Area Forecast Discussion
Issued by NWS Goodland, KS

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205
FXUS63 KGLD 051048
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
348 AM MST Mon Dec 5 2016

.SHORT TERM...(Today and tonight)
Issued at 346 AM MST Mon Dec 5 2016

Latest upper air analysis shows almost zonal flow over most of the
CONUS.  Within this flow is a deepening short wave trough over the
Great Basin.  At the surface an arctic front was over Montana,
Idaho, and northwest Wyoming. Behind the front temperatures were in
the teens and 20s. Ahead of the front temperatures were in the 30s.

Today well above normal temperatures are expected ahead of an arctic
front that will begin to move into the Tri-State Area during the
late afternoon and early evening.  Models have continued to speed up
the arrival time of the front through the forecast area.  An earlier
arrival time does seem warranted with the surface low over Southwest
Kansas.  This setup is favorable for fronts to move through faster.
Ahead of the front a pre-frontal trough will move through during the
afternoon.  Behind the pre-frontal trough northwest winds will
increase as a strong low level jet moves through.  However the warm
temperatures will create an inversion near the surface which will
keep the winds from mixing to the ground until the latter half of
the afternoon when the cold front begins to move through.  Am
anticipating the strongest winds to be along the front with brief
gusts around 35 MPH likely.

Tonight the front will move south of the Tri-State Area during the
evening.  As the front moves further from the Tri-State Area the
winds will decline.  The environment will saturate in the 700-600mb
layer behind the front.  However nearly all the lift will have moved
through ahead of the front.  There will be some lingering lift
behind the front.  This may lead to some flurries at most before the
shallow saturated layer moves out of the Tri-State Area.

Lows will be 35 to 40 degrees cooler than highs behind the front.
Wind chills will fall into the single digits overnight.

.LONG TERM...(Tuesday through Sunday)
Issued at 346 AM MST Mon Dec 5 2016

Main focus for this period will be the drastic cool down in
temperatures and the first accumulating snow of the season.  Overall
have good confidence this event will have low to moderate amounts of
snow, with low confidence of heavy snow occurring.  Wind gusts of 25-
30 MPH are expected over the southwest half of the Tri-State Area
Tuesday night into Wednesday morning as the snow moves in, with
slower winds over the northeast half where most of the snow will
occur. Main impact will be the wind chills in the single digits
below zero Wednesday morning and 10 to 15 below zero Thursday
morning.

Tuesday temperatures will warm some but not much as cold air
advection continues.  Wind chills in the single digits are expected
during the morning.  Winds will be light as a surface high moves
through.

Tuesday night through Wednesday morning a quick moving upper level
short wave trough will bring a chance for light snow to the entire
Tri-State Area.  The majority of the snowfall will fall over the
northern half of the Tri-State Area overnight where a band of
frontogenesis will develop from 700-500mb.  This band will not move
for several hours overnight.  The environment will be fairly stable
which will serve to limit the snowfall rates under the band of
frontogenesis.  Before sunrise the band will shift southeast ahead
of the 500mb trough axis, bringing accumulating snow to the
southeast quadrant of the Tri-State Area before exiting.  Meanwhile
a second band of frontogenesis will develop over the southern part
of the Tri-State Area overnight in the 700-600mb layer. The
environment will be much drier here limiting the amount of snowfall
possible under this band.  The snow will move southeast of the Tri-
State Area by Wednesday afternoon.  Total snowfall accumulations
around four inches are expected with amounts around an inch or two
over Cheyenne County CO and Greeley County.

If the environment were less stable higher snowfall amounts would be
expected.  Noticed some of the SREF model plumes are showing higher
snowfall amounts than last night, with two to three inches becoming
more of an average of the higher and lower members.  The CIPS 75th
percentile snowfall analysis for this event lined up very well with
the forecast in placement and amount.  The median snowfall from CIPS
has less than two inches for the Tri-State Area.  The past event
most similar to this one according to the CIPS analysis had snowfall
amounts of one to two inches.  However the 500mb trough was not as
deep as this one will be.  Overall the CIPS analysis increases
confidence that this event will not be generating large snowfall
amounts.

As the snowfall moves into the Tri-State Area the winds will
increase as a shallow mixed layer develops, allowing the LLJ to mix
down.  Gusts of 25 to 30 MPH are expected for the southwest half of
the forecast area.  This will lead to some blowing and drifting
snow, although this will not be enough wind to close roads just make
travel inconvenient at worst.  The slower winds will be over the
northeast half where the majority of the snow will be occurring
during the night and Wednesday morning.

Perhaps the greater impact with this storm system will actually be
the very cold wind chills beginning late Tuesday night.  Wind chills
in the single digits below zero are expected by early Wednesday
morning.  The coldest temperatures will be late Wednesday night into
Thursday morning when wind chills of 10 to 20 below zero are
expected.


Thursday through Sunday...
A fairly quiet weather pattern is anticipated in the extended
period, at least through the weekend. The upper system causing the
mid-week snow event will have shifted east of the area by Thursday
with a broad upper ridge building over the High Plains through the
end of the week with an associated warming trend. Guidance is
consistent with a zonal upper pattern with a few weak embedded
impulses next weekend. One difference out on Day 7 (Monday)
involves the timing and location of a weak-moderate strength short
wave trough. GFS has this feature moving through Sunday night and
Monday with a band of light precip over the forecast area while
the EC shows this feature more on Monday with the main impact
across Nebraska. For now the forecast remains dry Monday pending
later model runs.

The coldest temperatures with this Arctic surge will occur Thursday
with morning as a 1045 mb surface high settles over the Central High
Plains. Morning lows will be around zero and highs Thursday
afternoon will only reach the teens, both of which are about 20
degrees below normal. Temperatures moderate on Friday as the surface
ridge moves east, but snow cover will continue to hold temperatures
10-15 degrees below normal. 850 mb temperatures warm considerably by
Saturday with GFS showing temps around 7 C.  Still have some concern
as to whether high temps at the surface can rebound into the lower
40s by Saturday given snow cover, but for now accepted the forecast
init and will monitor as the week progresses.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1000 PM MST Sun Dec 4 2016

For KGLD and KMCK, vfr conditions expected through the period.

Southwest winds around 15kts with higher gusts at KGLD for
initial conditions will continue through 10z before falling below
12kts. Winds veer to the west under 10kts by 14z then northwest at
similar speeds around 17z. Winds start to increase by 19z with
peak winds from the north gusting 25 to 30kts in the 21z-01z
timeframe as a cold front moves through. Toward the end of the
period sustained north winds around 12kts expected. No
precipitation expected for this taf cycle.

For KMCK southwest winds 10kts or less expected through 16z before
shifting to the northwest around 17z. Winds start to increase in
the 20z-04z timeframe with gusts in the 25 to 30kt range possible
as a cold front moves through. At the tail end of the taf period
sustained north winds around 12kts expected. No precipitation
expected for this taf cycle.


&&

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

$$

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



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