Area Forecast Discussion
Issued by NWS La Crosse, WI

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553
FXUS63 KARX 072023
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
222 PM CST Wed Dec 7 2016

.SHORT TERM...(Tonight through Thursday)
Issued at 222 PM CST Wed Dec 7 2016

Cold cyclonic flow over western Great Lakes has dropped temperatures
below normal for a change, producing this cold air stratus and
occasional flurries or periods of snow. Winds also creating blustery
conditions with single digit wind chills - quite a change from
earlier this fall.

Still seeing a little bit of drifting snow with patchy slick spots
on more rural areas, otherwise weather fairly nil in short term.
Minor short wave may keep clouds around well into Thursday with more
occasional light snow. Temperatures should be fairly similar tonight
with winds staying up.

.LONG TERM...(Thursday Night through Wednesday)
Issued at 222 PM CST Wed Dec 7 2016

Certainly more to look at in later forecasts with snow threat over
the weekend AND even colder air pushing in next week.

Looks like by Friday upper low has shifted far enough east that
surface ridge finally builds in. Could see more sun and break in
snow flurry activity finally.

Main focus for weekend will be watching approach of short wave
trough in westerlies that comes out of the northern Rockies by
Saturday morning. Confidence HAD been growing for a snow event for
our area as this waves passes through Saturday night into Sunday.
But flip-flop in how US guidance handles strength of this wave, plus
big change in 07.12z ECMWF came across lowers that confidence down a
few notches sorry to say.

While last few GFS runs have been dropping 5-10 inches of snow
across our area by Sunday, 07.12z NAM is stronger now but only goes
out through 00z Sunday. ECMWF delays wave by at least 12 hours and
deepens it as it passes just south of the area. Will not get caught
up in details that far out and remain using a blend with more weight
on last few GFS runs that have been most consistent with each other.

07.12z NAM/GFS/Canadian have many prime ingredients for very
efficient snow event Saturday afternoon into Sunday morning. This
includes decent isentropic lift ahead of wave, deep and strong quasi-
geostropic forcing to aid lift, strong lift through dendritic zone
according to model soundings, and what could be elongated period
along frontogentic zone to add to amounts. IF this all plays out we
could see warning-level snows in parts of the area. Although a bit
early for snowfall amounts, looking at high-end advisory or low end
warning event perhaps? Suppose next 24-48 hours will provide more
answers.

Bottom line for forecast is snow chances were raised even more for
Saturday night especially. Small snow chances have also been added
for parts of Sunday and Sunday night based on how different 07.12z
ECMWF looks. Trends for this solution will also have to be monitored.

Other story in later periods is next shot of arctic air due early
next week. We are talking Days 6 and 7 but medium range temperatures
depict sub zero conditions for 24-36 hours perhaps with very cold
wind chills. Depending on how much snow we get this weekend could
have an impact on this airmass as well. 850/925mb temperatures
suggest 1 to 2 standard deviations anomolies so have tried to lower
temperatures next week. This could be another impact period with
wind chills and bears watching.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1111 AM CST Wed Dec 7 2016

Cold cyclonic flow overhead will produce widespread vfr/mvfr
stratocumulus along with scattered flurries through the period.
Plan on west to northwest winds in the 10-20kt range with gusts
around 25kt.

&&

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

$$

SHORT TERM...DAS/Shea
LONG TERM...Shea
AVIATION...DAS



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