textproduct: La Crosse

KEY MESSAGES

- Air quality concerns return tonight through Sunday as northerly winds bring wildfire smoke back to the area.

- Monday continues to show promise for severe weather potential, but details remain uncertain.

- Cooler temperatures and mostly dry weather are expected Tuesday through the end of next week.

DISCUSSION

Issued at 1240 AM CDT Sat Jul 18 2026

Today - Sunday: Air Quality Concerns Return

A cold front currently moving southward through the Upper Mississippi River Valley will continue sparking showers and storms over the next few hours. Model guidance is struggling to handle the ongoing convection, though most solutions suggest these storms should weaken and dissipate with time as they tend to outrun the greater instability and shear along the front. After the front fully moves south of the area Saturday morning, winds veer to the north and usher in a drier and slightly cooler airmass. Rather benign weather is expected for the remainder of the weekend as a result, although the northerly winds leave us open to the return of near-surface wildfire smoke. The 18.00z HRRR suggests higher concentrations of near- surface smoke begin to move into western Wisconsin Saturday evening, even reaching those along the Mississippi River in southeast Minnesota and northeast Iowa, and lingers through Sunday. Because of the increase in near-surface smoke density, air quality concerns increase Saturday evening through Sunday. Uncertainty does remain regarding exact fire and smoke behavior over the weekend though, so future Air Quality Alerts will have to wait until confidence in location and impacts increases.

Monday - Monday Night: Strong to Severe Storm Potential

Monday continues to look like the next most favorable day for strong to severe storm potential as an upper level shortwave trough dives southeastward into the Upper Midwest along with an associated mid-latitude cyclone at the surface. The Upper Mississippi River Valley will be well within the warm sector Monday with southerly winds advecting a moisture rich airmass into the region, increasing MUCAPE to 1500-2500 J/Kg with a gradient of instability setting up generally along the Mississippi River while a 500hPa jet streak overspreads the region, increasing 0-6km shear to 40-50kts resulting in impressive elongation in model hodographs by the afternoon.

There remains quite a bit of variation amongst the model guidance and their solutions run-to-run as far as the evolution of this event is concerned, though looking at the individual members of the 17.18z GEFS/EPS/AIGEFS/AIFS Ens there is an overall consensus of convection developing Monday morning, likely in the form of an MCS that travels southward along the instability gradient. That said, there is quite a bit of discrepancy as far as timing and location is concerned but the 17.19z NBM suggests probabilities for precipitation Monday morning are around 60-80%.

Another round of storms may be able to develop in the afternoon along the cold front as it moves through, but this is the main point of uncertainty currently due to afternoon development being dependent on how morning storms evolve. That said, current probabilities for precipitation Monday afternoon sit at 40-50% per the 17.19z NBM. All hazards continue to look probable with storms that develop Monday with large hail, damaging winds, a few tornadoes, and heavy rainfall.

Tuesday - End of Next Week: Cooler Temperatures and Mostly Dry

Once the cold front passes and the storms clear out late Monday night, there should be a noticeable difference across the area with an overall much cooler airmass expected for mid next week. Temperatures Tuesday and Wednesday will finally drop below average into the upper 70s to low 80s with dry conditions expected as a weak surface high pressure moves in behind the front. While a quick moving disturbance may bring some low rain chances to the area by late week, expect generally dry conditions and near normal temperatures to round out the next work week.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1240 AM CDT Sat Jul 18 2026

Ongoing showers and storms north of I-90 have been slowly moving southward along a cold front this evening. Confidence is not overly high in how far south these storms get, but thinking they may be able to impact sites along I-90 east of the Mississippi River (10-30%) so have included mentions in the KLSE TAF. After the cold front moves through, winds transition to the north with impacts from smoke slowly returning east to west this evening.

ARX WATCHES/WARNINGS/ADVISORIES

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