108
FXUS63 KARX 112322
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
622 PM CDT Fri Sep 11 2026

.KEY MESSAGES...

- Line of showers, possibly a rumble of thunder, late tonight.
  Overall impacts look to be minimal.

- Risk remains for heavy rain and possibly severe weather for
  late Monday through Tuesday, but the devil is in the details
  for how this event will unfold.

- Trending cooler for the latter part of next week with
  additional storms possible.

&&

.DISCUSSION...
Issued at 144 PM CDT Fri Sep 11 2026

Tonight: Line of Showers Moves Through

A narrow line of elevated showers and possibly a few
thunderstorms are progged to develop ahead of an approaching
cold front within a pocket of narrow mid-level theta-e
advection/30-40-kt LLJ above a stout lower tropospheric warm
nose. The window of opportunity for storms at a given location
is short (1-2 hours) and is predicated on the moistening of that
critical 800-700-mb layer in time. MUCAPE values of 500-1000
J/kg would certainly support general thunderstorms, though the
wind fields would limit any organization as indicated by the
complex hodographs. Most of the 11.12Z HREF members have this
convection waning by sunrise as it moves towards central
Wisconsin.


Monday - Tuesday: Heavy Rain/Severe Weather Risk

The main period of interest in the forecast remains from Monday
into Tuesday as an early fall extratropical cyclone ejects off
the northern High Plains and tracks across southern Manitoba and
Ontario. The attendant cold front slides southeastward with
return flow pushing warm sector PWATs close to 2 inches and warm
cloud depths of 12+ kft as Pacific moisture overruns lower
level Gulf moisture. While the thermodynamic environment will
support efficient rainfall processes, how and where this rain
falls will be dictated by the position of the front and
convective evolution ahead of the front, which is a source of
model variability between the medium range solutions. Recent
runs of the EPS/GEFS have started trending towards a more
progressive frontal passage, but there still exist a few members
that have the front more parallel to the mean upper level flow,
which would be more favorable for repeated rounds of heavy
rain. There are some solutions that fails to push the front
south of the area on Tuesday and linger the heavy rain potential
into Wednesday.

The risk for severe weather also hinges on how the warm sector
evolves during the day on Monday and the influences of the
morning convection, variables we will not have sorted out until
later this weekend.


Late Week: Possibly More Storms

Looking beyond early next week, the local weather pattern will
hinge on the evolution of Pacific Northwest wave Tuesday into
Wednesday. Roughly 20-30% of the current guidance have this wave
propagating eastward across the region and deepening, resulting
in the surface baroclinic zone lifting northward into our
region and being the focus for renewed rounds of storms and
heavy rain later in the week. These solutions look to be
falling more into the minority and some of the more recent
deterministic runs also are favoring this shortwave energy
cutting off over California and the northern stream energy
lifting northeastward and not affecting the region. The blended
NBM forecast understandably has low (20-30%) PoPs for much of
next week, but if the cutoff solution unfolds, we may stay dry
and cool for much of the remainder of the week--or until the
cutoff low finally ejects eastward.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 618 PM CDT Fri Sep 11 2026

The main aviation concern over the next 12 hours will be the
potential for thunderstorms, mainly at KLSE. Confidence
continues to be high enough to keep PROB30 mention for storms at
that site. KRST still has a potential for storms in the
vicinity, but confidence is too low (around 10-20 percent) to
mention in the TAF. Low clouds may also develop for a few hours
behind a frontal passage, which may result in brief MVFR
ceilings at both sites. KLSE has the higher potential in this
occurring so have dropped ceilings to MVFR with this TAF cycle.
The wind will shift from out of the south to out of the
northwest behind the front. Wind gusts could be as high as 20-25
kts during the day tomorrow.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...Skow
AVIATION...Muscha