Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 100939
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
330 AM CST Sat Dec 10 2016

.SHORT TERM...(Today through Sunday Night)
Issued at 330 AM CST Sat Dec 10 2016

Prolonged snow event for the region today through Sunday.
Several inches with lots of impacts to travel.

1) Forcing: Beefy amount of low level warm air advection and lift on
the 275-290 k isentropic sfcs push in from the southwest this
afternoon...ahead of a sfc warm front hanging just to the south. The
strong thermodynamics hang across the region into Sunday afternoon.
Good frontogenetic banding through the layers...focused northwest-
southeast across the area tonight. A ripple in the upper levels
progged to move across the frontogenetic/thermodynamic region this
evening/overnight before the main trough swings through Sunday
evening - pushing everything east. Likely some 300 mb jet
interaction late tonight/Sunday to further enhance the lift. Plenty
of forcing for snow production.

2) Snow Amounts: bufkit soundings point to a 300 mb deep dendritic
zone growth region this evening at the onset of the snow...but this
quickly shrinks to around 50 mb later this evening as the stronger
forcing moves in and the column undergoes some warming. The profile
does remains fairly isothermal through Sunday. Ratios at onset could
be 30:1, but likely settle into something closer to 15/20:1.

It`s a long duration snow, with a roughly west-east setup, helping
increase the accumulations. Model trends still favoring amounts from
5 to 8 inches, but the higher amounts aren`t necessarily south of I-
90 anymore. Some suggestions in the latest runs that it could be
right along the I-90 corridor. If qpf and/or snow ratios are a bit
higher, an additional 1-2 inches of fluff could occur.

3) Headlines: the track of the second/main shortwave takes it across
northern parts of the region, and provides a good forcing mechanism
for snow accumulations. The better accums likely fall along and
north of I-94 Sunday afternoon in this scenario, and could result in
4-6 inches total (overnight Sat-Sunday afternoon). Will issue a
Winter Weather Advisory for Clark and Taylor counties of north-
central WI for this time period to account for these higher expected
snow amounts.

Won`t upgrade the rest of the Winter Weather Advisory at this time.
Still see some threat for localized 8-10", but confidence not high
enough to go warning for any particular location.


.LONG TERM...(Monday through Friday)
Issued at 330 AM CST Sat Dec 10 2016

Focus for the forecast for the new work week rests on the amount of
extra clothing you will need to wear if venturing outside. It`s
going to get cold - potentially dangerously cold.

Models remain adamant on dropping an arctic airmass across the Upper
Mississippi River Valley for the middle part of the new week. 850 mb
temps progged to fall from near -7 C at 850 mb at 00z Tue to -23z by
00z Thu. NAEFS 850 mb temp anomalies range from -1 to near -3 now
during this period. Highs in the single digits above and lows in the
single digits below zero will be common for Tue-Fri. If there is a
good amount fo clearing any of those nights, low temps will tumble
another 5 to 10 degrees. The cold drainage area of west-central WI
could flirt with -20.

Winds aren`t expected to get too blustery next week, but they will
be a factor in how cold it feels. Even a 10 to 15 mph wind will add
significant bite to the air, and currently Wed night/Thu morning
looks to carry the coldest wind chills. Wind chill advisories may be
needed for some areas next week.

Eitherway, a lot more layers and limiting your exposure to the cold
would be a smart and safe way to go.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1007 PM CST Fri Dec 9 2016

Mid level clouds continue to work through the region, along with
occasional flurries. That will continue for another few hours,
before clouds scatter for a brief time Saturday morning. However,
look for clouds to thicken and lower from west to east into the
afternoon and evening, with light snow breaking out across the
region as conditions dip to IFR levels. Still looking like the
heaviest snow from this upcoming winter storm will occur roughly 06Z
through 18Z (after the current TAF period), with total accumulation
of 4 to 8 inches. Winds will remain light from the northwest
overnight, gradually shifting southeast at 6-12 knots later Friday
afternoon and evening.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 2 PM this afternoon to 6 PM CST
     Sunday for WIZ054-061.

     Winter Weather Advisory from 4 PM this afternoon to 9 PM CST
     Sunday for WIZ032>034-041>044-053-055.

     Winter Weather Advisory from 9 pm tonight to 9 PM CST Sunday
     for WIZ017-029.

MN...Winter Weather Advisory from 2 PM this afternoon to 6 PM CST
     Sunday for MNZ079-086>088-094>096.

IA...Winter Weather Advisory from 2 PM this afternoon to 6 PM CST
     Sunday for IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence


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