textproduct: La Crosse

KEY MESSAGES

- Showers and maybe a rumble of thunder south of I-90 this afternoon and tonight. Rainfall amounts increase as one travels south, with little for accumulation near I-90 to 1/2"-1" south of Highway 18.

- Cooler through Wednesday, warming back to around seasonable temperatures for the weekend.

- Risk for showers and storms returns for the weekend, but confidence in the timing and placement of any showers remains low (20-40% chance).

DISCUSSION

Issued at 125 PM CDT Tue Aug 4 2026

This Afternoon - Wednesday Morning: Periodic Rain and Storms

The line of showers and storms along a cold front that moved out of central MN early this morning faded by 9am as the attendant upper wave lifted into SW Ontario. The upcoming rain focus shifts to mainly south of I-90 for this afternoon and tonight as the lower tropospheric baroclinic zone/theta-e axis sags into Iowa and far southern Wisconsin (with convergence strongest in Iowa) and the right-rear quadrant of the upper level jet arrives.

Upstream radar trends over Nebraska and western Iowa continue to support that the highest rainfall amounts will be south of the forecast area, with lighter stratiform precipitation possibly advecting as far north as I-90 as we go through the afternoon and overnight. Latest HRRR runs support observational trends and take much of the heavier precipitation closer to I-80 late tonight. Could still pick up a quick 1/2 to 1 inch of rain in pockets along and south of Highway 18 before Wednesday morning given the ample deep moisture present, but otherwise the impacts from this rain look to be minimal.

Wednesday Afternoon - Thursday: Dry and Seasonal

Cyclonic flow lingers for the remainder of the week with a broad cutoff low centered over the far north-central CONUS and south- central Canada. Shortwave ridging passes through from Wednesday afternoon through Thursday with the main surface baroclinic zone displaced to the south, keeping the risk for any precipitation at bay. With the flow remaining weak, minimal lower tropospheric temperature advection is expected during this timeframe and highs will only rise into the lower 80s by Thursday despite the clearer skies.

Friday - Early Next Week: Seasonal Temps, Periodic Storms

Given the weak flow pattern we find ourselves in with the main jet stream shifted north to the U.S./Canadian border, confidence in the timing and coverage of storms for Friday and the weekend is low at this time. The deterministic solutions depict the possibility of multiple weak perturbations rotating through during this period, but the guidance differs on how far north the richer Central Plains airmass can advance, which will play heavily into the probability of any storms (and surface temperatures). Moving into early next week, the jet stream looks to sag southward and provide more support for organized convection. Again, the question of how exactly the thermodynamic and kinematic spaces line up will play heavily into storm strength and coverage.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1246 PM CDT Tue Aug 4 2026

Periods of showers and perhaps some rumbles of thunder are expected this afternoon and overnight which will result in MVFR ceilings and visibilities at times. Showers and the associated impacts will primarily remain south of I-90, though some model solutions continue to suggest low probabilities (25-35%) for SHRA at the TAF sites generally between 00z-06z, so have continued with PROB30 groups at both locations. Overnight, low level saturation associated with the showers may lead to IFR ceilings for areas along/south of Highway 18 as suggested by the 04.12z HREF/REFS which depict 30-50% probabilities for ceiling heights less than 1kft. Showers shift eastward Wednesday morning while skies slowly scatter out west to east throughout the day. Light northwest winds continue throughout the TAF period.

ARX WATCHES/WARNINGS/ADVISORIES

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