textproduct: La Crosse

KEY MESSAGES

- Severe thunderstorms are expected (>70% chance) across southeast Minnesota and western Wisconsin this afternoon and evening. Large hail of 2+ inches, damaging winds of 60-70mph, and heavy rainfall of 1-3" are all possible from these storms. There is narrow window of opportunity for a tornado threat, but if this threat is realized, a stronger tornado (EF2+) cannot be ruled out.

- Additional severe storms are likely over northeastern Iowa and southwestern Wisconsin Tuesday afternoon. Large hail of 2+ inches will be the biggest risk with these storms, but wind and heavy rain hazards remain on the table. Where exactly storms form will be dependent on how storms today evolve.

- Additional severe weather is possible both Wednesday and Friday. Details will become more clear as we get closer.

- Warm week ahead with high temperatures in the upper 60s to upper 70s, cooling down for the upcoming weekend.

DISCUSSION

Issued at 1237 PM CDT Mon Apr 13 2026

Today: Severe Weather This Afternoon and Evening

A surface low sitting over northeast Nebraska continues to make its way northeastward towards northern and eventually northeast Iowa. The low-level jet begins to increase by mid afternoon and reaches its strongest point during the evening with winds of 35 to 45 kts at 850 mb. Theta-e advection increases this afternoon, helping to reduce or knock out any remaining EML by the mid afternoon. This will result in rapid convective initiation along and north of the I- 90 corridor. Recent model trends have also started to show some convective initiation starting earlier this afternoon in northeast Iowa and far southwest Wisconsin. This will be something to monitor to see how it affects the rest of the afternoon. Discrete supercells look to be the dominant storm mode as the event gets underway. With very high mid-level lapse rates of 7.5 to 8.5 C/km and plenty of MUCAPE (2000 to 3000 J/kg), as well as curved and elongated hodographs, large to very large hail will be the primary threat with these initial storms. Right now, these storms appear to be strongest around the I-94 corridor in western Wisconsin and eastern Minnesota. There could always be some sort of wiggle with where exactly these storms end up as where these storms occur will be important for the next round of storms. Once these storms begin to congeal into a line, then the hail threat would diminish, however a wind threat would then be the primary threat.

Looking at the tornado risk, the main initial risk will be right along the warm front, however given the favorable shear with a couple counties of the warm front, the tornado threat does remain for those locations, especially if cell mergers or other interactions occur. The early afternoon convection could have a tornado threat too as it rides along an elevated warm front. The one caveat to this is that there remains quite a bit of CIN to overcome to make these storms surface based, therefore the primary risk would be hail with these storms. For the afternoon and early evening, if storms can attach themselves to the warm front and have a somewhat deviant eastward storm motion. With the amount of low level SRH available, these right moving supercells would have the best chance at ingesting the most SRH. Even further south of the warm front provides a decent tornado potential given that by the mid afternoon, there will be little to CIN needed to overcome so any boundary or perturbation that kicks off a supercell would also have a tornado potential. Lastly, as the supercells congeal into a line and shift southeastward across portions of northeast Iowa, southeast Minnesota and western Wisconsin the surface low moves up behind this line. This extra lift with a close to perpendicular 0-3km shear vector would indicate a QLCS tornado potential as this line propagates through the forecast area. In addition to this tornado threat, the wind threat would increase as the cold pools begin to form along the line. Make sure to stay tuned as we will have AFD updates during the afternoon and evening.

With these repeated rounds of storms, there is also a heavy rain potential. PWATs of 1 to 1.3" are in the 99th percentile based on the NAEFS. This means that there will be plenty of potential moisture for storms to use up. The 12Z HREF LPMM shows a wide swath of 1 to 3" across western Wisconsin from I-94 down towards the I-90 corridor. With this being a convective nature compared to stratiform, there will be potential for the heavy rain corridor to shift. As a result we have issued a Flood Watch for most of western and central Wisconsin given that soils are saturated from the recent and that the 6 hour flash flood guidance from the NCRFC is roughly 2 to 3.5" across the watch area.

