Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170710
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1210 AM MST Fri Nov 17 2017

.UPDATE...
Issued at 1210 AM MST Fri Nov 17 2017

Updated the forecast to delay the heavier onset of snow in the
mountains by a couple of hours. Also warmed the minimum
temperatures along the Front Range urban corridor by several
degrees due to the southwesterly winds that should continue
through the early morning hours.

UPDATE Issued at 844 PM MST Thu Nov 16 2017

Clouds were increased through overnight period for mountains and
plains. Satellite imagery showed more clouds than previous
forecast. Snow timing looks on track with snow developing in the
mountains after midnight.

&&

.SHORT TERM...(This evening through Friday)
Issued at 316 PM MST Thu Nov 16 2017

The lee wave clouds over the foothills and plains have been
thickening through the day. There is also some convective
cloudiness increasing over the mountains. Models keep a strong
west-southwesterly flow aloft over Colorado tonight and Friday.
Most of the models show 120-150 knots jet maximum by Friday
afternoon. The QG Omega fields show fairly decent ascent in the
synoptic scale tonight and Friday. Normal drainage winds are
expected overnight, perhaps enhanced a bit with some
southwesterly downsloping all night. Models keep downsloping going
early Friday. Models bring a decent cold front across sometime in
the afternoon. The GFS is quicker than the NAM and ECMWF. The
winds behind the front will be north-northwesterly. For moisture,
it increases this evening and is pretty deep after 06z in the
mountains. That continues through 00Z Friday afternoon late. The
plains will see an increase on mid and upper level moisture after
12z on Friday. The QPF fields bring in decent measurable
precipitation to the mountains after 12Z Friday morning, and
limited amounts over the plains by later Friday afternoon.
Concerning heavy snow and highlights in the mountains. There is
pretty deep moisture for the mountains and it gets fairly deep
after midnight tonight continuing through Friday. The mountain top
wind speeds are progged to be 30 to 50 knots. The directions are
a bit south of due west. The orographics are pretty good, directs
not perfect for our mountains. That with the synoptic scale
energy to boot, warning criteria snowfall amounts look good in
Zones 31, 33, and 34 from 06z tonight to 12Z Saturday morning.
Will go with "chance"s for rain over the plains, certainly behind
the front later afternoon Friday. Friday`s temperatures will be
fairly warm until the cold front moves across.

.LONG TERM...(Friday night through Thursday)
Issued at 316 PM MST Thu Nov 16 2017

The fast moving upper level trough will be passing over the state
tomorrow evening. A 150 knot jet will accompany the upper trough,
helping to drive the system. Jet streams over the state often
enhance the snowfall over the mountains. The band of moisture is
presently streaming over central California and northern Nevada.
Precipitation rates over the mountains will peak during the
afternoon and evening and then begin decreasing after midnight.
Quasi-geostrophic analysis shows super strong subsidence over the
state after 06z tomorrow night. On the plains, light precipitation
will develop through the evening as the best lift moves over the
state. Subsidence will spread out across the plains after
midnight. The Winter Storm Warning for the mountains will continue
through 5 AM Saturday morning, but may be cancelled a few hours
before that, when it becomes clear that the heaviest snow has
ended.

The next several days will feature flat ridging over the inter-
mountain west, with dry and mild weather over north central and
northeast Colorado. Temperatures will be about 10 to 15 degrees
warmer than normal, all the way through Thanksgiving Day. An
embedded short wave will shoot across the state with a few hours
of snow in the mountains Monday night. Snow accumulations will be
light, since the weather system will be moving across the state so
quickly. Long range models show another system possibly arriving
over the the state next Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 844 PM MST Thu Nov 16 2017

VFR conditions. Wind will become westerly, with 20 to 30 kt gusts
around 18Z. This will change to northwesterly winds gusting to 30
kts around 00Z.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 5 AM early this morning to 5 AM MST
Saturday for COZ033-034.

Winter Storm Warning until 5 AM MST Saturday for COZ031.

&&

$$

UPDATE...Kriederman
SHORT TERM...RJK
LONG TERM...Dankers
AVIATION...Sullivan


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