Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 111142

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

.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 12Z TAFS through 12Z Tuesday morning)
Issued at 542 AM CST Mon Dec 11 2017

Initial burst of snow has now ended across the region, with
conditions sitting at VFR levels for most locations. Approaching
low pressure should help to develop additional scattered snow
showers (possibly mixed with rain or even sleet) through the
morning, but timing and placement of those remains a big challenge
as they will be more hit or miss. Expect to see amendments as
radar trends bear out the better placement the next few hours.
Those rain/snow showers will dwindle through the afternoon hours
as a cold front arrives, with winds quickly shifting northwesterly
and increasing to 15-25 knots with gusts of 30+ knots as MVFR
stratus returns to the area. Winds will then remain gusty right on
through the night (though will gradually subside) while ceilings
lift and eventually scatter out after 06Z.




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