Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 042346

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

Issued at 546 PM CST Sun Dec 4 2016

Local radar and observations indicate all the significant snow has
moved out of central Wisconsin. There could be some remaining
flurries or drizzle for a couple hours this evening. Temperatures
are near freezing, so the drizzle could put a very light coating
of glaze on any untreated surfaces. Not expecting this to last
long enough to pose any significant problems. Will let the winter
weather advisory expire at 6 p.m. as scheduled.


.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

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 00Z TAFS through 00Z Monday evening)
Issued at 546 PM CST Sun Dec 4 2016

The back edge of the clouds has been working across southern
Minnesota this afternoon and is expected to move through both
airports this evening. Until the clearing does move in, expect
the ceilings to remain MVFR. Some concern for fog overnight as the
forecast soundings show the lowest levels of the atmosphere remain
saturated. However, countering this, should be the southwest winds
of 5 to 10 knots. Will include some MVFR visibilities at KRST but
for now keep KLSE clean. VFR conditions then expected from Monday
morning through the afternoon, but the next system will be
quickly advancing across the northern plains that could bring in
some MVFR ceilings right around 06.00Z.





LONG TERM....Rieck
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