textproduct: La Crosse

KEY MESSAGES

- Dangerous heat this weekend and Monday with daytime heat indices over 100 degrees expected across much of the local area, particularly on Sunday.

- Storm chances this weekend with the potential for some storms to become strong to severe. Damaging wind gusts and large hail would be the primary threats with any severe storms.

DISCUSSION

Issued at 409 AM CDT Sat Jul 25 2026

Heat Building Today & Storm Potential:

A warmer and moisture laden airmass has begun to push into the region overnight, a result of a slight eastward progression to the fairly pronounced upper-level ridge into the region. Consequently, expecting temperatures to respond accordingly with mean apparent temperatures in the NBM reaching around 100 degrees for portions of southeast MN where a Heat Advisory remains in effect. In addition to the heat, there are some low- end potential for isolated storms generally near and north of I-90 in Wisconsin where the thermal ridge is less prevalent and daytime heating may allow for the capping inversion, that resulted from the aforementioned warm advection, to break. If convection can manifest late this afternoon and into the evening, very favorable shear profiles noted by the elongated mid-level hodographs would suggest any isolated storms could trend supercellular, especially with around 2000-2500 J/kg of MUCAPE to work with. In this environment, large hail and damaging wind gusts would be possible with the aforementioned shear and instability accompanied with relatively steep low- level lapse rates and impressive DCAPE values to around 1500 J/kg due to a profound dry layer between 500-700mb (which may work to inhibit convection as well).

Heat & Storm Potential Increasing Sunday:

Continued south to southwesterly surface flow will continue to push a warmer airmass into the region through the weekend. As a result, there are high probabilities (60-80%) in the grand ensemble (GEFS/EC/Canadian ensemble) for heat indices to exceed 100 degrees with even some spots seeing heat indices nearing 105 degrees for Sunday. Given the confidence and in collaboration with neighboring forecast offices, have converted Extreme Heat Watch to an Extreme Heat Warning. The one caveat to this will be exactly how convection evolves on Sunday as this ridge nears...

Overall, convective evolution on Sunday appears fairly low confidence with pronounced capping in place across many of the model soundings and uncertainty on when various shortwave perturbations would traverse the area. The main concern comes later into the afternoon and evening as more favorable 500mb flow moves into northern WI with stronger forcing for ascent, however there remains uncertainty on how far east the ridge has progressed. There remains a very possible scenario that the ridge has pushed too far east through the local area that much of the evening convection would keep north and east of the area, however there are just as many solutions that would keep convection in play across the local area. In this scenario, an MCS trekking through the local area with a damaging wind gust risk would be of highest concern. Overall, it's inherently an inversely proportional relationship: if the ridge pushes further east, the confidence for dangerous heat indices (105F or greater) increases further and storm chances decrease; if the ridge struggles to push east, confidence for storms increases and dangerous heat decreases.

Heat Confidence Decreases Into Monday:

By the time Monday rolls around, the upper-level ridge hardly shifts much keeping our region in southwesterly surface flow to start the day on Monday. Consequently, expecting highs to yet again reach into the 90s for much of the local area with heat indices approaching 100 to 105 degrees south of I-90. As we head later into the day on Monday, guidance generally agrees on pushing a weak front through the area during the afternoon and evening. While confidence is fairly low (under 15% chance) for anything to develop along this front on Monday afternoon and evening at this point due to the lack of convergence along it and a pronounce dry layer in model soundings aloft, there remains respectable instability and shear in place in the event thermal profiles do become uncapped and forcing trends more favorably for convection. Have continued the previous Extreme Heat Watch Sunday night through Monday in collaboration with neighboring forecast offices given current apparent temperature forecasts only flirting near Warning criteria on Monday.

All said, confidence is fairly high for impactful heat through Monday with some questions how any convection many affect temperatures over this period. Convective trends are a bit lower confidence due to the ridge and its resultant capping not clearly defined across the area in model guidance. Shear profiles seem consistently sufficient for the development for severe storms during this period with elongated hodographs from a strong and persistent 250-500mb jet streak. But again, whether these can be utilized are heavily dependent on how much the ridge builds into the region.

Tuesday - Friday: Staying Warm with Some Storm Chances

As we head into the rest of the upcoming work week, northwesterly flow will allow temperatures to cool down just a hair but more importantly will lower our dewpoints to keep heat indices out of the 100 degree territory. With northwesterly flow returning during this period, will have to watch for any potential ridge-running shortwaves as the aforementioned upper-level ridge retrogrades slightly to the west. However, ensemble and deterministic guidance do not highlight any specific features at this point, but the pattern overall is favorable for these features to manifest.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1203 PM CDT Sat Jul 25 2026

Mostly MVFR CIGs across the region early this afternoon with some locations starting to scatter out to VFR across SE Minnesota and NE Iowa. Over the coming hours, all sites should return to VFR for the remainder of the afternoon. There are low chances for thunderstorms at the terminals overnight but confidence in northeastward extent remains too low to include with this package. NE Iowa looks to be the most likely area to see storms overnight but should confidence increase in these storms impacting the terminals, TEMPO groups may be needed in future packages. Prevailing winds will remain out of a general south/southwesterly direction at less than 12 kts.

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 morning for WIZ053>055-061. Heat Advisory from noon to 9 PM CDT Sunday for WIZ029. 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 morning for IAZ008>011-018-019-029-030.