textproduct: La Crosse

KEY MESSAGES

- Predominantly dry conditions exist today into Tuesday morning, though some isolated showers and perhaps a storm may occur Tuesday morning (10-20%).

- Shower/storm chances increase Tuesday afternoon and evening along a cold front, primarily north of I-90 (30-60%). Some storms could be strong.

- Mostly dry conditions return for the second half of the week with near-seasonable high temperatures in the low 80s expected.

DISCUSSION

Issued at 1215 PM CDT Mon Aug 24 2026

Today - Tuesday Morning: Primarily Dry, Low Shower/Storm Potential

Predominantly dry conditions are expected to continue today across the Upper Mississippi River Valley. A 500hPa shortwave trough across central Minnesota continues southeastward today, so can't completely rule out some stray showers this afternoon along a surface boundary currently across northeast Iowa/southeast Minnesota, though dry air in the 800-600hPa layer per RAP/HRRR soundings and mid-level water vapor imagery suggest any shower activity would be dependent on the degree of saturation that is able to occur and will likely be isolated in nature, if any can develop at all (<10%).

Valley fog may return again tonight into Tuesday morning under a similar set-up as last night which did result in some fog development within the Wisconsin and Kickapoo River valleys along with some other Mississippi River tributaries. Cloud cover is the main wrench in the forecast regarding fog potential as a thunderstorm complex is expected to develop over eastern North Dakota/northwest Minnesota this evening, resulting in cirrus overspreading the area overnight. Dependent on the timing of this cirrus, we may be able to cool enough such that some of the typically foggy river valleys see some development into the morning hours though increasing winds in the 500-1500ft layer may result in any fog development being fairly patchy.

The previously mentioned thunderstorm complex is expected to decay and dissipate as it translates southeastward given diminishing instability, but can't rule out some isolated to scattered showers and perhaps a rumble of thunder (MUCAPE of 100-300 J/kg per the 24.09z RAP) making their way into parts of southeast Minnesota/western Wisconsin Tuesday morning. Many CAMs do highlight this potential, resulting in 10-20% probabilities per the 24.12z HREF. Strong/severe storms are not anticipated with this morning activity.

Tuesday Afternoon - Evening: Strong Thunderstorm Potential

Greater confidence in storms comes Tuesday afternoon and evening as a stronger 500hPa wave currently situated along the United States/Canada border across Montana/North Dakota continues eastward. An associated surface low and cold front are expected to move through the region along with this upper level feature, sparking showers and storms across the Upper Midwest though the greatest potential exists north of I-90 (30-60%) where stronger QG forcing and surface convergence along the front exists per the 24.14z RAP. There is also an aspect of a weakening cap with northward extent. Ahead of this boundary, southerly winds usher moist air into the region through the day resulting in surface dewpoints climbing into the low 60s and MUCAPE increasing to upwards of 1000-2000 J/kg along the front. Increasing 500hPa winds associated with the approaching wave increases 0-6km bulk shear to 30-40kts with the vectors nearly perpendicular to the surface front which would suggest a discrete/supercellular storm mode and would be supportive of some strong to potentially severe storms. From a hazards perspective, large hail followed by strong to damaging winds appear to be the primary concerns given the favorable thermodynamic and kinematic environment. There is a conditional threat for a brief tornado with initial storm development given some weak curvature within the 0-1km layer per model hodographs, but this threat quickly wanes with time as storms begin to become elevated.

Wednesday - This Weekend: Mostly Dry and Near-Seasonable

Ridging begins to build back into the Midwest Wednesday through the late week behind Tuesday night's cold front. Stability associated with the ridge along with a slightly cooler and drier airmass moving into the region should largely keep us dry through the late week, though Wednesday may see some diurnal shower activity given steepened 0-3km lapse rates from the cooler air at 850hPa and some lingering low level moisture. This potential is very low however, generally <10% at this point. Temperatures are expected to be around 5 degrees of normal for this time of year though they do tend towards the warmer side of climatology, generally topping out in the low 80s. Shower and storm potential look to return this weekend.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 637 PM CDT Mon Aug 24 2026

VFR conditions are expected throughout the TAF period with southerly winds to around 8-14 kts. Sct to bkn middle and upper-level clouds are expected throughout the TAF period. Cannot rule out some valley fog (10-20% chance) at KLSE tonight. However, given the shallow light-wind layer in recent RAP soundings, thinking that it is unlikely at this point.

ARX WATCHES/WARNINGS/ADVISORIES

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