Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200546
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1146 PM CST Sun Nov 19 2017

.SHORT TERM...(Tonight through )
Issued at 200 PM CST Sun Nov 19 2017

Mild Monday, then a colder/raw/windy day Tuesday.

Low level warming, an increasing southerly fetch and ample sunshine
will result in a mild start to the new work week. Highs in the upper
40s to around 50 are expected for most - 5 to 10 degrees above
normal.

Models all in good agreement with driving an upper level shortwave
trough southeast across the region Monday night/Tuesday, with an
associated cold front slipping across the local area Monday night.
Some qg convergence with the shortwave, mostly upper/mid level and
across northern parts of MN/WI. Models all favoring keeping any pcpn
threat (at least in terms of measurable qpf) well north, where the
deeper saturation is expected along with the stronger forcing. That
said, low level lapse rates are quiet high thanks to a strong slug
of cold 850 mb air (temps fall from +6 C 18z Mon to -12 C 18z Tue).
Bufkit soundings even suggest a little weak instability. Increasing
RH in the 900-800 mb layer on Tue, post the front, might be enough
for some instability cu - potential showers/flurries? Not sold on the
threat enough to add to forecast, but its something to watch.

While the good lapse rates won`t necessarily result in snow showers,
they will help with mixing down stronger low level winds. This is in
addition to a tightening sfc pressure gradient late Mon night
through Tue as the sfc low passes to the north. Its going to be a
windy, raw day. Gusts in the low/mid 30s seem likely at this time,
especially in the open/unsheltered areas.

.LONG TERM...(Wednesday through Sunday)
Issued at 200 PM CST Sun Nov 19 2017

Fairly progressive upper level flow with shortwave ridge/troughs
transitioning quickly west to east across the conus. Question
locally isn`t so much about pcpn chances but the impact on
temperatures. After the cool down of Tue, upper level/sfc ridging
already working back in for Thanksgiving and Black Friday - warming
back to around +12 C by 18z Fri. There has been a little back and
forth in the models with how warm it could/would get - but trends
siding for mild conditions for the start of the holiday weekend.
Highs in the 50s for Friday look likely at this time. Colder air
returns for Sat/Sun as an upper level trough drops across the Great
Lakes.

The Friday night trough is set to spin across northern parts of the
region, dragging a cold front along with it. 150 kt 300 mb jet will
push it along, aiding in lift as it does. The EC is a little farther
south and faster with this system in the 12z run, favoring a shot
for pcpn from around i-90 northward. While previous GFS runs have
trended a bit drier, its 12z run is more in line with the EC - at
least in terms of bringing pcpn chances southward. The bulk of
the QPF in both models is north. Going to let consensus detail
chances for now.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1146 PM CST Sun Nov 19 2017

VFR conditions expected through the period with some occasional
high level ceilings overnight and again Monday evening. High
pressure over the Ohio River Valley will continue to move away
from the region. An area of low pressure across southern Canada
will stay well to the north of the area as it moves east through
Monday evening. It will push a cold front toward the area and with
a tightening pressure gradient ahead of it, look for sustained
south winds of 10 to 15 knots. A few gusts could occur at KRST
Monday afternoon, but forecast soundings show a very shallow mixed
layer with relatively uniform wind speeds and opted to not include
them for now.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...04



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