textproduct: La Crosse

KEY MESSAGES

- Precipitation chances increase overnight through Monday. Breaks in precipitation and storms expected through Monday with locally highest probabilities for strong to severe storms Monday afternoon-evening from northeast Iowa into southwest Wisconsin. All hazards (e.g., hail, damaging wind, isolated tornado) remain possible.

- Quick progression to heavy rainfall keeps confidence for river flooding low (<35%), highest on flashier rivers in northeast Iowa and southwest Wisconsin.

- Colder, slightly below normal temperatures expected through next week.

DISCUSSION

Issued at 300 PM CDT Sun Apr 26 2026

Incoming Precipitation Tonight & Afternoon Observations:

A semi-wrapped upper level perturbation progressing northeast on upper level water vapor imagery loops advects storm and precipitation chances from the Central Plains through the Upper Midwest tonight through Monday. While confidence for precipitation and storms is high during the overall period, local forecast area lies on the northern proximity of widespread, more intense storm probabilities.

Precipitation & Storm Timing Through Monday Night:

Initial precipitation chances progress from southwest to northeast tonight, slightly later than previous forecasts due to a slightly slower synoptic progression of the phasing trough. As high resolution reflectivity solutions spread northeast towards the forecast area tonight, a split in higher precipitation chances and heavier rainfall is suggested, due to splitting of stronger forcing mechanisms. The nose of the low level jet will be responsible for the higher reflectivity west of the forecast area through Minnesota due to location of wrapping and strengthening of the low center from stronger ageostrophic ascent while stronger isentropic upglide closer to the higher moisture keeps higher precipitation chances grazing the southern parts of the forecast area.

Eventually the higher moisture will overspread the local forecast area, increasing local precipitation and storm chances through Monday morning. Current confidence in storms through the morning hours is low as shallowing mid level lapse rates increase stability. A short reprieve in higher precipitation chances through the late morning and early afternoon ceases through the late afternoon hours as the upstream low center phases towards the local forecast area. This window is the most concerning for severe storms locally, primarily from northeast Iowa into southwest Wisconsin. Precipitation and storm chances continue into the nighttime hours as the low center traverses the forecast area.

While storms cannot be ruled out Monday morning or night, confidence is lower due to an overall lack of instability and disorganized hodographs, respectively. Although, while morning instability is limited, clockwise turning hodographs would suggest all severe hazards at play should storms form while nighttime storms have the opposite inhibition. While unstable air Monday night raises storms concerns, limited probability for organization as the tight cyclonic rotation causes chaotic wind profiles. Therefore, sub severe (strong wind, small hail) strong storms farther north remain the higher confidence situation Monday night.

Severe Storm Potential Monday Afternoon-Evening:

Strong shear and high instability collocate in a short window from the late afternoon to early evening over southern peripheral counties in northeast Iowa and southwest Wisconsin where the SPC Enhanced Risk lies locally. All hazards will remain at play as a weak meso frontal boundary lain through the forecast area due to differential diurnal heating from morning storms raises tornado potential given the additional near-surface curvature. Regardless, large hail and damaging winds will remain the more widespread local hazard.

Heavy Rain & River Flooding Potential:

While accompanying anomalous moisture (SPC RAOB Climatology / NAEFS & ENS M-Climate) increases local heavy rain threat and flooding concerns, quick progression, temporal separation in heavier rainfall, and large spatial separation in strongest storms keep local confidence for flooding low. Current concerns remain mostly in flashier rivers from northeast Iowa (i.e.,Turkey) and southwest Wisconsin (i.e., Kickapoo). However, current HEFS (26.00Z) probabilities (10-25%) for Minor flooding are based on slightly lower QPF forecasts than HREF confidence for 1" in these areas. Therefore, actual probabilities are slightly higher and should multiple rounds of heavy rainfall frequent these flashier river basins, causing higher QPF to be realized, confidence and forecasts will require adjustment.

Slightly Below Seasonable Temperatures Through The Week:

A Canadian Polar airmass attempts to poke south through the Upper Mississippi River Valley through the middle of the week, increasing frost/freeze probabilities initially Tuesday night locally. While initial timing of colder remains dependent on timing of trough ejection, synoptic agreement for colder air settling into region through the middle of the week increases some confidence for near freezing overnight temperatures by the end of the week in classically cold spots in central Wisconsin.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 622 PM CDT Sun Apr 26 2026

Plenty of uncertainty in the aviation forecast surrounding when exactly SHRA and TS will occur after 06z Monday. For each site, have elected to go with definite showers for a period Monday morning followed by a less-definite VCSH mention before a final round of TS occurs during the afternoon. That said, these timings are subject to change and a risk for TS will be present anytime showers are around, albeit at a probability level (20%) too low for a mention.

Confidence is higher that steadily increasing moisture will lead to MVFR and later IFR ceilings developing after 06z Monday. Winds will also be on the increase with gusts out of the southeast to 20-30 knots Monday becoming out of the northwest as a cold front sweeps through the area around the end of the period. Eventual improvement to VFR will occur after the end of the current period, potentially around 12z Tuesday.

ARX WATCHES/WARNINGS/ADVISORIES

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