Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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488
FXUS65 KBOU 131100
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
400 AM MST Sat Jan 13 2018

.SHORT TERM...(Today and tonight)
Issued at 400 AM MST Sat Jan 13 2018

Moderate northwesterly flow aloft will prevail over Colorado today
and tonight with the upstream ridge centered over Washington and
Oregon this morning. Mid and upper level moisture are entrained
in the upper level flow which will lead to some cloudiness over
eastern Colorado through the day. In the mountains, scatted light
snow showers continue over northwest facing slopes, but additional
accumulations should remain less than an inch or two. The upper
flow pattern will also produce gusty winds over ridges through
today and tonight. Wind gusts as high as 50 mph may cause local
blowing snow and obscuration of peaks, but conditions at highway
levels should be much more benign. Drier air will continue moving
into the state tonight which should cut off the snowfall in the
mountains and lead to mostly clear skies over the plains.
Temperatures should be around seasonal normals, not too hot or not
too cold for the middle of January.

.LONG TERM...(Sunday through Friday)
Issued at 400 AM MST Sat Jan 13 2018

Dry NW flow aloft will be over the area on Sun as a sfc lee trough
is in place over ern CO.  With downslope flow in place temps should
rise into the lower to mid 50s across much of nern CO except over
the far nern corner where readings may range from 45 to 50.

For Sun night into Mon an arctic fnt will move across nern CO with
much colder temps on Mon.  Still believe the ECWMF has a better
handle on cold airmass so will have highs ranging fm the teens over
the far nern plains with 20s closer to the foothills.  Highs will
likely occur in the morning and may slowly fall thru the day.
Meanwhile there will be a disturbance embedded in Nwly flow aloft
which will affect nern CO during the day with some minor QG ascent.
In addition nern CO will be in the favored right exit region of
upper level jet.  ECWMF and GFS cross-sections show differing
amounts of moisture with the GFS more moist while the ECMWF is a bit
drier.  Overall still believe there will be a good chc of light snow
developing across nern CO late Sun night thru Mon which will likely
spread into the Foothills and east slopes of the Mtns.  At this time
amounts look to be on the light side although some heavier banding
could occur in a few places in association with the upper level
jet.

By Mon night drier air will gradually spread across the area as
upslope component diminishes, thus any lingering snow should end in
the early evening hours.  On Tue dry NW flow aloft will be in place
as cold sfc high pres is over the cntrl US.  Shallow cold airmass
will modify some, however, there isn`t much of a downslope
component so ECMWF probably has a better handle on highs across
nern CO. For now will keep temps in the mid 20s over the far nern
corner with 30s eslewhere. If some weak downslope occurs in the
srn Foothills temps could rise into the lower 40s in the swrn
suburbs of Denver.

For Wed both the ECMWF and GFS show an upper level trough somewhere
over the region.  The GFS takes it across WY into ern CO while the
ECMWF moves it fm Utah across swrn CO.  Once again GFS ensemble data
has a large spread so confidence remains pretty low just like last
night.  Will go with a blended solution and keep in a chc of snow
for the mtns and keep the plains dry.  As for highs, 850-700 mb
temps continue to rise so will have readings mainly in the 40s
across nern CO with lower 50s possible around Denver.

By Thu an upper level ridge will build over the area which will lead
to drier and warmer pattern.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 400 AM MST Sat Jan 13 2018

An area of low clouds and fog has formed over eastern Boulder
County which is being advected southward over KBJC. Visibilities
have dropped to a half mile, but the extent of fog and low clouds
is quite limited. KDEN and KAPA remain in the clear with no
indication that the area of low clouds is going to spread much
further. The LIFR conditions at KBJC should continue through 6 AM
or 7 AM and then begin improving. Mid and high level clouds
should continue streaming over eastern Colorado through the day
but any ceilings should remain well above 6000 feet AGL. Winds
shoudl remain below 12 knots as they blow out of the southwest to
northwest. Typical drainage winds are expected tonight as skies
trend toward mostly clear after sunset.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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



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