Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 151758
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1158 AM CST Mon Jan 15 2018

.SHORT TERM...(Today through Tuesday)
Issued at 300 AM CST Mon Jan 15 2018

High Impact Weather Potential: Periods of snow to continue today
into tonight with some additional light accumulation. Some blowing
snow concerns continue west of the Mississippi River, with wind
chill issues also arising for those same areas.

Love it when a forecast comes together as expected! And that`s
been hard to come by this winter so far. Well advertised closing
upper low continues to drop across the region early this morning,
with that feature dropping directly overhead into this evening
before departing through the Ohio Valley Tuesday evening. In the
low levels, stacked low pressure will meander across southern Lake
Michigan today, prolonging broad but persistent warm advection
ascent for many areas east of the upper low track, which
translates to locales near and east of the Mississippi River in
this case. Interesting feature to watch in this setup remains
sharp low level convergence within an inverted trough axis
currently laid up across Lake Michigan (helping drive a band of
intense snow), with that feature expected to slip westward through
the day and into the evening.

Given that setup, do expect to see a narrow band of more intense
snowfall within the broad shield of persistent light snow for many
areas, but exact placement remains somewhat of a challenge. In all
likelihood, that axis will migrate westward through the evening up
to the Mississippi River, and could produce a quick inch or two
within a narrow corridor as it meanders westward, in addition to a
broad inch or two falling just from persistent light snow through
the 12 or 18 hour period into late evening. From a ratio standpoint,
while the depth of the dendritic growth region does shrink from what
we saw yesterday evening (when some impressive 30-40 to 1 ratios
were noted!), we do still maintain a roughly 5-6kft DGZ depth and
also increase it near the surface into the afternoon/evening.
Suffice it to say that some travel impacts will remain through the
day and the current Winter Weather Advisory into Wisconsin looks
quite good at this point, though may need to shorten it up a
little in time.

Other component will be increasing wind across areas up to the
Mississippi River within sharp low level cold advection, with 25-30
knots in the mixed layer translating into 30 mph gusts at times.
Already seeing visibility reductions west of the Miss River due to
likely blowing/drifting snow given the very fluffy nature of the new
snowpack, and that should continue through late afternoon before
diminishing this evening. Not so much of an issue farther east with
a baggy gradient in the vicinity of the inverted trough axis, with
wind chills also becoming an issue farther west as Arctic air dumps
in with the aforementioned stronger winds. Current Wind Chill
Advisory looks very well trended at this point through Tuesday
morning, with snow gradually winding down later tonight into Tuesday
morning, though we may deal with some lingering pesky clouds for
part of Tuesday.

.LONG TERM...(Tuesday Night through Sunday)
Issued at 300 AM CST Mon Jan 15 2018

A nice quiet stretch of weather still expected through the remainder
of the work week as broad low level ridging crosses the area into
midweek, followed by a flattening of the flow regime and warmer air
working back north by Thursday into Friday. Source region of that
warmer air remains rather dry off the Plains, so not anticipating
widespread stratus and/or drizzle issues as that warmer air runs up
over the snowpack, but highs cracking freezing by Friday appear very
likely. Thereafter, increasing hints for stronger energy to eject
northeastward from the southern Plains sometime this coming weekend,
though plenty of questions about timing/placment of that system (big
ensemble spread) as well as what impact(s) it may bring up this way
in terms of wintry weather. Suffice it to say at this point that the
potential for some wintry precipitation does exist, but we`ll have
to iron out the details over the coming days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1158 AM CST Mon Jan 15 2018

Light snow will continue to fall through the evening hours at
both sites, with IFR visibilities through the afternoon. A
transition to flurries will occur at RST for the evening hours,
but gusty northwest winds around 25 kts will cause some blowing
snow leading to MVFR visibility. The transition to flurries at LSE
will be around 06Z, but with lighter winds, not anticipating any
visibility reductions. In fact, may be holding onto 2 SM mention
at LSE for too long, but snow will be slightly heavier at LSE, so
will keep it through 06Z for now. Based on upstream observations,
rising ceilings will also be seen with the transition to
flurries, remaining MVFR at RST (around 2500 ft AGL), but moving
into the VFR category at LSE (3500 ft AGL). Snow should come to an
end completely for both sites by Tuesday morning. Some guidance
hints at VFR conditions for RST by the end of the TAF period, but
confidence not high enough to include mention at this time.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until midnight CST tonight for
     WIZ032>034-041>044-053>055-061.

     Winter Weather Advisory until 6 PM CST this evening for WIZ017-
     029.

MN...Wind Chill Advisory until noon CST Tuesday for MNZ079-086>088-
     094>096.

IA...Wind Chill Advisory until noon CST Tuesday for IAZ008>011-018-
     019-029-030.

&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...CA



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