textproduct: La Crosse

KEY MESSAGES

- Storm chances increase this afternoon, low potential (15%) for some becoming strong/severe with damaging winds as the main hazard.

- Periodic shower and storm chances continue from Saturday night into midweek.

- Temperatures remain near normal for the next week with highs in the mid 70s to mid 80s expected.

DISCUSSION

Issued at 355 AM CDT Fri Aug 7 2026

Ongoing Fog & Increasing Storm Potential:

Light southwest winds continue through the early morning, gradually increasing dewpoint temperatures into the low to mid 60s. Concurrent cooling of surface temperatures into the low to mid 60s is resulting in fog formation primarily locally in northeast Iowa. Additional, more widespread impacts from FG have been stifled by off surface winds of 10-20 mph on local VWPs. Therefore, while Patchy FG is evident on satellite imagery, impacts have remained minimal. Any fog that does form will dissipate by the mid- morning.

A mid-upper level wave begins to take shape during the mid- morning hours through central Minnesota, reaching the local forecast area by the early afternoon, eventually exiting through the evening. Recent Convective Allowing Model (CAM) dProg/dt has been exhibiting a MCS resemblant feature developing with said wave. An initial capping inversion will limit initial instability, 1000 to 2000 J/kg of MLCAPE, during the morning. As this MCS moves further into our CWA, instability gradually increases as the CAP decreases. This could enhance the damaging wind gust threat as the DCAPE values grow as we get into the afternoon, still not as favorable as they could be with values around 700 to 850 J/kg from various CAMs. The bulk shear also increases as the wave moves through with values of 40 to 50 kts.

The main threat with this system would be damaging winds, but since this is a northwest flow regime, this storm complex will likely wobble a bit in the model guidance before settling on a track. Storms may also initialize along the front further north where better forcing is at. Any storms that form along the front would be discrete at a first, but then form into lines or clusters rather quickly due to the messy 3 to 6km shear profiles in the hodographs. Overall, while confidence in storms is increasing, the exact location of both this complex and any afternoon storms remain uncertain.

Saturday Night - Friday: Periodic Storm Chances

Quasi-NW/zonal flow remains the dominant flow pattern in both ensemble and deterministic guidance over the coming week. With the cold front passage today, this will shift storm chances further to our south for Saturday. By Saturday night a low forms in the Central Plains which in turn shifts the baroclinic zone back north over portions of our forecast area for both Sunday and Monday. There still remains quite a bit of uncertainty regarding how storms will form and where exactly they form. The GFS has the boundary further into our area compared to the CMC and ECMWF which keep it further into central Iowa for Saturday night then bring it back north for Sunday into Monday. Given that we will be in the aforementioned northwest flow pattern, any perturbation could be enough to cause storms to form whether along a boundary or become a MCS and move through the area. These mesoscale details are tough to pin down this far out and are directly impacted by the previous day's convection.

By midweek, guidance has been in decent agreement that this boundary shifts south of the local area keeping the majority of the precipitation chances south of the CWA. Similar to the last few discussions, with good agreement on the flow pattern and daily storm chances, high temperatures are likely to stay in the normal to slightly below normal range with highs in the mid 70s to mid 80s.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1247 AM CDT Fri Aug 7 2026

Initial forecast concern and aviation impact is overnight into early Friday morning FG potential primarily within river Valleys, affecting KLSE TAF site among smaller airports in southwest Wisconsin. Confidence has decreased some given current in situ wind speeds being observed inherently mixing lowest levels of atmosphere. Webcam imagery looking over the Mississippi River Valley at 07.06Z TAF issuance shows low level saturation trying to form although has actually been slightly clearing over the last couple of hours. Therefore, have included SCT002 at TAF issuance and tempered early morning impacts into a TEMPO IFR group.

Subsequent impacts will be line of potential storms progressing from west to east through the afternoon evening. Higher confidence west and north of local TAF sites as storm probabilities somewhat separate from eastern Minnesota into western Wisconsin. Have continued with previous PROB30 at both TAF sites, tightening up window based on temporal confidence.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ029-030.