textproduct: La Crosse

KEY MESSAGES

- Hot temperatures in the upper 80s to low 90s are likely (50-80%) across the region Monday and Tuesday, leading to heat indices in the upper 90s to around 100F.

- Warm temperatures continue through the end of the week with the potential for showers and storms increasing again late Thursday into Friday (10-30%).

DISCUSSION

Issued at 152 PM CDT Sun Jul 12 2026

Rest of Today

Non-impactful weather continues through the rest of the afternoon and overnight tonight as high pressure remains the dominant feature. Some valley fog should be able to develop again tonight under clear skies and light winds, especially in the Wisconsin River Valley, but should dissipate fairly quickly after sunrise Monday morning.

Monday - Tuesday: Hot Temperatures

Increasing heat is the main concern in the short-term as impressive upper-level ridging remains situated across the western half of the United States. While the main ridge axis and associated highest heat is expected to remain west of us, 850hPa thermal ridging nudges into portions of Minnesota and Wisconsin generally along/north of I-90 on Monday, along the northern edge of high pressure situated over southern Wisconsin. Temperatures at this pressure level around 24-26C continue to be depicted in the various ensemble suites (12.06z GEFS/EPS/GEPS/AIGEFS/AIFS), suggesting surface temperatures reach into the upper 80s with the 12.13z NBM indicating a 50-80% chance of exceeding 90F. The previously noted southern shift of this thermal ridge in the 11.12z LREF has since shifted northward again in the 12.00z LREF, a trend also depicted in the 12.12z REFS/HREF. Because of this, thinking the highest temperatures Monday should remain generally along and north of I-90 unless another southerly shift were to take place, but given the current location of the surface high and 850hPa ridge, it may be challenging for these temperatures to sink further south.

Given the temperatures expected, attention turns to heat indices and heat related impacts. As mentioned in earlier discussions, the main difference between heat to start this week and the heat from a few weeks ago is that a drier airmass is currently in place. Because of this, dewpoints are far less likely to reach the upper 70s with the 12.00z LREF suggesting only a 10-20% probability to exceed 75F. Given the drier atmosphere, confidence in exactly how hot heat indices will get is not overly high, especially with the potential for deeper mixing north of I-90 as slightly higher 925-850hPa flow across these areas could lead to somewhat efficient turbulent mixing into drier air in the 850-700hPa layer. If this occurs, it would result in lower dewpoints and by association, lower heat indices, perhaps failing to reach 100F.

All of this said, dewpoints are currently expected to reach the upper 60s to low 70s Monday, resulting in heat indices in the mid to upper 90s, nearing/exceeding 100F for a few hours in some locations. HeatRisk and the WBGT also suggest heat related impacts are favored so have opted to issue a Heat Advisory for portions of western to central Wisconsin along with Wabasha County in Minnesota for Monday afternoon.

The 850hPa thermal ridge sags southward for Tuesday as troughing traverses the northern side of the ridge, slightly breaking down the mid to upper-level pattern and bringing potential heat impacts to a greater portion of the Upper Mississippi River Valley. Deterministic guidance suggests that the 850hPa ridge and surface high pressure should remain solidly in place such that the warmest 850hPa temperatures end up across eastern Wisconsin, but ensemble means suggest 23-24C should be in place at 850hPa over much of the area Tuesday. There's also less concern with dewpoints mixing out on Tuesday as compared to Monday as the low-level wind field will be rather light owing to the high pressure in place. Because of the favorable conditions for heat indices near/exceeding 100F shifting further south for Tuesday, the Heat Advisory may need to be expanded southward if current trends continue.

This is all a very long and drawn out way to say it's going to be hot over the next couple days. Ensure you frequent breaks if outside and stay well hydrated!

Wednesday - Friday: Warmth Continues and Shower/Storm Potential

With the stout upper level ridge in place through at least mid- week warm temperatures stick around the upper Midwest, although slightly cooler compared to earlier in the week as the thermal ridge continues southward. Along with the continued warmth, little potential for showers/storms will exist across our area while this ridge remains in place. Heading into the late week though, the upper level ridge begins to break down as various troughs ride over its northern extent. Plenty of uncertainty in how the upper level pattern will ultimately evolve at this point as the various ensemble members suggest many different solutions, but precipitation potential increases again late Thursday/early Friday morning (10-30%).

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 629 PM CDT Sun Jul 12 2026

VFR expected through the forecast period. Low confidence in river valley fog as off surface low level winds expected to negate fog-supportive light wind layer. Although, more susceptible Wisconsin River Valley may see some MVFR-LIFR FG affecting KOVS through Monday morning.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Heat Advisory from 11 AM Monday to 9 PM CDT Tuesday for WIZ017- 029-032>034-041>044. MN...Heat Advisory from 11 AM Monday to 9 PM CDT Tuesday for MNZ079. IA...None.