Area Forecast Discussion
Issued by NWS La Crosse, WI

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960
FXUS63 KARX 222030
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 PM CST Wed Nov 22 2017

.SHORT TERM...(This evening through Thursday)
Issued at 230 PM CST Wed Nov 22 2017

22.20Z analysis shows a weak short-wave moving into the southern
Canadian prairies with some modest returns on regional radars across
northern MN into northwest WI. This wave will continue to slide east-
southeastward tonight, bringing chances for some light snow or
flurries mainly across Taylor/Clark Counties. Latest short-range
guidance (RAP/HRRR) has backed off on measurable QPF this evening
due to a lack of deep moisture/lift, so cut back on POPs into the 20-
50 percent range. Any accumulation should be very light, perhaps a
tenth or two at most.

One caveat to keep an eye on tonight will be the potential for some
freezing drizzle. Some model soundings are showing a loss of ice on
the backside of the departing wave. However, upstream cloud-top
temperatures from satellite show values generally -10 Celsius or
colder, so kept all precipitation as snow tonight. If some freezing
drizzle does develop, it should be brief.

Surface high pressure ridge moves into the region for Thanksgiving
Day resulting in dry conditions and mostly sunny skies. With 925 hPa
temperatures rising into the +1 to +6 Celsius range by 00Z Friday,
afternoon highs should top out in the upper 30s to mid 40s for most
locations. Winds will be light, generally from the west-northwest.

.LONG TERM...(Thursday night through Wednesday)
Issued at 230 PM CST Wed Nov 22 2017

A mild Pacific airmass will advect across the region Thursday night
and Friday ahead of an approaching cold front and upper trough. 925
mb temps rise to 7-10C, with NAEFS 850 mb temp standard anomalies
nearing +2 to +3. High temps should be in the 50s in most areas,
possibly even reaching 60 in spots. The cold front will swing
through during the afternoon with some low-level cold advection in
its wake. There will be a decent moisture plume ahead of the mid
level wave, with precipitable water values rising up to about 0.7
inches. However, the strongest synoptic lift is progged over
northern Wisconsin where the highest chances for rain showers will
reside Friday afternoon. The 22.12Z ECMWF is a little farther
south compared with the GFS with the upper wave, and would
suggest some potential for a few showers farther south across the
area.

High pressure will build back across the area Friday night and
Saturday, with quiet weather expected. Temps will be knocked back
behind the frontal passage for Saturday, but still seasonable temps
in the 30s and 40s are expected.

Models are in agreement on upper-level ridging building in for
Sunday into Monday, allowing for dry weather and above normal
temperatures. A shortwave trough is forecast to move from the
Pacific Northwest towards the Great Lakes early next week, but there
are significant differences on the timing and strength of this
feature, and the 22.12Z model solutions are even more divergent than
the 22.00Z runs. Will maintain a model consensus forecast, which
brings a chance of precipitation to the region Tuesday into
Wednesday. Thermal profiles suggest rain and snow would be the
dominant precipitation types.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1135 AM CST Wed Nov 22 2017

A quick-moving Alberta Clipper will move across the region this
evening and overnight. While there could be a few flurries, any
accumulating snow will be well north of TAF airfields and will
maintain a dry forecast at this time. Ceilings will drop this
evening, however, but remain well above 3000 ft agl. Expect cloud
cover to dissipate later tonight with mostly clear/sunny skies by
Thanksgiving morning. Light south-southwest wind will be the
rule through tonight, shifting to the west-northwest after 23.11Z.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Rogers
LONG TERM...JM/Hollan
AVIATION...Rogers



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