Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 012335 AAA
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
535 PM CST Thu Dec 1 2016

.SHORT TERM...(This evening through Friday)
Issued at 324 PM CST Thu Dec 1 2016

Tranquil weather will highlight the next 24 hours over western and
north central Nebraska as an area of surface high pressure settles
into the area. Upper level cloud cover is expected to increase over
the forecast area as flow aloft steadily becomes southwesterly owing
to upper level low closing off over the Four Corners region. Model
guidance has begun to indicate the potential for fog as temperatures
cool overnight in northwest Nebraska and into the central Sandhills.
However, deterministic models appear to be overestimating the
spatial expanse of the current surface snow cover, which leads to
uncertainty with how the models are handling surface temperatures
and moisture flux. Upper level cloud cover tonight may also keep
temperatures a few degrees warmer than forecast. Opted to leave any
mention of fog out of the forecast for now due to low confidence. If
fog were to develop, it would likely be patchy with visby above 1sm
at most locations.

Not much change to the forecast for Friday. The presence of surface
high pressure centered near the cwa will keep winds light. H85 temp
advection remains nearly neutral in the persistent northwest flow in
the mid-levels. Highs were kept similar to today with low to mid 40s
in our southern zones, and mid to upper 30s in the north.

.LONG TERM...(Friday night through Thursday)
Issued at 324 PM CST Thu Dec 1 2016

Friday night through Sunday...1030mb Pacific high pressure builds
through the Central plains Saturday followed by sfc low pressure on
the Nrn High plains. The forecast focuses on sky condition since
that would impact temperatures the most. Saturday is expected to be
mostly sunny. The Srn Plains system will be exiting east and this
should present drying aloft. A second batch of high clouds should
move in Sunday. The models are not clear on the abundance of cloud
cover but a fresh batch of cirrus is expected to move off the
mountains in Wyoming and spread into Wrn and Ncntl Neb.

The temperature forecast adds bias correction and generally
suggested highs and lows a degree or two cooler. This would produce
highs in the 40s Saturday and Sunday with about a 5 degree rise
Sunday associated with a building thermal ridge which will move
overhead Sunday night. Lows both mornings fall into the teens and
20s. The 12z gridded MOS is also lighter but suggests 1 to 6 inches
of snow with highest amounts focused on the Cheyenne divide and Swrn
Neb. Meanwhile the experimental FIM shows heavy snow across Wrn KS
and Ern Colo so the model consensus is poorly focused.

Sunday night through Thursday...the ECM and GEM are the slower
models waiting until Monday night for the arctic front to move
through. The GFS and ensemble are faster bring the front through
Monday. A blend of the models suggests light snow Monday night
through Wednesday morning as the arctic air wrings all moisture from
the air. There are some weak dynamics moving east from WY suggested
by the GFS ensemble. This could affect the area Tuesday with the
better snowfall rates...still light.

Todays models continue to show a strong lead short wave moving
through Srn Canada hastening the arrival of the arctic front. The
GEM was weaker with this system and therefore focuses more dynamics
and potential for snowfall across Nebraska. The GFS ensemble was not
far behind and suggested 3-4 inches of snow throughout Wrn and Ncntl
Nebraska. The GFS operational was mostly dry shunting the dynamics
farther south across KS. The 12z gridded MOS is also lighter but
suggests 1 to 6 inches of snow with highest amounts focused on the
Cheyenne divide and Swrn Neb. Meanwhile the 12z ECM and experimental
FIM show heavy snow across Wrn KS and Ern Colo so the model
consensus is not well understood.

The forecast follows a multi model blend which resembles the GFS
ensemble and Gridded MOS for a 30 to 40 POP Monday night through
Wednesday morning. Snowfall amounts of 1 to 3 inches are in place
for this forecast. Note that forecast snowfall amounts are highly
dependent on the track of an upper level disturbance which will
likely change between now and Monday night.

H700mb temperatures fall from 0C Monday night to -20C Tuesday night
and this should drive every bit of moisture from the atmosphere as
snow. Precipitable water falls from 0.25-0.33 inches to 0.10 inches
in the same time. Wind chill values could reach -5F to -15F by
Wednesday morning. Snow ratios rise to 20 to 1 which supports light
fluff snow and a gradual lowering of the dendritic growth zone. WPC
has backed down the probability of significant snowfall less than 30
percent.

The arctic air should move off the high plains Thursday with a very
modest warming across Southwest Nebraska...highs near freezing.
North Central Nebraska remains in the teens for highs.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 531 PM CST Thu Dec 1 2016

Mid and high clouds over western Nebraska this evening will lift
to the northeast through the night. Winds have decoupled this
evening and will be light and variable tonight and through the day
on Friday with surface high pressure over head. Visual flight
rules expected.


&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Martin
LONG TERM...CDC
AVIATION...Power



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