textproduct: La Crosse

KEY MESSAGES

- Heaviest rainfall locally affecting southernmost counties from northeast Iowa into far southwest Wisconsin through Thursday with 1" to 2" expected, heaviest tonight into Thursday morning.

- Diminishing, low (<20%) flooding (river/areal) threat due to southern shift in forecasted heavy rainfall amounts.

DISCUSSION

Issued at 111 AM CDT Wed Sep 30 2026

Through Thursday: Widespread Rainfall

Widespread light to moderate showers have overspread much of the Upper and Mid Mississippi River Valleys overnight with QPE totals on the low side generally at or below 0.25 inches. This activity is forming within an axis of increased mid-level moisture with synoptic support from strong southwest flow aloft ahead of an upper low/trough across the Desert Southwest. Totals through the overnight hours and into mid morning may reach 0.5-0.75, mainly for areas south of the IA/MN border where some heavier returns are showing up on radar. Heavier rainfall expected later in the day with limited instability as pWats increase overnight and through the day tomorrow from strong 850 mb moisture transport into the region.

An break in rainfall is expected for much of the area before subsequent, likely heavier, rainfall forms during the afternoon, continuing into early Thursday morning. As mentioned earlier, with strong 850 mb moisture transport into the region, pWats will likely climb to 1.75+ inches, potentially approaching 2" across our far southern counties (Grant/Clayton) (30.00Z HREF). Similar to previous forecasts, the overall axis for heaviest rainfall continues to shift south into Central Iowa, aligning with the overall trend in the EC ensemble for many days now. Therefore, current forecast confidence for locally heaviest rainfall looks to be limited to far southern portions of Southwest Wisconsin (Grant and potentially Crawford/Richland Counties) and far southern portions of Northeast Iowa (Fayette and Clayton Counties) with less than 1" likely elsewhere locally by Friday morning.

NBM 30.01Z 1"+ rainfall probabilities from 60 to 80% in the aforementioned counties appear slightly earlier with a sharp gradient/cutoff to the north. LREF 29.12Z has a more broad area across northeast Iowa and Southwest Wisconsin for its probability of 1 inch of rainfall or greater (40-90%) with mean totals generally in the 0.5-2 inch range across the region. With the southern shift in heavy rainfall, the flooding threat is starting to dwindle, especially for area rivers. 90-95th percentile amounts from this system looked to be in the 2.5-4.5 inch range and this would likely create some areal and river flooding concerns but this concern seems to be diminishing for our local area. A cold front is expected to move in through the day on Thursday which will start to usher in a drier airmass. It will make slow progress through the region as high pressure builds in behind it with rain slowly ending from northwest to southeast late Thursday night.

Friday into Early Next Week: Mostly Dry and Trending Cooler

The H300 jet stream is forecast to sit across southern Canada and may dig south at times into the Great Lakes region to northeastern US this weekend into early next week. With a cold front south of the local forecast area and some cooler air filtering in due to the troughing, daily high temperatures will be a few degrees cooler into early next week. The cooler air mass will be more noticeable at night with lows dropping into the 40s to 30s. As of now, Monday morning looks to be coolest morning over the next week with the coldest temperatures potentially approaching freezing across central Wisconsin. Mostly dry conditions are expected during this time frame with the exception being on Saturday as there are low chances for light rain showers over the northern half of the CWA.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1249 AM CDT Wed Sep 30 2026

Building MVFR-IFR ceilings from southwest to northeast will affect western half of the forecast area, including both TAF sites (KLSE & KRST) through Wednesday morning. Have added extra FM groups for expected timing at both TAF sites in 30.06Z TAF issuance. Precipitation chances will remain mostly south of both TAF sites until the later forecast hours in current TAF period through Wednesday night into early early Thursday morning. Higher confidence affects smaller airports from northeast Iowa (KDEH, KOLZ, K3Y2) into far southeast Minnesota (KCHU) and southwest Wisconsin (KY51, KOVS, KPDC, KPVB).

ARX WATCHES/WARNINGS/ADVISORIES

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