textproduct: La Crosse

KEY MESSAGES

- Dry and warming conditions are expected through mid-week with highs in the 70s for most through Thursday.

- Showers and storms are likely (60-90%) Thursday evening and overnight. Some potential for a strong to severe storm exists, but confidence remains low.

DISCUSSION

Issued at 149 PM CDT Mon Apr 20 2026

Tuesday - Thursday: Dry with a Warming Trend

Rather benign weather continues through the middle of the week as a longwave ridge located over the western United States slowly shifts eastward. Southerly winds under the ridge usher warmer temperatures northward into the area, resulting in temperatures warming into the 70s through Thursday for most of the area. With only a few degrees of spread amongst the 20.13z NBM membership, confidence in these temperatures is high.

Ahead of the ridge, a weak shortwave trough evident on water vapor imagery over the Montana/Wyoming region this afternoon slides southeast on the eastern side of the ridge into the Upper Midwest. Forcing associated with this ripple invigorates an area of low pressure over the northern Great Plains tonight before quickly phasing with a surface low over Canada. This will result in a weak surface front plunging through our area early Tuesday. However, a lack of moisture and strong warm layer aloft associated with subsidence from the ridge should suppress precipitation potential across our area as this front moves through, keeping shower and storm development to our southeast over south-central Wisconsin and northern Illinois come the afternoon hours. Outside of this feature, broad subsidence and high pressure will result in dry conditions through the middle of the week.

Thursday - Friday: Showers and Storms

As the upper longwave ridge continues eastward, longwave troughing off the west coast of the United States this afternoon will fill in behind, moving into the northern Plains late Wednesday into early Thursday. Taking on a slight negative tilt, this wave is depicted to develop a stout mid-latitude cyclone over the north-central United States. The cold front associated with this cyclone shifts through our region late Thursday into Friday, bringing with it showers and storms (60-90%). Ensemble and deterministic guidance continue to depict instability developing ahead of the front, mainly along and west of the Mississippi River, upwards of 1000-1250 J/kg SBCAPE in the deterministic guidance although the 20.00z GEFS/GEPS continue to depict 20-40% probabilities for greater than 1000J/kg. Regardless, this available instability would be sufficient for thunderstorm development, but the biggest question is the strength of any storms. 0-6km wind shear is weak at best (15-20kts in the 20.12z GFS) with much of the shear residing in the 0-3km layer (20-30kts). Given the orientation of the 0-3km shear vector is largely parallel to the surface boundary, a linear storm mode is expected along the front resulting in gusty winds being the primary hazard. Given the weak shear and modest instability, would not expect overly strong updrafts in this environment and as such confidence in strong to severe storms developing remains low. However, AI/ML guidance continues to depict some potential for severe storms over our western areas where a slightly more favorable environment will exist at convective initiation, so this remains a period to monitor.

Cooler temperatures are ushered in behind the front, limiting highs to the mid 50s to low 60s through the weekend and into next week before the potential for showers increases again early next week.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1220 PM CDT Mon Apr 20 2026

The greatest impact to aviation over the next 24 hours is the potential for low level wind shear overnight. Southerly surface winds around 10-15KT with gusts of 15-25KT this afternoon begin to diminish overnight while a strong low level wind field of 35-45KT situates between 1-2kft. This is expected to lead to a period of low level wind shear between 03z-12z, especially from northeast Iowa into central Wisconsin. Confidence in low level wind shear is slightly lower at KRST as surface winds may remain slightly stronger as compared to those areas further east so have opted to not add to the TAF with this issuance, but will be something to remain mindful of as tonight approaches. Outside of the low level wind shear concern, little impact to aviation is expected this afternoon and overnight with VFR conditions expected.

HYDROLOGY

Issued at 149 PM CDT Mon Apr 20 2026

Flooding continues along the Wisconsin and Yellow Rivers this afternoon where flood stage is exceeded at both Necedah, WI and Muscoda, WI. Water levels along the Yellow River have risen slightly in the last 12 hours at Necedah, WI, which is now sitting in moderate flood stage. With no additional precipitation expected over the next few days, this river is expected to begin cresting overnight, falling back to minor flood stage Tuesday afternoon and below flood stage on Wednesday. The Wisconsin River at Muscoda remains in minor flood, but continues to trend lower this afternoon, and is expected to fall below flood stage early Wednesday morning.

ARX WATCHES/WARNINGS/ADVISORIES

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