Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 061749

Area Forecast Discussion
National Weather Service La Crosse WI
1149 AM CST Wed Dec 6 2017

.SHORT TERM...(Today and tonight)
Issued at 310 AM CST Wed Dec 6 2017

Water vapor and 500 mb analysis early this morning is indicative of
a very wintry pattern over the north central CONUS with northerly
flow across the area on the western periphery of a deep upper trough
south of Hudson Bay. One shortwave trough was clipping northern
Wisconsin with some light snow/flurries while another upper wave and
stripe of mid-level frontogenesis produced some flurries over
parts of Iowa with relatively clear skies in between.

For today, expect another chilly and breezy day. Mixed layer winds
won`t be as strong as yesterday, but mixing up to 900 to 850 mb
should help bring down some gusts to 30 mph. A broad upper trough
will rotate southeastward through the day, and although lift is not
particularly strong, with cyclonic flow and soundings indicating a
relatively deep saturated snow growth zone, expect at least
scattered snow shower/flurry development today into tonight which
could amount to a light coating of a few tenths of an inch. Temps
will be similar to Tuesday, with highs mostly in the 20s and lows
tonight in the upper single digits and teens.

.LONG TERM...(Thursday through Tuesday)
Issued at 310 AM CST Wed Dec 6 2017

A drier airmass will work into the region on Thursday behind the
upper trough passage allowing for more sunshine, although with still
cold highs in the teens and 20s. It continues to look like a
stronger upper trough will dive down the backside of the longwave
trough later Friday and Friday night. The 06.00Z GFS/NAM/ECMWF all
show the upper wave and left exit region of an upper jet crossing
the area late Friday with potential for some accumulations (an
inch or two?) of fluffy snow. There are still some relatively
small differences in the timing/placement of the wave among
models, but the model signal has been quite consistent for several
days now and have trended precip chances higher at least across
western WI with the highest chances Friday evening.

Behind that system, high pressure will build back in for the start
of the weekend with dry weather expected. While much of the
available guidance suggests the stable eastern US trough/western US
ridge pattern won`t be going anywhere anytime soon, a brief
moderation in temps looks likely by Sunday. Highs are expected to
climb back into the 30s with an intrusion of Pacific air and
westerly low- level flow. If this does occur, it should be short-
lived with re-amplification of the upper ridge/trough pattern by
early next week, allowing more cold air to drop across the area.
This may be accompanied by chances for light snow/flurries within
cyclonic flow as an upper trough rotates across the area.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1149 AM CST Wed Dec 6 2017

Clear skies will come to an end during the early afternoon hours
as an MVFR cloud deck in the 1500 to 2500 ft agl range continues
to slowly approach from the north. Some light snow is also falling
out of this deck, with some MVFR visibilities being observed.
Gusty northwest winds will also be seen through much of the TAF
period, with gusts near 25 kts possible through the evening and
overnight hours. Given these winds, it is possible that some brief
IFR visibilities could be observed, but with the snowfall
expected to be rather light, confidence is not high enough to
include any mention. Snow is expected to come to an end by 3Z,
with ceilings rising to VFR levels. Could see a few flurries
through the overnight hours, but no visibility restrictions are
expected should this occur. Clouds will then begin to exit the
area from west to east early Thursday morning, with wind speeds
slightly decreasing throughout the day.




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