371
FXUS63 KARX 291047
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
547 AM CDT Tue Sep 29 2026

.KEY MESSAGES...

- Widespread rainfall potential increases this afternoon,
  continuing through Thursday. The heaviest rainfall is favored
  across northeast Iowa into southwest Wisconsin where the
  potential for 2+" of rainfall is 40-60%. Localized amounts of
  3-4+" are possible.

- High temperatures will remain seasonal in the 60s to 70s.

&&

.DISCUSSION...
Issued at 1230 AM CDT Tue Sep 29 2026

Today - Thursday: Widespread Rainfall

An upper level low is expected to develop across the Desert
Southwest this morning after becoming cutoff from a longwave
trough across the western United States. After this cutoff
occurs, the longwave trough continues eastward across the
northern United States and knock`s on the Midwest`s door this
afternoon. Ahead of these features, southerly flow advects
tropospheric deep moisture across the Central Plains into the
Midwest, characterized by PWATs of 1.5-1.75 inches. The deep
moisture and forcing associated with the upper level features
will spark widespread moderate to heavy rainfall beginning this
afternoon which largely continues through Thursday. The main
caveat is that a break in the rainfall looks to occur Wednesday
morning behind the trough and ahead of the cutoff low which
begins to lift northward towards the Midwest on Wednesday,
bringing another round of heavy rainfall Wednesday afternoon
into Thursday.

Still some uncertainty with regard to where the axis of
heaviest rainfall sets-up through midweek. The ECMWF suite
(ECMWF/EPS/AIFS) have been very consistent with more southward
solutions, putting northeast Iowa into southwest Wisconsin most
at risk for higher rainfall amounts. In comparison, the GFS
suite (GFS/GEFS/AIGFS) has been more variable in the location of
this heavy rain axis having favored a northward solution 24
hours ago, but has begun to trend southward towards the ECMWF
solutions in recent runs. Currently thinking northeast Iowa into
southwest Wisconsin are the most likely areas to see the
highest rainfall totals given these trends, especially for those
along and south of Highway 18. However, where this axis sets-up
may still change further as there is the potential for the
heaviest rainfall to largely remain south of the area and across
central into eastern Iowa (20-30%). This is seen in the 28.12z
LREF cluster analysis, but the EFI has also largely kept the
greatest signal for anomalous rainfall potential to our south.

Regardless of where the heavy rainfall axis sets-up, currently
expect the heaviest rainfall to occur Wednesday afternoon into
Wednesday night as a strengthening 850hPa low level jet surges
another plume of moisture northward, this time associated with
the remnants of Hurricane Polo as it gets absorbed into the mean
flow when the cutoff low across the Southwest lifts northward.
RAP/HRRR soundings also suggest some elevated instability may be
present during this period, generally around 300 J/kg, leading
to some convective enhancement and locally higher rainfall
totals. Current probabilities for amounts of 2+" sit around
40-60% in the 29.01z NBM with the potential for amounts of 3-4+"
where convective enhancement occurs. Flooding concern remains
through Thursday across portions of northeast Iowa, southwest
Wisconsin, and southeast Minnesota, especially if higher end
rainfall totals are realized. Urban and street flooding along
with river rises are the main concerns although flash flooding
is possible, especially where showers and storms frequent in
rapid succession. Rainfall ends Thursday as a cold front moves
through the region and high pressure slides southeastward into
the Midwest.

Friday into the Weekend: Drier and Trending Cooler

In the wake of the cold frontal passage, temperatures should
slowly trend cooler this upcoming weekend as broad scale
troughing attempts to dig south over the Great Lakes region.
Daytime highs are not forecast to be all that much cooler, with
temperatures remaining in the mid 60s. Where the cooler air will
be more noticeable will be overnight, with overnight lows drop
into the lower 40s to mid 30s. Dry conditions are currently
expected but there may be a low chance for light rain on
Saturday if moisture moves in quick enough out ahead of another
southern surge in the upper level trough.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 545 AM CDT Tue Sep 29 2026

Most area river valleys have been able to develop valley fog
this morning with IFR/LIFR ceiling and visibility restrictions
at sites within these valleys, including KLSE. Expecting valley
fog to dissipate between 14-15z, though there is some potential
impacts could linger through 16z at KLSE. Showers and perhaps a
storm move into the region from the west this afternoon,
generally after 17z. MVFR/IFR visibilities are expected under
heavier rainfall. Ceilings also begin to lower towards 3-5kft as
showers/storms move in and are expected to become IFR this
evening and overnight. Otherwise, southerly winds are expected
through the TAF period with gusts up to 20KT possible this
afternoon west of the Mississippi River.

&&

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

&&

$$

DISCUSSION...Falkinham/Muscha
AVIATION...Falkinham