textproduct: La Crosse

KEY MESSAGES

- Near freezing temperatures likely in favored low-lying sandy bog locations in Jackson and Monroe counties tonight.

- The well-advertised risk for heavy rain remains for Monday afternoon into Tuesday morning. Cannot fully rule out localized flooding, but the storm complex may be too progressive to result in more widespread impacts.

- Seasonal temperatures for the upcoming work week with additional storms possible mid to late week.

DISCUSSION

Issued at 145 PM CDT Sun Sep 13 2026

Tonight: Clear and Cold

A 1022-mb surface high pressure cell is sliding out of North Dakota and into Minnesota this afternoon and continues its eastward march overnight. Clear skies, light winds, and drier continental air should result in favorable conditions for some of the coldest temperatures we've seen thus far this meteorological fall. Upstream temperatures fell into the lower 30s along the North Dakota/Canadian border and similar temperatures are expected over northern Wisconsin tonight. MOS guidance is targeting the sandy bogs of Jackson and Monroe county for falling into the lower 30s as well, so have issued a Frost Advisory for these two counties tonight.

Monday Afternoon - Tuesday Morning: Moderate to Heavy Rain

Increasing mid-tropospheric theta-e advection begins in earnest Monday morning in the immediate passage of the mid to upper level ridge axis, but it will take until later in the afternoon for the surface pattern to catch up. This has resulted in a slightly later forecast arrival time of the rainfall Monday, but the rain should reach most locales before the late afternoon. The focus for heavier rainfall amounts remains on Monday evening into early Tuesday morning as the deeper lower tropospheric moisture arrives and warm cloud depths/PWATs support efficient rainfall processes.

However, the surface cold front will be steadily make its way from northwest to southeast during this period, keeping the axis of heavy rain fluid in space and possibly limiting the overall impacts from this event. There is still a modest signal (30-50%) for 1-2 inches of rain for much of the forecast area, but any pockets of higher amounts will be more mesoscale driven and likely not resolved until the event is ongoing. By Tuesday morning, the front should be on the verge of exiting the forecast area and taking the rainfall with it.

Mid to Late Week: Seasonal Temperatures, Periodic Rain

Broad subtropical ridging remains in force across the southern and southeastern U.S. through the week. This will act to keep the lower tropospheric baroclinic zone that brought our early week rainfall from sinking too far south--likely only as far as the lower Missouri River Valley by Tuesday night. A northern stream wave passing along the U.S./Canadian border may act to pull some of this moisture northward, though how far northward remains a source of uncertainty in the medium range solutions.

Should the front shift to the northern side of the solution envelope, we would need to monitor the potential for more heavy rain, mainly over northeastern Iowa into southwestern Wisconsin. This idea is reflected well in the latest EC EFI where the actual EFI values are less than 50%, but there is a notable shift of tails indicating that those outlier members have respectively high rainfall amounts (in excess of 3 inches).

The synoptic pattern is progged to amplify slightly at the end of the week as a cutoff low over the western CONUS begins to migrate eastward. How fast this trough advances remains poorly resolved and the aforementioned uncertainties in the northern extent of the baroclinic zone after midweek makes the precipitation forecast beyond Wednesday one of lower confidence. What we can say with higher certainty is that temperatures should remain in the 60s and 70s for highs, a solid taste of late summer/early fall weather.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1220 PM CDT Sun Sep 13 2026

While VFR conditions are favored to continue over the next 24 hours, reductions due to approaching widespread showers and thunderstorms may lead to reductions at RST near the tail end of the period. Otherwise, only issues look to be around OVS overnight when the usual Wisconsin and Kickapoo valley fog/stratus look to develop. Widespread reductions are likely after 18z Monday.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Frost Advisory from 2 AM to 8 AM CDT Monday for WIZ034-042. MN...None. IA...None.