Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 132355

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
455 PM MST Wed Dec 13 2017

.SHORT TERM...(Tonight through Thursday night)
Issued at 252 PM MST Wed Dec 13 2017

Models very similar in handling of shortwave trough moving into
our area from the northwest. Ahead of the trough, extensive band
of mid level clouds across NE UT and the N and Central areas of
western CO have put a damper on temperatures today. And tonight`s
cloud cover expected to spread across much of the remainder of our
CWA along with some mixing of air in lower levels due to frontal
system should result in higher min temperatures tonight than last
night throughout our CWA.

H7 temperatures expected to drop about 8 degrees C by late morning
on Thursday. Snow densities will also be decreasing as the colder
temperatures spread in and moisture associated with the shortwave
trough is lifted. However, not a lot of moisture with the precipitable water values with the shortwave this
morning were only around 0.3 of an inch while forecast max mixing
ratios for our area tonight and Thursday are barely over 2 g/kg.
So, still only expect light snow accumulations in the mountains
from this progressive shortwave trough, generally 1-2 inches with
some areas up to 3 inches along the continental divide. Isolated
spots along the continental divide could receive up to 6 inches.

Rapid post-trough drying expected on Thursday. Then clear skies
Thursday night with low dew point temperatures will result in min
temperatures overnight in the single digits and teens across our
CWA, with a few of the coldest spots likely dipping slightly below
zero F.

.LONG TERM...(Friday through Wednesday)
Issued at 252 PM MST Wed Dec 13 2017

Upper ridge axis to our west on Friday is expected to shift
eastward and across our CWA Friday night as the next Pacific shortwave
trough pushes inland. That system is expected to produce another
round of light snow for the mountains as it moves across our area
Saturday and into Sunday, likely producing amounts similar to what
will occur tonight into Thursday.

Then it looks like we should expect some overrunning moisture at
times Monday through Tuesday night under a northwest flow aloft
on the east side of an upper ridge. Any significant moisture in
this overrunning situation for our our CWA likely to be confined
to the northern tier of NW CO, and then any precipitation should
be minimal.

Wednesday should be another dry day as the GFS and EC then move
the upper ridge axis over our area ahead of a Pacific trough which
presently appears that it will likely be stronger and more moist
than its predecessors within this forecast period. However, from
Thursday onward the models significantly differ, as the GFS is
still bringing the Pacific trough bodily into our CWA while the EC
holds off the trough and develops a closed low in the Pacific
northwest. Forecast confidence high through Wednesday of next
week, then low confidence thereafter.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 447 PM MST Wed Dec 13 2017

Broken to overcast mid and high level clouds will continue to
increase this evening as a cold front approaches the area. Radar
showed light precipitation targets moving into Northern Colorado
and Utah. Rain and snow showers will continue to spread south
through the 00-12z time frame. Winds will be light turning
northerly overnight. MVFR conditions are possible with lowering
ceilings and snow at KASE KEGE and KTEX. Elsewhere, mostly VFR
conditions are expected. Higher terrain will likely be obscured
overnight with lowering ceilings and snow.




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