Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 180408

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

Issued at 908 PM MST Fri Nov 17 2017

Forecast is generally on track. The main precipitation band is
dropping south of Denver this hour and is south of Interstate 70
in the mountains. Snow level is near 6000 feet. Lighter snow will
continue in the mountains through the night. Minor changes at this
hour are higher PoPs in areas south/east of Denver for the next
several hours for the rain band, with lower PoPs further north.
There has been a bit less wind behind the band, but there is
another pressure surge coming into southeast Wyoming that should
increase the winds again between about 3 and 6 am. Could be some
flurries with that as well, but low level should be dry enough
that there isn`t any accumulation.


.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 06Z TAFS through 06Z Saturday night)
Issued at 908 PM MST Fri Nov 17 2017

Rain/snow band will move out of the Denver area in the next hour
or two with conditions improving. There may still be areas of MVFR
ceilings overnight, ending between 12z and 14z. Instrument
approaches will likely be needed at KDEN until then.


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



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