textproduct: La Crosse

KEY MESSAGES

- Warm and muggy today and Wednesday with highs in the mid to upper 80s today and the mid 80s to low 90s for Wednesday. Heat indices near 90 today and the mid 90s to low 100s for Wednesday

- Strong to severe storms are possible tonight into Wednesday morning. Large hail and damaging winds are the primary threats.

- Severe storms likely Wednesday afternoon and evening with large hail, damaging winds, and tornadoes possible.

- Another conditional threat for severe weather exists Thursday across northeast Iowa and southwest Wisconsin.

DISCUSSION

Issued at 1255 AM CDT Tue Jun 9 2026

Today: Fog Early, Warm and Muggy Weather Arrives

Areas of fog continue through the morning hours given ample moisture available from the rainfall that fell yesterday afternoon and evening under clearing skies as a shortwave ridge builds into the region. Pockets of 1/4 mi visibility or less are possible through the morning commute so ensure you take precautions when heading out the door.

As the fog burns off through the mid morning hours, low level warm air advecting northward into the Midwest along with rising heights overhead associated with the ridge will result in rising temperatures across the Upper Mississippi River Valley. 08.18z deterministic solutions depict 925hPa temperatures sitting around 23C and 19C at 850hPa, which is in-line with the 08.12z LREF mean for these pressure levels. Assuming boundary layer mixing to these levels, surface temperatures in the mid to upper 80s appears reasonable, further supported by 08.18z NWP/AIWP ensemble solutions which depict interquartile ranges clustered in this range. The southerly flow also ushers in dewpoints in the upper 60s to possibly the lower 70s this afternoon which would result in heat indices climbing to around 90 this afternoon.

Apart from the warm and humid conditions, today looks to be dry from a precipitation perspective. Elevated instability above a stout warm nose in the 800-700hPa layer from the aforementioned warm advection is depicted in model soundings, but with the strong capping inversion in place, broad subsidence associated with the ridge aloft, and the lack of a notable forcing mechanism, convective development appears unlikely.

Tonight: Stronger Storms Possible

As we head into tonight, a warm front and low level jet advance northward into the Upper Midwest from Nebraska/Iowa as the upper ridge shifts east and troughing across the Plains moves into the region. Forcing along the front along with convergence on the nose of the low level jet will support convective development late tonight into Wednesday morning (40-70%). Fairly impressive instability builds in along the front, generally 2000-3000 J/kg, plenty for storms that develop to pose a severe threat through early Wednesday morning. The biggest hindrance to the severe threat is an overall lack of wind shear, only around 15-20kts of effective shear per the 08.21z RAP, which would suggest a lack of updraft/downdraft separation and fairly short-lived storms. However, the ample instability would support large hail and damaging winds in storms that develop through the mid morning hours Wednesday.

Wednesday: Warm and Humid, Afternoon Severe Threat

Another period of warm and muggy conditions is expected Wednesday afternoon although there is a bit more uncertainty in how warm we'll be able to get, dependent on how the morning's storms evolve. Much of the 08.18z ensemble suite suggests high temperatures rise into the upper 80s with little variation in the 25th-75th percentile. The consistent exception is the NBM, which has tended to be warmer than other solutions and suggests temperatures climb into the low 90s. Have tempered the NBM slightly to come more in line with the other available guidance, especially with the uncertainty in how the morning will influence the afternoon temperatures, but still results in heat indices in the 90s, nearing 100F for those in river valleys.

Wednesday afternoon brings the potential for another round of severe convection, but also has some dependence on how the morning's round plays out. Currently, our area looks to be solidly south of the aforementioned warm front, allowing for SBCAPE to build during the day, in excess of 3500 J/kg. A cold front is then expected to move through this environment during the evening hours, providing lift for convective development. 0-6km bulk shear increases along this front, generally 25-35kts, which should support severe storm development although the greatest shear appears to be slightly displaced behind it. Model hodographs also highlight low level cyclonic curvature favorable for supercell development. The overall current expectation is for severe storms to develop late Wednesday afternoon, initially as supercells before growing upscale to a linear mode, continuing into the evening with all hazards possible.

The main point of uncertainty is how the morning convection affects destabilization later in the day. If the morning storms linger longer than currently expected or cools surface temperatures more than expected, this would limit the spatial extent of destabilization and result in a lower severe threat for some areas. All this said, the SPC currently has our area in a level 3/5 for severe weather potential with AI/ML severe guidance also indicating increased probabilities for severe weather.

Thursday: Slightly Cooler, Conditional Severe Weather Threat

After the cold front passes through on Wednesday night, a low ejects out of the southern Rockies. This low moves off to the northeast towards the mid-Mississippi River Valley. There is better deep layer shear for Thursday and modest instability builds in. There is quite a bit of uncertainty on the path of this low and how much we can recover from Wednesday. The area of potential concern would be northeast Iowa and southwest Wisconsin as storms look to fire early in the afternoon ahead of another cold front. This front is stronger than Wednesday's and will play a bigger role in keeping temperatures in the mid 70s to low 80s. Overall, while storms will fire on Thursday afternoon, the location of these storms is uncertain due to exactly where any outflow boundaries set up from Wednesday and how much we can recover. The better severe weather threat remains to be on Wednesday but a threat for northeast Iowa and southwest Wisconsin could exist, and as a result SPC has a 15% or slight risk for severe weather for these locations due to the conditional potential.

The forecast turns quieter and cooler for the end of the week with near to below average highs for the weekend.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1255 AM CDT Tue Jun 9 2026

Widespread IFR to LIFR ceilings and fog persist for the overnight hours, clearing out during the mid-morning hours. VFR conditions are then forecast for the remainder of the TAF period. A band of showers and storms does start to lift northward west of the Mississippi River before 06Z, spreading further east between 06-12Z.

ARX WATCHES/WARNINGS/ADVISORIES

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