966
FXUS63 KARX 130537
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1237 AM CDT Sat Sep 13 2025

.KEY MESSAGES...

- Warmer temperatures expected for the weekend and early next
  week with highs in the 80s to perhaps near 90 in some
  locations.

- Scattered showers and storms (20-40% chance) this evening and
  tonight and possibly (10-30%) Sunday night. Additional
  periodic rain chances (20-50%) for Wednesday through Friday of
  next week.

&&

.DISCUSSION...
Issued at 1258 PM CDT Fri Sep 12 2025

Rest of Today - Tonight: Scattered Showers and Storms Possible

The overall synoptic pattern today displays two key features of
interest as depicted in GOES-19 water vapor imagery and 12.15z RAP
500mb heights. The first of these is a narrow but elongated upper-
level ridge that is quickly amplifying northward into the local
area. As this occurs this evening, a mid-level shortwave
impulse will traverse the northern periphery of the ridge
pushing it through the local area. This along with an axis of
low-level theta-e advection, will be the instigating mechanism
for an axis of showers and storms to move into southeast MN
early this evening and continue meandering east into the
overnight hours. Overall the environment is fairly lackluster
with skinny instability profiles that are mainly elevated early
on in the overnight hours. As a result, expecting any convection
that does develop to be fairly weak and slow to develop,
primarily showers. However, as we get later into the overnight,
increasing instability associated with an axis of 850mb moisture
transport overnight may provide an extra "kick" for convection
to become slightly more vigorous as shown in several of the
CAMs. This would likely still sub-severe given the questionable
0-6km shear being under 30 kts in the 12.15z RAP.

Saturday - Tuesday: Summertime Warmth Returns

As we head into the weekend, the aforementioned upper-level ridge
amplifies into the local area with 850mb temperatures surging to
around 20-24C. As a result, much of ensemble guidance is in fairly
strong agreement for temperatures over the weekend with the grand
ensemble (GEFS/EC/Canadian ensemble) having only a couple degrees of
deviation in the inter-quartile range for high temperatures with
values in 80s across the area. Overall, the 12.00z Extreme
Forecast Index has decent probabilities (60-90% of EC members)
to be warmer than model climatology this weekend and early next
week. However, with only a few members approaching the 99th
percentile of model climatology, thinking that this round of
warmth will not be reaching daily records. The warmest period
will likely be this weekend as the synoptic upper-level ridge
does get nudged slightly eastward to start the new work week as
a mid-level trough swings through the Dakotas.

Speaking of this mid-level wave, cannot rule out some precipitation
chances for Sunday night as the grand ensemble (GEFS/EC/Canadian
ensemble) has some probabilities (20-40%) for measurable
precipitation west of the Mississippi River. However, remains
unclear exactly how conducive the atmosphere would be with
subsidence from the present ridge still a factor along with sounding
profiles in the 12.12z suggesting a fairly robust capping inversion
during this time period.

Wednesday - Friday: Slight Cooling Trend, Rain Chances Increase

As we approach the middle of the upcoming work week, deterministic
and ensemble guidance generally agree on bringing some form of a
secondary shortwave into the Upper Midwest which will attempt to
push the previously mentioned ridge eastward. This will aid in
advecting a slightly cooler airmass into the region of which the
grand ensemble (GEFS/EC/Canadian ensemble) lowers median high
temperatures closer to normal for this time of year during this
period. Still some disagreement amongst ensemble members,
particularly towards Friday with a wide inter-quartile range in
high temperatures (middle 60s to lower 80s), likely due to
larger disagreements between various ensemble clusters on how
much the trough wedges itself into the area.

As far as precipitation chances are concerned, cluster analysis of
the grand ensemble depicts two general solutions, one where the
trough firmly pushes into the region and one where the ridge that
has dominated this forecast cycle lingers to the east.
Interestingly, the majority of the EC membership (around 65%)
favors a more persistent ridge scenario where precipitation
chances are more minimal (around 10-40% chance in this cluster
later next week). This is contrasted by the majority of the GEFS
members (around 75%) which favor a faster progressing shortwave
which precipitation chances would be very likely (70-90% chance
late week). Considering that the overall synoptic pattern
remains in question, any finer details regarding precipitation
trends are challenging to determine at this time.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1235 AM CDT Sat Sep 13 2025

A band of showers and storms roughly along and north of an EAU
to DLL line gradually shift southeastward overnight and depart
the region by sunrise. Localized MVFR to IFR visibilities are
possible in any of the heavier showers. VFR conditions are then
forecast for the rest of the day into the evening, though the
potential for fog will need to be monitored for overnight. Winds
will be from the south to southeast at around 5-10 kts for the
TAF period.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...Skow