Area Forecast Discussion
Issued by NWS La Crosse, WI

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168
FXUS63 KARX 161759
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1159 AM CST Fri Feb 16 2018

.SHORT TERM...(Today through Sunday)
Issued at 156 AM CST Fri Feb 16 2018

High Impact Weather Potential: Light accumulating snowfall looking
quite likely for Saturday. Winds could be a concern for Sunday as
well.

Active weather regime in the works through the weekend and beyond,
with quite a few systems of interest to be closely watched. Can`t
say that for today though, with low level ridging working into the
picture and delivering what should turn out to be a sunny late
February day, albeit much colder than the past two days with ongoing
cold advection through midday in the wake of an earlier cold frontal
passage.

Bigger focus is set on later tonight into Saturday with the arrival
of our next upper wave and associated cold front. Decent slug of
low/mid level warm advection ascent maximized across our local area
ahead of those features should do its best to accomplish top-down
saturation, with a few-hour window of mainly light snow increasingly
likely through midday Saturday, perhaps lingering a little into
Saturday afternoon as well with the passage of the actual shortwave.
Still some question about how far west the better saturation will be
realized (NAM not really wanting to play ball across western
counties) but the overall idea for maybe an inch of wetter snow
looks pretty good at this time.

Next wave still on track to skirt to our north on Sunday, with a
surface cyclone tracking across central Minnesota into northern
Wisconsin, putting the majority of the area within the warm sector.
Very tight thermal gradient aloft should really help crank the
winds, with guidance the past few days downright impressive showing
70+ knots up around 850mb centered at 18Z Sunday. Not a chance we`ll
be able to mix that high, even in the warm sector, but even mixing
to 900mb should help us realize surface gusts of 30-35 mph. Will
have to closely monitor trends, as just a slight more depth to
mixing would put us really close to some advisory-level gusts in
spots simply given the strength of winds aloft. Will also be
watching precip potential near/north of the elevated warm front,
particularly north of I-94 where warm advection is maximized for
some potential of light snow or rain, pending thermal profiles.
Still appears the better precip risk will be more into northern
Wisconsin, which is a slightly farther north shift over previous
guidance.

.LONG TERM...(Sunday Night through Thursday)
Issued at 156 AM CST Fri Feb 16 2018

Active weather regime looks set to continue through at least the
early portions of the work week, with a shift in the flow regime to
a western CONUS trough and southeast CONUS ridge, favoring a tight
baroclinic zone stretched across the Midwest and several precip
chances along that feature. No shortage of detail issues to be
worked out in this setup, but trends the past 48 hours strongly
indicate our next good precip chance will come on Monday with an
elongated axis of frontogenetical forcing stretched across the area,
and lift aided by the right entrance region of a potent upper jet
laid out across southeast Canada. Good moisture working north toward
the area, with PWAT values pushing 0.75 inches just to our east, but
the big question remains thermal profiles with increasing hints that
we`ll deal with a pretty sizable warm nose aloft for part or even
all of the area. Huge spread among ensemble guidance at this
juncture but this one should have a pretty solid cold air feed from
the north so it definitely bears watching.

Beyond that, some snow chance looks to linger into Tuesday as well
but with quiet weather returning for midweek as high pressure again
exerts its influence across the area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1159 AM CST Fri Feb 16 2018

For this afternoon through tonight, winds will be the main concern
as ceilings and visibilities remain at VFR levels. Surface winds
around 10 kt will shift from northwest to south-southwest by early
evening. A strong low-level jet is forecast to develop tonight,
which will create wind shear concerns. Expect 2 kft southwest
winds to reach 40-50 kt from around 17.06Z to 17.12Z. Surface wind
speeds should also increase at KRST overnight, with some +20 kt
gusts possible.

An upper-level disturbance moving in from the west is forecast to
produce snow across the area Saturday morning. Details will likely
need fine-tuning in future TAF issuances, but be prepared for IFR
visibilities and MVFR ceilings as the snow moves through.

&&

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

$$

SHORT TERM...Lawrence
LONG TERM....Lawrence
AVIATION...Hollan



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