361
FXUS63 KARX 240037
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
637 PM CST Sat Nov 23 2024

.KEY MESSAGES...

- One last day of warmer weather on Sunday before colder
  weather sinks in for next week and beyond. Wind chills by next
  weekend fall to the single digits above/below zero.

- Light rain/snow mix Sunday night into Monday morning with the
  risk for snow creeping into the forecast for Wednesday, mainly
  south of Interstate 90.

&&

.DISCUSSION...
Issued at 215 PM CST Sat Nov 23 2024

Tonight - Sunday: Cloudy, but Warm

A decaying ribbon of 600-mb frontogenesis attendant with an
upper level 105-kt jet streak/PV lobe brought mid-level clouds
to the region, but the presence of a dry sub-cloud layer kept
any impacts limited to a few stray flurries at best. The
upstream ridge builds in for tonight and Sunday with steady warm
air advection taking place tonight as lower tropospheric
temperatures south of I-90 rise from +2 to +5C between this
afternoon and midday Sunday. A dense mid-level cloud shield
originating off the Pacific lingers through the night and into
Sunday, preventing overnight temperatures from falling too far,
but also limiting insolation during the daytime on Sunday.
Highs still look to top out in the 40s areawide, and looking at
the longer range ensemble members, this may be the warmest day
we see for the next 2 weeks.

Sunday Night - Monday: Next Round of Light Rain/Snow

The upper ridge shunts off to the east Sunday afternoon with a
weak/disorganized lee cyclone ejecting off the Front Range
Sunday night and lifting into the southern Great Lakes region by
Monday afternoon. Ahead of this broad 1007-mb low, easterly
flow under the mid-level warm front will lead to a steady
saturation of the surface to 800-mb layer while increasing
isentropic ascent through this corridor will increase the
potential for drizzle overnight. Did increase PoPs over the NBM
given the drizzle soundings noted in the HRRR/RAP as well as the
higher LREF/HREF QPF signal north of I-94 into the day on
Monday (70-80%+).

Confidence in exact precipitation amounts is not overly high
given the disorganized nature of the cyclone, but impacts look
to be minimal given the warm near-surface temperatures (only a
10-20% chance of seeing temperatures below 32 degrees before
sunrise Monday north of I-94) that should keep precipitation
mainly as rain and limit any snowfall amounts. What is more
certain is that this system heralds the arrival of colder air
that will stick around for quite some time. Temperatures remain
steady or fall through the day on Monday with lows in the teen
Monday night.

Tuesday into Next Weekend: Colder, Periodic Bouts of Snow

The upper level pattern takes a notable shift from midweek
onward with the previous zonal flow pivoting to a northwesterly
tilt and advecting polar air southward for the Thanksgiving
holiday period. A second shortwave wraps southeastward from the
Canadian Prairies through the north central CONUS late Tuesday
into Wednesday. The medium range solutions differ on how far
north the baroclinic zone can recover before this wave arrives,
resulting in different low tracks and placement difference in
the accompanying snow band. The EPS clusters have been bringing
the deformation zone further northward compared to the more
compressed GEFS members and it is worth noting that 60-70
percent of the EPS members bring some measurable snow into
northeast Iowa and southwest Wisconsin. Given that the wave is
still 3-4 days out and is not the best resolved, did not make
too many adjustments to the lower NBM PoPs, but this system
does bear monitoring given the busy holiday travel period.
Colder air floods southward for late in the week and next
weekend as highs by Friday stagnate in the 20s and lows fall
into the single digits.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 546 PM CST Sat Nov 23 2024

VFR conditions through tonight with deteriorating conditions
Sunday. Forecast soundings show moistening mostly top down
through Sunday morning, however they differ on how quickly the
lower levels will saturate (MVFR ceilings develop). For now,
will trend from morning/midday to the afternoon from southeast
MN into western WI with deteriorating conditions expanding
across northeast IA and southern WI.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Zapotocny