textproduct: La Crosse

KEY MESSAGES

- Storm chances (30-60%) return mainly Friday night with low potential (<10%) for severe thunderstorms unless the timing of these thunderstorms shifts into the late afternoon hours of Friday or Saturday.

- Widespread rain is very likely (80-90%) Monday. Heavy rain and perhaps flooding may occur, particularly if locations receive appreciable rain early Sunday ahead of the main rain event (30% chance).

DISCUSSION

Issued at 125 PM CDT Wed Sep 9 2026

Thunderstorm potential returns Friday night

Friday into Saturday, longwave upper trough will advance over Canada with this feature extending southward over the Upper Midwest. Weak surface ridge in the eastern CONUS should lead to southerly moisture fetch, setting the stage for a chance (30-60%) of showers and thunderstorms as the associated surface front pushes southeast. With westerly winds aloft ramping up on the equator-ward side of the upper trough, plenty of shear looks to be available for organized convection. However, most guidance bring the front through the CWA by mid-morning Saturday, leading to little in the way of instability. Therefore, current thinking is that the potential for a severe thunderstorm is low (<10%) and, if it were to occur, would favor far southwest Wisconsin early Saturday afternoon before the front fully clears the CWA.

Rainy Monday with flooding potential

Moist advection resumes rather quickly following Saturday's frontal passage with this ramping up considerably into Monday. 09.00z NAEFS/ECENS PWAT values increase to the 90th and 99.5th percentile respectively before cooling aloft ahead of another longwave trough and increasing WAA lead to widespread rain. Moderate (2"+) amounts of rainfall appear to be good bet north of I-90 (55-70%). While the overall system is progressive and thus flood risk would be limited by duration of the event, at least the 09.00z EC depicts rain developing along the warm front much earlier than other guidance. This seems to be reflected in 09.00z ECENS EFI output which shows an area where many members are toward the 80th-90th percentile climatologically for QPF, as expected given plenty of forcing and moisture as discussed above, with a few more extreme members which would represent the potential earlier start to rain. At this time, this output is mainly within west central Wisconsin north of I-90. If this were to occur, could see a risk for flooding develop. Will need to continue watching this period closely over the coming days.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1215 PM CDT Wed Sep 9 2026

VFR conditions should (80%) prevail at RST/LSE through the next 24 hours but there is a small (20%) chance for fog to spread northward to these terminals around 09-12z Thursday. This fog is expected to mainly affect the usual areas around the Wisconsin River valley. As a front slides southeast this afternoon, some gusts to 25 knots out of the west northwest will occur under clearing skies.

ARX WATCHES/WARNINGS/ADVISORIES

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