104
FXUS63 KARX 171051
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
551 AM CDT Thu Sep 17 2026

.KEY MESSAGES...

- Showers (45-90%) and perhaps (5-15%) a rumble of thunder overnight
  with no impacts aside from lightning expected.

- Widespread rainfall on Friday and Saturday with rainfall
  amounts of 1-3" trending more likely with locally higher
  amounts possible. Flooding and river rises may occur where the
  heaviest rainfall amounts fall.

- Additional rain chances (20-50%) into early next week with
  cooler than normal temperatures.

&&

.DISCUSSION...
Issued at 1212 AM CDT Thu Sep 17 2026

Showers, perhaps a rumble of thunder overnight

2 disturbances, the first over IA and the second over western MN,
will roll eastward overnight. Moistening atmosphere ahead of these
waves, as evidenced by spreading fog and stratus, should allow for
some showers to develop with these potentially (45-90%) occurring in
our CWA. Progged soundings show just a touch of instability ahead of
these waves so a few rumbles of thunder (5-15% chance at a given
location) could occur, an outcome borne out by a bit of sporadic
lightning ongoing in central MN as of 03z. With this instability
being modest and elevated, am not concerned about any strong to
severe storms. Additionally, overall forcing is weak and
progressive, so flooding concerns are minimal as well.

Widespread rain Friday into Saturday

Upper low barrels eastward from OR eastward to WY Friday into
Saturday, leading to lee pressure falls in the central High Plains.
As this occurs, surface high builds in ON/QC in the wake of an upper
low moving from James Bay to Atlantic Canada. Continued easterly
flow across much of the Great Lakes coupled with southwesterly flow
across the southern and central Plains looks to reinforce a front
with this feature becoming quasi-stationary somewhere in the
southern Upper Midwest. Stout upper high over the low Mississippi
Valley will also help drive that southwesterly low level flow which
will advect large amounts of moisture from the Gulf to the region -
PWATs are progged to reach the high end of GEFS/ECENS climatology on
the 16.12z runs. This moist 850/700mb flow looks to be roughly
normal to the front and, with upper support in the form of a lead
disturbance Friday and an additional shortwave Saturday, locations
near the stalled front will see multiple (25th-75th values in 17.01z
NBM are around 2-4") inches of rain with potential (15%) for more
than 5". Localized flooding would be possible with this amount of
rain. Main question remaining appears to be exactly where that quasi-
stationary front sets up. Unfortunately, vast majority of guidance
has it somewhere in our forecast area. Once the location becomes a
bit more clearer, a Flood Watch may be needed ahead of Friday.

Additional rain chances next week

After the heavy rain threat departs to the east on Saturday, the
forecast area will be in-between that system and another weather
system approaching from the west. An H300 cutoff low pressure
system will continue to slowly trek east late this weekend into
next week. Timing and evolution of the low pressure vary in the
ensemble guidance, which leads to uncertainty regarding the
timing and location of any potential rainfall on Sunday into
Monday. Given the low confidence, will keep the broad PoPs from
Sunday into Monday. PWAT values will be a bit lower than the
previous few days so the potential for heavier rain will be
lesser with the next system. Even with that being said, the
saturated soils and higher river levels will make it easier for
flooding to occur so that may be an impact once again for the
second system. After that system moves over the region, the
forecast upper level pattern gets more uncertain as there is
quite a bit of model disagreement at this time. Through this
time frame, temperatures should remain slightly below average to
near average for late this weekend into the middle of the next
work week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 545 AM CDT Thu Sep 17 2026

Low ceilings will lead to LIFR to MVFR conditions for the first
half of this TAF cycle. KLSE is currently VFR, but the
expectation is that low clouds will develop back in after rain
showers that are near the terminal exit off to the east. The low
clouds should slowly lift through the day with VFR conditions
forecast to return near or shortly after 00z. The wind will
continue to have an easterly component and the speed should be
sustained around 10 kts or less.

&&

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

&&

$$

DISCUSSION...Ferguson/Muscha
AVIATION...Muscha