textproduct: La Crosse

KEY MESSAGES

- Showers and storms persist into the evening and overnight, particularly across northeast IA. Some storms may be strong to severe with damaging wind gusts, large hail and locally heavy rainfall.

- Additional showers and storms are likely (60-80%) for Friday evening and night with the potential for some strong to severe storms.

- Near-normal temperatures through Saturday with highs in the middle 70s to lower 80s. High temperatures trend below normal by Sunday, hovering around 70 degrees.

DISCUSSION

Issued at 139 PM CDT Tue Sep 8 2026

This Afternoon - Overnight: Additional Showers and Storms, Some Strong to Severe Possible

Showers and storms this morning have gradually exited the region with an initial axis of 850mb moisture transport that is interacting with the slowly eastward progressing front and was responsible for much of the showers/storms this morning. As we head into the evening, a secondary axis of 850mb moisture transport related to the increasing nocturnal low-level jet will aid in reinvigorating convective development by late afternoon through the overnight. Overall, the environment looks somewhat favorable for severe weather with hodograph presentation due to favorable mid-level shear being present in RAP soundings across northeast IA. This combined with initial MUCAPE values of around 2000 J/kg would support the potential for some initial discrete supercells before clustering into a multi- cellular/linear complex as this moisture transport overrides the front. As a result, thinking there is a brief window for some severe hail before damaging wind gusts would be the primary threat. One important caveat to note though is that the severe potential in the local area is also contingent on exactly how this moisture transport axis orients itself which may remain to our south by evening and thus keeping most of the convection to our south.

Heavy rainfall will be a possibility as well with the moisture transport overriding the boundary allowing for storms to develop on the front with precipitable waters also approaching 2 inches. Additionally, warm cloud depths remain around 4km so overall a fairly favorable environment for heavy rainfall. Currently, the recent HREF has some higher probabilities (30-60%) for rainfall amounts over 1 inch across northeast IA with the 90th percentile amounts in the HREF suggesting some 2-3" amounts cannot be ruled out. However, this again comes with the caveat that there remains some uncertainty on the exact location of where the 850mb moisture transport will set up this evening, so there is a scenario where the bulk of convection remains to our south. One additional scenario that a few of the CAMs depict as well is additional convection developing with the actual synoptic front pushing through the local area, not associated with the 850mb moisture transport axis. Overall confidence in this scenario is somewhat low as it is unclear if enough instability will be present due to being clouded over for much of the daytime and the main moisture plume remaining to the south. Regardless, would expect convection to exit the region by early Wednesday morning as the synoptic front passes through.

Wednesday - Thursday: Drier, Near-Normal Temperatures

As we head into Wednesday and Thursday, upper-level ridging and surface high pressure build into the region. Consequently, expecting fairly dry conditions during this period. With some northwesterly flow into Thursday, expecting a slight dip in temperatures with highs in the middle 70s to near 80. However, even though the cold front passed through the local area Wednesday morning, temperatures will still remain near-normal due to upper-level ridging being in place.

Friday - This Weekend: Shower/Storm Chances Return, Slight Cool Down

By the time we reach Friday and the weekend, precipitation chances will be on the increase as an upper-level trough and attending surface cold front pushes through the Upper Midwest later Friday and into Saturday morning. As a result, the grand ensemble (GEFS/EC/Canadian) has fairly high probabilities (75-95%) for measurable precipitation Friday night and into early Saturday morning. The severe potential for this period remains somewhat questionable as the timing of the wave would favor convection reaching into the local area after dark when instability would be waning. Consequently, much of the AI/ML severe outlook guidance keeps our severe potential to the west of the local area as the timing of the wave would need to be slightly faster to push the probabilities eastward. Otherwise, temperatures cool down past Saturday with highs potentially falling into the 60s to lower 70s across the area as northwesterly flow reinstates itself across the region. Some guidance would suggest a wave that pushes through northern WI on Sunday bringing the potential for rain back into the region, so thinking that the medium probabilities (30-50%) are feasible in the NBM for Sunday.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1159 AM CDT Tue Sep 8 2026

Showers and storms will continue to be the primary aviation concern as we head into the evening with additional rounds of convection likely into the overnight. Currently, the highest probabilities for storms to develop remain south of I-90. However, given that some CAMs attempt to develop some additional convection further north this evening, have opted to include a prob30 for both KLSE and KRST. As we head overnight and into Wednesday morning, IFR cigs and fog will become the primary concern generally around 09z Wednesday and onward given recent rainfall. Winds will begin the TAF period from the south but will gradually shift to northwesterly by the end of the TAF period as a front moves through the region.

ARX WATCHES/WARNINGS/ADVISORIES

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