Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 240523

Area Forecast Discussion
National Weather Service La Crosse WI
1123 PM CST Thu Feb 23 2017

.SHORT TERM...(This evening through Friday night)
Issued at 330 PM CST Thu Feb 23 2017

A dangerous and impactful winter storm will impact the region
from Tonight into Friday night.

The 23.12z continued their shift southeast overnight. The surface
low is now tracking from central Kansas to Burlington Iowa by
sunrise Friday and Muskegon Michigan by sunset Friday.

The models are in general agreement where the warm conveyor belt
will be with this system. This will bring anomalous moisture into
the region. Precipitable water values climb into the 0.50 to 0.75
inches tonight and remain around a half inch on Friday. Warm air
advection will result in rain across the area this evening and
then transition to snow and maybe some freezing rain as cold air
advects into the region at the surface and aloft.

In addition for late tonight, southerly winds aloft will bring
instability into areas along and south of the Interstate 90
corridor. Elevated CAPES in these areas climb up to 250 J/kg and
700-500 lapse rates up to 8 C/km. This could result in some
scattered elevated thunderstorms. The Storm Prediction Center has
a marginal risk of severe storms ahead of this surface low for
late tonight. If any severe weather did happen occur, it would be
marginally severe hail.

Further to the north, additional scattered storms may develop
along a band of 800 to 700 mb frontogenesis which will be located
either along or north of Interstate 90. This development will be
due to the release of slantwise convection. The 23.15z SREF is
showing the potential for hourly snow rates of up to 2 inches an
hour along this frontogenetic band between midnight and 9 AM. Snow
rates this high will make it extremely difficult for road crews
to keep up.

A tightening pressure gradient late tonight and Friday morning
will cause northeast winds to increase into the 20 to 30 mph
range with wind gust up to 45 mph. North winds will slacken a bit
during the afternoon and then become northwest and increase back into
the 20 to 30 mph range with gusts to 40 mph on Friday night. This
is a result of cold air advection and steep low level lapse in
the wake of this system. As typical, the highest winds with this
event will be west of the Mississippi River where the combination
of winds and falling snow will produce blizzard conditions. In
addition significant drifting may cause road closures. This could
include the interstates.

For the day Friday, a dry slot will move into southwest and
central Wisconsin. This dry air will cut off ice seeding from
aloft. As a result, there will be a transition to rain and
freezing rain. Meanwhile a deformation band of snow will be
located along and north of Interstate 90 in Wisconsin and across
southeast Minnesota and northeast Iowa.

On Friday night, this deformation band will move east across the
area. With a deep dendritic layer initially, snow to liquid
ratios will climb into the 15-20 to 1. This fluffier snow will
readily move, so there will be considerable blowing and drifting.
This will keep the blizzard conditions going west of the
Mississippi River.

With a further southerly track of the low, the heavy band track
was shifted south. The 10 to 16 band of snow now extends from
Austin and Winona Minnesota to Medford Wisconsin. For tonight, a 2
to 5 inch band of snow will be found north of a Charles City Iowa
to Mauston Wisconsin line. Elsewhere snow amounts will be up to 2
inches. For Friday, a 4 to 8 inch band of snow will be located
west of a Charles City Iowa to Black River Falls Wisconsin.
Elsewhere snow amounts will range from 1 to 4 inches. On Friday
night, and additional 1 to 3 inches of snow will fall across the
area. This snow will be initially very wet which will put a
strain on the body. Those shoveling are suggested to take
frequent breaks.

.LONG TERM...(Saturday through Thursday)
Issued at 330 PM CST Thu Feb 23 2017

Other than a couple weak low pressure systems this time period
looks to be less impactful. After below normal temperatures
Saturday and Saturday night, above-normal temperatures will return
to the area.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1123 PM CST Thu Feb 23 2017

IFR/LIFR conditions will be the general rule for the foreseeable
future at both KRST/KLSE as a winter storm moves across the
region. KLSE could see a rain/snow mix for a portion of the night
before changing to all snow, but KRST will see periods of
moderate to heavy snow through the night and into Friday. When
combined with northeast wind gusts up to 30 kts, visibility likely
to drop to 1/2SM or less for the majority of the period in
blowing/drifting snow. Visibility not expected to be as impacted
at KLSE until later Friday as a heavier snow band moves across the
MS River Valley. On top of all this, some thunder snow is possible
in the early overnight hours at both TAF sites. Conditions may
slowly improve at KRST late in the period as snow pushes east and
winds begin to diminish, but snow should continue at KLSE through
the period. Overall, very poor conditions for aviation operations
through the period.


WI...Winter Weather Advisory until 6 AM CST Saturday for WIZ043-044-

     Winter Storm Warning until 6 AM CST Saturday for WIZ017-029-

MN...Blizzard Warning until 6 AM CST Saturday for MNZ079-086>088-

IA...Blizzard Warning until 6 AM CST Saturday for IAZ008>010-018-019.

     Winter Weather Advisory until 6 AM CST Saturday for IAZ011-029-



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