textproduct: La Crosse

KEY MESSAGES

- Mild and dry through Friday afternoon with highs in the mid 70s to low 80s.

- Shower and storm chances return Friday night into Saturday morning (30 to 60%). Severe potential is low (<10%) with these storms.

- Widespread rain is likely Monday (70 to 90%). There is a heavy rain and flooding potential, especially for locations that pick up rain on Sunday prior to this event.

DISCUSSION

Issued at 1230 AM CDT Thu Sep 10 2026

Friday - Saturday: Storm Chances Return, Slight Cool Down

An upper level low is expected to rotate across the western Hudson Bay Friday with a longwave upper trough pivoting across the Northern Plains and Upper Midwest through Saturday. At the surface, a trailing cold front is expected to swing through the Northern Plains during the day on Friday. With a surface high departing to the east, the pressure gradient will tighten across the Upper Midwest allowing for ample return flow and subsequent destabilization through the day. Westerly winds on the lee side of the side of the trough axis are expected to increase Friday afternoon into Saturday morning, helping to introduce plenty of shear across the region. With this instability and shear, storms are expected to form in the vicinity of the cold front. However, guidance has backed off on the speed of this frontal boundary, bringing it through our area by mid Saturday morning when there will be little to no instability to work with. Guidance as also trended further north with the shear so the environment across our area does not look overly conducive for severe thunderstorms. Rain showers and sub-severe thunderstorms look more likely with the frontal passage at this time with a low chance (less than 10%) for a severe storm Saturday afternoon across Southwest Wisconsin where the front may not have cleared the area just yet. Even though the front that moved through will be a "cold front", zonal flow aloft will prevent any significant cool down for Saturday with highs still in the mid to upper 70s.

Sunday - Mid Next Week: Heavy Rain Monday, Much Cooler Mid Week

On Sunday, an upper low over the Pacific Northwest will begin to eject to the northeast as a strong ridge builds over the Southeastern US. This will lead to a belt of strong southwesterly flow over our region for the first half of next week. Moisture advection ramps up after the passage of Saturday's cold front but it isn't until late in the day Sunday into Monday that the bulk of the deeper moisture works its way into the Upper Mississippi Valley. At the surface, a warm front is expected to lift north into the area by the morning hours on Monday with strong 850 mb moisture transport into the frontal boundary. ECMWF pWATs are in the 90th-99.5th percentiles with a broad swath of 1.75 inches averaged across the area 00Z Monday - 00Z Tuesday. WPC already has most of our area in their Day 5 Slight Risk for Excessive Rainfall, indicating a potential for heavy rainfall leading to flash flooding. While looking at the EFI, the shift of tails or SOT has the area north of I-90 highlighted, a similar area to where the NBM has the highest probabilities of 2 inches or more rainfall over a 48 hour period ending at 7am Tuesday morning. It should be noted that looking at the raw NBM data vs the bias corrected NBM data shows a vastly differing picture. The raw NBM data is much lower (half an inch to almost an inch lower in some places) which seems to be more in line with the 09.12Z LREF probabilities. Given the recent wet period we've had across the area, its easy to see why the bias correction of the NBM is trending a little on the high side. Some of these totals will likely be lowered in the coming days but there is still a very real chance for a heavy rainfall event that could lead to flooding. The pWATs and warm cloud depths will be there but the question is whether storms along the boundary will train enough to cause a flooding problem. This will be something to keep an eye on over the coming days. The soaking rains will also help to knock temperatures down quite a bit with highs by mid week likely only reaching into the upper 60s to low 70s, much more representative of the fall timeframe we're in.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 550 AM CDT Thu Sep 10 2026

Fog has developed over the Wisconsin River Valley and some of the Mississippi River Valley tributaries. All fog will dissipate by mid-morning. Other than the fog this morning, expect VFR conditions through the TAF period. Light and variable winds continue through mid- morning becoming more west to northwest by the late morning. Winds then shift to the southeast by this evening.

ARX WATCHES/WARNINGS/ADVISORIES

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