Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 172209

Area Forecast Discussion
National Weather Service Denver/Boulder CO
309 PM MST Fri Nov 17 2017

.SHORT TERM...(This evening through Saturday)
Issued at 309 PM MST Fri Nov 17 2017

...A winter storm will continue to impact the mountains with snow
and the plains with a mix of rain and snow along with winds through
this evening...

The main energy for this storm is just entering the northern
mountains of the Park and Gore range and south into Grand and Summit
county. Increased energy ahead of the trough will bring increased
snow amounts and rates to the higher terrain for the next few hours.
Rates of 2 to 3 inches per hour will be possible at times as the
energy moves through. This could greatly impact driving conditions
over the higher passes between 3 and 5 pm. Lightning has been seen
on WV over the higher terrain and into Weld county so some
thundersnow could be possible. Elsewhere a cold front has entered
Weld county and south of Wyoming a few hours ahead of current model
guidance. This will drop temperatures 10 to 15 degrees and increase
winds to 30 mph from the north. As the cold air moves south along
the urban corridor in conjunction with the added moisture and lift
associated with the trough a light rain and snow mixture will be
possible this evening. Some northern counties could switch over to
all snow given the cooling airmass before subsidence moves in but
amounts will generally be less than 1 inch with most areas seeing a
trace to half an inch on grassy surfaces. QG energy will go from -15
mb/hr to +30 behind the trough so precipitation and gusty winds will
decrease quickly behind the trough given the strong subsidence.
Ceilings will gradually clear overnight with lows dropping into the
single digits to teen in the mountains and 20s on the plains. Roads
that became wet due to rain or snow will freeze overnight creating
hazardous driving conditions for early risers on Saturday. Saturday
will see partly cloudy skies with temperatures more in line with
seasonal normals in the upper 40s.

.LONG TERM...(Saturday night through Friday)
Issued at 309 PM MST Fri Nov 17 2017

Generally benign weather is expected through the next week. The
one exception will be Monday night and early Tuesday. Sunday and
Monday are going to feature warmer weather as dry and moderate
westerly flow aloft dominates the weather picture. The flow
pattern aloft is expected to be progressive with an upper ridge
moving over the state Monday. This will bring the warmest
temperatures of the early week. High temperatures on the plains
will be in the lower 60s. A strong surface high pressure area is
expected to build over Montana and the Dakotas Sunday and Monday
which will move cooler air into northeast Colorado on Tuesday.
These cooler temperatures will be accompanied by a passing upper
level disturbance that should bring some light snow to the
mountains. The plains are expected to remain dry as the upper
system quickly moves out onto the Great Plains by Tuesday
afternoon. The GFS and ECMWF operational models show the light
precipitation over the northern mountains early Tuesday morning,
but QG diagnostics from both models show only weak dynamic forcing
for ascent with this upper trough. The system will have been much
stronger as it moved over northern California and Oregon on
Monday, so that all that is left for Colorado is a weakening upper
system. Will hold on to scattered pops over the mountains for
Monday night and Tuesday morning. Accumulations in the mountains
will only be an inch or two.

After Tuesday morning`s upper disturbance passes, another upper
level ridge will build over the southwestern United States with
warm temperatures and dry weather across Colorado through the end
of the week. This upper ridge looks like it will hold in place
well into next weekend.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 309 PM MST Fri Nov 17 2017

Winds will gradually switch from the west to NW then North with
the passage of a cold front. Currently the front is over the Ft.
Collins area and is expected possibly between 23 and 00z, which
is a few hours before previous model guidance suggested. Expect
gusts from 32 to 34 with frontal passage and dropping
temperatures. A mixture of rain and snow will be possible with
MVFR conditions between 02 and 06z. By 08z conditions will
gradually improve for BJC and DEN and 10z for APA. VFR conditions
are expected by then with winds switching around to drainage by
14z for the remainder of the TAF period.


Winter Storm Warning until 5 AM MST Saturday for COZ031-033-034.



LONG TERM...Dankers
AVIATION...Bowen is the U.S. government's official web portal to all federal, state and local government web resources and services.