textproduct: La Crosse

KEY MESSAGES

- Shower and storm chances (30-50%) return tonight into Thursday morning with minimal impacts expected.

- There is increasing confidence in heavy rainfall on Friday into Saturday across the entire area with potential rainfall amounts of 1-3 inches with locally higher amounts possible. Flooding and river rises may occur where the heaviest rainfall amounts occur.

DISCUSSION

Issued at 139 AM CDT Wed Sep 16 2026

Rainfall Potential Overnight Into Thursday Morning:

Passing low level anticyclonic flow evident on area VWPs has ushered in a cooler, drier airmass over the forecast area compared to previous few days with the recent frontal boundary shunted just south into central Iowa. The anticyclonic flow center traverses east of the forecast area through today, ushering in return flow and the aforementioned frontal boundary with accompanying increased moisture into tonight. Associated precipitation chances increase locally tonight as mid level shear vorticity lobe and transient ageostrophic ascent within the equatorward entrance region of a passing upper level jet streak causing meager cyclogenesis. Overall impacts appear minimal given diurnal timing abstaining more unstable airmass upstream of the forecast area into central Minnesota.

Heavy Rain Friday Into Saturday:

Subsequent cyclogenesis of a Rocky Mountain Low through the Northern Plains through Thursday returns heavy rain potential across the Upper Mississippi River Valley initially Friday morning. Band of strong low level frontogenesis collocated with 1.5"-2"+ PWATs results in heavy rain probabilities quickly increasing through Friday shifting east into Friday night. Strengthening of the low through Friday night persists heavier rain potential into Saturday morning across the forecast area. LREF (15.12Z) probabilities quickly increase through Friday into Friday night with 40%/70% for 2" of rainfall in 24 hrs in the GEFS/EPS. While overall placement may vary some, the area of higher rainfall (2"+) values is quite widespread. Resultant increased concerns for river flood primarily from west- central (Black River) into central (Yellow River) and southwest Wisconsin (Kickapoo River). As the flashiest of these rivers, highest impacts would be along the Kickapoo River should this solution come to fruition. While the combination of lagged initialization (GEFS) with 72 hour forecast window limits accompanying river flooding probabilities (HEFS), GEFS rainfall probabilities remain lower than EPS/GEPS, increasing flooding impact concerns and probabilities above current values.

Early Next Week: Staying Cooler Than Normal, Additional Rain Chances

As the rainfall from Friday and Saturday departs the local area, northeasterly flow around the surface low will likely keep temperatures slightly below normal into Sunday with median high temperatures in the NBM hovering in the middle 60s to near 70. The main point of forecast uncertainty as we head into next week will be revolving around a potential cut-off upper-level low which guidance has substantial disagreements on how to handle at this point in the forecast cycle. Consequently, the NBM maintains some low-end precipitation probabilities (15-40%) at this point from Sunday through Monday which seems reasonable given the wide range of solutions with this system. However, given the presence of this low in the region into early next week, thinking that below normal temperatures will maintain with median high temperatures in the NBM hovering in the upper 60s to around 70 degrees.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1229 PM CDT Wed Sep 16 2026

VFR conditions this afternoon and early evening will give way to MVFR and eventual IFR conditions overnight as showers and low-level moisture lower cigs and bring some fog potential to the region. Showers will likely move into the region near or just after midnight with MVFR to IFR reductions likely. Cannot rule out a few thunderstorms given the weak MUCAPE present, however confidence (10- 20%) was too low to include in the TAF. Eventually rain departs towards daybreak with lingering low-level moisture bringing some potential for both IFR cigs and vsby reductions during the morning hours. Winds will generally remain light and out of the east throughout much of the TAF period.

ARX WATCHES/WARNINGS/ADVISORIES

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