Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 161800
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1100 AM MST Thu Nov 16 2017

.SHORT TERM...(Today through Friday)
Issued at 355 AM MST Thu Nov 16 2017

Teleconnections upstream are evolving such that the persistent
trough that has been lingering off the central left coast of NOAM
will be replaced by ridging by this weekend. As this system breaks
from the west and sweeps across the northern CONUS it will set the
stage for a decent shot of precipitation across the Colorado
mountains and some of the adjacent high valleys. There is a cold
tap to the this storm but unfortunately it arrives on the tail end
of the event and we will be dealing with the warm phase and
fluctuating accumulating snow levels tonight through Friday
afternoon. The other element of this event which prevents this
storm from being more robust is the dry air currently in place
with PWAT slightly below normal.

There is a decent atmospheric river pointed at California this
morning which will bring some moisture to our region with the
subtropical jet lifting into the central Rockies by sunrise.
However it appears the coastal mountains will be absorbing much
of this moisture before it takes on the dry Great Basin. Highs
remain above normal today and likely tomorrow ahead of the cold
front which doesn`t bode well for snow impacting roadways, but
with convection it will be snowing heavy at times at higher
altitudes beginning by the pre-dawn hours Friday. With the
subtropical jet merging with the polar jet over our central
mountains tomorrow windy conditions are likely and this will add
another element of impact to the region where the highest QPF is
likely.

The coldest air will hover near our northern border through mid-
day on Friday then begins a push southward toward sunset. Falling
temperatures possible across the NW CWA by mid afternoon. This
front combined with upper dynamics will help the northern
mountains accumulate snow which may linger well into Saturday
morning as the dendritic temperature lowers to mid mountain behind
the front. With wind and snow combined felt warnings probably
best way to go in the northern and central mountains. Farther
south not as confident with drier air arriving shortly after the
cold front. Highway 550 passes likely to be impacted with wind and
some snow at times but below the crest of the pass confidence not
as high for impacts so went with and advisory. One concern will
be the north facing slopes...especially Ouray to Red Mountain pass
with CAA funneling into the Gorge. Snow amount details in the
WSW.

.LONG TERM...(Friday night through Wednesday)
Issued at 355 AM MST Thu Nov 16 2017

NAM12 and GFS20 shows the cold front through NE UT and NW CO by
sunset Friday and approaching the Interstate 70 corridor. The
models are in good agreement in showing the front south of a line
from Moab to Delta to Aspen about 03Z, 8 PM. The 700 mb winds turn
quickly to the NNW with frontal passage and cold advection behind
the front will be significant. This wind direction is not ideal
for orographic snow in the Elkhead and Park Mountains, Zone 4, but
can be a good snow producer on the West through North-facing
slopes in the Flattop Wilderness, the Grand Mesa, and the Gore and
Elk Mountains (Zone 10). Snowfall that began high up earlier will
drop to the just above the lower valley bottoms, about 5000 feet
above sea level, by midnight Friday evening.

The front will be moving through the San Juan Mountains around
midnight and the shift to NNW winds may bring enhanced snowfall to
the Gorge area south of Montrose to around Ouray and Red Mountain
Pass above Ouray.

The 700 mb cold pool of -16 C will travel through central CO late
Friday night and early Saturday morning. Moisture will be
diminishing quickly after midnight and most of the snowfall should
be over by noon Saturday. Temperatures behind the front will be
run about 15+ degrees cooler on Saturday.

High pressure, dry conditions and a gradual warming trend is
expected Sunday and Monday. A weak shortwave trough will clip the
northern CO and UT border areas Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1100 AM MST Thu Nov 16 2017

Breezy pre-frontal winds will sweep over eastern Utah and western
Colorado this afternoon/evening ahead of an approaching Pacific
storm. Meanwhile, clouds will be increasing over the area but CIGS
aren`t expected to lower below ILS breakpoints at KRIL, KEGE,
KASE, KGUC and KTEX until after midnight. Later tonight showers
are expected to impact KEGE, KASE, KTEX and KGUC resulting MVFR
visibility with brief IFR visibility and MVFR ceilings possible.
Winds will remain blustery in the higher elevation airports,
especially when combined with showers.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from 11 PM this evening to 5 AM MST
     Saturday for COZ018-019.

     Winter Storm Warning from 11 PM this evening to 5 AM MST
     Saturday for COZ004-009-010-012-013.

UT...None.

&&

$$

SHORT TERM...15
LONG TERM...CC
AVIATION...NL



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