Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 160850
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
250 AM CST Sat Dec 16 2017

.SHORT TERM...(Today and tonight)
Issued at 250 AM CST Sat Dec 16 2017

Early this morning, light warm advective snow will continue mainly
north of I-94. Upstream observations show visibility between 2
and 5 SM, so additional accumulation should be minimal, generally
under an inch. This snow will diminish and lift northward through
the morning, with a return to dry conditions this afternoon.
Otherwise, expect mostly cloudy skies through the day with a large
gradient in temperatures from north to south. Highs across the
north will only be in the mid 20s, while some spots across northeast
IA into far southwest WI could reach 40 degrees, especially if
the clouds break a bit this afternoon.

For tonight, 16.03Z SREF is showing higher probabilities for lower
visibility south of I-90 with the potential for some fog in the
vicinity of a warm/stationary front. For now, will keep fog out
of the forecast given uncertainty in the amount of low-level
moisture and because skies appear to remain mostly cloudy through
the night. Something to watch and may need to be added later
today. Nighttime lows will be mild for mid-December standards,
dropping into the lower to mid 20s.

.LONG TERM...(Sunday through Friday)
Issued at 250 AM CST Sat Dec 16 2017

Sunday will be cloudy, but dry as a weakening short-wave passes to
the south across northern IL into southern MI. Surface high pressure
will build across the forecast area late in the day, resulting in
light northeast wind and temperatures in the lower to mid 30s.

Another short-wave moves across the Upper Midwest Monday into
Tuesday. However, moisture is limited so light snow chances
should be confined to northern WI Monday night. Warm air advection
ahead of this wave Monday will allow temperatures to rise well
into the mid to upper 30s for most areas. Some spots across the
south are also likely to top 40 degrees. Tuesday`s highs will be a
couple degrees cooler in the wake of a passing cold front, but
should still rise into the 30s for most areas. Both Monday and
Tuesday will also be breezy...from the southwest on Monday, then
switching to the northwest on Tuesday.

A large eastern Pacific trough dives into the intermountain west
on Wednesday with a lee cyclone starting to take shape across
eastern CO by 00Z Thursday. Broad warm advective snows develop
across the Dakotas into northern MN late in the day, moving into
northern WI by Thursday morning. Given good model agreement
between the GFS/ECMWF, likely POPs seem reasonable for this time
north of I-90. Models then diverge Thursday into Friday with the
timing and track of the ejecting surface low. The faster GFS
lifts the low quickly northeastward across IA/southern WI and into
central MI, whereas the ECMWF favors a more southerly track
across the Central Plains and into central IL/northern IN. That
said, both solutions drag a deformation snow band across the
forecast area sometime Thursday night into Friday, although the
ECMWF is a bit more robust. Run-to-run model consistency has not
been great with this system and expect additional changes before
solutions converge. Because of this, way too early to provide
meaningful details, but something to continue to watch.

A return to dry, but much colder conditions looks likely late
Friday into next weekend with daily highs back into the teens to
mid 20s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1120 PM CST Fri Dec 15 2017

Cigs/WX/vsby: mvfr cigs have shifted a bit north, and trends favor
keeping them away from KLSE. Will go VFR cig forecast for both TAF
sites through the better part of Saturday. Some -sn may continue a
couple hours past 06z, possibly brief impacts on vsby.

GFS/NAM then suggest a return of low mvfr cigs later Sat evening
from the north. Not entirely sold on this, but some consensus here,
so will add to the forecast.

Winds: light south/southeast will become more east on Sat. Light
tonight and under 10 kts for Sat.


&&

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

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION.....Rieck



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