textproduct: La Crosse

KEY MESSAGES

- Temperatures and humidity gradually increasing through midweek with highs in the mid 70s to mid 80s.

- Thunderstorm chances return Tuesday afternoon and evening. Some could be strong, mainly across the northwest half of our forecast area.

- Lingering showers possible on Wednesday, with next chance of rain over the weekend.

DISCUSSION

Issued at 1239 AM CDT Mon Aug 24 2026

Fog potential this morning, gradual increase in warmth/moisture

Cirrus from convection over North Dakota will continue to spill into the area early this morning. This complicates the forecast for potential fog development in valleys and low-lying areas, in what would otherwise be a decent synoptic setup with high pressure overhead. But evening HRRR runs trended toward some breezier winds of 10-15 knots in the 500-1500 ft layer. All this suggesting that fog may be more patchy this morning.

There is an outside chance some decaying convective showers from the Northern Plains would be steered southeastward in the upper flow to clip areas west of the Mississippi River with some showers this afternoon. Several 24.00Z CAMs are showing this, but the HRRR is mainly dry.

Daytime highs will be warming a bit today into midweek as southerly return flow develops. Moisture will also gradually be on the increase ahead of a pronounced upper shortwave trough progged to cut across northern Minnesota/Wisconsin toward Wednesday. Dewpoints will rise back into the 60s, and with a feed of Gulf moisture there is a >70% likelihood for precipitable water to climb above 1.25 inches by Tuesday afternoon.

Storm chances on Tuesday, some could be strong

Strong storm chances on Tuesday will hinge on magnitude of instability and its ramifications on how robust updrafts can become. GEFS 23.18Z probabilities for CAPE >1000 J/kg range from about 60-80% west of the Mississippi River to 50% or less in western Wisconsin. This was a slight decrease from the 12Z run as models are grappling with a potential EML and less favorable mid-level lapse rates. Capping and instability profiles will be most favorable for convection over our northwestern counties. That's also where favorable deep layer shear is most likely, with elongated hodographs perpendicular to an approaching cold front. Thus, it bears watching how all these elements will ultimately come together Tuesday afternoon-evening, with some strong to possibly severe storms looking to be a possibility.

Rest of the week

Cyclonic flow aloft persists into Wednesday which could foster some diurnal shower activity. The upper shortwave departs by Thursday with 850mb temps decreasing slightly overhead through Friday. The overall pattern shifts heading into next weekend as warm air advection ramps up. This will support a return of rain/storm chances but details are pretty murky that far out.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 551 AM CDT Mon Aug 24 2026

River valley fog/stratus has developed this morning with latest observations keeping this out of LSE. With the sun beginning to rise, have continued to keep this out of the LSE TAF. Otherwise, VFR conditions with either variable or southwesterly winds are expected to prevail with increasing mid to high level clouds. Should those clouds fail to move over the region and/or dissipate after 00z Tuesday, more extensive river valley fog would likely develop. For now, that is not expected, so have left any hints at valley fog out of the final 6 hours of the TAFs.

ARX WATCHES/WARNINGS/ADVISORIES

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