textproduct: La Crosse

KEY MESSAGES

- Dangerous heat continues Tuesday with indices 95 - 105+ degrees across the local area. Lower confidence for Wednesday depending on precipitation chances.

- Periodic storm chances Tuesday, Tuesday night, Wednesday, and Wednesday night. Strong to severe storms possible Wednesday albeit location and strength remain forecast discrepancy/unknown.

DISCUSSION

Issued at 1139 PM CDT Mon Jun 29 2026

Persistent Pattern Wavering Confidence Into The Weekend:

The strong synoptic anticyclone took shape over the southeast CONUS on Monday with maxima to record 500 mb heights in 30.00Z ROABs seen at ILX, ILN, RNK, FFC, BMX, JAN, SGF, and LIX, while centered over OHX. LREF confidence remains high (100%) for these anomalous heights to remain centered over the southeast through midweek gradually shifting east to the Mid-Atlantic Coast for Independence Day before widespread inter/intra ensemble model disagreement. Additional, earlier inter-ensemble disagreement regarding the synoptic pattern across the central CONUS affects local forecast confidence through midweek.

Extreme Heat Tuesday & Storm Chances:

High confidence (80%) for daytime high temperatures from the high 80s to mid 90s for Tuesday, similar as Monday, with low to mid 70 degree surface dewpoint temperatures. Lower confidence in rebounding of increased surface dewpoint temperatures along our northwestern periphery after overnight convection and again Tuesday night with additional similar precipitation chances expected along western and northern periphery. Additional, zonally oriented area of storms also possible overnight into Wednesday morning depending on frontal boundary location in relation to strength and location of area of higher pressure.

Low-Medium (18-41%) Confidence Wednesday:

Most recent GEFS (29.18Z) run threw a wrench in model agreement through midweek by limiting synoptic forcing for any precipitation and storms unlike other ensembles or its previous runs. The resultant shunt north of higher precipitation and storm potential along and north of the forecast area is unlike the EPS & GEPS which paint high (75-100%) probabilities for measurable precipitation across much of the forecast area Wednesday afternoon and night. Highest amounts and probabilities seen in the EPS with 80-100% probabilities for 0.5" in 24 hours ending at 12Z Thursday.

Strong to Severe Storms Possible (14%-34%) Wednesday:

Strong to severe storms remain possible on Wednesday albeit low confidence given the aforementioned spread in potential scenarios. Machine learning severe hazard models exhibit this dependence on their parent models as GFS solution exhibits a wider coverage and hazard threat while ECMWF associated models paint the southeastern half of the forecast area with 30-45% probabilities. While primary threat would be damaging winds, tornado risk in latter AI models depend on ability of clearing skies given ongoing precipitation probabilities. Large hail would be the lower, secondary risk given the very warm atmosphere raising a melting hail signal.

Temperatures Through Midweek:

Therefore, the GEFS solution is a few degrees higher for temperatures than other LREF members with daytime highs persisting in the low 90s for Wednesday, potentially requiring headline issuances whereas other runs and models abate apparent temperatures into Heat Advisory or lack thereof, depending on cloud cover and storm coverage dropping dry bulb temperatures to wet bulb temperatures. Therefore, have abstained from extending current headlines or raising additional headlines through midweek given the potential /slight/ reprieve in most extreme, dangerous heat indices.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1238 AM CDT Tue Jun 30 2026

During the past hour, showers and isolated storms have developed across northeast Iowa, southeast Minnesota, and west-central and north-central Wisconsin. This is in response to moisture convergence associated with a 40-knot 850 mb jet and upper level divergence associated with the right entrance region of a 50-knot 300 mb jet. Expect that this precipitation will gradually dissipate and move out of the area in about 2 hours.

Afterward the focus will be on a MCS in northeast Nebraska. This should approach the area toward day break. Current thinking is that it will be dissipating as it approaches and moves northeast through southeast Minnesota, and west-central and north-central Wisconsin.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Extreme Heat Warning until 9 PM CDT this evening for WIZ029- 032>034-041>044-053>055-061. Heat Advisory until 9 PM CDT this evening for WIZ017. MN...Extreme Heat Warning until 9 PM CDT this evening for MNZ079- 086>088-094>096. IA...Extreme Heat Warning until 9 PM CDT this evening for IAZ008>011-018-019-029-030.