Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 121004

Area Forecast Discussion
National Weather Service La Crosse WI
404 AM CST Thu Jan 12 2017

.SHORT TERM...(Today and tonight)
Issued at 403 AM CST Thu Jan 12 2017

At 3 AM, a band of snow was indicated by radar from Audubon Iowa
to Boscobel Wisconsin. The snow band formed along an area of 700
to 600 mb frontogenetic forcing. Overall, the NAM is handling
this feature the best and it shows this band of snow continuing to
move northeast along and north of the Wisconsin River through 9 AM
this morning. BUFKIT soundings show that there is only a 50 mb
layer in the dendritic growth zone. This along with limited
moisture will limit the snow total to the 1 to 2 inch range.

A thick veil of high clouds will move quickly into the area
tonight in advance of a short wave trough moving out of the
Dakotas. These clouds along with the boundary layer remaining
mixed will likely slow down the temperature fall during the
night. Since these clouds will move into the areas along west of
the Mississippi River sooner, stayed near to slightly above the
MOS minimum temperatures in that area. Meanwhile in central and
north-central Wisconsin opted to go cooler than the MOS minimum
temperature forecast. A light north wind will produce wind chill
of 20 to 30 below north of Interstate 90, and from 5 to 20 below
elsewhere. Due to the light winds, opted not to issue a Wind
Chill Advisory.

.LONG TERM...(Friday through Wednesday)
Issued at 403 AM CST Thu Jan 12 2017

On Friday afternoon and night, the 12.00z models continue to show
that a short wave trough will move through the Upper Mississippi
River Valley. Much of the lift associated with this wave goes into
saturation, so there are some questions on how much moisture will
be available for this system to work with. In addition, there are
still a lot of questions on where the strongest lift will be
located. The GFS and NAM would suggest that the entire area will
see light snow. Meanwhile the GEM and ECMWF only have it south of
Interstate 90. BUFKIT soundings show that there will be a brief
time period where there will be at least 50 to 100 mb in the
dendritic growth zone. This could enhance the snow rates enough
that a few areas could see anywhere from a half to 1 inch. With
uncertainty on the location of snow, kept the chances in the 20 to
30 percent range from now.

From Sunday afternoon into Tuesday, there continues to be a
concern of a wintry mix mainly along and south of Interstate 90
and mainly snow north of this Interstate. At this time, it looks
like an elevated warm layer will move into areas along and south
of Interstate 90 from late Sunday afternoon into Monday morning.
As this layer advances north, snow will quickly change to sleet
and freezing rain. If the boundary layer warms enough on Monday,
this wintry mix could change over to rain and then as cold air
moves back into the area on Monday night it will change back to a
wintry mix. Strong 850 mb moisture transport will bring an
unusually moist air mass northward into the region. Precipitable
water values climb into the 0.75 to 1 inch range. This is 2 to 3
standard deviations above normal and these values will be close to
the January records at both Chanhassen and the Quad Cities. As a
result, it looks like we could see another round of heavy
precipitation falling across the region. The main question is in
what form will this precipitation will fall. As a result, there is
much uncertainty on both ice and snow accumulations. In addition
if this ends up being more rain, there will be a quick run off
into area rivers and streams which could potentially result in
flooding and ice jams. This system will be closely monitored in
the days to come.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1133 PM CST Wed Jan 11 2017

A fast-moving upper wave will bring a lowering of ceilings to
LSE/RST through sunrise, with a brief window of light snow
expected to impact LSE but with any accumulation mainly one-half
inch or less (higher amounts south of the terminal site). RST now
looks to stay mainly dry, save for a few flurries possible at
times. Skies should clear from the west through late morning, with
winds becoming gusty for a time as a cold front approaches into
the afternoon. There is some risk for a brief window of MVFR
ceilings along that front, though confidence in that is on the
lower side at this time.




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