958
FXUS63 KARX 232340
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
640 PM CDT Sat Aug 23 2025

.KEY MESSAGES...

- Much cooler temperatures expected from today through Tuesday
  with highs struggling to escape the 60s. Overnight lows from
  Monday through Wednesday morning will be in the upper 30s to
  lower 50s.

- Small chances (10-30%) for sprinkles and showers this weekend.

&&

.DISCUSSION...
Issued at 1256 PM CDT Sat Aug 23 2025

Today - Tuesday: Much Cooler, Small Shower Chances

A very noticeable pattern change is underway as a surface cold front
pushed through the region last night bringing us our first taste of
early fall temperatures. The main synoptic feature that we can thank
for this pattern is due to a strong upper-level/sfc low pressure
center located in Ontario, Canada and will very slowly push
eastbound over the next few days. With the local area situated in a
upper-level northwesterly flow regime, cold air advection behind the
aforementioned cold front will keep our temperatures in the upper
60s to lower 70s for today. Cannot rule out (10% chance) some
isolated sprinkles this afternoon and evening as some shallow 0-3km
MUCAPE builds in, however the forcing is pretty nebulous so not
surprised that the CAMs are fairly limited in any sprinkle/shower
coverage.

As we head into Sunday, an upper-level front with attending
potential vorticity advection will push through the area during the
early afternoon. As this occurs, increasing 0-3km MUCAPE to around
250 J/kg and steep 0-2km lapse rates to around 8-9 C/km will ensue
which will be more than sufficient to induce to shower activity,
primarily near and north of I-94 where lapse rates are more
favorable. Overall, not expecting much QPF considering the dry
precipitable waters and only medium probabilities (40-70%) for 0.01"
of rainfall across the area with any of these in the grand ensemble
(GEFS/EC/Canadian ensemble). Regardless, had enough confidence to
include some isolated to scattered shower mention for much of the
local area on Sunday afternoon.

A fairly remarkable airmass for August then centers itself over the
region with geopotential height falls behind the upper-level front
later into Sunday and Sunday night. 850mb temperatures in the 23.12z
NAM/GFS fall to around 5C for portions of the area. The 23.00z NAEFS
standardized temperature anomalies even pick up on some
stratospheric intrusion with above normal temperatures at 200mb.
This makes sense given the tropopause depicted in RAP/NAM soundings
during this period is at around 250mb with the stratospheric
inversion atop it. Low temperatures will be cool, dare I say chilly
in some spots, by Monday morning with most spots in the 40s to lower
50s. Some of the lower percentiles of the NBM would suggest some
middle to upper 30s are even possible in portions of west-central WI
on Monday and Tuesday morning which when considering the light sfc
winds and minimal sky cover, does not seem unrealistic in our local
cold drainage locations. High temperatures underneath this airmass
will struggle to escape the 60s for many as the grand ensemble
(GEFS/EC/Canadian ensemble) has very low probabilities (0-20% chance)
for highs above 70 degrees through Tuesday.

Wednesday - Friday: Gradually Warming Up

Looking towards Wednesday, the upper-level trough begins to progress
east enough that some upper-level ridging tries to sneak into the
area, hence advecting a warmer air mass and increasing our high
temperatures slightly back into the 70s. As upper-level flow trends
more northerly with the departure of the aforementioned strong upper-
level low/trough, some indication that some shortwave perturbations
could sneak through the region late this week and into the week. As
of right now, there remains fairly substantial differences between
deterministic guidance with how they resolve these features. There
are some low to medium probabilities (30-45% chance) in the grand
ensemble (GEFS/EC/Canadian ensemble) for measurable precipitation,
however given the uncertain in how any shortwaves will manifest
during this period, confidence is low in exact timing and location
of any precipitation later into the upcoming week.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 641 PM CDT Sat Aug 23 2025

The combination of cyclonic flow and cold air aloft will result
in a 3-6K scattered to broken deck through this evening. It will
become scattered overnight and then become broken after 24.14z.
There may be even some showers on Sunday afternoon, but
confidence was not high enough to include them in the TAFs at
this time.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...Boyne