textproduct: La Crosse

KEY MESSAGES

- Sunday morning storm chances progress from west to east through the local forecast area with large hail and damaging winds as the main threats within strongest storms.

- Extreme heat indices of 100+ degrees expected Monday and Tuesday with confidence temporarily decreasing for Wednesday before returning later in the week.

DISCUSSION

Issued at 111 AM CDT Sun Jun 28 2026

Strong to Severe Storms Possible This Morning:

Line of storms progressing east through the Northern Plains at 28.04Z expected to continue through the overnight, nearing the Upper Mississippi River Valley this morning. The extremely phased negatively tilted upper level trough on GOES WV imagery will cause additional forcing and cyclogenesis through the morning hours collocated with an enhanced low level moisture gradient over the Mid-Missouri River Valley in 28.00Z soundings. The northern edge of the accompanying instability gradient will be capable of strong to severe storms, elevated along the nose of the 700 mb jet.

Elevated storms will limit overall hazards to damaging winds and potentially very large hail should the northern edge of instability collocate with highest shear along the frontal boundary. The severe storm threat progresses east through the forecast area through the early afternoon hours, depending on exact location of frontal boundary and subsequent drier 700mb air punching northeast. Discrepancies between high resolution models in exact location of highest reflectivity through the morning hours hinges on the location of this convective- inhibitive airmass building northeast related to the location of ribbon of enhanced low level moisture.

Lingering Storm Chances Increase Monday Night:

Additional storm chances through Sunday are possible as the low level jet intensifies with enhanced low level moisture through the Upper Mississippi River Valley. Currently forecasted speed convergence zone quickly progresses north of the local forecast area, keeping highest storm probabilities along the western, northern, and eastern peripheral counties Sunday afternoon, evening, and night; respectively.

Storm Chances Monday Night:

Confluence of the upper/mid level pattern through Monday amplifies a driving upper level jet streak from the Rocky Mountain West through south-central Canada, amplifying and advecting the extratropical cyclone wobbling over the Rocky Mountain West to the east-northeast. Contention between the area of lower heights colliding with the anomalous upper level heights limits overall confidence for eastern extent of resultant linear storms forming through the Northern Plains potentially subsequently affecting the Upper Mississippi River Valley. A more eastern solution to the area of higher heights would permit stronger storms farther east, potentially affecting the local forecast area.

Dangerous Heat Through Midweek:

The anomalous (max percentile - SPC Climatology) area of higher heights centered over the southeast through the start of the week will drive 25C 850mb temperatures through the Upper Midwest initially Monday, 13C above Model Climatology. Resultant surface temperatures in the 90s with the 70 degree isodrosotherm strewn north of the forecast area will cause Heat Indices of 100+ degrees Monday and Tuesday initially. A slight reprieve remains possible on Wednesday as most anomalous warmth advects east-northeast through the Great Lakes within southwest flow and storm chances increase. Therefore, have issued /initial/ Extreme Heat Warning through Tuesday until confidence for Wednesday increases.

Resurgence of similarly anomalous low level warmth through the end of the week returns Extreme Heat concerns across the Upper Midwest.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 111 AM CDT Sun Jun 28 2026

Main forecast challenge for this cycle involves the evolution and impacts of the convective complex over the central Dakotas as of 28.06Z. High-res model guidance generally features a weakening trend in the convection as it propagates eastward across southern Minnesota and northern Iowa through 28.15Z. If the storms remain intact, they will bring IFR/LIFR visibility and MVFR to IFR ceilings as they pass the terminals. There is a potential for strong wind gusts of 30-50 knots along with small hail. Previous forecast appeared to have a good handle on the forecast details for now. Will continue to monitor over the next several hours and may need to introduce lower flight categories than the current forecast indicates. Thereafter look for a return to VFR conditions which will persist into late evening. A few models suggest mist and fog development after 29.03Z and a potential for scattered showers. Felt the potential for those weather types was too low to include in the forecast at this time.

CLIMATE

Issued at 1241 AM CDT Sat Jun 27 2026

With 850 mb temperatures 2 to 2.5 standard deviations warmer than normal, there will be a potential for some warm low temperature records to be tied or broken south of Interstate 94 from Monday into Wednesday.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Extreme Heat Warning from 8 AM Monday to 8 AM CDT Tuesday for WIZ029-032>034-041-042-053>055-061. MN...Extreme Heat Warning from 8 AM Monday to 8 AM CDT Tuesday for MNZ079-086>088-094>096. IA...Extreme Heat Warning from 8 AM Monday to 8 AM CDT Tuesday for IAZ008>011-018-019-029-030.