Tuesday: Severe Weather Potential for Northeast Iowa and Southwest Wisconsin

Storms from Monday will be out of the local area by early Tuesday morning. An upper level wave moves over the Upper Midwest and in conjunction with the cold pools from overnight, the moisture gets pushed southeastward setting up a moisture axis in far southwest Wisconsin and into northeast Iowa. The main uncertainty for Tuesday is how far south does the outflow from todays storm reach and if the boundary can shift northward at all. The 15Z RAP shows this via the theta-e advection where the boundary shifts into Grant county and gets pushed slightly further north into Crawford and Richland counties in Wisconsin and Allamakee, Clayton, Fayette counties in Iowa. Similar to today, the mid level lapse rates for Tuesday remain high, around 7.5 to 8.0 C/km, and there will be even more shear than today due to the upper level wave moving overhead. This would indicate a large hail risk being the primary threat. That being said, with the amount of low level SRH available, if a right moving deviant supercell can get going, this will provide a tornado risk. As cold pools develop from the storms in northeast Iowa and southwest Wisconsin, this would push any severe threat out of the forecast area by the middle of the evening.

Wednesday-The Weekend: Warm Week with Multiple Storm Chances

Heading into Wednesday, an upper level trough shifts over the central Plains and the Upper Midwest. There will be some morning convection in Iowa and into far southwestern Wisconsin. This may inhibit any severe potential, however a surface low shifts into central and into northern Iowa by the evening providing more lift as theta-e advection increases during the day. Based on the NAM and GFS there is a potential triple point that sets up in northeast Iowa, far southeast Minnesota, and southwest Wisconsin that would introduce a tornado threat near this occlusion. Other than this threat, there will also a be damaging wind and hail threat across the aforementioned areas.

Thursday looks to be dry as we begin to transition back to southwest flow by late Thursday evening. The low-level jet increases during Friday afternoon helping to bring in higher PWATs. Based on the NAEFS, the PWATs for Friday are already in the 90th percentile for this time of year. Another severe weather chance is possible as we have this increased moisture ahead of a cold front that moves through the area late Friday night. Temperatures through the week will remain in the 60s and 70s until Saturday. Plenty of stormy weather is expected this week so make sure to stay tuned for further updates regarding todays severe weather threat as we will have updated discussions throughout the afternoon and evening highlighting any changes to the forecast.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1237 PM CDT Mon Apr 13 2026

Mostly MVFR to VFR conditions across the area currently with some lingering fog creating some IFR/LIFR CIGs/visibilities across SE Minnesota. All sites should improve to at least MVFR by mid afternoon before we start to see storms develop along a frontal boundary, currently just north of the terminals. Storms will likely create MVFR/IFR CIGs and visibilities as they move east across the region this evening and into tonight. After the storms move out an area of low stratus and fog will redevelop, especially across NE Iowa and SE Minnesota. This will mainly impact the KRST terminal but KLSE could see a few hours of BR, and potentially FG. Conditions should clear out through the morning hours tomorrow.

HYDROLOGY

Issued at 1237 PM CDT Mon Apr 13 2026

Heavy rainfall potential for today as PWATs remain in the 99th percentile. HREF LPMM shows a wide swath of 1 to 3" along and north of I-90. Due to the convective nature of these storms for today, the heavy rain swath could shift. With saturated soils, if 2 to 3" falls, this may cause flooding to occur, especially with 6 hour flash flood guidance of 2 to 3.5". Where the models have the heavy rain band set up right now, would mostly impact the Black and Wisconsin River basins. Another thing to watch out for is mudslides as we have not greened up so any area that has hills alongside a road could be susceptible to a mudslide.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Flood Watch from 4 PM CDT this afternoon through Tuesday morning for WIZ017-029-032>034-041>044-053-055. MN...None. IA...None.