textproduct: La Crosse

KEY MESSAGES

- Air quality concerns continue through Monday morning as wildfire smoke remains situated across the region.

- Monday continues to look favorable for severe weather, especially in the afternoon, but uncertainty remains in the overall details.

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

DISCUSSION

Issued at 1249 AM CDT Sun Jul 19 2026

Today: Air Quality Concerns Continue

Dry conditions are expected today as low-level ridging and surface high pressure remain the dominant synoptic features across the Upper Midwest. The main concern today is air quality as near surface wildfire smoke continues to overspread western Wisconsin and portions of southeast Minnesota under weak northerly flow that veers to the south by late this morning. Despite the 19.00z HRRR/18.18z REFS suggesting the near-surface smoke density will be less compared to what was seen last week, air quality will still be unhealthy to very unhealthy, especially across Wisconsin where smoke density will be greatest. As such, Air Quality Alerts are in effect through Monday morning across Wisconsin and southeast Minnesota.

Monday - Monday Night: Severe Storm Potential

The upper level pattern begins to break-down tonight into Monday as a 500hPa trough currently situated over British Columbia treks eastward atop a flattening ridge located over the central United States. In response to this wave, a surface low deepens across southern Canada along with the associated frontal zones.

Ahead of these features though, a quick moving shortwave trough reflected in the 700-500hPa layer looks to shift southeastward from the Dakotas, following an approaching MUCAPE gradient situated across central Minnesota into southeast Iowa. 18.12z-18.18z CAM runs suggest an MCS develops in response to these features, moving southeastward into portions of southeast Minnesota and northeast Iowa. Quite a bit of uncertainty in how strong this complex is by the time it gets into our area as it begins to outrun the better instability and shear, but can't rule out some stronger winds gusts and locally heavy rainfall.

Heading into the afternoon, a strengthening 500hPa jet streak overspreads the Upper Midwest, increasing 0-6km bulk shear to an impressive 55-60kts per the 18.21z RAP. In conjunction with the increasing wind shear, low level moisture surges into the region during the afternoon forcing surface dewpoints into the low to mid 70s, resulting in MLCAPE values of 2500-4000 J/kg ahead of the aforementioned cold front that will be shifting southeastward through the afternoon and evening hours. Ample synoptic scale forcing in the 1000-500hPa layer associated with the upper wave and surface boundary is evident in QG analysis from the 18.18z GFS/ECMWF/NAM/Canadian combined with the volatile atmosphere suggests this environment should be well suited to support severe convective development.

All hazards are going to be on the table during the afternoon. Deep layer shear vectors oriented nearly perpendicular to the surface cold front will support supercell development initially before growing upscale into a linear mode. With the initial development, large hail will be favorable, especially with 700-500hPa lapse rates of 7.5-8.5 C/km before transitioning to more of a wind threat given DCAPE values of 800-1200 J/kg and PWATs in the 1.5-1.8 inch range which could result in precipitation loading and stronger downdrafts. Heavy rainfall and localized ponding is also a concern given the juiced up atmosphere, but current expectations are for a fairly progressive event which will limit overall flooding potential, though areas that see multiple rounds of storms would be more susceptible to localized flooding. As far as tornado potential goes, model hodographs highlight favorable curvature in the 0-1km layer with the 18.21z RAP suggesting 0-1km SRH will be on the order of 100- 150 m2/s2, favorable for a few tornadoes to develop.

The main uncertainty in the forecast at this point is related to the timing and location of afternoon/evening storms with the evolution of the morning MCS being a primary driver of this uncertainty. If it tends to move slower than currently expected or lingers longer into the late morning/early afternoon, destabilization for the afternoon/evening storms may be hindered which would act to reduce their coverage and intensity. All of that said, the 19.00z runs of the CAMs (such as the HRRR/RRFS) are beginning to suggest this MCS fails to make it through Minnesota (or even develop at all), instead diving southward along the CAPE gradient across western Minnesota and western Iowa. If this scenario plays out, afternoon/evening convection would be even more favorable to develop and may develop earlier than currently expected as there will be little in the way to inhibit destabilization. Assuming there's no issue from the MCS standpoint, another point of uncertainty is related to timing/location owing to potential capping. the 18.12z LREF has quite a bit of spread regarding the location of the 12C isotherm at 700hPa, suggesting it could be as far north as Eau Claire (20% chance), though the highest probabilities exist across southeast Minnesota and northeast Iowa (60-80%). If this capping is able to hold against the forcing from the front, storms would become more favorable over northern Wisconsin. However, this seems like a lower potential scenario as GFS soundings suggest the cap is not over strong and would likely be overcome.

Despite all of the uncertainty surrounding the details of Monday, the thermodynamic and kinematic parameters continue to look favorable for severe weather development, especially in the afternoon/evening. So, even though confidence is not high in timing/location of storms, confidence at this point is fairly high in that if storms develop, they will become severe.

Outside of the severe potential, another concern Monday comes in the form of heat, primarily across northeast Iowa. The uncertainty surrounding how convection will unfold leads to fairly low confidence regarding how high heat indices will get, but given the low level moisture surge/increasing dewpoints, the 18.12z LREF does suggest 10-30% probabilities of 100+F heat indices Monday afternoon.

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

In the wake of the cold front, northwest winds will usher a far cooler airmass into the region for the middle of next week. The 25th- 75th percentiles of the various ensembles suites cluster highs around the upper 70s to low 80s Tuesday through Thursday, with only a few outliers climbing into mid 80s, a much needed break from the heat endured over the last few weeks. Along with the cooler temperatures, primarily dry conditions are expected as upper level ridging and surface high pressure over the western United States builds eastward. That said, the 18.12z LREF does suggest a 10-30% chance for some showers/storms to develop late this week as a few weak shortwaves move through the region but as is to be expected, there is quite a bit of discrepancy amongst the various ensemble members.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1249 AM CDT Sun Jul 19 2026

Smoky conditions move into much of the region early this morning and linger through the rest of the forecast period. The highest smoke density occurs this morning into the early afternoon. This will be when the visibilities are expected to be at their lowest, meaning MVFR conditions likely with possibility (40 to 60%) of IFR visibilities during this time. Visibilities are expected to improve by the evening. Winds will be light and variable.

ARX WATCHES/WARNINGS/ADVISORIES

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