textproduct: La Crosse

KEY MESSAGES

- Periodic precipitation is expected through this evening. Potential focuses on a round overnight, another round during the morning hours, and a third round during the afternoon and evening. If everything comes together, the third round may feature severe thunderstorms with mainly a damaging wind risk and a low tornado risk. While we cannot yet dismiss this possibility, the probability of everything coming together has trended downward.

- Quick progression to heavy rainfall keeps confidence for river flooding low (<20%), highest on flashier rivers in northeast Iowa and southwest Wisconsin.

- Colder, slightly below normal temperatures expected through next week. A frost or freeze may occur Friday and Saturday mornings.

UPDATE

Issued at 1124 AM CDT Mon Apr 27 2026

As the line of showers depart late this morning and early this afternoon, winds gusting to 45 to 55 mph have been observed in their wake in northeast Iowa and southwest Wisconsin. Caused by strong subsidence on the backside of the line, these winds should last for about 30 minutes at any given location and then lessen. Based on velocity data from KARX, these winds could spread as far north as I-90.

DISCUSSION

Issued at 1233 AM CDT Mon Apr 27 2026

Severe storm potential this afternoon

Overnight into this morning, initial rounds of precip look to work their way northeastward to our forecast area ahead of a pair of lead disturbances ejecting northeast of an upper trough over E CO as of 05z. After the morning round, much stronger forcing for ascent arrives via the main body of the upper trough, leading to widespread showers and, given cooling temperatures aloft above increasingly moist low levels, some thunderstorms. This setup may yet provide potential for severe storms - 27.00z HREF joint probabilities indicate a 40-90% chance for sufficient instability, shear, and a lack of inhibition for severe storms to develop. That said, trend across guidance suggests most favorable conditions will be displaced well to our south with the influence of morning showers and mostly cloudy conditions limiting destabilization. Additionally, progged mid and upper level shear characteristics have trended toward a less favorable outcome for supercells to maintain themselves with short hodographs in the 3-6km layer. If enough surface destabilization occurs, cannot rule out a risk for mainly damaging wind given potential for rapid upscale growth due to the large amount of forcing and, given sfc-3km bulk shear values of 35 kts or greater, a stray QLCS tornado.

As for risks from excessive rain, fast motion of thunderstorms should limit flash flooding risks. Concerns mainly focus on flashier basins for eventual river flooding but HEFS probability for reaching minor in these basins has trended downward, now generally 15% or less, as peak rain amounts appear very likely (90%+ per 27.00z HREF) to remain under 2".

Turning cooler after today

Upper troughing becomes predominant over the eastern third of North America, including the Upper Midwest. Temperatures will run around or a bit cooler than normal as a result. Focus on impact continues to mainly look at Friday and Saturday mornings in the wake of another cold front. NBM continues to point toward the possibility for a frost (70-95%) or freeze (25-70%) on these mornings, particularly in Clark/Taylor Counties, with the 27.01z run.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 549 AM CDT Mon Apr 27 2026

Low-MVFR to IFR conditions are expected throughout much of the TAF period with off and on showers and storms moving through the region. Probabilities remain high (60-80%) in the HREF/NBH for cigs to fall to MVFR levels over the morning with some potential (30-50%) to fall to IFR heights, however have opted to hold off on prevailing IFR mention given minimal upstream obs showing IFR conditions. Highest probability for TSRA remains in the afternoon as much of the CAMs have more robust convection across the area, however confidence is low in how widespread this will be but IFR vsby reductions are likely underneath any storms. Winds shift to northwesterly behind a frontal passage during the evening with winds of 15-20 kts and gusts as high as 30 kts. IFR cigs seem plausible with the HREF having high probabilities (50-70%) for IFR reductions after 03z Tuesday.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...None.