Area Forecast Discussion

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 (40-60% 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 200 PM CDT Sun Jul 26 2026

Today and Tonight: Dangerous Heat and Severe Storms

Low clouds have finally mixed out across much of the region with some mid/high clouds rounding the crest of the ridge. Even with these high clouds, many locations are already seeing early afternoon heat indices in the high 90s to around 105 with continued climbing expected through the duration of the afternoon. Dew points in the low to mid 80s have been observed over portions of Central Iowa this afternoon and southwest winds are slowly advecting this excessive moisture into Northeast Iowa and beyond. The Extreme Heat Warning will be in effect for most of the area until 9PM as dew points in the 70s to low 80s areawide will keep heat indices over the century mark well into the evening hours.

Given the very warm and unstable airmass in place over the region, storms are expected to fire across portions of Northern Minnesota/Wisconsin in the vicinity of Lake Superior later today as a shortwave impulse rounds the ridge and starts to make its way southeast into the Upper Midwest/Great Lakes region. This looks to be the main focus for thunderstorm development but other weaker impulses across the Dakotas/Central Minnesota could set some storms off later this afternoon - though confidence in this scenario is lower given convective debris from residual storms out west for areas along the Minnesota/Iowa border. Forecast soundings across Central Wisconsin show ample instability with 2000+ J/kg of MUCAPE and 35-50 kts of effective shear just outside the periphery of the ridge. Initial supercells across Northern MN/WI are expected to grow upscale into more of an MCS type feature. Initial supercells would pose an all-hazards risk, though primarily large hail and damaging winds as 0-1 km shear and helicity is not looking overly favorable for tornadoes. Steep lapse rates aloft around 8 deg C/km would favor large hail growth but warm temperatures aloft might temper this risk overall. Winds look to be the main threat with forecast DCAPE values between 1000-1500 J/kg. As we move through time and storms congeal into more of a cluster, wind will become the prevailing threat, especially as this looks to be happening into the evening/overnight hours where the inversion will start to set up and storms will start to become more elevated in nature. This cluster is expected to work its way south/southeast through Wisconsin into the overnight hours before moving off towards the Lake Michigan coastline.

Monday and Monday Night: Heat Risk Continues and Storm Potential

Skies will start to clear out behind the remnants of the morning system and with dew points still in the 70s to low 80s across the region, heat indices are once again expected to climb to between 100- 110 for many tomorrow, with the warmest conditions expected across Northeast Iowa and Southwest Wisconsin. Locations further north and west across Southeast Minnesota will start to see a slight reprieve by the end of the day as a cold front starts to move through the region, shifting winds to the northwest around noon. Though ambient temperatures will still climb into the 90s for many, this will allow some slightly drier air to start to mix in from the northwest, which will start to fend off some of those upper 70s dew points, helping to lower those across Southeast Minnesota. The rest of us will unfortunately not feel the reprieve until Tuesday when temperatures are in the 80s and dew points are back in the 60s.

Lingering activity from the overnight hours across West Central and Southwest Wisconsin could pose a marginal severe risk as it will be in an area of warm advection. The better lift will have passed with the shortwave impulse earlier but enough lingering instability will allow for a marginal hail and wind risk to persist into the morning hours for our far eastern zones. Overall concern later in the day tends to shift to the east as the upper trough and shortwave impulses take aim more at the Great Lakes/Michigan than western Wisconsin though some spotty showers and storms could pop up across Central/Southwestern Wisconsin tomorrow afternoon on the periphery of the ridge. Confidence in activity this far west tomorrow is much lower (around 20%) with most likely staying dry.

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 TUESDAY/

Issued at 640 PM CDT Sun Jul 26 2026

VFR conditions are expected through the TAF period with the potential for storms east of the Mississippi River late this evening and into the overnight. Overall confidence has been decreasing for overnight storms reaching the Mississippi River, however have opted to maintain a prob30 at KLSE as some CAMs still suggest this possibility. If any storms do manage to reach the TAF site, strong wind gusts may occur, however the highest probabilities for storms overnight are currently north and east of I-94. Otherwise, a frontal passage during the afternoon on Monday will switch winds from southerly to northwesterly and will increase to around 10-15 kts.

ARX WATCHES / WARNINGS / ADVISORIES

WI...Extreme Heat Warning until 9 PM CDT Monday for WIZ041-042- 053>055-061. Extreme Heat Warning until 9 PM CDT this evening for WIZ032>034. Heat Advisory until 9 PM CDT Monday for WIZ032>034. Heat Advisory until 9 PM CDT this evening for WIZ017-029. Heat Advisory until 9 PM CDT Monday for WIZ043-044. MN...Extreme Heat Warning until 9 PM CDT Monday for MNZ096. Extreme Heat Warning until 9 PM CDT this evening for MNZ079- 086>088-094-095. Heat Advisory until 9 PM CDT Monday for MNZ079-086>088-094-095. IA...Extreme Heat Warning until 9 PM CDT Monday for IAZ008>011-018- 019-029-030.