for winds to top 30 mph with a 70% chance for 45+ mph gusts. While the gust probabilities may be inflated due to the presence of the ARW in this ensemble, this suggests close consideration will be needed for a Wind Advisory overnight into Wednesday morning. Surface snow conditions will also need to be monitored - while the period of freezing rain and rain described in NE IA and SE MN described above should lead to a crust developing on the surface of the snow pack, if the top of the snow pack remains susceptible to blowing, very low visibilities could result and a pivot toward blizzard headlines would need to be considered.

Very cold Saturday and Sunday

After another upper trough swing southeastward over the Great Lakes, an even colder air mass invades the region. Lows Saturday and Sunday mornings are favored to be below zero with wind chills of -25 or lower possible. Will focus on the details of this upcoming cold snap in the coming days.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 534 AM CST Tue Dec 9 2025

Poor aviation conditions through much of the next 24 hours. IFR ceilings and patchy FZDZ are ongoing at the start of the period. While FZDZ tapers off, IFR ceilings remain, with prospect for a short break around midday. Next weather system dives out of the northwest, leading to IFR ceilings returning and potential for FZRA/SN/RA. At LSE/RST, a short period of FZRA is expected before RA takes over. After a short break in precip, strong cold front dives southward after 03z, leading to gusts to 30-35 knots and potential for a short, intense burst of snow showers. Due to low confidence in occurrence and timing, have covered this last part with PROB30 mentions.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST Wednesday for WIZ032>034-041>044-053>055-061. Winter Storm Warning from 3 PM this afternoon to 6 AM CST Wednesday for WIZ017-029. MN...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST Wednesday for MNZ079-086>088-094>096. IA...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST Wednesday for IAZ008>011-018-019-029-030.