textproduct: La Crosse

KEY MESSAGES

- Showers and storm potential later this afternoon through the overnight with the highest chance for storms (40 to 70%) in western Wisconsin.

- Seasonal temperatures in the 70s to lower 80s are forecast each afternoon into early next week.

DISCUSSION

Issued at 1200 AM CDT Thu Aug 20 2026

Today - Friday: Dry This Morning, Showers and Storms During the Afternoon and through the Overnight

A cooler and drier air mass remains in place into the early afternoon. Temperatures this morning will fall into the mid 40s (along and north of I-94) to mid 50s. With light and variable winds combining with clear skies, river valley fog is expected across many river valleys this morning. This fog should lift by the mid-morning. Heading into the afternoon shortwave trough and associated surface low begins to move across northern Minnesota and far southwestern Ontario. Ahead of this low, moisture advection increases helping to kickoff a line of showers that may make it into our northwestern CWA by the mid-afternoon, however with these showers fighting drier sub- cloud layer air, it will be difficult for these showers to make it any further. During the evening, a little instability builds into (generally less than 1000 J/kg of MLCAPE) the CWA, still ahead of a cold front that will eventually make its way through the forecast area on Friday. CAMs have supported a second line of clusters of storms forming behind the initial line of showers. With the limited instability and weaker shear expected, there is a low chance for organized severe weather to happen. These storms look to outrun the instability gradient as the early morning progresses. One thing that has been a little development with some of the more recent CAMs is highlighting another area of storm development along the theta-e gradient as it moves through the region. This particular area would have greater instability so some stronger storms may be possible for portions of northeast Iowa and far southwest Wisconsin during the early afternoon. While the better severe potential remains off to our west for this evening and to our southwest (better shear across Central Plains) for Friday, some gusty winds and small hail may be possible with some of the storms that impact our CWA.

This Weekend into Early Next Week: Seasonal and Mostly Dry Conditions

Forecast guidance remains consistent in building a ridge off to our west and having it gradually weaken over our area during the weekend. This would lead to mostly dry conditions as the wave paths would be to our north through Sunday. A weak wave moves from the northern Plains into the central Plains on Monday which could give a small chance of showers and storms but the better potential looks to be on Tuesday. Ensemble and deterministic guidance continues to favor a low coming down into the Upper Midwest and an associated cold front potentially providing a line of storms to pass through the area. We will continue to monitor as there are quite a number of details to work out before next Tuesday, such as how does the previous day's precipitation impact Tuesday's chances. One thing that is of higher confidence is the temperatures as our area would remain under the influence of a trough that will keep temperatures seasonable. Highs are looking like they will be in the low 70s to low 80s from Saturday through Monday.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1241 AM CDT Thu Aug 20 2026

The potential for valley fog will be the primary aviation concern overnight with light winds, clear skies and favorable dewpoint depression trends at KLSE. As a result, have opted to include some fog mention at KLSE to address this potential, with confidence remaining low on if 1/4sm will occur. Given questions on if we can get a southeast wind overnight, have opted to not include prevailing 1/4SM for now but will amened as needed. Otherwise, winds will increase for the afternoon to around 8-12 kts from the south to southwest. A disturbance approaches the region during the late evening hours with the CAMs showing some potential for storms to move through the local area. Consequently, have opted to include a prob30 for storms at both TAF sites to address this potential.

ARX WATCHES/WARNINGS/ADVISORIES

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