Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 030603

Area Forecast Discussion
National Weather Service La Crosse WI
1203 AM CST Sat Dec 3 2016

.SHORT TERM...(This evening through Saturday)
Issued at 322 PM CST Fri Dec 2 2016

At 3 PM, extensive cloudiness remains across the Upper Mississippi
River Valley. Soundings show that this low level moisture will
remain across the area through this time period. With these
clouds, the low temperatures will not cool as much as the model
consensus indicates. Since the diurnal temperature range has been
generally 5 degrees or less for the past 4 days, raised the
minimum temperature consensus up to meet this.

.LONG TERM...(Saturday night through Friday)
Issued at 322 PM CST Fri Dec 2 2016

From Saturday night into Sunday, a short wave trough will move
northeast through the Upper Mississippi River Valley. Soundings
show that the precipitation will be primarily snow. As the
boundary layer warms and ice is lost aloft on Sunday, this
precipitation may change over to a rain/snow mix or rain as it
ends. With there being up to 100 mb of dendritic growth (between
700 and 600 mb) and omega co-located with this layer, snow to
liquid ratios will likely be in the 10-13 to 1. With a liquid QPF
of 1 to 2 tenths, snow totals look like they will be primarily in
the 1 to 2 inch range. This fits well with a majority of the SPC
and GEFS plumes.

From Monday night into Tuesday night, the 02.12z operational
models of the GFS, GEM, and ECMWF are in fairly good agreement
that there will not be phasing between the northern and southern
streams. In this scenario, one surface low would track through
western and northern Minnesota, and the other surface low would
track from the western Gulf States northeast into the Lower Great
Lakes. As a result, it looks like we could potentially see no snow
from this system or just some light snow accumulations north of
Interstate 90. If these 2 streams happen to phase, we would
likely see a much stronger low move northeast through our area. At
this time, this scenario does not seem as likely as it did a
couple of days ago.

From Wednesday into Thursday, both the GEM and ECMWF develop
another surface low over Colorado and this low tracks east across
the Central Plains and Tennessee River Valley. This is a much
further southeast track than the ECMWF was showing 24 hours ago.
As a result, its snow looks to stay south and southeast of the

With the potential of little to no snow on the ground from
Thursday through Friday, our model consensus temperatures may be
too low for this time period. This makes sense because 50 percent
of the ECMWF ensembles members have high temperatures in the 20s.
This would fit in well with a little to no snow on the ground
scenario. Meanwhile if there is a snow cover, we would be likely
looking at high temperatures in the teens. Local studies have
shown that temperatures are typically 10 degrees warmer than when
there is snow (1" or greater) on the ground.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1200 AM CST Sat Dec 3 2016

The area of clearing has edged a little to the northeast this
evening and there is still a concern that this could advected over
the area Saturday as the flow turns more to the southwest.
However, the 03.00Z continues to maintain high levels of moisture
at 925mb underneath the inversion but does show drying just above
this at 850mb. Given that the moisture is under the inversion,
opted to stay pessimistic and keep the MVFR ceilings in place. A
short wave trough and cold front will approach from the west
Saturday evening with light snow. This system does not look like
it will affect either airport until after 04.06Z.




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