Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 070907

Area Forecast Discussion
National Weather Service La Crosse WI
307 AM CST Thu Dec 7 2017

.SHORT TERM...(Today and tonight)
Issued at 307 AM CST Thu Dec 7 2017

A quiet period is expected today and tonight. The mid-level trough
axis has swung through the area with increasing subsidence helping
to dry the column and gradually put an end to the light snow and
flurries. Satellite imagery/obs indicated some clearing early this
morning to the west in Minnesota and would expect some of this
clearing to continue to work eastward through the morning,
although we may see some mid/high clouds through the day as a
secondary trough axis rotates through. Winds will be weaker today
with only around 20 kts winds atop a rather shallow diurnal mixed
layer. It will another chilly day with highs mostly in the 20s.
Increasing clouds are expected tonight within a broad warm
advection regime, with maybe a flurry or two.

.LONG TERM...(Friday through Wednesday)
Issued at 307 AM CST Thu Dec 7 2017

Main focus during this period is late Friday/Friday evening with
increasing chances for a period of accumulating snowfall.

There continues to be good agreement among models with a strong
upper shortwave diving south out of Canada on Friday, with
additional upper support from a left exit region of an upper jet. As
the fast-moving wave drops south, a period of strong mid to upper QG
forcing will drive a band of snow southeastward across the region.
Right now consensus places the highest chances along and east of
the Mississippi, centered on Friday evening. A period of moderate
to strong deep lift within the snow growth region will lead to a
several hour window for snow Friday evening. Even with a very dry
environment, a fluffy inch or two of snow is possible, locally 3,
especially near and east of the Mississippi, before subsidence
behind the wave quickly puts an end to the snow later on Friday
night. In addition, a period of gusty winds may follow in the wake
of the wave with a strengthening pressure gradient behind the
surface low and strong cold advection, especially west of the
Mississippi. The strongest winds may end up west of the
accumulating snow, but something worth watching.

The weekend itself is shaping up to be quiet as high pressure builds
in behind the departing upper wave. Strong low-level warm advection
Saturday night with a push of Pacific air will allow temps to
recover from the 20s on Saturday into the 30s or even maybe low 40s
in spots on Sunday.

The northwest flow pattern will continue early next week, keeping
temps near or below average. Despite some differences with timing
and placement, both the 07.00Z GFS/ECMWF indicate a series of
upper waves will continue to rotate through the flow into early
next week, with chances for light snow at times. There is a
general consensus of Sunday night into Monday and again late
Tuesday and Tuesday night for the higher chances, although
confidence is not high at this range.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1115 PM CST Wed Dec 6 2017

As of 05z, the trailing edge of the MVFR cloud deck and areas of
MVFR vsbys in -SN were about to exit south of both the KRST/KLSE taf
sites. Once these clouds/-SN exit, good VFR expected this taf period
with BKN 8K-15K ft clouds for the overnight hours, then sct 14K-20K
ft clouds for most of the day on Thu. Moisture already starts to
return Thu evening, but clouds in the 00-06z period looking to be
mid level in the 7K-10K ft range.

Trend has been for less gustiness of the NW winds this evening and
trend is now for a bit less wind this taf period. NW winds 10-15kt
expected thru about 18z, with the winds decreasing and shifting to
the southwest for Thu evening.




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