textproduct: La Crosse

KEY MESSAGES

- The risk for severe storms across the region is increasing for this afternoon with all hazards possible. The main uncertainty in the forecast revolves around when the storms form, which will dictate what areas see a certain threat.

- Near to below freezing overnight low temperatures through the weekend. A few snow flurries cannot be ruled out on Saturday, mainly along and northeast of I-94.

- Dry conditions and warming temperatures expected for the start of next week.

DISCUSSION

Issued at 221 PM CDT Thu Apr 16 2026

Severe Storms Friday

A quiet and sunny Thursday is expected to give away to a rather stormy Friday across the area. A busy forecast is expected with a potentially significant severe weather event across the area. So lets get into the details.

A deep trough is expected to move into the Rockies early tomorrow morning, gradually sliding east into the plains. At the surface, a series of lows will extend from North Dakota into the Central Plains with a cold front connecting them. As the upper trough moves east, ascent in the southwest flow ahead of it will overspread the area, interacting with the cold front at the surface. A stout warm sector is expected to develop out ahead of the cold front as moisture surges northward with increased low level southerly flow bringing 60+ degree dew points into the region late tomorrow morning. Combined with 70-80 degree ambient temperatures, this will allow for 2500-3500 J/kg of CAPE to develop by early afternoon with a weak capping inversion in place. Once this capping erodes with daytime heating, its essentially game on for storms to form along and ahead of the front with the combined upper level ascent and surface forcing from the front. Storms are expected to go up during the afternoon, quickly becoming supercellular and likely severe amid 30-50 kts of effective shear. Initial threats with this activity will be the potential for large to very large hail given steep mid level lapse rates and significant cooling aloft allowing for ample CAPE in the HGZ. The other main threat with this supercell activity will be the potential for strong tornadoes. An 850-700 mb jet around 40-60 kts out of the south will help to increase low/mid level curvature in the hodograph. If surface flow can back more to the southeast, a solution put forward by the 16.12 NAM, this would create even more low level helicity. And given the proximity to the surface low, an enhanced corridor of tornado potential is looking more likely across portions of Wisconsin and Iowa tomorrow. Eventually storms will grow upscale into more of a QLCS type feature with the threats transitioning to damaging winds and QLCS tornadoes (tornadoes will be a threat no matter the storm mode tomorrow).

The main point of contention will be how early the low level capping erodes and storms can start to initiate. Current thinking is that this will take place during the early afternoon right around the Mississippi River. The timing of the front will also be a point of contention because is storms fire more to the west, they may become more linear by the time they get to our eastern zones (though this is a low confidence scenario at less than 20%). If storms fire farther to the east than zones to the west might not even see any severe weather. So the placement of initiation will be a key detail as it will help define what hazards, if any, a given area is likely to see. These storms will also be efficient rainfall producers with the 16.12 HREF mean showing widespread 0.5-1 inches of QPF across the region (highest totals east of the Mississippi). If a situation where discrete cells ahead of the front develop with a more linear storm mode directly along the front, this could mean repeated activity for some locations. Many places across Southwest and Central Wisconsin do not need any more rain with continued areal and river flooding ongoing. A current reasonable worst case scenario would be 1.5-2+ inches, mainly east of the Mississippi. A lot of it will depend on the exact track of the strongest storms and higher localized amounts will certainly be possible.

Cooler and Drier Saturday and Beyond

As the front pushes through the region, cold air advection will start up shortly behind it. This will usher in much cooler temperatures across the area with lows Friday night into Saturday falling into the upper 20s to mid 30s. The low is expected to move in a northeasterly track into Ontario through the day Saturday. Because this has trended a little further northeast with each forecast update, the chances for snow showers Saturday morning are looking lower and lower. Wouldn't be surprised if we don't see any snowflakes by the time all is said and done. That being said, if we do see a few snowflakes, they should not accumulate given road and ground temperatures are well into the 50s with a recent stretch of 70 degree temperatures. In any case, temperatures Saturday will be 20- 30+ degrees cooler than where they were on Friday - welcome to spring in the Midwest! The good news is that with this cooler air comes a much drier airmass as a surface high moves in from the Canadian Plains by Sunday. This will create some minor fire weather concerns for Sunday as RHs will drop to as low as 25% with winds gusting to nearly 20 mph out of the northwest on Sunday. This will be something to monitor after Friday's severe storms. RHs generally tend to level out by Monday as temperatures start on a gradual upward trend with southerly surface flow bringing warmer, more moist air back into the region. Precipitation chances don't look to return until next Wednesday night.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1250 AM CDT Fri Apr 17 2026

VFR conditions continue for the rest of the night with an MVFR CU field developing towards late morning and continuing into the afternoon. Thunderstorms are expected to develop along and ahead of a cold front that moves through during the afternoon, some of which could be severe and produce large hail and damaging winds. South to southeast winds of 10-20G25-30kts increase through the morning with winds backing to the northwest at 10-20G20-25kts behind the front for the evening and overnight.

HYDROLOGY

Issued at 221 PM CDT Thu Apr 16 2026

A Flood Watch has been issued for Southwest Wisconsin and portions of West Central Wisconsin given the chance for additional showers and thunderstorms Friday afternoon and evening. These areas have already seen copious amounts of rainfall over the last week with many rivers experiencing signficiant flooding (enough to close some roads in multiple counties). Outside of river flooding, there remains a lot of ponding across the region in the valleys The sunshine today will certainly help some but not nearly enough. With another .5 to 1+ inches of rain expected with Friday's activity, any additional QPF will be problematic and only exacerbate existing problems. Mudslides also look to be a problem as we haven't seen a full green up yet so roots have not taken a strong hold yet. Rivers across Wisconsin are likely to see additional rises, especially the Kickapoo, Yellow, Black, and Wisconsin Rivers.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Flood Watch from this afternoon through Saturday morning for WIZ042>044-053>055-061. MN...None. IA...None.