textproduct: La Crosse

KEY MESSAGES

- The severe weather threat looks lower for tonight. As a result, the Storm Prediction Center has shifted the Slight Risk further south. The northern extent of the Slight Risk now only extends north to Interstate 90 where before it extended as far north as northeast Minnesota.

- Patchy to areas of frost possible in north-central and central Wisconsin on Tuesday night and Wednesday night.

DISCUSSION

Issued at 120 PM CDT Mon May 18 2026

This Afternoon and Tonight

The squall line that moved through our area last night has moved south into the Interstate 70 corridor. South of this line, the temperatures are in the lower 80s and dew points ranging from the mid-60s to lower 70s. With rain cooled air north of this boundary, this air mass will remain south of our forecast area for tonight. As a result, we have seen a reduction in the instability available for the storms along the cold front tonight. Surface-based CAPES which looked to be in the 1500 to 2500 J/kg range yesterday are now only up to 750 J/kg. In addition, the stronger 0-3 km and 0-6 km shear remains post frontal. The CAMs are progressively moving the squall line further and further south. Much of the consensus in the CAMs has this squall line moving east across southern Iowa and northern Missouri. Further north, there are more scattered thunderstorms. This has reduced the severe weather threat because there would be less coalescing of the cold pools.

Due to this, we reached out to the Storm Prediction Center and was able to get a more southern shift in the Day 1 Slight Risk. It is now south of Interstate 90. There is now a Marginal Risk from Interstate 90 north into Upper Michigan. If there is severe weather, it would occur between 19.03z and 19.07z. The primary threat would be damaging winds.

Tuesday

A northern stream shortwave trough will move northeast across western and northern Minnesota and northern Wisconsin. This will result in some scattered morning showers. The strong cold air advection in the wake of the cold front will continue into the day. High temperatures for the day will occur around midnight in the mid- and upper 60s. Temperatures during the day will be in the 50s and 60s.

Tuesday Night and Wednesday night

The combination of mostly clear to partly cloudy skies and light winds will allow temperatures to fall into the 30s and 40s. There could be the potential for even colder temperatures in central and north-central Wisconsin. This could result in some patchy to areas of frost in our traditional cooler areas of central and north- central Wisconsin.

Friday into the Weekend

A northern stream shortwave will move slowly east through the region. As this occurs, there will be periodic showers and storms. Like yesterday, both the 0-3 and 0-6 km shear remain less than 30 knots. As a result, the probabilities for organized severe weather look low.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 703 PM CDT Mon May 18 2026

VFR conditions continue for most locations through the evening, with the exception of southeast Minnesota and north central Wisconsin where MVFR CIGS will continue through much of the day tomorrow. MVFR to IFR CIGS push in behind the rain during the overnight before lifting to MVFR by late morning. Showers and thunderstorms move into northeast Iowa and southeast Minnesota this evening and then into western Wisconsin between 03 and 05Z. Light rain may continue through the overnight before clearing out by sunrise. Southwest to southeast winds continue through the overnight until the cold front passage between 08 and 14Z across the region which will turn the winds to the northwest.

ARX WATCHES/WARNINGS/ADVISORIES

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