Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 111727

Area Forecast Discussion
National Weather Service La Crosse WI
1127 AM CST Mon Dec 11 2017

Issued at 1127 AM CST Mon Dec 11 2017

Intense vorticity maximum dropping southeast across Iowa late this
morning. Plan on this system to continue dropping east-southeast
through eastern Ia/northern IL this afternoon. Looking for wintry
mix to come to an end as we get into dynamic cooling through the
column as deformation snow band sets up from far northeast IA into
far southern WI. Snow should come to an end by this evening. Not
looking for much accumulation through the afternoon, generally
less than an inch across this area. Otherwise, plan on northwest
winds increasing through the afternoon as pressure gradient
tightens on the backside of deepening surface low over lower
MI/IN. Gusts will likely be in the 30-40 mph range by late in the


.SHORT TERM...(Today and tonight)
Issued at 320 AM CST Mon Dec 11 2017

At 3 AM, a band of snow was moving east through western Wisconsin.
This was associated with warm air advection ahead of a rather
vigorous vorticity maximum moving through eastern North Dakota.
The 11.00z models are in good agreement that this system will move
southeast through southwest Minnesota and Iowa this morning and
through northern Illinois this afternoon. This system will bring
with it elevated CAPES (up to 100 J/kg above 700 mb) and steep
700-500 mb lapse rates. These will be mainly located south of
Interstate 94. As a result, expect scattered rain and snow showers
to move into the area during the mid to late morning and then
exit the area by mid to late afternoon. A few locations could even
see up to 1 inch of snow under a heavy snow shower. May also have
to watch out for the potential of some light freezing rain, sleet
and a rogue lightning strike.

Strong northwest winds will develop across the area this afternoon
and then continue into the evening. Wind gusts will be in the 30
to 40 mph. This may make travel difficult for high profile

.LONG TERM...(Tuesday through Sunday)
Issued at 320 AM CST Mon Dec 11 2017

On Tuesday, strong cold air advection will cause 925 mb
temperatures to fall into the -9 to -15C. This will result in high
temperatures ranging from the teens to mid 20s. The coldest
temperatures will be in central and north-central Wisconsin.

From Wednesday through Friday night, the pattern will remain
rather active with several short wave troughs moving across
northern Minnesota and northern Wisconsin. The models continue to
struggle on the timing and the southern extent of the snow with
these systems. At this time, it looks like the best chance of snow
will be found along and north of Interstate 94. Confidence was not
high enough in any time period to go more than a small chance.

In addition to this, the upper air pattern will flatten some.
This will result in more Pacific air masses than arctic
intrusions; thus, temperatures are expected to become warmer-
than-normal as we head toward the weekend.

As we head toward Saturday night and Sunday, the models continue
to struggle on the track and strength of a low pressure system
moving through the region. Both the ECMWF and GEM have a band of
snow in the forecast area. Meanwhile, the GFS has this system well
south of the area.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1127 AM CST Mon Dec 11 2017

Intense mid-level trough/low dropping through eastern IA this
afternoon with wintry mix precipitation moving southeast of the
KLSE/KRST TAF sites. Otherwise, northwest winds will be on the
increase through this afternoon, lasting into tonight in tight
pressure gradient on the backside of this departing system. MVFR
cloud cover looks to gradually scatter out this evening with MVFR
expected 03z.




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