128
FXUS63 KARX 070915
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
315 AM CST Sun Dec 7 2025

.KEY MESSAGES...

- Snow likely (50-80% chance) near and north of I-94 Monday
  night. Snow accumulations of around an inch or less are
  currently expected.

- A clipper system moves through the area bringing rain/snow
  Tuesday afternoon through Wednesday morning. Most snow
  accumulations are favored north of I-94 where probabilities
  (50-80%) are increasing for amounts of 2" or greater.
  Elsewhere, snow will either mix with or changeover to rain,
  limiting any snow accumulations.

- Colder than normal temperatures expected each day next week
  except on Tuesday. Temperatures get progressively colder
  starting Wednesday with increasing probabilities (60-80%
  chance) for highs in the single digits come Saturday.

&&

.DISCUSSION...
Issued at 315 AM CST Sun Dec 7 2025

Today - Monday: Below Normal Temperatures, Light Snow Monday Night

As snow exits east early this morning, northwest flow will establish
itself over the region as the parent upper-level trough pushes east
of the Upper-Mississipi Valley. As this occurs, surface high
pressure will move into the area allow for some clearing in sky
cover and aid in bringing cold advection into the area. Therefore,
highs will take a tumble for today with values only reaching into
upper single digits above zero to the teens and overnight lows
falling to around 0.

Temperatures will moderate some for Monday as the surface high
pushes southeast of the local area with temperatures returning into
the 20s for highs. The next feature to watch will be overnight on
Monday as a weak shortwave pushes through northern WI during the
overnight hours. Based on the current track of this system, this
would likely confine much of the precipitation potential to near and
north of I-94. Overall forcing with this wave is fairly weak with
much of it rooted in mid-level QG convergence and not much
frontogenetic footprint. Consequently, snowfall probabilities for an
inch or greater are really only confined to north of Hwy 29 in
Wisconsin and are not overly robust (40-60% chance) within the grand
ensemble (GEFS/EC/Canadian ensemble).

Tuesday: A Brief Warm-Up with Rain/Snow Likely, Accumulating Snow
Potential Near and North of I-94

For Tuesday, a more substantial clipper system will follow on the
heels of the Monday night wave that will take a similar path through
the northwesterly synoptic flow across the northern half of
Wisconsin. Overall the dynamics with this wave are more favorable as
the deterministic global models (GFS/EC/NAM) generally agree on
developing a robust surface low with fairly prominent warm advection
in the surface warm sector. Near and north of the surface low, the
07.00z NAM depicts some fairly robust sloping fgen in the 600-800mb
layer and isentropic lift which would provide some favorable ascent
for a band of moderate to heavy snow to develop over portions of
north-central WI during the evening hours on Tuesday and into the
overnight. Consequently, probabilities are already fairly high (50-
80% chance) in the grand ensemble (GEFS/EC/Canadian ensemble) for
snowfall amounts in excess of 2 inches assuming a 10:1 snow to
liquid ratio north of I-94, which granted this SLR could be slightly
higher given the present fgen.

Further south of the low, the warm air advection in the low-levels
should keep precipitation to either a rain/snow mix or just plain
rain for much of the event Tuesday and into Tuesday night with the
NBM keeping temperatures in the middle to upper 30s south of I-94.
Additionally, GFS/NAM soundings for this event show a warm nose at
800mb at KLSE which combined with above freezing surface temps
would only further support a more rain favored solution. Not
seeing too much signal for any freezing rain potential out of
this as the grand ensemble only has very low probabilities
(0-20%) for any measurable ice accumulations.

Wednesday - Saturday: Getting Progressively Colder, Possibly Bitter
Cold by Friday/Saturday

As we head into Wednesday morning, the surface low of the
aforementioned system pushes east of the local area subjecting the
region to both a strong surface pressure gradient and sharp cold air
advection. Consequently, could see a brief period where
precipitation transitions back over to snow for areas south of I-94.
However, probabilities for accumulations of an inch of greater are
very low (10-30% chance) south of I-94 during this period in the
grand ensemble (GEFS/EC/Canadian ensemble). However, could see some
breezy wind gusts Wednesday morning as the grand ensemble has
relatively high probabilities (40-70%) for wind gusts over 30 mph,
particularly in unsheltered areas of northeast IA and southeast MN.

After this system completely departs our region, the progressively
colder temperatures into the second half of the week and next
weekend will be the main story. As we continue past Wednesday,
persistent northwesterly flow and a descending shortwave on Friday
will usher in some very strong cold advection into the region with
stronger northerly flow. As a result, there is an increasingly
strong signal for bitterly cold temperatures Friday and into
Saturday with the inter-quartile range for highs in the grand
ensemble generally staying in the single digits above zero for
Saturday. This is further supported by the 06.12z EFI which already
has an 70 to 90 percent chance for maximum temperatures to be
colder than model climatology with a shift of tails of 0 present
areawide which is a footprint of a few EC members having highs
below 0 for Saturday. Needless to say looks like a fairly cold
period later in the week. As far as precipitation chances, there
does not seem to be any clear tangible wave outside of the
aforementioned Friday wave shown in deterministic guidance. As a
result, see mostly broad brushed medium probabilities (30-60%
chance) for measurable snow in the grand ensemble from Thursday
through Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1118 PM CST Sat Dec 6 2025

IFR conditions associated with ongoing snow should continue for
the first 1-6 hours of the period, tapering off west to east
over that time frame. As snow departs, some MVFR ceilings may
remain briefly, but VFR conditions should return areawide by
12z. Remaining 18 hours should be VFR with relatively light
winds, a welcome change for aviation interests. Next chance for
reductions looks to be after 06z Monday when some low ceilings
may affect areas west of the Mississippi.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 AM CST early this morning for
     WIZ053>055-061.
MN...Winter Weather Advisory until 6 AM CST early this morning for
     MNZ096.
IA...Winter Weather Advisory until 6 AM CST early this morning for
     IAZ011-030.

&&

$$

DISCUSSION...Naylor
AVIATION...Ferguson