Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 161055

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

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

Teleconnections upstream are reshaping 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 up
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
and we will be dealing with the warm system with wavering
accumulating snow levels tonight through tomorrow afternoon. Two
cons preventing this storm from being more robust is the dry air
currently in place with PWAT near to 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 is
appears the coastal mountains will be absorbing much of this
moisture and then it will take on the dry Great Basin. Highs again
stay 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 high altitudes
beginning by the pre-dawn hours tomorrow. With the subtrop jet
merging with the polar jet over our central mountains tomorrow
windy conditions are likely and this will add another element of
impact to this region where the highest QPF is likely. The
coldest air will hover near our northern border through mid-day on
Friday then begin a push 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
besides 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. See no reason to
change anything with the current Winter Storm Watch product.

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 12Z TAFS through 12Z Friday morning)
Issued at 355 AM MST Thu Nov 16 2017

VFR conditions will dominate the forecast for the first 12 to 18
hours of the 16/12Z forecast. High and mid level cloudiness will
be increasing through the day ahead of the next system. However
cigs should stay above ILS break points. Conditions this evening
will quickly begin to deteriorate over the mountains with
widespread obscuration of the terrain leading to showers
approaching the mountain terminals. ILS break points will be met
at KASE and KTEX with MVFR possible by sunrise as areas of
moderate to heavy precipitation set up. Winds will also be
increasing along the ridetops with turbulent mixing likely.


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.



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