textproduct: La Crosse

KEY MESSAGES

- Dangerous Sunday and potentially Monday with daytime heat indices over 100 degrees expected across much of the forecast area for Sunday. An Extreme Heat Warning is in effect for Sunday for much of the area given the high heat indices.

- Storm chances return late tonight and again Sunday afternoon and evening. There is some potential for severe storms to occur with damaging winds and large as the primary hazards with any severe storm.

DISCUSSION

Issued at 152 PM CDT Sat Jul 25 2026

Today-Monday: Hot and Humid with Storm Chances

After a break from the hot and humid conditions, they are returning today and lingering through Monday. A ridge that has been sitting off to our west has begun to build eastward towards the Upper Midwest. This amplification of the ridge brings warmer and humid conditions for the next few days. The 850mb temperatures increase today and furthermore on Sunday with temperatures ranging from 24 to 26C based on the mean HREF 850mb temperatures. Despite the cloud cover from this morning, temperatures will get into the mid to upper 80s for most locations with some areas getting into the low 90s. The areas that see the warmest temperatures, basically our western tier of counties and Wabasha and Olmsted counties are in a Heat Advisory for today as heat indices should get near 100F and up to 105F. Most other locations across the forecast area will see heat indices in the upper 80s to upper 90s.

Focusing on Sunday, there is also a decent EFI signal where values of 0.7 to 0.9 exist indicating that the forecasted temperatures are on the warmer side of climatological normal. Dewpoints, aided by the corn sweat, are expected to get into the mid and upper 70s for most areas. Portions of northeast Iowa and southeast Minnesota could see dewpoints in the low 80s. Combining both of these we get heat indices in the 100 to 115F range! The areas that have the best chances at seeing the 110F+ heat indices are more focused in northeast Iowa and along the Mississippi River Valley. Poor overnight recovery into Monday is possible as apparent temperatures stay in the mid to upper 70s for most locations. Uncertainty remains for how hot the area gets on Monday due to potential convection. This all being said, there is an Extreme Heat Warning for most of the CWA for Sunday with a Heat Advisory for Clark, Taylor, Juneau, and Adams counties. As the ridge gradually shifts back south, a front comes through the Upper Midwest. The timing of this front will play a role in how hot we truly get on Monday. Current forecasted heat indices are in the low 100s for areas south of I-90 and in the mid to upper 90s to the north. If the front is slower to pass through, then the higher temperatures and dewpoints will be around longer, helping to reach heat headline criteria. Due to the uncertainty for Monday regarding the timing of this front and the potential convection or convective debris, have kept the Extreme Heat Watch in place for northeast Iowa and far southwest Wisconsin.

As we turn our attention to the thunderstorm chances over the next few days, they sure are difficult to forecast! Within this pattern, the low-level shear is not impressive (mainly in the 10 to 25 kts range for 0-1km shear), while the deep layer shear has some modest values to it (around 40 to 60 kts of 0-6km shear). Instability wise, there is plenty of it, 2500 to 4000 J/kg of MLCAPE. There is also quite a few perturbations that pass through the Upper Midwest that could be helpful for storm development. CAMs have come into good agreement that an MCS is expected to form in South Dakota this evening and make its way eastward along the theta-e gradient. Earlier runs of some of the CAMs brought this MCS all the way to our western half of the CWA, however only a couple CAMs remain that continue to support that. By Sunday, as mentioned previously, a few waves move through the area increasing convective potential, however there is low confidence on exact locations of storms for the afternoon and early evening. Instability and shear will be present all day, depending on morning convective debris the destabilization could be delayed. CAMs have shown scattered storm development across the entire CWA with each model showing different locations. With strong northwest flow, 40 to 50 kts in the midlevels, these storms would race southwestward with a damaging wind or hail risk. The main problem for Sunday is if the capping in place will be overcome by the weak waves that move through. If this occurs then there could be quite a few storms out there. Then the attention would turn to outflow boundaries and what those could do as they interact with storms. Confidence does increase for the later evening as a slightly more defined wave pushes into Wisconsin. This would increase storm chances for areas east of the Mississippi River. By Monday, a front moves through the region, however there does not appear to be good convergence along the front and combining this with the capping in place, storms are not expected to fire for Monday afternoon and evening.

Tuesday-Saturday: Warm Temperatures Continue with Storm Chances

The ridge shifts westward just enough and northwest flow remains in place. Both of these will mean temperatures cool down slightly, into the mid to upper 80s but it also means that the 70F dewpoints would be less likely to occur. Heat indices will also stay in the 80s to around 90F. With this flow pattern, ensemble guidance has low precipitation chances through midweek with better chances as we head towards the weekend. Another thing to note is that given the northwest flow pattern, we will have to watch for any waves that ride around the ridge as these would impact portions of the Upper Midwest.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 637 PM CDT Sat Jul 25 2026

MVFR cigs are expected to scatter out slightly this evening across the area resulting in sct low-VFR cigs into the overnight. With some additional moisture moving into the region overnight, the recent HREF has some respectable probabilities (20-50%) for MVFR cigs to return for a brief period at KLSE early in the morning. Otherwise, a decaying MCS may progress (20-40% chance) into portions of southeast MN and northeast IA overnight which may bring some strong wind gusts along with it. However, confidence that it will maintain its strength into the local area remains too low to include in the TAF. Additional storms will be possible during the afternoon hours on Sunday across the region, however with hi-res models not painting a clear picture for how this would evolve at this point, have opted to hold off on any precipitation mention at this time.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Extreme Heat Warning from noon to 9 PM CDT Sunday for WIZ032>034-041-042-053>055-061. Extreme Heat Watch from Sunday evening through Monday evening for WIZ053>055-061. Heat Advisory from noon to 9 PM CDT Sunday for WIZ017-029-043- 044. MN...Heat Advisory until 8 PM CDT this evening for MNZ079-086-087- 094. Extreme Heat Warning from noon to 9 PM CDT Sunday for MNZ079- 086>088-094>096. IA...Heat Advisory until 8 PM CDT this evening for IAZ008-018. Extreme Heat Warning from noon to 9 PM CDT Sunday for IAZ008>011-018-019-029-030. Extreme Heat Watch from Sunday evening through Monday evening for IAZ008>011-018-019-029-030.