020
FXUS63 KARX 010858
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
358 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Low (<15%) chance in scattered storms grazing western
  peripheral counties in southeast Minnesota this evening into
  tonight.

- Low (<30%) confidence in initial storm chances through
  Tuesday. Storm chances increase (50-80%) Tuesday night through
  Wednesday. Low (<5%) confidence for severe storms.

- Cold Wednesday through the weekend with overnight lows from
  the 30s in central Wisconsin to 40s elsewhere locally.

&&

.DISCUSSION...
Issued at 156 AM CDT Mon Sep 1 2025

Temperatures Top Out In The Mid 70s Today:

Little change in the overall pattern keeps similar conditions
today as Sunday with high temperatures pushing the mid 70s
across the local forecast area. While the main area of ongoing
storm activity associated with a disjointed synoptic axis of
dilatation extending from the Ohio River Valley through South
Dakota on early morning GOES water vapor imagery will remain
south and west of the local forecast area, a weakening upper
level trough will shunt increased low level theta e farther east
through Minnesota, potentially allowing diurnally induced
scattered storm activity to graze western peripheral counties in
southeast Minnesota this evening. However, lingering low level
cold air will limit local impacts evident in potential storm
decay should storms shift slightly southeast.

Low Storm Confidence (25%) Overnight Through Tuesday:

Contention between the lingering cooler, drier air and an
impending upper level trough sagging south-southeast through
southern Canada on Tuesday continues storm discrepancies
overnight through Tuesday. The most boisterous solution in the
HRRR (01.00Z) reinvigorates a line of southeasterly sagging
storms through central Minnesota overnight, causing a disjointed
line of storms across the local forecast area Tuesday
afternoon. While other high resolution model solutions also
suggest similar, the southeastern extent will be abruptly
challenged as they outrun the better forcing due to temporary
stagnation in the synoptic pattern before reinvigoration in the
aforementioned upper level trough. Will be close trend to
monitor in coming forecasts should initial timing of storms need
to be quickened.

Storm Potential Tuesday Night Through Wednesday:

The rapid progression of an upper level trough, currently
evident in a tropopause fold over the Northwestern Territories
of Canada with 75th-90th percentile 250mb temperatures in the
Inuvik, NT 01.00Z RAOB, perpetuates limited confidence in local
impacts through Wednesday. Furthermore, as a result of a
subsequent PVU dipole, accompanying injection of inertially
unstable air, and a jetlet/westerly jet invigoration, the upper
level low expected to quickly halt and stall along the northern
periphery of the Great Lakes. The quick halt in meridional
propagation again decreases local confidence in impacts as LREF
membership holds low formation and subsequent propagation
northeast of the local forecast area over Ontario, Canada.

Current confidence in storms is highest (50-80%) overnight
Tuesday through Wednesday (LREF) as instability (500-1500 J/kg)
pools along the frontal boundary. The rapidly changing nature of
the responsible tropopause fold limits confidence in strong to
severe, evident in individual LREF member sounding hodographs
plumes. Longer hodographs suggest ample shear in the mid to
upper levels accompanying the extratropical cyclone however the
overnight lack of diurnally aided instability keeps overall
confidence <5% in machine learning severe weather models.

Heavy precipitation brings 30-50% LREF probabilities for 0.5"
of QPF in 24 hours primarily in Wisconsin.


Colder Midweek Through The Weekend:

Higher confidence impacts will be colder air across the Upper
Mississippi River Valley after Wednesday. A slightly colder
solution for Friday night and Saturday night compared to
previous forecasts is a result of a stronger solution to the
closed low churning over southern Canada.

Local forecast area expected to drop into the 30s in central
Wisconsin to low 40s elsewhere initially overnight Wednesday
through Thursday morning then again overnight Friday and
Saturday (60-80% confidence). Minimal (<20%) confidence in
impacts from frost with NBM probabilities for below 37 degree
temperatures limited to climatological cold spots in central
Wisconsin.

NAEFS and ENS standardized anomalies of -2 to -3 suggest quite
anomalous cold for this time of year. While ECMWF extreme
forecast index of -0.7 also suggests anomalous cold, a shift of
tails of 0 shows that an extreme event is unlikely. Therefore,
current forecast confidence for record cold at La Crosse, WI or
Rochester, MN is low (10-30%) through the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1208 AM CDT Mon Sep 1 2025

Like the past several days, conditions are favorable for the
development of valley fog. However, there is still some
uncertainty whether this fog will impact KLSE or not, so just
stayed with the current forecast MVFR fog. This fog will likely
dissipate around 01.14z.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...Boyne