textproduct: La Crosse

KEY MESSAGES

- Dangerous heat today across much of the area with heat indices reaching 105-115 degrees south of I-94. Heat will likely continue into Monday with increased probabilities (50-70%) for heat indices over 100 degrees south of I-90.

- Increasing confidence for storms this evening and overnight with highest probabilities (40-70% chance) east of the Mississippi River. Some storms may be severe with damaging wind gusts and large hail being the primary threats.

DISCUSSION

Issued at 300 AM CDT Sun Jul 26 2026

Dangerous Heat Today:

The eastern extent of an upper-level ridge extending into the local area will dictate daytime heat indices and storm chances. Currently, the recent HREF has very high probabilities (over 80%) for heat indices to reach over 100 degrees areawide with respectable probabilities (30-70%) for heat indices to reach over 105 degrees south of I-94. This is mostly due to the fact that the NBM has fairly high confidence (70-100%) for dewpoints reaching over 75 degrees for areas south of I-94. While 80 degree dewpoints are likely (30-70% NBM), resulting in heat indices over 110 degrees, have tempered 85 degree dewpoints from select sites in northeast Iowa in collaboration with neighboring forecast offices. Given the expected dangerous heat, an Extreme Heat Warning is in effect for areas along and south of I-94.

Storm Potential Today:

The main forecast challenge will be how convection develops later into the afternoon and into the evening. The ongoing signal in CAMs is for early evening convective initiation from a shortwave impulse and enhancing upper-level jet streak progressing into northern WI. The main remaining question is exactly how far west convective initiation occurs in lieu of the aforementioned upper-level ridge. Overall, confidence is increasing for portions of western WI at risk for storms as much of the 00z CAMs favor convecting east of the Mississippi River.

A fairly conducive severe weather environment persists as storms shift southeast due to stronger middle/upper-level flow in the recent RAP supports both MCS maintenance and/or supercells with any discrete storms. Consequently, current confidence for both large hail and damaging winds as main threats, even some very strong wind gusts (Over 74 mph) with favorable DCAPE values over 1000 J/kg, especially should any bowing segments occur in linear modes.

Should the aforementioned ridge axis advect farther east, convection will likely be east of the local area due to capping from warmer temperatures aloft. Although, the recent 00z HRRR suggested additional storm development farther west through the Mississippi River Valley due to propagating outflow boundaries.

Summarily, a fairly complex setup this evening and overnight into Monday, although confidence is increasing slightly for storms to develop by evening across portions of west/north- central WI with a risk for damaging wind gusts and large hail. Thinking that extreme heat is high confidence (over 80%) as confidence for afternoon storms is lower at this point with the higher confidence period being more into the evening hours in light of the recent CAMs and when the stronger flow aloft works its way in.

Heat Risk Continues Monday:

As we head into Monday, a weak surface boundary will push into the area during the afternoon and evening hours which will re-establish northwesterly flow across the local area. As a result, expecting dewpoints to decrease behind this front which should keep heat indices tempered slightly for areas north of I-90. That being said, the grand ensemble (GEFS/EC/Canadian ensemble) has been fairly consistent with high confidence (50-70% chance) for heat indices over 100 degrees for areas south of I-90, thus have upgraded the ongoing Extreme Heat Watch to an Extreme Heat Warning. Should diurnal timing and progression of the frontal boundary affect realized Heat Indices, these areas may require additional amendment to an Advisory or potentially removal. Given varying criteria with more southern latitude forecast offices that near climatologically warmer thresholds, collaboration in neighboring forecast offices persisted Extreme Heat Watch.

Monday Storm Potential:

Some storms cannot be ruled out (10-30% chance) in west- central WI for Monday morning and into the afternoon which may contain some severe threat, however this window would be relatively brief as the the main forcing with the associated shortwave pushes east of the region fairly quickly. Would also need to watch later into the afternoon with the aforementioned weak boundary that pushes through which could initiate storms as well which would be accompanied with a severe threat as the aforementioned upper-level jet streak remains in place.

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 /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1215 PM CDT Sun Jul 26 2026

Mostly VFR conditions present across the area with a few sites still lingering at MVFR from morning cloud cover. Low clouds will continue to mix out with all sites returning to VFR in the next hour or two. From then, generally VFR conditions should persist for most locations outside of those impacted by some storms this evening/overnight and some potential valley fog along the Wisconsin River Valley. The main concern through the period will be the aforementioned storm potential, which is looking to be more focused to the east of the Mississippi River in Central Wisconsin. Did add some PROB30s to the KLSE TAF as they will be on the periphery of the area that could be impacted by the expected cluster(s) of storms overnight. Should confidence in location increase/decrease into the evening, this will likely need to be adjusted. Chances for rain/storms at the LSE terminal should diminish after 12Z. Confidence in any storms west of the river remains too low to include any mention at the KRST terminal so have left them dry. Winds will remain out of a general southerly direction for much of the period before veering more to the west by late tomorrow morning.

ARX WATCHES/WARNINGS/ADVISORIES

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