Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 091745
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1145 AM CST Mon Dec 9 2019

.UPDATE...
Issued at 1134 AM CST Mon Dec 9 2019

Band of snow moving through associated with sharp cold front
continues to produce impacts to travel. While bulk of remaining
drizzle will change over to all snow as cold air and ice fill in,
roads becoming snow covered very quickly. Band seems to be
hovering just below that Snow Squall Warning criteria, but still
has many of the features - narrow band, quick impact, gusty winds,
flash freeze, etc.  See latest SWOMCD for this feature.

After coordination with surrounding areas, will continue to adjust
advisory criteria to align with passing snow band. While feature
is moving east at a good clip, impact along seems to warrant more
headlines. Meanwhile will be clearing headlines from the west but
again, impacts may be slow to improve.

Some concern going into this evening too with sharply falling
temperatures and freezing going on that accident numbers could
stay up. Will continue to assess.

&&

.SHORT TERM...(Today)
Issued at 353 AM CST Mon Dec 9 2019

Wintry mess continues to be the main forecast focus today. Have
favored the ConsShort model blend and RAP for the next 12 hours.

Still notable uncertainty in the potential for freezing drizzle,
especially over western parts of the service area.  Models are in
good agreement that in advance of the main wave, probability of ice
in the cloud is low.  However, the depth of the saturated surface
layer may be too shallow to support freezing drizzle.

Latest HRRR and RAP runs show 2 distinct areas of rain/drizzle. The
first develops in the warm sector before sunrise across IL into WI.
This area has higher confidence given the deeper low level
saturation. The second area is a narrow band immediately ahead of
the snow band. So essentially, for SE MN and NE IA, precip should
begin as freezing drizzle, then change rapidly to snow. Given the
timing of this wintry mix near the end of the morning commute, and
in collaboration with neighboring offices, have expanded the winter
weather advisory to include all of our southeast MN counties and
most of our NE Iowa counties.

.LONG TERM...(Tonight through Sunday)
Issued at 353 AM CST Mon Dec 9 2019

Cold air will begin to spill into the region tonight as the
system responsible for the precipitation today pulls away and a
large area of Canadian high pressure begins to settle in over the
Upper Midwest. This high will drift southeast across the region
through Tuesday evening before moving off into the Ohio River
Valley. A reinforcing shot of cold air should arrive later Tuesday
night into Wednesday morning and looks to bring the coldest
temperatures to the area. The air at 850 mb looks to be around
-18C, which is about 1 standard deviation below normal, so while
 it definitely will be cold, it does not look to be record
 setting. Low temperatures for Tuesday night/Wednesday morning
 look to range from the teens below across north-central Wisconsin
 (thanks to some fresh snow cover) to the single digits above and
 below zero for the rest of the area. Wednesday night/Thursday
 morning should again have low temperatures in the single digits
 below zero for much of the area north of Interstate 90. Wind
 chills will be a concern both of these night with values dipping
 into the teens below zero and flirting with 20 below over
 portions of Clark and Taylor Counties. Right now, this does not
 look to be widespread enough for last enough to need a wind chill
 advisory, but trends will have to be monitored for this
 possibility. The cold snap will end Thursday as warmer spread
 rapidly back over the area with highs in the 20s and 30s expected
 to close out the week.

In between the two areas of high pressure, a short wave trough
will rotate across the Upper Midwest Tuesday night. A weak area of
surface low pressure looks to scoot from the Dakotas to the Ohio
River Valley and could produce a little bit of light snow on the
north side of its track in a zone of weak frontogenesis in the
850-500 mb layer and will carry a small chance of some light
across mainly northeast Iowa late Tuesday night.

Once this system moves past the area, the upper level flow will
transition to a zonal pattern. Several short wave troughs look to
move from the Pacific Northwest, across the northern Rockies and
across the Upper Midwest from Thursday through the weekend. Right
now, none of these system look to be exceptionally strong which
will keep the precipitation chances mainly in the 20 to 40 percent
chances. Precipitation types may become a concern at times with
these systems as they may not be strong enough to consistently
generate ice in the clouds. Fortunately, some of these concerns
will be mitigated during the day when temperatures should be warm
enough for mainly just rain at times.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1134 AM CST Mon Dec 9 2019

LIFR conditions will continue as band of snow along cold front
continues to impact the area. In addition expecting northwest
winds to increase significantly as peak cold air advcection kicks
in this evening. Snow will be relatively short lived so conditions
should gradually improve to IFR and possibly MVFR later this
evening, but eventually some drier air in highly subsident flow
takes over and clear things out. VFR will return overnight, but
ceilings could come back in later Tuesday as cold air advection
continues.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for WIZ017-
     029-033-034-041>044-053>055-061.

     Winter Weather Advisory until 3 PM CST this afternoon for WIZ032.

MN...Winter Weather Advisory until noon CST today for MNZ079-086-087-
     094.

     Winter Weather Advisory until 3 PM CST this afternoon for MNZ088-
     095-096.

IA...Winter Weather Advisory until noon CST today for IAZ008-009-018-
     019.

     Winter Weather Advisory until 6 PM CST this evening for IAZ011-
     029-030.

     Winter Weather Advisory until 3 PM CST this afternoon for IAZ010.

&&

$$

UPDATE...Shea
SHORT TERM...DMD
LONG TERM...04
AVIATION...Shea


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