Area Forecast Discussion
Issued by NWS Goodland, KS

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515
FXUS63 KGLD 230556
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
1056 PM MST Thu Feb 22 2018

.SHORT TERM...(This evening through Friday)
Issued at 153 PM MST Thu Feb 22 2018

Precipitation has left the area. So the main issue to deal with will
be freezing formation and how dense does it get. Clouds will clear
out gradually. At the same time the winds will become light and
variable. Some locations received some precipitation but not a lot
of the area. Air mass is already cold and moist. So expect fog to
develop as the clouds clear out.

However even though the high resolution output indicates that fog
will form they differ on exactly where it will develop first and
where the lowest visibilities will be. Went with a blended guidance
approach. I have patchy freezing fog developing mid to late evening.
Then I have areas across the entire area from then through mid
morning on Friday. There looks like it will be dense but do not know
exactly where. So will included patchy dense.

Temperatures will be tough due to variable amount of cloud cover.
Went ahead and used the forecast blend.

.LONG TERM...(Friday night through Thursday)
Issued at 324 PM MST Thu Feb 22 2018

Main focus for this period will be the winter weather Friday night
through Saturday.  A winter storm watch has been issued for
locations along/north of Highway 24, expect for Norton County where
the highest snowfall amounts will be.

Friday night an upper level short wave trough will approach from the
west.  As lift from the trough overspreads the forecast area,
moisture advection will also occur in the lowest half mile or so.
The environment will saturate deep enough to support precipitation
from west to east during the night.  As the precipitation spreads
east it may alternate from snow to freezing drizzle or vis versa due
to the depth of the saturated layer varying from deep enough to
support snow to only being able to support freezing drizzle.

By midnight convective theta-e lapse rates will move over locations
east of Highway 27, lasting through the rest of the night and into
Saturday morning.  These lapse rates will be in the dendritic zone
where the strongest lift will also be occurring.  However this will
be east of the deeper saturated environment over the west third of
the forecast area.  Because of the strong instability in the mid
level dry air, there was initially concern that only freezing
drizzle would form, with a possibility of snow.  If any snow forms,
this will change the freezing drizzle to snow.  However this is
dependent on convective snow forming, which may or may not happen.
Confidence in convective snow occurring is moderate.

Behind the potential convective snow and freezing drizzle the
saturated layer will be deep enough to support snow.  In addition
this is where a band of frontogenesis will also develop.  Theta-e
lapse rates are close to zero, so this would support moderate to
possibly heavy snowfall.  Foresee one main band of moderate
snowfall, with possibly a very narrow area of heavy snow in it, with
the band north of I-70 mainly.  South of the forecast area another
band of snow will move northeast.  Saturday morning the further
south band from the night will move over the southeast part of the
forecast area while the further north band continues to move
northeast out of the forecast area.  Snow will end from west to east
Saturday morning, possibly lingering into the afternoon.  Have the
watch lasting through the day in case the snow ends up exiting the
forecast area later than currently expected.

Regarding precipitation type have moderate confidence of snow being
the dominant type due to the potential setup for convective snow.
Could see some thundersnow over the southeast half of the forecast
area. Confidence is on the low side regarding how predominant the
convective snow will be versus freezing drizzle.  When models have
been indicating drizzle is the predominant type for an upcoming
precipitation event, they have been too warm and snow ends up
occurring instead of freezing drizzle, including the light
precipitation from Wednesday night. With this in mind did keep a
mention of freezing drizzle in the forecast since the depth of the
saturated layer supports that. Bottom line, high confidence for snow
but moderate confidence regarding if convective snow will occur,
moderate confidence for freezing drizzle and low confidence for the
areal/temporal extent of the freezing drizzle versus convective snow.

Impacts for this event will be snowpacked roads and reduced
visibilities down to a quarter mile from the high snowfall rates.
Locations over the southeast part of the forecast area southeast of
a Sharon Springs to Oakley and Norton line could have 2"/hour
snowfall rates if convective snow develops.  These bands will be
quite narrow if they occur. Due to the low confidence of where these
bands will form, kept snowfall amounts in line with model consensus.
The longer the freezing drizzle lasts the more ice will accumulate
on surfaces.  A thin sheet of ice may develop with snow on top of it
for this same part of the forecast area as mentioned above.  Some
blowing/drifting snow may occur southwest of a Yuma to Goodland and
Oakley line once the snow ends as northwest winds increase behind
the precipitation.

Due to the snowfall and northwest winds Saturday, current highs for
the day are probably a few degrees too warm.

A couple other chances for precipitation are forecast for the latter
half of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1030 PM MST Thu Feb 22 2018

Initial Conditions: At 06Z, conditions ranged from VFR in northeast
Colorado to widespread MVFR-LIFR stratus and patchy fog in northwest
Kansas and southwest Nebraska.

06Z TAF Period: Challenging forecast. Light/variable or calm
winds will prevail through early to mid afternoon. GLD and MCK
are located on the W/NW periphery of a large swath of IFR/LIFR
ceilings and MVFR/IFR fog extending from central KS into portions
of northwest KS and southwest NE. With mostly clear skies, and
lingering snow on the ground just N and NW of Goodland, it appears
likely that stratus/fog will continue to expand west/nw across the
region. LIFR conditions associated with very low ceilings or
dense freezing fog will be possible, particularly between 09-15Z.
Stratus/fog are expected to gradually lift/scatter to VFR by late
morning/early afternoon (AOA 18Z). Light/variable winds will
become ESE at 15-20 knots by the end of the TAF period (~00Z Sat).

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Winter Storm Watch from Friday evening through Saturday
     afternoon for KSZ001>003.

CO...Winter Storm Watch from Friday afternoon through Saturday
     afternoon for COZ090.

NE...Winter Storm Watch from Friday afternoon through Saturday
     afternoon for NEZ079>081.

&&

$$

SHORT TERM...BULLER
LONG TERM...JTL
AVIATION...VINCENT



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