Area Forecast Discussion
Issued by NWS La Crosse, WI

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886
FXUS63 KARX 230910
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
305 AM CST Wed Jan 23 2019

.SHORT TERM...(Today through Friday)
Issued at 305 AM CST Wed Jan 23 2019

While snow ended up being about half of what was originally expected
with this storm system (decided to take a more southern, weaker
track), the snow isn`t quite done with the local area yet. Currently
the sfc low was moving northeast toward central IL. Bands of snow are
spread northward of the low with good low level frontogenetic
support. However, west/northwest of the low another band of snow was
developing, more associated in the 700:500 layer. RAP points to good
frontogenetic lift in this region and slides it across KLSE through
about 15z. DGZ deepens for a couple hours within the lift and
saturation is plenty deep. A quick 1-2" of fluff is possible, with
impacts to the morning commute. This band looks fairly tight ~
approx 40 miles or so. Could be a region of very light snow, more
min accums south of this band and north of the bands closer to the
sfc low. Might come as a surprise for some who expected snow to be
done by now. Will extend the Advisory until 15z with this in mind,
continuing the warning til 15z.

Good agreement between the suite of models in dropping a mid level
shortwave trough southeast from Canada, spinning across the
northern great lakes late tonight through Thu. Not an overly strong
QG response, but relatively deep. Some low level warming leads the
system in, with strong cooling/cold air advection as the shortwave
marches through. Moisture shallows out though as your move from
north to south (x-sections, bufkit soundings), keeping the higher
threat for light snow across the north. Looks cold enough for ice in
cloud, even in the shallow cloud layers. Of interest is the deep DGZ
currently indicated in the GFS. 20:1 (or more) ratios would result,
with a fluffy 1-2" possible. For now, will keep chances generally
north of I-94.

Pressure gradient tightens sharply by Thu morning as this shortwave
moves through, and winds will become strong and gusty from the
north/northwest. Although fresh snowfall was not as much as previous
forecast, snowpack of 4+ inches currently on the ground across much
of the area. While a fresh snow would be a lot easier to move, with
sustained winds of +20kts expected for the wind prone/open
unsheltered areas of SE MN/NE IA, drifting snow is likely - and some
blowing (lifting higher in air, reducing visibilities) also possible.
See the potential for a Winter Weather Adv west of the Mississippi
River for Thu for blowing/drifting. Driving could be difficult at
times, especially high profile vehicles.

Attention then turns to the cold air, with a well forecast,
consistent message in the models for a punch of arctic air moving in
Thu night/Fri morning. NAM/GFS/EC all point to 850mb air around -25C
by 12z Fri. Lows into the teens below zero still on tap. The
pressure gradient will be slackening overnight Thu as high pressure
slips southward, just west of the local area. But enough wind that
wind chills from 35 to 20 below are still expected. Dangerously
cold. Advisories (warnings?) will be needed for all of the area Thu
into Fri morning.

.LONG TERM...(Saturday through Tuesday)
Issued at 305 AM CST Wed Jan 23 2019

First off - yup, still going to be cold. No change in that, other
then just how cold it will be. Models haven`t been very consistent
within nor between themselves in the chill of the arctic air they
are going to plunge across the area for the end of the week into
next week...just that it will happen. EC is now the colder of the
two for the start of the new work week - 10 degrees colder at 850 mb
compared to the GFS. The EC would then hold that cold through the
week while the GFS suggests some ridge building and moderating
temps. Not jumping on the EC yet, but suffice to say, the winter
cold (below normal) will hold for at least another week.

With northwest flow a loft dominating through the better part of
next week, there is always the threat for a weak perturbation to
spin across the region. Hard to discern ripples this far out.
However, the GFS and EC continue to key in on a couple stronger
shortwaves. The first is progged to drive across the northern great
lakes Sat night. Could bring a quick hitting light snow to the
region.

The second shortwave of note has a better chance for accumulating
snows locally with both models dropping that upper level wave
southeast through the northern plains, diving across the Upper
Mississippi River Valley Sunday night Monday. Latest 00z runs favor
a track that would favor the higher accumulations across the south,
although previous EC was a bit more north. All in all, both would
drop a few inches of fluffy accumulations - potential adv snows as
it looks right now. Not a ton of confidence in positioning yet, but
its a system that bears watching and could/would have impacts for
the Mon morning commute.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1139 PM CST Tue Jan 22 2019

General improvement has been noted through the evening as lower
ceilings and visibilities starting to shift southeast with main
short wave and associated winter precipitation. While some IFR still
being observed south, conditions have lifted to mainly MVFR for the
time being.

This trend will continue overnight it appears, but satellite and
METARs show bands of lower clouds mixed with VFR that will make TAF
forecasting a bit tricky.

As wave exits the area, generally improving conditions expected with
short term ridge building in later Wednesday. VFR conditions should
be more widespread as winds back.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 9 AM CST this morning for
     WIZ041>044-053.

     Winter Storm Warning until 9 AM CST this morning for WIZ054-055-
     061.

MN...Winter Weather Advisory until 9 AM CST this morning for MNZ096.

IA...Winter Weather Advisory until 9 AM CST this morning for IAZ010-
     011-019-029.

     Winter Storm Warning until 9 AM CST this morning for IAZ030.

&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Shea



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