Area Forecast Discussion
Issued by NWS Goodland, KS

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020
FXUS63 KGLD 031024
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
324 AM MST Sat Dec 3 2016

.SHORT TERM...(Today and tonight)
Issued at 319 AM MST Sat Dec 3 2016

Latest upper air analysis has a closed low over Northern Mexico with
the trough axis extending north from it into the Northern Plains.
Ahead of the closed low water vapor imagery indicated a plume of
higher moisture concentration.  Within this plume of water vapor was
an area of precipitation, ranging from rain over Southwest Kansas to
snow over the Tri-State Area.  Due to weak lift and less water vapor
to work with over the Tri-State Area, the snowfall has been very
light, more like flurries.

This morning am expecting the light snow to increase in coverage as
the 700mb trough just west of the Tri-State Area deepens.
Frontogenesis, although weak, will also increase as the trough
deepens and stability will decrease.  Higher mixing ratios will
increase as well over the southeast and east portion of the Tri-
State Area.

Hi-res models differ regarding how long the expanded snowfall area
will linger over the Tri-State Area before shifting to the east.
Current forecast may have the snowfall lingering too long before
exiting but a few of the hi-res models support having the snow
linger into the afternoon.  The snow will reach its greatest areal
extent by late morning before shifting east.  The snowfall will
remain over the southeast 1/3 of the Tri-State Area during its
greatest extent.

This afternoon the snowfall will shift east ahead of a 700mb trough
which ejects out of the main trough that will linger just west of
the Tri-State Area.  Snowfall will end before late afternoon.

Kept the precipitation as snow, even into the afternoon, based on
wet-bulb zero heights being too low to support rainfall.  Am
thinking temperatures will warm as the snowfall is ending.  Even if
temperatures warm into the upper 30s during the afternoon with snow
ongoing, wet-bulb zero heights are too low for the snow to change to
rain.

.LONG TERM...(Sunday through Friday)
Issued at 319 AM MST Sat Dec 3 2016

Main concerns will be chance/amounts of snow from Tuesday into
Wednesday and how cold do the temperatures get during this time.
Satellite continuing to show an active and amplified flow from the
Pacific into North America.

Sunday through Monday will be dry as the trough axis that was west
of the Tri-State Area shifts east.  Dry northwest flow will
transition to zonal flow by Sunday night.  Highs on Monday will be
above normal ahead of an arctic cold front to move through Monday
night.

Monday night an upper level trough will drop south out of Canada.
Accompanying this trough will be an arctic front.  Behind the front
northwest winds gusting around 35 MPH are expected.  Am anticipating
strong cold air advection to occur behind the front causing
temperatures to quickly fall once the front moves through.

Models differ by about 3 hours or so regarding when the front will
move through.  Have higher confidence that the front will begin to
move through during the early evening as apposed to the late
afternoon.  If the front moves through during the late afternoon,
the winds may be stronger, gusting around 40 MPH, and highs may be
cooler.

Snowfall will move in behind the front as well.  There may be a
brief window of rain during the early evening before temperatures
cool enough to change the precipitation to snow.  Based on the
strength of this front, am thinking the initial precipitation may
start as rain then rapidly change to snow.  Models show the snowfall
being a short duration event, lasting two or three hours over a
location before ending.  There may be some blowing snow due to winds
gusting 35 MPH.  The snowfall will end before sunrise Tuesday.

Wind chills behind the front will fall into the single digits after
midnight.  Some locations may fall to zero for wind chill around
sunrise on Tuesday.  This will be a drastic change from highs in the
low 50s the previous day.


Tuesday through Friday...
Models coming into better agreement on this time period.
Main/strongest portion of the upper trough lies well to the north.
However in the northwest flow behind the main upper system, a
significant shortwave trough will rotate through late Tuesday
afternoon into Wednesday morning. Frontogenesis is rather strong
but the theta-e lapse rates are not very favorable to get a good
response from the lift.

Considering the amount of cold air advection and how strong the
shortwave trough is, believe that the probability of snow will end
up being rather high but the amounts will not be very high due to
the fast nature of the system and the unfavorable lapse rates. As a
result I did not change what the forecast blend gave me for pops and
amounts but would not be surprised if the chances get nudged up the
closer we get to the event.

What appears and has appeared fairly certain is the large amount of
rather significant cold air that will accompany this upper system.
The Canadian, Ecmwf, and Gfs disagree a little on how cold this air
mass will be with the Canadian being the coldest while the Gfs is in
the middle but only a little colder than the Ecmwf. The Gefs 850 mb
temperature ensemble mean tends to fit in the middle of the
deterministic output.

As a result I felt confident enough to lower the forecast blend
maxes from Tuesday into Thursday. The maxes look to be too warm
especially on Tuesday. I did not make huge changes but did start to
trend those maxes down, and if the ensemble/deterministic output
continues to be close, additional adjustments will need to be made.
The mins may not be too bad considering there may be some cloud
cover around, and made little to no adjustments to them. Of course
all these temperatures could change if we end up getting more snow
than currently expected.

Something else to be watching. The combination of the winds and
these cold temperatures will produce wind chill temperatures well
below zero. Depending on how the details work out, wind chill
highlights may be needed during this time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 930 PM MST Fri Dec 2 2016

For KGLD and KMCK, vfr conditions expected through the period.
Winds generally from the south or southwest at the beginning of
the period with an expectation of veering to the southwest then
west after 03z under 10kts. No precipitation expected.


&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...JTL
LONG TERM...BULLER/JTL
AVIATION...99



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