Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 090440

Area Forecast Discussion
National Weather Service Denver/Boulder CO
940 PM MST Thu Dec 8 2016

Issued at 935 PM MST Thu Dec 8 2016

Snowfall now underway in the high country. West-northwest winds
of 30-40 mph also producing some blowing snow. Weather spotter
reported momentary white out conditions while driving over
Berthoud Pass in the past hour. Regional radars indicate light to
moderate snowfall up along the Continental Divide with passage of
a weak upper air disturbance in moderate northwest flow aloft.
However...water vapor satellite imagery shows a break in the
moisture immediately upstream from Colorado. Consequently could
see a modest drop off in snow intensity next couple of hours but
not necessarily a drop off in wind speeds. Actually models
indicate an increase in the cross mtn flow with an increase in mtn
top stability. It`s after midnight when the high country should
see a notable increase in snowfall rates with the arrival of the
next wave of moisture and qg forcing marked by the wide area of
precipitation indicated on radar over sern Idaho...swrn Wyoming
and northern Utah at this time. Higher west-northwest facing mtn
slopes and passes could see 1-2 inch per hour snowfall rates
during the pre-dawn hours with the passage of this disturbance.
Blowing snow also a good bet esply on the passes. A winter weather
advisory is in effect for mtn zones 33..34 and 31 now until 5 pm
mst tomorrow. Orographically favored northwest slopes could end up
with close to a foot of powder by afternoon. As for the
plains...dry conditions will prevail next 24 hours but wouldn`t
rule out occasional bursts of very light snow or flurries blowing
down off the higher foothills. Still no accumulation for lower

UPDATE Issued at 518 PM MST Thu Dec 8 2016

Zone and point forecasts were updated and sent out a short time
ago. Adjusted a handful of the weather and sky cover grids starting
Saturday out through Wednesday night. Removed any mention of rain
in the high mtn valleys and went with a rain/snow mix during the
day light hours Saturday and Sunday in the Front Range foothills
to coincide better with the wetbulb freeze level. Also added a bit
more sky cover in areas with pops 20 percent and greater.


.SHORT TERM...(This afternoon through Friday)
Issued at 330 PM MST Thu Dec 8 2016

Moderately strong northwesterly flow aloft will continue over the
forecast area tonight and Friday. The synoptic scale energy is
benign tonight and Friday. Normal diurnal wind patterns are
progged for the plains and drainage winds are progged overnight.
foothills tonight and Friday. The higher mountains can expected
west and northwesterlies strong enough for some blowing snow.
Models have moisture increasing and getting pretty deep for the
mountains and current satellite pictures concur with this. The QPF
fields show fairly decent precipitation/snowfall amounts in the
mountains tonight and Friday. Snow advisory criteria looks fine in
the mountains with the moisture and orographic enhancement. Will
leave highlights as is. For temperatures, Friday`s highs will be 8
to 13 C warmer than today`s highs.

.LONG TERM...(Friday night through Wednesday)
Issued at 255 PM MST Thu Dec 8 2016

Moist flow from the NW will continue into the extended generating
more orographic snow in the Mountains. Snow fall will wind down a
bit Friday night into Saturday with some light snow still expected
with continued orographic influence. The plains will remain dry on
Saturday with a lee side low near the base of the Foothills keeping
winds downsloping onto the plains warming temperatures into the 50s
for Saturday. The strong WNW flow will bring increased wind gusts to
the mountains but with little shear near mountain top and
subsequent stable layer do not expect the winds to make it down
the Foothills. Winds of 35 to 40 in the mountain valleys to speeds
up to 60 near mountain top will be possible Through the day
Saturday creating blowing and drifting snow and potential
hazardous driving conditions for weekend travelers.

Saturday night into Sunday models have the upper jet dropping south
into the Northern mountains combining with a conveyer belt of
Pacific moisture to increase snowfall over the mountains Saturday
night through Sunday. Looking at 700 mb...temperature values are
higher then with the previous storm with the influence of WAA from
westerly flow aloft. Therefore expect a lower snow to liquid ratio
with this storm and heavier more wet snow. Current QPF models 12
hour accumulations from 0.30 to 0.60 with the higher amounts over
west facing slopes. This could equate to snowfall amounts of 4.5 to
9 inches and combined with continued wind gusts up to 50 mph an
advisory may be needed. A cold front will move into the northern
plains from Wyoming bringing slightly cooler air. The increased NE
flow on the plains behind the front will have to compete with the
strengthening surface low close to the foothills in achieving
desired upslope. Will keep a slight chance on the plains Sunday
morning but confidence is low for much precipitation on the plains.
Temperatures will only be slightly cooler then Saturday with highs
in the 40s.

For next week the upper level pattern will continue to be strong
from the WNW. Models are coming into better consensus with an
arctic push of cold air from the north bringing temperatures on
the plains back to the teens and 20s and possibly below zero
overnight by mid week. The only model that keeps it further east
is the EC so will do an average of temps for that period with more
emphasis to the cooler side. Snow will continue in the mountains
with the only difference through the week being intensity. This
will change as the days go on seeing where models put jet
placement and the best lift. Temperatures for next week will hover
around normal with the drop by mid week then back above freezing
by Thursday.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 935 PM MST Thu Dec 8 2016

Light and variable winds in the Denver metro area at present time
still expected to become predominantly a drainage flow in the
next hour or two. Speeds will generally be light...under 10 kts.
Otherwise it will stay dry with cigs at or above 12k feet for the
next 24 hours.


Winter Weather Advisory until 5 PM MST Friday for COZ031-033-034.



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