Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 101150
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
450 AM MST Sat Dec 10 2016

.SHORT TERM...(Today and tonight)
Issued at 450 AM MST Sat Dec 10 2016

Satellite imagery over the western United States shows the deep
moisture heading towards the central Rocky Mountains as strong
westerly flow aloft drives the storm our direction. The abundant
moisture and strong westerly flow are going to produce heavy
orographic snows in the mountains, beginning this afternoon and
continuing through Sunday. Snowfall will become heavy at times and
strong winds over higher elevations will produce poor visibilities
due to blowing snow. will be upgrading the Winter Storm Watch to a
Winter Storm Warning. Snow amounts of 1 to 2 feet are going to be
possible as the storm passes. Will also issue a Winter Weather
Advisory for North Park and Middle Park, for snow amounts of 6 to
10 inches in those high mountain valleys.

On the plains, conditions will remain dry through this evening due
to the strong westerly flow pattern aloft. Some showers may move
across the plains later tonight, but precipitation amounts will be
limited by the dry conditions at low levels. Precipitation may
begin as rain or a mix of rain and snow in the evening, but then
change over to snow by midnight due to evaporative cooling
effects. Temperatures across the plains will be quite mild today
due to the downsloping flow across the region.

The primary weather story of the day is going to be the hazardous
conditions developing in the mountains tonight because of the
heavy snow and winds.

.LONG TERM...(Sunday through Friday)
Issued at 450 AM MST Sat Dec 10 2016

A disturbance will move across nrn CO in wnw flow aloft Sun morning
and then should be east of the area by aftn.  Snow will continue in
the mtns thru the morning hours but will decrease by midday as drier
air begins to spread across.  Although snow will decrease gusty
winds will produce widespread blowing snow abv 10000 ft.  Across the
nern CO a cdfnt will move across early in the morning and may
provide a brief period of upslope flow.  As the disturbance moves
across in the morning there could be a good chc of snow across
portions of nern CO.  Right now it appears best chc would be along
and north of a Denver to Akron line so have raised pops into the chc
category.  By midday day snow threat will end as disturbance moves
east of the area.  As for highs readings will range fm the mid 30s
across the far nern corner with lower 40s around Denver.

For Sun night thru Mon wnw flow aloft will remain across the area
with limited moisture embedded in the flow.  Although orographics
will remain favorable in the mtns moisture depth is rather shallow
so only some light snow is expected.  However winds will remain stg
at times abv 10000 feet so expect quite a bit of blowing snow over
the higher passes.  Across nern CO it will be dry with with aftn
highs in the upper 30s to mid 40s.  Also will see wnw gusty winds in
the foothills and across the the plains nr the WY-NE border by aftn.

By Mon Night into Tue moisture will increase once again in wnw flow
aloft with more orographic snow expected in the mtns. Position of
upper level jet could also enhance snowfall especially along and
north of I-70. Across nern CO another fnt will move across the
plains with shallow upslope flow developing by aftn. There could
be a chc of snow nr the WY border by aftn as this area will be nr
the upper level jet. As for highs temps will drop back into the
upper 20s to mid 30s over nern CO.

For Tue night into Wed orographic snow will continue in the mtns.
Position of upper level jet may still lead to enhancement of
snowfall rates once again along and north of I-70.  Over nern CO
another shot of colder air may affect the plains with some increase
in upslope flow.  Position of upper level jet will determine where
best chc will be with banded areas of heavier snow certainly
possible. Currently best chc looks to be closer to the WY-NE border.
Highs will range fm the upper teens nr the WY-NE border with lower
to mid 20s elsewhere.

By Wed night into Thu the flow aloft will be wly with cross-sections
still showing abundant moisture embedded in the flow. Thus will
continue to see periods of orographic driven snow in the mtns.
Across nern CO there are some differences between the ECMWf and
GFS with regards to sfc ptrns. The ECMWF shows sely low lvl flow
developing as cold sfc high pres is over the cntrl US while at the
same time the GFS has another surge moving into nern CO in the
aftn with the flow more ely. In addition the GFS has an upper
level jet over the area with far more moisture across nern Co vs
the ECMWF. As a result the GFS solution would bring another chc of
snow to portions of nern CO while the ECMWF would have a drier
solution. This far out hard to say which soluton is the best so
will just keep in some low pops over nern Co with highs in the mid
20s to lower 30s.

For Thu night into Fri the flow aloft will become more swly as an
upper level trough dvlps over the wrn US.  Snow would continue in
the mtns however amounts would probably be lighter as swly flow is
not as favored except in zn 31.  Over nern CO there could be a chc
of snow as upper level jet will be over the area with moist sw flow
aloft.  Both the ECMWF and GFS show another possible surge of colder
air at some point either in the aftn or evening as well.


&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 450 AM MST Sat Dec 10 2016

Even though conditions in the mountains will be deteriorating
through the day as the next winter storm moves in, on the plains
the strong westerly flow aloft will produce drying at the mid
levels, and therefore little impact on aviation through the
afternoon and evening. Cloud heights should remain well above 6000
feet AGL, and winds will be 10 knots or less until mid-afternoon.
Later in the afternoon, KBJC may see an increase in westerly
winds. Later this evening, a few showers of rain or snow may move
across the Denver airports. Precipitation amounts should be light
and ceilings are expected to remain above 5000 feet AGL. Overnight
may see some light snow flurries, but no snow accumulations are
expected as ceilings remain in the VFR category.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 2 PM this afternoon to 11 AM MST
Sunday for COZ031-033-034.

Winter Weather Advisory from 2 PM this afternoon to 11 AM MST
Sunday for COZ030-032.

&&

$$

SHORT TERM...Dankers
LONG TERM...RPK
AVIATION...Dankers



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