Area Forecast Discussion
Issued by NWS La Crosse, WI

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992
FXUS63 KARX 161740
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1140 AM CST Mon Jan 16 2017

.SHORT TERM...(Today through Tuesday)
Issued at 350 AM CST Mon Jan 16 2017

Wintry weather is moving in, and looks to be an icing event for most
of the local area. Impacts to travel will occur.

Precipitation spreading northeast across IA early this morning,
fueled by broad low level thermodynamics and the push of the low
level jet/moisture transport.

1)Setup:

The strongest warm air advection/isentropic upglide will gradually
lift into southeast WI by 00z Tue...with the nose of the 850 mb
moisture transport/jet pointing into northeast IA. The low level
frontogenetics strengthens by this time, also slowing lifting
northeast through tonight. A secondary band of west-east running
frontogenetic forcing indicated in the NAM around 600-700 mb. Could
fuel-result in another band (mildly enhanced) on the northern fringe
of the main pcpn area.

500 mb shortwave trough moving out of the southern plains this
morning, spinning across northern IL tonight. Its associated sfc low
mirrors its path. Meanwhile, coupled 300 mb upper level jet still
looks like it will play a role, enhancing all the available lift
from late afternoon through the evening.

Northern stream shortwave trough drops into MN later tonight, giving
the system a push east, but also likely accentuating the lift/pcpn
region across the north.

The sfc low clears into Mich Tue morning, with the northern stream
shortwave trough shifting into eastern WI by 00z Wed.

2) Outcomes/PCPN types:

Complex scenario today into Tue with ample warming in low layers and
potential loss of ice (here and there) bringing a variety (all) pcpn
types into play.

As it looks right now, partial/full melting looks more likely
initially this morning, with sleet/freezing rain band resulting.
This band should shift north through the morning with freezing rain
most likely just south of there as the warming (and depth of that
layer) continues.

Rain becomes more likely across northeast IA/southwest WI with temps
inching above freezing. That said - road temps still cold, so
freezing could continue on roads, sidewalks. Southeast MN-western WI
looks like a mixed bag for the better part of the afternoon. Might
settle into one dominate type, but too hard to ferret out which one
quite yet.

Precipitation makes it way north of I-94 by this evening, and that
looks like mostly snow at this time. The wintry mess continues
elsewhere.

Most of the accumulating pcpn will be done by 12z Tue as the system
makes its way. Shallowing out of the cloud layer removes ice from
the cloud, but not much lift to suggest that drizzle/freezing
drizzle would occur.

Icing still looks to be the main threat into Tue. Amounts from
freezing up to 2/10 of an inch continue to look likely. The bulk of
the snow accumulations will fall north of I-90 with 1-2 inches. The
setup also looks favorable for sleet, so a few tenths of that.

3) Headlines:

Winter Weather Advisory looks good for the moment. Can`t completely
rule out the potential for more than 1/4 inch of ice along/south of
I-90, but not confident enough to warrant an upgrade to a warning.
That will be monitored closely. Have added Clark county in WI to the
advisory, per coordination with surrounding offices.

.LONG TERM...(Wednesday through Sunday)
Issued at 350 AM CST Mon Jan 16 2017

GFS/EC still in lock-step with building and amplifying upper level
ridge across the Upper Mississippi River Valley for the latter half
of the work week. 850 mb temps around +8 C with NAEFS 850 mb temp
anomalies from +1 to +2. Highs in the 40s look like a good bet for
the bulk of the local area Wed-Sun, perhaps flirting with 50 at some
locations Saturday. Its a January thaw most will appreciated.

With the warm up will come some release of the snow pack into the
river systems, and a potential for ice jams. Something to monitor.

By the weekend though the models shift the strong ridge to the east,
in a quasi-blocking pattern configuration. Strong trough after
trough progged to barrel into the west coast, hitting this "wall"
and lifting pieces of energy northward across the region. Its a
rather active setup which would result in periods of pcpn from
Friday into next week. Not a lot agreement in timing/positioning of
the various features, and will let the model blend chances roll in
the forecast for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday noon)
Issued at 1140 AM CST Mon Jan 16 2017

MVFR/IFR conditions in low clouds/BR/-RA/FZRA to continue spreading
across the area this afternoon and evening. Temps to continue slowly
warming to near above 32F, especially at valley sites like KLSE.
This will help limit the icing, which is looking to be more common
at higher elevations and ridge tops were temps may end up more in
the 30-32F range thru the evening. Precip to gradually diminish/
move out after midnight and thru Tue morning, but a broad low
IFR/MVFR stratus deck and some BR is looking to remain over the area
thru the morning. Some improvement Tue afternoon as the main sfc-mid
level circulation pulls away and drier sfc-850mb air spreads in from
the NW as ridging starts to build into the area.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST Tuesday for WIZ054-055-
     061.

     Winter Weather Advisory until noon CST Tuesday for WIZ041>044-
     053.

     Winter Weather Advisory from noon today to noon CST Tuesday for
     WIZ029-032>034.

MN...Winter Weather Advisory until noon CST Tuesday for MNZ086>088-
     094>096.

     Winter Weather Advisory from noon today to noon CST Tuesday for
     MNZ079.

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

&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION.....RRS



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