textproduct: La Crosse

KEY MESSAGES

- Showers likely (40-70% chance) late this afternoon and into the overnight with rainfall amounts generally around a tenth of an inch or less. Additional storms likely (40-80% chance) in southwest WI and northeast IA with some potentially being strong with hail and gusty winds late Friday evening and overnight.

- Warmer temperatures beginning Friday and continuing into early next week with highs in the upper 70s to 80s. There is a small chance (10% chance) temperatures may warm into the upper 80s to near 90 on Friday, mainly in river valley locations.

- More active weather pattern this weekend through Tuesday with periodic chances for showers and storms. There is potential for strong to severe storms throughout this period with Sunday and Monday currently posing the greatest risk.

DISCUSSION

Issued at 147 PM CDT Thu May 14 2026

Rest of Today - Saturday: Warmer on Friday with Periodic Showers/Storm

Upper-level ridging pushes eastward today ushering in zonal flow into the overnight and for the day on Friday. As the upper-level ridge that was situated over our region pushes eastward, a shortwave on the eastern periphery of the zonal flow regime will push into the local area with some accompanying warm air advection in the low- levels. Consequently, much of the CAMs push an axis of showers through the local area late this afternoon and into the overnight, exiting east by sunrise. Overall, probabilities for rainfall amounts over 0.2" in the recent HREF are not overly high (under 40% chance), so not expecting overly robust rainfall amounts.

As we head into the daytime hours on Friday, temperatures will be noticeably warmer in light of this warm air advection with highs reaching into the 80s for many spots on Friday. Given the fairly pronounced mixing shown in the RAP/HRRR soundings, would not be shocked if temperatures overachieve slightly, potentially getting close to the 90 degree mark in some spots (10% chance). However, this is contingent on exactly how deep we mix, of which the HRRR/RAP are the most aggressive. Otherwise, a stationary boundary will set up across the area with this warmer airmass in place with dewpoints pushing into the low to mid 50s. MUCAPE values respond accordingly in the RAP with values of around 1000 J/kg across the area. While there is fairly steep low-level lapse rates resulting in a pronounced low-level dry layer, will need to watch if any surface parcels can overcome this layer and convective along and south of this boundary during the evening hours on Friday. IF a stronger or severe storm can develop in the warm sector south of this stationary boundary (Generally along and south of I-90), fairly elongated hodographs across guidance would suggest a supercellular mode could manifest with the potential for large hail (up to golf ball sized) and strong wind gusts.

Saturday features continued zonal flow aloft which will keep temperatures warmer with highs remaining in the upper 70s to 80s. Some weak shortwave perturbations can be noted in ensemble members which may result in some shower potential for the afternoon, most notably the RRFS which tries to bring an axis of convection through the region during the late morning hours. An axis of convection then will lift into the region during the evening hours on Saturday and into Sunday morning as well. Once again hodographs look fairly elongated in the GFS/NAM late Saturday afternoon and evening which would suggest the potential for some supercellular structures initially across northeast IA and southwest WI. With MUCAPE values of around 1000-1500 J/kg and mid-level lapse rates of around 7-7.5 C/km, would think that large hail would be the main concern with any strong to severe storms. Deep layer shear eventually wanes later into the evening, so would expect storm organization to become more messy with time into the overnight hours.

Sunday - Tuesday: Active Pattern with Additional Shower/Storm Chances, Potential for Severe Storms on Sunday & Monday

The pattern turns much more active beginning on Sunday as an upper- level trough situated over the Rockies attempts to push eastward, leaving our area in a southwesterly flow pattern. As this occurs, a very profound axis of 850mb moisture transport pushes north into the Upper-Mississippi River Valley on Sunday afternoon and evening, bringing dewpoints into the 60s for a sizable portion of the area. As a result, the grand ensemble (GEFS/EC/Canadian ensemble) has high probabilities (50-80%) for SBCAPE over 1000 J/kg during this time period. Overall, with the sharp warmer and moisture advection regime moving into the region, soundings in the deterministic GFS and grand ensemble (GEFS/EC/Canadian ensemble) would suggest a more elevated storm environment on Sunday with a warm nose present. Additionally, shear profiles are somewhat questionable with an inter-quartile range for effective shear in the grand ensemble (GEFS/EC/Canadian ensemble) ranging from 20 to 30 kts, likely more of a hail environment with updrafts that do not sustain as well.

Confidence for how the severe potential will evolve diminishes somewhat as we start the upcoming work week as the main driver will be tied a synoptic cold front that will progress through the region early next week. Overall, confidence is very high that there will be ample moisture in place during this period as the grand ensemble (GEFS/EC/Canadian ensemble) has very high probabilities (80-100%) for dewpoints over 65 degrees during the day on Monday. The key questions that remain for how Monday (or possibly Tuesday?) will be related to the exact timing of the aforementioned front and how the features aloft develop as this occurs. Currently, the deterministic GFS and EC depict vastly different scenarios. In the GFS scenario, this would have the trough over the Rockies translate into the Great Plains and quickly become negatively-tilted as it pushes into the Midwest on Monday evening. This would coincide with the frontal passage which would allow for favorable exit region dynamics resulting in a strongly forced environment for organized convection with all hazards possible late Monday afternoon and evening. The EC has effectively a 24 hour shift from the GFS where it does not bring the cold frontal passage into region until Tuesday which in turn would make Monday's forecast much more challenging as any convection would be related to any shortwave perturbations in southwesterly flow with weak flow aloft potentially hindering organized storm development and thus making severe potential more uncertain.

With multiple rounds of storms seeming likely, there is some signal for heavy rainfall as well with the NBM having relatively high probabilities (40-80%) for rainfall amounts over 1" during this period. The NBM even has some medium probabilities (20-60%) for 2" or more as well. Overall though, given the synoptic uncertainties previously discussed, seeing low confidence in ensemble datasets such as the 14.00z EC Extreme Forecast Index for QPF which has a broad brushed shift of tails of 0 but no tangible probabilities. This would suggest that there are members that contain anomalously high rainfall totals, but confidence is low on where this will occur and exact timing.

In any case, main takeaways from this forecast is confidence is very high (over 80%) that we will see periods of storms over the next few days, some of which having the potential to become severe. However, much of the severe potential on Sunday and particularly on Monday will be dictated on how upper-level features resolve which deterministic and ensemble guidance is having disagreements at this juncture. Regardless, this will certainly be a period of time to monitor as forecast details will likely change regarding Sunday and Monday.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1249 AM CDT Fri May 15 2026

Strong south winds through the morning gradually turn clockwise, becoming south-southwesterly by the early afternoon. Line of storms initiates along local northwestern peripheral counties, near KRST TAF site, through the early evening, progressing east into the nighttime hours. While confidence is high for storms, northern and western extent limit specific confidence at both TAF sites (KLSE & KRST). Therefore, have included VCTS in both TAFs at longer TAF hour which will require further refining on timing and location in coming forecasts. Line of storms progress east of the area near the terminus of 15.06Z TAF period.

Storm chances along southern peripheral counties in northeast Iowa and southwest Wisconsin for Saturday become more widespread again for Sunday.

ARX WATCHES/WARNINGS/ADVISORIES

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