textproduct: La Crosse

KEY MESSAGES

- Severe thunderstorms are expected (>70% chance) mainly along and north of Interstate 90 this afternoon and evening. Large hail of 2+ inches, damaging winds of 60-70mph, and heavy rainfall of 1-3" are possible from these storms. There is a 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.

- The risk for severe weather returns for the forecast for Wednesday and Friday afternoon/evenings, but details remain spare at this time.

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

DISCUSSION

Issued at 200 AM CDT Mon Apr 13 2026

This Afternoon and Evening: Severe Weather Details

Overall, there have been no major changes with forecast severe threat morphology later this afternoon and evening. Guidance over the last 24 hours has come into better agreement with the position of the surface warm front that lays out from roughly west to east between I-90 and Highway 10, which will serve as the focus for the vast majority of the severe weather later today. Increasing isentropic ascent and theta-e advection over the front should quickly overcome any residual EML by 20-22Z along the boundary, resulting in rapid convective initiation and eventually multiple supercells within a short order. These supercells are expected to grow upscale into clusters that propagate/train to the east through the evening.

Favorably curved and elongated hodographs will support large hail of 2+ inches in diameter with any rotating supercell updraft. The only hail detriment could come in the form of interactions with nearby supercells that could result in the storms taking on more of an HP structure and having the hail transition into more of a heavy rain threat. This conglomeration of cold pools, however, would increase the risk for damaging winds of 60-70 mph from these clusters as they work eastward through the evening. Training motions along the lower tropospheric front are favored once the supercell mesocyclones can become established and deviant eastward motion ensues, with individual HREF member outputs showing swaths of 2-3+" of rain where these cells train. Given the lack of moisture uptake by the vegetation/crops, such rain rates would raise the flash flood risk as well as river flooding.

The tornado risk is the most challenging to assess. Given that CI is focused for the most part right along the front, the northeast mean flow would push these supercells north of the front. However, a look at forecast HRRR profiles on the "cold" side of the boundary still shows the potential for surface- based parcels for maybe a county or so north of the wind shift, something to watch closely later this evening when assessing any tornado risk as cells undergo mergers and other interactions. The big question is whether we can get deviant eastward storm motions from any supercell before it rides over the front. The nearly eastward right-moving supercell vectors would promote continued ingestion of very favorable low level SRH. A look at forecast soundings further into the warm sector does not show much for an EML for several counties south of the warm front, so any small perturbation could kick start a discrete warm sector supercell that would have a chance at producing a longer tracked tornado. Again, while the ingredients for tornadoes appear to be in play this afternoon, whether they are realized remains to be seen and will likely be limited in space and time.

Tuesday Afternoon: Severe Weather Risk into NE IA and SW WI

The influence of the upper wave over the Dakotas moving east over southwestern Ontario and outflow from thunderstorms this evening look to shunt appreciable moisture southeastward overnight with the northern extent of the moist axis setting up across far southwest Wisconsin and adjacent parts of northeast Iowa by Tuesday afternoon. The big forecast uncertainty is just how far south the convective outflow can advance, with multiple 13.00Z HREF members lingering the moisture further north (towards I-90) compared to the global models. The CAMs typically struggle with the influence of these convective cold pools and keep the convection too far north, so am leaning on the global models which keep the severe weather threat confined to the original region noted above.

Along and southeast of this delineation, the risk for afternoon severe storms increases quickly with large hail and damaging winds being the main hazard given the unidirectional shear profiles and MLCAPE values of 1500-2500 J/kg. A deviant right- moving supercell in this kinematic environment would still ingest appreciable SRH values, so a tornado risk cannot be fully ruled out. Given that both left and right moving supercells would be favored and the general synoptic forcing mechanism, the expectation is that storms would grow upscale rather quickly and the cold pool cause the line to sink further into Iowa and Illinois through the afternoon.

Warm Week Ahead with Multiple Chances for Storms

The initial longwave responsible for our early week severe weather events begins to eject across the Front Range on Wednesday, resulting in a surface low lifting across the Mid- Missouri River Valley on Wednesday morning. There is the typical placement/low structure discrepancies at this time range, but there are hints that a triple point could set up across the forecast area during the afternoon on Wednesday, potentially introducing a tornado risk with any storms along or near this occlusion. Looking ahead to Friday, a secondary, more progressive upper tropospheric longwave trough ushers a cold front southeastward through the Upper Midwest. The degree of return flow/moisture ahead of this front is in question and will dictate any severe weather threat that accompanies its passage Friday evening.

We stay warm through the work week (highs in the upper 60s to upper 70s) with the degree of mugginess depending on which side of the oscillating baroclinic zone one finds themselves on. Along and south of this front, dewpoints will be in the upper 50s to mid-60s while values in the upper 40s to low 50s will be found to the north. This Gulf moisture sinks south for Thursday and may return back northward for Friday. We finally break the stretch of warmth for the weekend as a deeper cyclone lifts along the cold font and pulls Canadian air into the Upper Midwest. We could even see some snow over the weekend as the deformation zone wraps across the region. As is to be expected, there are significant differences in the structure and placement of the deformation zone, but about 20% of the EPS solutions bring 1-4 inches of snow mainly along and north of I-90. There is still plenty of time for the forecast to change at this range, but the run-to-run consistency of the EPS is noteworthy.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 550 AM CDT Mon Apr 13 2026

A band of IFR to LIFR ceilings and visibilities along and southwest of a RGK to DLL line should lift shortly after sunrise into an MVFR to VFR cloud deck. Attention then turns to this afternoon as a line thunderstorms develops mainly near an MKT to OWA line that then spreads east and southeast through the area throughout the evening before departing around 04-07Z. Conditions in the heavier storms could fall to IFR/LIFR with heavy rain, strong winds, and hail. Winds remain generally from the south at 5-15kts south of the line of storms and more southeast to east to the north.

HYDROLOGY

Issued at 200 AM CDT Mon Apr 13 2026

With local PWATs remaining around the 90th percentile over the next 3 days, concerns for localized heavy rain will continue. At this time, relatively higher concern for several hours of training storms focuses on the warm frontal convection discussed above. Should initiation focus along the warm front as hinted at by several CAMs, an east-west axis of west-central WI could easily see 2-3"+ of rain, an outcome reflected in 13.00z HREF PMM data. As discussed, this axis is favored (70%) to be somewhere north of the I-90 corridor which would tend to affect the Black and Wisconsin basins. Still some amount of uncertainty in the frontal position but watching the position of the warm front closely today for both hydro and severe storm concerns.

CLIMATE

Issued at 114 PM CDT Sun Apr 12 2026

Potential Record Warmth Today & Tuesday (Record/Forecast):

April 13th High Temp Warm Low ----------- -------- ------- Rochester, MN 83 (2023) / 75 59 (1941) / 54 La Crosse, WI 85 (2023) / 77 63 (1941) / 57

April 14th ---------- Rochester, MN 87 (2003) / 71 56 (1976) / 55 La Crosse, WI 90 (2003) / 76 60 (1883) / 58

ARX WATCHES/WARNINGS/ADVISORIES

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