Area Forecast Discussion
Issued by NWS Grand Junction, CO

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342
FXUS65 KGJT 161010
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
310 AM MST Sat Dec 16 2017

.SHORT TERM...(Today through Sunday)
Issued at 310 AM MST Sat Dec 16 2017

High clouds were increasing over the area early this morning ahead
of an approaching Pacific trough. Latest models looked a bit
slower than earlier runs, and have cut back moisture back further.

Mid and high clouds will continue to spread over the region today
as the trough pushes southeastward across the Great Basin. The
front associated with this system now arrives over the eastern
Uinta Mountains early this afternoon, or about six hours later
than previous runs had indicated. With little low level moisture
in the airmass ahead of the front, shower chances over the higher
terrain of northeast Utah will hold off until the late morning
with chances improving during the afternoon. Southeast of the
front there will be clouds but no precipitation. The cloud mass
will inhibit warming today, but not appreciably.

Though there were timing differences with the latest model runs,
they remained consistent in stalling the front over northeast Utah
while they trough splits and the lion`s share of the energy moves
to old Mexico. Consequently, shower chances continue over the
eastern Uinta`s but nowhere else during the night. Clouds will
moderate overnight lows to some extent. Clouds thin over the area
on Sunday as the southern extension of the trough closes off over
northern Mexico and the open trough to the north pushes eastward.
Advection of colder air aloft will bring temperatures down just a
little, though afternoon highs will still remain above seasonal
norms.

.LONG TERM...(Sunday night through Friday)
Issued at 310 AM MST Sat Dec 16 2017

The upper level low pressure system will continue to dive
southward away from the region on Sunday night into Monday
morning. Our attention will turn back to north and west on Monday,
as cloud cover and lingering moisture behind the trough axis
grazes the northern zones. The NAM indicates the potential for a
few snow showers in the Park range, but any accumulations would be
less than an inch in the higher terrain.

The next system arrives on Wednesday evening. The 0z GFS has
trended slightly lower in QPF totals with this event, otherwise
most of the main details remain the same. Precipitation will
overspread the northern mountains after sunset ahead of a frontal
boundary headed south and east through eastern Utah and western
Colorado. Timing between the ECMWF and GFS remains fairly on
track, with the front somewhere along the Wyoming border by
midnight Thursday, and headed south trough the western slope on
Thursday morning and early afternoon. 700mb temperatures will
crash into the teens below zero through this period, resulting in
snow levels dropping to the valley floors area-wide. The 0z GFS
keeps liquid QPF totals under 0.5 inches even in the mountains,
less than in the past day`s model cycles. The ECMWF does show a
few pockets around 0.5 inches in the central mountains and San
Juans, which would equate to Advisory level snowfalls for several
areas desperate for some winter weather. Guidance is in fairly
good agreement on bringing precipitation to an end by Friday night
as the low pressure system cuts off over Arizona.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 310 AM MST Sat Dec 16 2017

An approaching Pacific storm will bring increased clouds to
eastern Utah and western Colorado. However, the storm`s energy
will shift to the south leaving little to no chance for showers
across the region through the next 24 hours. Therefore, expect VFR
conditions and CIGS above ILS breakpoints during the period.
Winds will be light and generally terrain driven.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...MAC
AVIATION...NL



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