textproduct: La Crosse

KEY MESSAGES

- Above normal temperatures are expected throughout the week.

- Dry conditions continue before low potential for precipitation returns this weekend (10-30%).

- There is high forecast uncertainty regarding temperatures and rain chances early next week.

DISCUSSION

Issued at 1236 PM CDT Tue Oct 20 2026

Rest of Today - Friday: Dry with Above Normal Temperatures

Rather mundane weather continues across the region over the next several days as tropospheric deep ridging remains the dominant synoptic feature across much of the United States. Rising heights and warm air advection associated with this ridging sets up favorable conditions for above normal temperatures across the Upper Mississippi River Valley as 850hPa temperatures top out around 9C- 11C. As a result, afternoon high temperatures top out in the mid 60s to low 70s through Friday while overnight lows fall into the 40s and 50s, roughly 15-20 degrees above normal for this time of year. Confidence in this unusual warmth is high given very little spread in the 10th-90th spread of the various ensemble suites, but did trend the temperature forecast towards the 90th percentile of the NBM to account for the potential of efficient mixing and overachieving temperatures.

A couple chances for fog development also occur this week: Tonight- Wednesday morning and Wednesday Night-Thursday Morning. The second period looks to be more favorable for widespread fog as the 850hPa ridge axis and light winds more directly situate over the region, setting up a favorable scenario for efficient radiational cooling and thus fog development. The 20.12z REFS already suggests 40-60% probabilities for visibility less than 3 miles during this timeframe. Tonight into Wednesday morning is slightly less favorable owing to stronger winds in the 925-850hPa layer, but sufficient cooling should be able to occur under mostly clear skies such that at least the more susceptible river valleys should see some development. Otherwise, with the ridging in place and lack of substantial forcing or moisture, a precipitation free forecast is in place through the remainder of the week.

Saturday - Sunday: Low Precipitation Potential Returns

The upper level ridge begins to break down late this week, shifting eastward this weekend while a 500hPa trough moves across southern Canada and a cutoff low develops across the southwest United States. In response to the approaching upper low, surface cyclogenesis occurs across the northern Great Plains before the mature low lifts northward into Canada. As this feature lifts north, a surface cold front looks to move through the Upper Midwest, providing some weak forcing for precipitation this weekend. However, timing and location of this boundary is a bit uncertain and the more favorable environment for rainfall looks to occur across central Minnesota where deeper moisture is currently forecast to be present. So, while precipitation may return this weekend, probabilities are rather low, around 10-30%.

Early Next Week: Higher Forecast Uncertainty

As we head into early next week, quite a bit of uncertainty surrounds the forecast as deterministic and ensemble model suites vary significantly in their evolution of the atmosphere. Solutions such as the GFS/GEFS/AIGFS and Euro/EPS/AIFS suggest this weekend's frontal boundary stalls out across our area while another 500hPa trough along the United States/Canada border phases with the cutoff low across the Southwest, continuing eastward and sparking showers along said boundary on Monday. However, the Canadian/GEPS solutions depicts the 500hPa ridge retrograding back into the Upper Midwest early next week, resulting in predominantly dry conditions. Due to these variations, low and rather nebulous precipitation probabilities exist for early next week, around 10-20% in the 20.13z NBM. This uncertainty is also reflected in the temperature forecast as ensemble guidance has fairly large spreads in the 25th-75th percentiles, upwards of 10 degrees. However, the overall temperature trend for early next week at this point is towards more seasonable temperatures.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 619 PM CDT Tue Oct 20 2026

High pressure will provide clear skies and south winds under 10 knots. Unlike this morning, the boundary layer looks more mixed. This should result in less valley fog on Wednesday morning.

ARX WATCHES/WARNINGS/ADVISORIES

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