206
FXUS63 KARX 131847
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
147 PM CDT Sun Sep 13 2026

.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.

&&

$$

DISCUSSION...Skow
AVIATION...Ferguson