Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 162347

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
447 PM MST Thu Nov 16 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 341 PM MST Thu Nov 16 2017

Significant moisture is on the way as an atmospheric river is moving
into central California starting today. This fetch of moisture
extends past 159 degrees west (longitude of Hawaii), signaling a
very strong source of moisture which will bring unseasonable
moisture to the region for a short period of time while the upper
level jet pushes it into Utah and Colorado. Windy conditions have
already developed at higher terrain, and these winds will increase
further on Friday as the 150 kt ULJ slings across Utah and Colorado.
Because of this system being relatively warm for a winter storm, we
are anticipating big snow amounts above 10000 feet, but a quick drop
off to no accumulation as one decreases in elevation.

Precipitation will generally begin as snow above 9500 feet tonight,
with rain/snow mix possible as low as 8000 feet in convective
showers. The cold front associated with this system does not advect
cooler air into extreme northwestern Colorado until Friday
afternoon, across the I-70 corridor until the evening hours, and
southward into the San Juans until late Friday as well. As the cold
front progresses northwest to southeast through eastern Utah and
western Colorado, the snow level will drop, but very dry air will
also entrain into the region. This is expected to shut precipitation
off quickly overnight Friday night into Saturday.
Models are hinting at a possible Gorge effect south of Montrose in
NNW flow Friday night lingering into the morning hours. 700mb flow
seems a little light for this effect, but it is a possibility.

.LONG TERM...(Saturday through Thursday)
Issued at 341 PM MST Thu Nov 16 2017

By Saturday morning, dry northerly flow should shut down all
precipitation as high pressure moves back into the Great Basin.
Cool seasonable temperatures will persist for a couple of days
behind the cold front, especially with weak inversions developing
overnight. A weak weather disturbance is expected to move into
northern Utah and Colorado Monday evening and early Tuesday...riding
over the high pressure. Confidence is low to moderate on this
feature because of some waffling between forecast model runs. Dry
weather returns midweek before the next possible weather disturbance
at the end of the work week from the west.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 422 PM MST Thu Nov 16 2017

Ceiling heights will continue to lower overnight over all
terminals. Southwesterly flow will transport moisture over the
region aloft with some virga/vicinity shower activity in the
higher terrain after nightfall. Temperatures will remain warm
initially as this system moves through overnight and into Friday
morning with mostly liquid precipitation in the valleys. Higher
elevations will mix with and change to snow later on Friday as a
front passes from north to south through the western slope. Expect
times of IFR and LIFR during the heaviest precipitation, which
will occur generally from 22z onward tomorrow afternoon.


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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