314 FXUS63 KARX 291840 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 140 PM CDT Mon Jun 29 2026 .KEY MESSAGES... - Dangerous heat persists through at least Wednesday, but oppressive temperatures/humidity linger through late week. An Excessive Heat Warning remains in effect for most of the region while a Heat Advisory remains in effect for Taylor County in Wisconsin. - Periodic storms are possible this week (20-40%), but timing/location remains uncertain. Storms that develop could become strong to severe. && .DISCUSSION... Issued at 139 PM CDT Mon Jun 29 2026 This Afternoon - Tuesday: Dangerous Heat and Storm Potential Dangerous heat is expected areawide over the next 24-36 hours. A very moist airmass remains in place this afternoon with dewpoints in the mid to upper 70s across much of the area which is expected to remain in place throughout the day Tuesday. Overall expectations are for temperatures to climb into the low to mid 90s given 850hPa temperatures of 20-22C, resulting in heat indices around 75F tonight and in the upper 90s to mid 100s during the day Tuesday. There is some concern for strong/severe storms tonight, mainly northwest of a line from Charles City, IA to Wausau, WI (10-30%) though expectations are for most of (if not all of) these storms to miss our area due to strong capping in place given 700hPa temperatures of 12+C. However, there are some CAM solutions suggesting a line of convection moves west-east through the region after midnight on the nose of an strengthening nocturnal low level jet and 850hPa moisture transport. Confidence is low in which scenario will win out, but currently leaning towards most storm activity remaining out of our area as this has the greatest consensus amongst model guidance. Regardless, if storms do affect the area tonight, the primary hazard will be damaging winds. Additional concern for strong/severe storms comes Tuesday afternoon, mainly north of I-94 (20-30%). The expected heat and humidity Tuesday will continue to support the volatile atmosphere in place with MUCAPE values exceeding 3000 J/kg in most model solutions along with effective bulk shear of 30-35kts. Within this environment, a surface boundary associated with the surface low over southern Canada lays out and stalls from northeast to southwest from northern Wisconsin to northern Iowa with the favorable atmosphere in place ahead of it. Above the surface features, a ribbon of 700hPa positive vorticity and divergence associated with the right entrance region of a nearby jet core could support storm development, although the overall QG forcing is fairly weak and nebulous. The biggest question is if convective initiation can even occur in this environment. 700hPa temperatures remaining around 12C may make it challenging for convection to develop, especially given the nebulous forcing. Many CAM solutions do suggest the bulk of development remains across northern Wisconsin. There is also the issue of how the storms overnight evolve and their influence on where mesoscale boundaries set-up which would also influence convective initiation. All of this said, if convection is able to develop, expectations are for damaging winds to be the primary threat. The aforementioned warm temperatures aloft make large hail unfavorable as WBZ heights are forecast to be above 10kft, but certainly can't rule out some smaller stones up to 1 inch given the ample instability. Wednesday - Friday: Hot/Humid Conditions Continue and Storm Chances Wednesday morning brings additional strong/severe storm potential (50-70%) along the aforementioned stationary boundary as it lays out west-east across the region. A subtle shortwave lifts northward atop this feature with ample moisture remaining in place. MUCAPE of 2500+ J/kg will exist along the boundary with 30-35kts of effective bulk shear. Damaging winds and hail up to 1 inch again seem possible with storms that develop during this period. Slightly cooler temperatures are depicted in ensemble suites Wednesday through Friday as the upper ridge begins to shift ever slowly eastward although temperatures still remain in the upper 80s to low 90s. The evolution of any possible convection may also act to further temper afternoon highs. However, dewpoints remain in the low to mid 70s and with little temperature relief overnight, confidence is high in heat impacts lingering through at least Wednesday. Holiday Weekend - Early Next Week: Seasonable, Additional Showers and Storms As we head into the holiday weekend, the upper level pattern becomes more zonal as compared to today/Tuesday allowing various shortwaves to traverse the mean 500hPa flow. These shortwaves will tend to knock down temperatures aloft as well as at the surface with an overall cooling trend noted in the 29.00z LREF. Surface highs fall into the low to mid 80s, near normal for this time of year, although there is a fair degree of uncertainty in exact temperature values as the 25th-75th percentile spread is around 5-10 degrees with some outliers still suggesting the 90s could be in play. Additional shower and storm chances also exist over the holiday weekend with the 29.13z NBM currently suggesting 30-60% probabilities for measurable rainfall, but there is still plenty of variation to work out over the coming days. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1231 PM CDT Mon Jun 29 2026 Gusty southerly winds will persist through the TAF period with VFR conditions expected. As a low pressure system slides across the Upper Midwest, there is a low chance (20%) for passing showers after midnight tonight. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Extreme Heat Warning until 9 PM CDT Tuesday for WIZ029-032>034- 041>044-053>055-061. Heat Advisory until 9 PM CDT Tuesday for WIZ017. MN...Extreme Heat Warning until 9 PM CDT Tuesday for MNZ079-086>088- 094>096. IA...Extreme Heat Warning until 9 PM CDT Tuesday for IAZ008>011-018- 019-029-030. && $$ DISCUSSION...Falkinham AVIATION...JAW