textproduct: La Crosse

KEY MESSAGES

- Another round of fog possible tonight, mainly along and south of I-90.

- The threat for storms returns Friday afternoon, some of which could be on the stronger side.

- Periodic storms pepper the forecast from Saturday night through early next week with localized heavy rain the main threat.

- Temperatures remain near seasonal norms for the next week.

DISCUSSION

Issued at 145 PM CDT Thu Aug 6 2026

Tonight: Fog Potential

Weak return southerly flow is spreading eastward across the region this afternoon behind the surface high pressure cell that brought our sunny skies today. This will aid to slowly bring slightly higher dewpoints northward over the next 24 hours. This increase in moisture is progged to either bring another round of fog or low stratus later tonight into Friday morning. Given the advective component of this scenario, stratus may be slightly more favored over fog, or it may be a case where the lower valleys see stratus and the upper ridgetops see fog. As with this morning, dense fog is possible into northeast Iowa and southwest Wisconsin. This fog/stratus looks to burn off by mid to late morning ahead of our approaching cold front.

Friday Afternoon-Evening: Storm Details

A compact shortwave rotating around a broad, quasi-stationary south-central Canadian low ushers a cold front out of the Dakotas later this evening, with the boundary bifurcating Minnesota from SW to NE by midday Friday. Forecast soundings ahead of the front show a modestly stout cap in place that may be difficult to breach given the weakness of the attendant upper level support. Most CAMs do develop some form of convection along the front, but with varying degrees of location and coverage. In fact, the 12Z HRRR really struggles to develop much for any convection across the local area--keeping it further north where forcing may be slightly stronger and inhibition less.

Should surbace-based convection occur, there will be 1000-1500 J/kg of MLCAPE to realize and a mean cross-boundary steering flow that could keep cells more discrete. That being said, the complexities of the 2-6-km hodographs--plus the forcing being along the front--will likely result in cells growing upscale to lines or clusters in fairly short order and limiting any hail threat. Pockets of strong winds would be the main hazards with these storms

Saturday Night - Tuesday: Periodic Rounds of Storms

The culprit cold front bringing tomorrow afternoon/evening's storms slides to around the I-80 corridor in Iowa/Illinois by Saturday morning. However, with the upper tropospheric pattern transitioning more to a quasi-NW/zonal flow, the next subtle ripple in the flow helps promote lee cyclogenesis along the Front Range that lifts the baroclinic zone northward. The medium range solutions differ considerably on the degree of convective initiation along this lifting warm front between Saturday night and Sunday, but deterministic forecast soundings from the GFS show a rather primed setup with the potential for organized convection by Sunday afternoon. The question becomes whether storms can break through the cap and exactly where/when that occurs, a tough question to answer at this range in the forecast. With the mid to upper level steering flow having a substantial boundary parallel component, training storms and locally heavy rain would be a concern.

Moving into early next week, this baroclinic zone slowly sags southward, its exact position driven by how convection unfolds over each successive day. The Monday into Tuesday timeframe could feature an MCS tracking along the boundary as depicted in various ensembles, but location and timing are highly variable and there is not much else to hand one's hat on.

With the increasing risk for convection each day and weak north to east flow to the north of the boundary, the temperature forecast for the weekend and early next week will feature highs at or slightly cooler than average.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1216 PM CDT Thu Aug 6 2026

Fog/stratus looks to spread northward overnight tonight potentially reaching LSE/RST around sunrise Friday. Confidence is high enough it will reach LSE to include LIFR conditions and, while it looks to be mainly due to stratus in valley locations, have included an LIFR visibility as well just in case winds reduce and the stratus deck lowers. For RST, due to lower confidence, have held a low MVFR mention as a heads up for now with a view toward trending toward IFR/LIFR or VFR as the northward progression of the trouble becomes clearer over the next 15 hours. Conditions should return to VFR by the end of the period. Looking ahead, TS will likely (60%) return sometime after 18z Friday.

ARX WATCHES/WARNINGS/ADVISORIES

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