253
FXUS63 KARX 121828
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
128 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Slight chance (15-25%) for very light showers Sunday.

- Widespread rain is a near certainty (95%) Monday into Tuesday
  with the potential for localized flooding. If exact details
  come together (<5%), a severe storm could occur Monday.

- Periodic rain potential continues Wednesday through Friday.
  While this is favored to focus to the south of our area, some
  areas could see multiple rounds of rain with an attendant
  risk for flooding issues as the week goes on.

&&

.DISCUSSION...
Issued at 124 PM CDT Sat Sep 12 2026

Spotty light showers Sunday

Upper wave currently over Saskatchewan looks to dive southeast over
Lake Superior Sunday. In addition to helping advance the cold front
moving through the forecast area today this may also kick off a few
very light showers as the mid-levels will still have a decent amount
of moisture remaining in them as the base of the upper wave moves
through the forecast area. Have therefore added 15-25% mentions of
light showers with very low QPF. Those outdoors shouldn`t be
surprised if rain occurs briefly but impacts are not expected.

Rain with localized flooding risk Monday into Tuesday

In the wake of Sunday`s upper wave, surface high builds in the Great
Lakes. First bona fide Fall-like temperatures look to occur Monday
morning when some areas in our northeast could (20-50%, highest in
Taylor County) see temperatures in the upper 30s.

As this upper wave continues to head east over the Atlantic Ocean,
surface high shifts eastward accordingly. As this occurs, upper low
churns eastward over MT toward southern SK/MB. Strong southwesterly
jet aloft on the equatar-ward side of this feature will both lead to
the low deepening and broad lee surface pressure falls across the
central and northern High Plains. Consequently, robust southerly
moist advection will occur between the eastern surface high and the
lee trough across the Plains with 700/850mb moisture transport
ramping up over our CWA Monday morning. Expect showers and perhaps a
few thunderstorms to develop as a pair of disturbances eject
downstream during the afternoon and evening hours and then again
when the surface front arrives from the northwest early Tuesday.
With high PWAT values expected (12.13z NBM values approach 2") and
deep warm cloud layers, showers will produce rain efficiently with a
good chance (50-70%) for rain totals to exceed 2". Given the setup
with 1-2 round of moderate to heavy rain developing in the vicinity
of a warm front before additional rain occurs with the crashing cold
front, there exists potential for localized high end amounts with
the small (5-15%) chance for 4"+ to occur focusing on portions of
northeast Iowa. Thus, while the progressive nature of the overall
system and probabilistic output suggest little risk for widespread
flooding issues, the potential for localized problems looks to be
present.

Very low severe storm potential Monday

With the aforementioned southwesterly jet sliding closer to the CWA
by Monday afternoon/evening and southerly winds ramping up at the
surface, oodles of wind shear look to be present, including at the
near surface, where sfc-500m SRH could top 200 m2/s2 per 12.12z GFS.
However, given the strong moist advection, destabilization will be
an issue as increasing clouds limit insolation and profiles begin to
trend moist adiabatic. Therefore, while we cannot let our guard down
as even modest amounts of surface-based instability would be enough
for a tornado risk, at this time it appears highly unlikely (95%)
said instability will in fact develop.

Periodic rain Wednesday through Friday

With moist of the upper support for they Monday/Tuesday system
remaining to our north, cold front looks to stall across NE/IA/IL
with quasi-zonal flow aloft persisting over the northern CONUS.
Thus, as shortwaves move across the Midwest, additional rounds of
rain look to develop in the vicinity of the front. Some of this
activity may (20-60%) sneak into our CWA, particularly in northeast
Iowa and southwest Wisconsin. While no additional hazardous periods
stick out at this time, would need to monitor any areas that receive
heavy rain Monday/Tuesday for additional flooding concerns.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 124 PM CDT Sat Sep 12 2026

VFR conditions are expected over the next 24 hours. Clouds will
generally decrease over the next 6 hours before increasing once
again from 00z to 18z Sunday. Lowest cloud bases should remain
at 5 kft or greater, however. A light shower or two may (15-25%)
occur after 12z Sunday but visibility reductions are not
expected.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Ferguson