Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 110332
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
832 PM MST Sat Dec 10 2016

.UPDATE...
Issued at 819 PM MST Sat Dec 10 2016

Appears heaviest snow has ended for the time in the mountains, as
webcams and observations sites showing mainly just light snow and
flurries. Radar imagery has also shown a decrease in echoes in
the past several hours as well. Expect snow to increase in the
mountains again later this evening and towards midnight as next
deeper swath of moisture with the upper trof and strong jet pushes
across Northern Colorado. This can be seen in current satellite
imagery and upstream observations across Northern Utah and Western
Wyoming. Will continue with current warnings in place given that
heavier snow will move back into the Northern mountains before
midnight. Temperatures have been marginal over high mountain
valleys for snow, especially Kremmling which is still at 41
degrees. Should be some additional cooling overnight with some
snow accumulation still expected.

Weak surface front will also move across the plains of Northeast
Colorado later tonight with the best chance of snow east of the
urban corridor. Overall current forecast in good shape and will be
just making some minor adjustments.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 320 PM MST Sat Dec 10 2016

Moderate to heavy snow has spread into the northern Colorado
mountains over the last few hours. This band of moisture will
remain in about the same area through this evening, then drop
south with the trough axis late tonight and early Sunday morning.
No real change to the forecast, but I reworded our products to
emphasize that the heaviest snows over two feet will likely be in
the wilderness areas north of I-70, with 10-20 inches on the main
passes. Exception could be Rabbit Ears Pass which should be on the
high end. Strong winds are limited to areas above 10,000 feet, but
there is at least enough wind for drifting in North and Middle
Parks. Current warnings/advisories look good. For the plains I
focused the PoPs a bit more on the time just before the trough
passage as westerly flow should maintain a dry subcloud layer that
will limit the chance of showers reaching the ground through this
evening. Still a chance of some showers for a few hours on Sunday
morning, probably a quick hit with temperatures near or above
freezing so not too worried about significant amounts.

Skies should be clearing during the day over the plains, with a
lingering shallow cloud layer upstream of the Front Range.

.LONG TERM...(Sunday night through Saturday)
Issued at 320 PM MST Sat Dec 10 2016

Sunday night and Monday...a strong west/northwest zonal flow will
remain over the region. Spatial cross-sections fm the NAM12 show
moisture decreasing in the mountains Sunday night...weak mid level
subsidence in the evening, then weak qg ascent as a system passes
across Wyoming overnight. There is a brief amplification of the
mountain wave after 06z. Not a very long duration wave, but the
mountains east of the Continental Divide and higher foothills
could see some wind gusts to around 60 mph. On Monday...weak to
moderate downward QG through the day but strong orographics in
place. Mid level lapse rates not bad, around 6.5c/km. In addition,
moisture still in place up to 600 mb. Wly winds at 35 kts and 700
mb temperatures around -10c, still yield snowfall amounts in the
4-8 inch range fm the rhea/thaler snow model. As a result,
potential for advisory criteria snowfall in the mountains during
the day. By Monday night, the moisture depth decreases
significantly but still enough for areas of light snow along the
higher west facing slopes. The next wave of Pacific moisture moves
into the high country Tuesday afternoon into Wednesday. Should
see another round of heavy snow and strong winds in the mountains
at that time. Colder across the northeast plains on Tuesday as a
surface high pushes another surge of cold air into the region.
Stronger jet aloft should allow for a chance of snow to spread
across the lower elevations, but overall do not expect much in
the way of accumulations outside of a localized band. Wednesday
night into Thursday, the jet stream is progged to lift north into
Idaho and Wyoming with a broad ridge amplification. Still snow in
the mountains but coverage will drop off especially east of the
Continental Divide, but areas of blowing snow will likely persist
above timberline. By the end of next week, could see another round
of moderate to heavy snow develop in the mountains. The ridge
axis will shift east with trough moving into western Nevada by
that time. Moisture ahead of a continued strong west/southwesterly
flow aloft. Across the northeast plains, Arctic airmass pushes
through the region with the help of a 1040mb surface high. Frigid
airmass will be in place Saturday and Saturday night, with Pacific
moisture overrunning it. As a result, chance of snow will spread
across the lower elevations, especially near the foothills and
Palmer Divide where some shallow upslope will be possible. At this
time, it looks like the arctic airmass should remain over the
northeast plains into early next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 819 PM MST Sat Dec 10 2016

Surface winds have been all over the place this evening but
appears things will be settling down to a light southeast wind
later this evening before the weak frontal push after 10z
tonight which will shift winds a bit more easterly. Ceilings will
also lower with the push but looks like any precip will likely
stay just east of the terminals so will go with a VC in the
updated evening TAFS.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 AM MST Sunday for COZ031-033-034.

Winter Weather Advisory until 11 AM MST Sunday for COZ030-032.

&&

$$

UPDATE...Entrekin
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Entrekin



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