textproduct: La Crosse

KEY MESSAGES

- Widespread precipitation and storm chances Wednesday morning progress from northwest to southeast. Locally strongest storms from western through southern peripheral counties in southeast Minnesota and northeast Iowa into southwest Wisconsin could potentially (15%-30%) become strong to severe with large hail and damaging winds as the main threats.

- Low confidence in lingering storm chances, some strong to severe, through the late morning into early afternoon. A lot will depend on the amount of clearing skies permitting local storm initiation through the late afternoon and early evening as low pressure passes over the forecast area, driving additional linear & potentially scattered semi-discrete storms. Large hail and damaging winds will continue to be the main threats with tornado threat dependent on amount of destabilization. - Low confidence in precipitation and storms Thursday slightly increases for Friday as transient precipitation darts from northwest to southeast.

DISCUSSION

Issued at 121 AM CDT Wed Jun 17 2026

Ongoing Observations & Morning Storm Threats:

Surface observations tonight exhibit two areas of cyclonic rotation from the Central through the Northern Plains, evidence of cyclogenesis through Wednesday evening. Interaction between these lows through the morning will drive initial local precipitation and storm chances as they converge and morph into a elongated, stronger low before eventually further phasing into a double-barrel low by Wednesday night.

As the southern low progresses east-northeast through the early morning hours, tightening of the attendant warm sector will aide in rapid intensification of the collocated low level jet, resulting in narrow 15-20 ubar/s corridors of ascent near the 295K isentropic surface. Nocturnally anticyclonic curving of the low level jet aided by east-southeast advection of the northern low along an enhanced upper level jet streak in GOES derived upper level winds due to synoptic confluence in GOES WV imagery loops will result in strongest storms through the early morning hours also sagging east- southeast. Current trajectories of this quickly intensifying and changing pattern grazes stronger storms along our southwestern peripheral counties in northeast Iowa and potentially into southeast Minnesota. These strongest storms could quickly become severe with large hail and damaging winds as the main threats.

Severe Storm Chances Through Wednesday:

Details (i.e., strength, timing, coverage) surrounding additional subsequent storm chances through the rest of Wednesday depends on northern and eastern extent of energy consolidation between low pressure areas, evident in disagreement between high resolution models (17.00Z).

A more phased orientation between low centers through the early morning before consolidating into a stronger, elongated low would result in a southern shunt of increased moisture, limiting /highest/ local overall severe threat (NAM/Fv3 17.00Z).

However, more HREF members (HRRR/ARW 17.00Z) solutions suggest a less-phased, more meridional orientation and interaction between converging low level areas of lower isoheights allowing increased moisture to advect farther north into the forecast area, causing unstable air (1000-1500 J/kg SBCAPE) to bifurcate the southern half of the forecast area, increasing strong to severe storm chances through the afternoon and evening as the eventual low center drives breaking linear storms across the forecast area.

Additional storms through the late morning into the early afternoon cannot be ruled out as well, potentially strong to severe should the PBL recover /if/ skies find a way to clear in the wake of departing storms. Given the higher confidence for morning preciptiation, this is a lower confidence scenario but available instability and shear values suggest a scenario to remain cognizant of through the daytime hours.

Main concern for large hail and damaging winds with later storms as well. Tornado risk will hinge on amount of clearing to destabilize the PBL, subsequently overcoming any lingering inversion causing SBCIN/MLCIN.

Low Confidence For Precipitation Thursday:

Northern extent of increased moisture advection through early Wednesday morning also affects precipitation chances through Thursday as HREF (17.00Z) allude to limited (100-300 J/kg) of SBCAPE advecting southeast along the southwest-northeast oriented frontal boundary with meager low level (850mb) cold air advection. Therefore, have increased a line of low PoPs (<24%) away from NBM based on high resolution solutions albeit a bit more spatially and temporally agreeable than individual member solutions.

Friday Precipitation Chances:

The tail end of the extended ribbon of mid level positive vorticity lifts slightly northeast as the synoptic pattern begins to change, causing additional, albeit transient, precipitation and storm chances to dart across the forecast area for Friday. Low confidence in storms as most (75%) members of EPS (16.18Z) suggest 500-1000 J/kg of MUCAPE across the area while GEFS (17.00Z) limits SBCAPE below 500 J/kg somewhere near/over the forecast area. Accompanying shear values will be spatially limited in the lower levels, primarily and strongest unidirectionally in the mid levels from the stronger mid to upper level winds.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1229 AM CDT Wed Jun 17 2026

VFR conditions currently present across the region. Areas of showers and storms are currently moving southeast through the northern Great Plains and into the Midwest. Most of these are scattered and fairly light in nature with the heaviest activity expected to remain south and west of the terminals in Central Iowa. As such, have gone with some TEMPO groups to cover the shower activity early this morning. Another round of rain and storms will develop this afternoon, though there is significant uncertainty with this batch as it will hinge quite a bit on the morning activity and how quickly it vacates. The chance for PoPs will remain quite high so have gone with prevailing showers but instability is less certain so have gone with PROB30s for the thunderstorm coverage. The afternoon prevailing groups may need to be adjusted to TEMPOs as coverage may be a bit more scattered in nature given latest hi-resolution CAMs. MVFR to IFR CIGs will build in during the morning hours and continue through the end of the period with generally MVFR to IFR visibilities expected with both batches of showers and storms. Rain will start to come to an end by late in the period, moving off to the east after 00Z. Southerly winds will pick up early this morning and veer quickly to the west/northwest behind a frontal boundary that passes through this afternoon. Gusts will gradually diminish into the evening hours but should hang on through the end of the period.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...None.