482
FXUS63 KARX 241120
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
520 AM CST Mon Nov 24 2025

.KEY MESSAGES...

- Precipitation chances increase through today with widespread
  light accumulations expected by Tuesday morning and a narrow
  band of 0.25" to 0.5" possible.

- Precipitation chances temporarily lower Tuesday morning,
  increasing Tuesday night with a switch to snow overnight into
  early Wednesday morning. Current confidence of 70-95% for
  measurable snowfall along and north of Interstate 94 in
  central Wisconsin.

- Increased winds overnight Tuesday through Wednesday with cold
  temperatures bring apparent temperatures from the teens to
  single digits.

- Cold temperatures stick around through the weekend.

&&

.DISCUSSION...
Issued at 324 AM CST Mon Nov 24 2025

Early Morning Observations:

An area of upper level confluence evident in GOES upper level water
vapor imagery has taken shape overnight laying from lee of the
Rocky Mountains through South Dakota into Minnesota, between a
closed upper level low advecting east-northeast along the
Nebraska-Kansas border and an upper level trough progressing
east through the western Dakotas. Resultant upper level speed
divergence enhanced the upper level subtropical jet streak in
GOES derived upper level winds, rapidly shedding the increased
moisture content previously accompanying the closed low to the
northeast, spreading across the Upper Midwest overnight. While
the associated upper level speed convergence abutting the
northern periphery of the area of confluence is mixing this
moisture through the atmosphere, additional moisture residing
within the northern wave (90th percentile PWATs of 0.5" at BIS
and GGW 24.00Z & 23.12Z RAOBs previously mostly in the mid
levels according to POES derived Advected Layer Precipitable
Water Values) and moisture within low level return flow (80th
percentile 850mb dewpoints at OAX 24.00Z RAOB) will all work
together to increase local precipitation potential initially
this afternoon.

Precipitation Chances Today & Tonight:

Main area of precipitation expected along the low level convergence
zone collocated with the lobe of increased low level moisture
draped southwest to northeast across the local forecast area
later this morning, until eventually eradicated by subsequent
cyclogenesis Tuesday evening/night. Initial isentropic upglide
near 290K will be aided by lobes of low level frontogenesis and
ageostrophic ascent within the aforementioned /further/ enhanced
anticyclonically curved upper level jet streak downstream of
the closed low attempting to rejoin parent upper level flow as
an open wave from the Missouri to Mississippi River Valleys.
While confidence in overall, widespread rainfall amounts from
0.01" to 0.1" is high (60-90%) during this time, a southwest to
northeast oriented narrower band of higher amounts from 0.25" to
0.5" remains a confidence buster and forecast challenge.
Confidence in meridional location of band is main concern with
highest rainfall amounts and rates dependent on extent of
aforementioned low level frontogenesis. Current HREF membership
meridionally varies locally from Dodge County, MN through Clark
County, WI in the Fv3 to Fayette County, IA to Adams County, WI
in the ARW. Regardless, additional synoptic forcing will
provide widespread rainfall with LPMM/PMM near 0.1" by Tuesday
morning.

Rainfall Persists Tuesday:

A short reprieve in rainfall Tuesday morning appears possible as the
forcing surrounding the closed low shunts east through the Ohio
River Valley. The low level moisture axis and frontal boundary will
remain draped over the forecast area however, potentially
persisting light rain chances area wide although highest in
locally northern most counties of central Wisconsin where
veering winds provide isentropic upglide and baroclinic
moisture flux causes meager moist baroclinic instability and
potential weak cyclogenesis along the boundary.

Confidence in precipitation chances increases through Tuesday as the
upper level trough off the Pacific Northwest phases through the
Northern Plains provides additional cyclogenetical forcing over
the forecast area Tuesday night into Wednesday morning.
Ensemble spaghetti MSLP contours suggest a slower, deeper trend
to this surface low as it advects northeast over the Great
Lakes through Wednesday, potentially perpetuating local impacts
from the wrap around cold air combined with a moist quasi-
comma head of 0.25" to 0.5" PWATs trailing the low center.
Current confidence in cyclogenesis tracking across the forecast
area initially increases area wide precipitation potential from
intensifying frontogenesis south of the low center pushing east
Tuesday evening/night with wrap around precipitation lingering
north of Interstate 90 Wednesday morning and afternoon. Enhanced
low level cold air advection in the wake of the low passage may
further saturate the lowest levels and require longer duration
PoPs into Wednesday night however current individual ensemble
and cluster confidence keeps probabilities <10% at the current
forecast hour.

Snowfall Tuesday Night Through Wednesday:

Duration remains the main forecast discrepancy regarding local
snowfall amounts as ensemble soundings suggest a quick switch in
precipitation type Tuesday night through Wednesday as the
wraparound precipitation takes hold north of Interstate 90.
Ensemble confidence in snowfall amounts has remained steady for
1" along and north of Interstate 94, assuming a 10:1 SLR. Given
higher SLR expectations, may see first 1" of snowfall as far
south as Interstate 90 (40-60% confidence) overnight Tuesday
into early Wednesday morning. How long snowfall lingers locally
north of Interstate 94 will determine locally higher impact
potential. Concurrent increased winds will exacerbate widespread
snowfall impacts with decreasing visibilities.

Quick Cooling Midweek:

The rapid deepening is accompanied by a polar airmass sinking into
the Mid Missouri to Mid Mississippi River Valleys by midweek with
850mb temperatures less than 10C below normal. The intense low level
cold air advection combined with the extremely tightened pressure
gradient will steepen low level lapse rates and increase winds
across the forecast area overnight Tuesday into Wednesday, lasting
through Wednesday night. While neither the ECMWF (24.00Z) or
GFS (24.00Z) show pressures below 500mb on the 1.5 PVU surface,
both their ensembles suggest sustained winds of 20+ kts and
gusts of 34+ kts. Both models have been slowly increasing
confidence for these values over their recent runs as well.
Therefore, have increased winds off of National Blend guidance
in collaboration with neighboring offices to better align with
expectations.

As a result, apparent temperatures in the 40s today through Tuesday
quickly drop to the teens and single digits across the forecast
area potentially as early as Wednesday morning. While spread in
minimum temperatures is minimal, 2-3 degree IQR in NBM,
confidence in magnitude and timing of initial winds potentially
concurrent with diurnal cooling and the large impact wind speed
has on apparent temperature calculations, overall confidence in
minimum wind chill values . NBM shows 80-90% confidence between
0 and 28 degrees Tuesday increasing to 100% for Thursday night.


Staying Cold Into The Weekend:

Regardless of exit timing for increased high (80%) confidence for
even colder temperatures Wednesday night into Thursday morning
and through the weekend with ensemble confidence for the 20
degree isotherm diurnally draped or grazing the forecast area
through the weekend; concurrent with <10 degree apparent
temperature probabilities increasing through the weekend.
Overall confidence in the pattern wanes through the weekend,
depending on exit behavior of the mid-week low, with 10F IQR in
the NBM come Saturday night as precipitation chances increasing
from the southwest.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 516 AM CST Mon Nov 24 2025

VFR conditions currently present across the area with MVFR/LIFR
stratus/fog building northeast out of Central Iowa. In the coming
hours, CIGs will likely drop to MVFR for both RST and LSE with
continued degradations expected for both sites through this
afternoon. Light rain is expected to move into the terminals after
18Z with some impacts to visibilities possible (likely in the
MVFR category). Conditions will further deteriorate to low end
IFR/LIFR tonight with continued chances for rain and drizzle.
Winds are expected to remain out of the south/southwest at less
than 12 kts through the period.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...Barendse