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 135 PM CDT Sat Jul 18 2026

Today - Sunday: Air Quality Concerns Return

Post-frontal northerly winds have already started to bring some more smoke down from the Canadian wildfires into the Upper Mississippi River Valley, with some of it already mixing down to the surface creating slight visibility reductions. The concentration of near surface smoke is expected to increase later this evening and especially overnight, primarily for our Wisconsin counties and portions of SE Minnesota. Forecasted smoke does not look to be nearly as dense as it was earlier in the week but visibility reductions are expected with Air Quality Alerts already out for the entire state of Wisconsin through noon Monday. All the smoke that gets pushed south tonight will then start to make its way back north as surface winds shift back to the south/southeast, meaning the smoke is going to be sticking around in some capacity through much of the day on Sunday. Concentrations are expected to get lighter through the day Sunday as the nighttime inversion breaks and allows for diurnal mixing. With the smoke partially limiting daytime heating tomorrow, high temperatures will be moderated in the low to mid 80s.

Monday - Monday Night: Strong to Severe Storm Potential

As the upper ridge across much of the central CONUS starts to flatten out and retrograde slightly to the west, this is putting the Upper Midwest in more progressive northwesterly flow aloft. Late Sunday into Monday, an upper trough is expected to strengthen across the Canadian Plains, dropping southeast into the Upper Midwest and Great Lakes. At the base of this trough, a 500 mb jet max will overspread the Upper Midwest through the day on Monday. At the surface, a low pressure center will be located north of the Canadian border, likely in Western Ontario by 12Z Monday. A trailing cold front over northern Minnesota and the Dakotas is expected to slide southeast into the region by the evening, providing ample lift at the surface. A very moist and potentially extremely unstable airmass is forecast to develop through the afternoon with forecast soundings showing 3000-4000+ J/kg of SBCAPE with between 50-70 kts of effective bulk shear. All hazards are possible with the initial supercellular growth along the cold front but a wind threat will be favored overall as forcing along the front and the overall progressive nature of the system will likely result in quick upscale growth into a bowing linear feature. Forecast DCAPE values are also expected to exceed 1000 J/kg, favoring downburst wind potential. These storms will produce a quick bout of heavy rain given forecast pWats between 1.5-1.8 inches but with the progressive nature of the storms, a flash flood threat is not currently anticipated. One of the main limiting factors in confidence for the event as a whole is the likelihood of an early Monday morning MCS moving through the region. If this can move out as quickly as many models are suggesting in the 00/12Z suites, the thermodynamic and kinematic profiles would suggest a medium-high chance of severe storms across the area Monday afternoon and evening. If this MCS moves in slower than anticipated and/or lingers longer into the morning, this could limit the recovery for the afternoon/evening activity, potentially limiting their intensity. Details on timing, especially with this morning activity will be crucial to how Monday's event ultimately plays out so further refining is to be expected over the next 36-48 hours, especially as hi- resolution guidance and CAMs start to come into range.

Tuesday - End of the 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 /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1215 PM CDT Sat Jul 18 2026

An area of high pressure moves into the region this afternoon and evening behind this morning's cold front. With this high pressure, light winds and VFR conditions will prevail. Light northerly winds will advect smoke in from the north, which may bring MVFR ceilings into the area after midnight. Winds veer around to the south Sunday, but will remain light so the smoke is expected to linger through at least the weekend across the area.

ARX WATCHES/WARNINGS/ADVISORIES

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