textproduct: La Crosse

KEY MESSAGES

- Foggy conditions/low stratus this morning followed by dry conditions through this evening.

- Warm temperatures continue today with highs in the mid 80s followed by slightly cooler temperatures for Sunday and Monday with highs in the mid 70s to low 80s.

- Shower and storm chances return Sunday for northeast Iowa and southeast Minnesota (20 to 40%) with the next widespread rain chance (50 to 80%) for Tuesday into Wednesday.

DISCUSSION

Issued at 1225 AM CDT Sat Sep 5 2026

Morning Fog:

Foggy conditions expected this morning as a ridge builds into the Upper Midwest. Light northeast winds coupled with a moist airmass of dewpoints near 70F and a stabilizing atmosphere will all aid in fog development. The fog may be dense at times with the 00Z HREF suggesting a 20 to 40% chance for visibilities to drop below 1/4 mile. Any fog or low stratus that develops will likely dissipate by mid-morning.

Showers/Storms Return Sunday:

Dry conditions will be with us through this evening until a wave moves down from northern Minnesota late tonight into Sunday. Several CAMs show showers and storms sparking off this wave from eastern SD to central Minnesota early Sunday morning. Showers and storms continue down into northern Iowa through Sunday afternoon and evening. Some of these could get into portions of northeast Iowa and southeast Minnesota (20 to 40%). Any strong to severe storm chances should stay off to our west as local area shear remains quite weak. Additionally, as the ridge continues to build northward, low level dry air will be in place resulting in a cap across much of forecast area.

Showers/Storm Potential Persists Monday:

Another wave moves northeastward into northern Minnesota and far northwestern Wisconsin into Monday, potentially resulting in showers and storms for some of our northwestern counties (15 to 25%). Despite the ridge building in, temperatures will only be slightly above normal as surface winds will be out of the southeast.

Additional Shower/Storm Chances Into Midweek:

The upper level pattern shifts to zonal/southwest flow due to an approaching shortwave trough heading into Tuesday. All three of the GFS, ECMWF, and CMC have this trough and associated cold front passing through late Tuesday into Wednesday. There are some differences in the timing of the front with these models and can expect these details to get ironed out as forecast hour nears. Moisture transport increases early Tuesday ahead of the front which gives the region its first dose of precipitation chances as the front eventually moves through late Tuesday into Wednesday where the latest NBM has 50 to 80% PoPs with the frontal passage.

Current uncertainty on coverage of convection is due to potential low level dry air that storms would have to overcome. Therefore, lower PoPs may be realized during this timeframe. A low chance for severe weather is expected with frontal passage due to 35 to 45 kts of effective shear and 500 to 1250 J/kg of MLCAPE. Most AI and ML guidance have a low chance (5 to 15%) for any kind of severe weather to occur. With a shift towards more southwesterly flow in the low levels, temperatures increase back up into the mid to upper 80s for Tuesday before falling back down into the mid 70s to mid 80s for Wednesday.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 605 AM CDT Sat Sep 5 2026

Main impact through the 05.12Z TAF period is ongoing FG primarily west of the Mississippi River Valley at TAF issuance. While KLSE has remained P6SM through the overnight, ridgetops are fully obscured and patchy visibility impacts may still occur yet. Have persisted 1/4SM at KRST based on ongoing observations. May see TEMPO lifting before based on surrounding webcams wavering FG thickness.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ086-087- 094-095. IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ008-009- 018-019.