Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 060930

Area Forecast Discussion
National Weather Service La Crosse WI
330 AM CST Tue Dec 6 2016

.SHORT TERM...(Today and tonight)
Issued at 330 AM CST Tue Dec 6 2016

Forecast concerns include morning precip today followed by coldest
air of the season so far.

A focused band of precip near the frontal zone is making slow
eastward progress across the area early this morning. Observations
have shown much of the precipitation to be falling as snow, with
some light rain/drizzle/freezing drizzle along the leading edge
of the precip. The precip should continue to lift northeastward,
likely weakening through the morning, with southwest Wisconsin
likely missing out on much of the precip. Visibilities have been
reduced at times to 1-3 miles in the snow southeast Minnesota,
northeast Iowa, and west-central Wisconsin leading to some
slushy/snowy roads that could make for slick travel for the
morning commute. There may be some fog as well out ahead of the
front/precip this morning.

Winds will become gusty from the west following the cold frontal
passage with daytime highs likely to be this morning. There is some
clearing this morning into eastern SD, and NAM soundings indicate
some drying working into the area through the day. However, it
remains to be seen how much clearing will be realized with low-
level moisture remaining trapped beneath a steep inversion. Temps
falling into the teens to near 20 by tonight and blustery west
winds will knock wind chill values down towards the single digits
by later today or tonight, quite the change from early this

.LONG TERM...(Wednesday through Monday)
Issued at 330 AM CST Tue Dec 6 2016

The cold weather following our prolonged period of mild weather
will be the weather headline through late week. Model guidance has
been consistent in keeping the coldest airmass over the area
Wednesday-Friday with 850 mb temps bottoming out around -14 to
-15C by Friday. With a pretty tight pressure gradient in place
between the departing low across eastern Canada and strong high
pressure nosing into the plains, winds will remain breezy into
Thursday. The wind combined with temps in the teens and 20s will
keep wind chills in the single digits in many places even during
the daytime hours with below zero wind chills possible, especially
at night as temps fall into the teens. Winds will at least lighten
by Friday under the surface high, although air temps may be
coldest on Friday.

Cyclonic flow aloft and the passage of a surface trough may help to
produce some light snow/flurries under a low stratus deck
Wednesday Night/Thursday, but with little accumulation.

Heading into the weekend, the main forecast concern remains the
potential for snow with an upper trough forecast to eject out of the
Rockies within relatively zonal flow. Global 06.00Z model runs
continue to support this scenario, but differ somewhat on strength,
location, and timing. The ECMWF remains weaker and is also farther
north with the bulk of the precip compared with the GFS/GEM.
Ensemble guidance also indicates substantial variability among
solutions. Thus, it is too early to have confidence in any specifics
yet, but there remains the potential for accumulating snow this


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1134 PM CST Mon Dec 5 2016

The band of light precipitation has formed this evening in the
warm air advection zone ahead of the cold front that was working
across western Minnesota. So far the precipitation has been light
but as the forcing continues to increase as the short wave trough
approaches, expecting that the precipitation will get a little
heavier for awhile overnight and produce a period of IFR
ceilings with MVFR visibilities for both airports. Once the
precipitation ends the visibility will come back up to VFR and the
ceilings should follow a few hours later. However, the VFR
conditions are not expected to last very long. Cyclonic flow will
set up behind the cold front with plenty of low level moisture
trapped below the inversion. This should allow MVFR ceilings to
move back in during the afternoon and then remain through the
evening. The west winds will also become gusty behind the front
and these should continue into the evening as well as the good low
level lapse rates remain in place.




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