Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 042103
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
300 PM CST Sun Dec 4 2016

.SHORT TERM...(Tonight through Tuesday)
Issued at 300 PM CST Sun Dec 4 2016

Concerns are 2-fold:
1) Dense fog and/or low stratus tonight
2) Precipitation chances Monday night-Tuesday

Snow has made steady progress east, but probably won`t clear
Adams/Juneau WI counties until 6 pm. Opted to extend to advisory for
those counties, letting it expire elsewhere. Expect some impacts
through the evening for travel with many roads snow covered, slushy
and slick.

The challenge for the rest of tonight is the potential for fog
and/or stratus development. Current cloud mass is progged to shift
northeast through the nighttime hours, although it could hang tough
in the I-94 corridor. RAP more pessimistic, compared to the
NAM12/GFS, with slower clearing. Some high clouds then start to
spill in from the west near 12z ahead of a shortwave trough over the
Northern Plains. Meanwhile, winds stay fairly stiff through the
night - both at and just above the surface. That said, the fresh wet
snow pack will be a great moisture source, and hrrr/rap/nam bufkit
soundings keep a saturated near sfc layer through the night.
Certainly suggestive of either thick fog or low stratus. Winds would
usually point to more stratus, but could be an advective type fog
scenario.

Confidence not high on which way it will play out, but too much
consensus to dismiss the potential. Will go with areas of fog for
now...especially west of the Mississippi where the clearing is more
likely. If fog manifests, it could become dense - which would result
in a dense fog advisory. Something to watch.

That next shortwave swings across the region Monday night-Tue with
the bulk of its forcing holding to the north. It will drag a sfc
front through the local area though and that looks to have a
relatively strong, but very narrow band of frontogenetic forcing.
Saturation could be an issue, at least with pcpn type potential.
North-south running x-section keeps the deepest saturation generally
north of I-94. To the south it quickly shallows out, and loses any
ice in the cloud. Pcpn type would be liquid - and depending on sfc
temps - freezing rain/drizzle would be possible. Whatever falls
looks to be short lived - but a quick 1/2 inch of snow in the north,
and that freezing potential in the south - allude that it won/t
necessarily be an impact-free frontal passage.

.LONG TERM...(Wednesday through Sunday)
Issued at 300 PM CST Sun Dec 4 2016

Temperatures are going to be the big story for the later half of the
week. Significantly colder air will funnel southward across the
Upper Mississippi River Valley post the Tue system. The GFS and EC
drop 850 mb from around +2 C at 00z Tue to -16 C by 00z Fri. NAEFS
850 mb temp anomalies are around -1 to -2. The cold air starts to
moderate a bit by the end of the weekend as the next potential snow
maker moves in from the west. Highs look to hover near 20 Wed-Sat.

The weekend is showing some promise for accumulating snows as both
the GFS and EC want to drive an upper level shortwave trough across
the northern plains and then through the local area sat/sun.
Previous GFS run was more robust/quicker compared to the EC, and
would have favored more accumulations. 12z run came in weaker
though, more like the EC. Something to watch for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1137 AM CST Sun Dec 4 2016

The back edge of the snow has just past KRST and it will move east
of KLSE between 04.19z and 04.20z. Additional snow amounts at KLSE
will be up to a half inch. In the wake of this snow, MVFR
visibilities will continue through much of the afternoon, and
ceilings will be in the IFR to MVFR range. Both the ceilings and
visibilities will gradually become VFR tonight and remain that way
into Monday morning. If we decouple tonight, we may have to watch
for the potential for some fog for late tonight and Monday morning.

&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for WIZ043-
     044.
MN...None.
IA...None.

&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Boyne


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