Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170951
AFDBOU

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

.SHORT TERM...(Today and tonight)
Issued at 245 AM MST Fri Nov 17 2017

...A Winter storm today and tonight will impact the mountains
with snow, the plains with mainly winds...

A positively tilted upper trough over the Pacific Northwest, and
another subtropical jet stretching across California, Nevada and
Utah will combine forces for a windy winter storm today through
tonight. Strong west-southwest flow aloft has kept minimum
temperatures across most of the area quite moderated, with
readings in the 50s and 60s over the foothills, plains and even
some in the high mountain valleys.

Overall the system has slowed slightly, with not much snow into
the far northern mountains, but rain and snow has nudged into the
I-70 corridor from the southern subtropical jet. Expecting the
PCNW upper trough to start digging southeast pretty quickly, which
will be bringing much colder air. Believe we`ll start to see the
heavier bands of snow arrive over the northern mountains before
sunrise. Snowfall rates in the mountains today will be in the 1/2
to 1 inch per hour rate, with some bands having the potential to
produce up to 2 inches or more in an hour. Have decreased some of
the forecasted snowfall total over South Park as it seems they`ll
be struggling with downsloping winds almost all day. Still looking
for snowfall totals in the mountains, especially above 9000 feet
to be in the 6-12 inch range, with some spots reaching 18-24
inches. The best chance for the amounts above a foot will be over
the mountains of Rocky Mountain National Park and of the Park and
Gore ranges. The strong winds gusting to 50 mph from this system
will reduce visibilities in blowing snow.

With the strong, mostly downsloping pattern of the southwest
winds, have decreased pops over the Front Range urban corridor for
most of this morning and early afternoon, as well as increased
max temperatures as well. As northeastern Colorado becomes under a
favored location from both jets later this afternoon, with upward
QG vertical motion in the 20 to 25 mb/hr, have increased pops
across the plains with the strong cold front expected to push down
soon after. An precipitation that falls over the plains will start
as rain, with snow likely mixing in after 8 or 9 pm. Strong cold
bora type winds will follow in behind the front, likely gusting to
40 mph across the plains, and temperatures plummeting. Believe
precipitation will be hard to form just east of the foothills
along the urban corridor especially northern areas that will fight
the downsloping effects of northerly winds off the Cheyenne Ridge
as well. By midnight, strong subsidence with downward QG motions
of 35 mb/hr will have diminished most of the precipitation, except
light orographic snow possibly still falling in the mountains,
with only another inch to fall at best. Temperatures across the
area will be down in the teens and 20s, with winds slowly
decreasing.

.LONG TERM...(Saturday through Thursday)
Issued at 245 AM MST Fri Nov 17 2017

A broad flat ridge of high pressure will build over the region
over the weekend with a drying and warming trend in store for
Colorado. There will still be some breezy conditions on Saturday over
the mountains and plains in the wake of Friday nights wave and
lingering subsident airmass over the region. A weak ripple moves
through the fast northwest flow on Sunday night with some enhanced
winds for the mountains and east slopes. Cross sections show cross
barrier flow around 40kt and some mountain top stability so could
see some higher gusts in the 50-60 mph range over wind prone
areas. Airmass looks quite dry with this system so no precip
expected.

A stronger system will move over Colorado on Monday
night with the next chance for snow in the mountains and cooler
temperatures for all areas on Tuesday. This is a fast moving
system so expect any snow accumulation will be on the lighter
side in the mountains. The plains could see an isolated snow
shower but moisture is limited.

The ridging aloft rebuilds for Tuesday through Thursday with
another dry and warm period for this time of year. The GFS is
advertising the next system to slide over northern Colorado in the
Friday night time frame while the European solution maintains more
ridging and continued dry. Certainly quite a bit of varied model
solutions going into next weekend so won`t put much stock in any
one solution.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 245 AM MST Fri Nov 17 2017

Strong southwesterly winds will continue through most of the day
today ahead of a strong cold front this evening. Wind should
become westerly, with 20 to 30 kt gusts around 18Z. This will
change to northwesterly winds gusting to 30-35 kts around 00Z as
the cold front pushes down. A few showers will be possible, but
will likely downslope over the Front Range urban corridor,
including DEN, APA and BJC. There will be a chance of ceilings
going down to 040-050 with the passing showers - and should stay
mainly rain over the 3 main terminals. Cold bora type winds will
continue the strong northwest winds through 06z and possibly all
the way to 12z, with skies clearing quickly.

&&

.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.

&&

$$

SHORT TERM...Kriederman
LONG TERM...Entrekin
AVIATION...Kriederman



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