Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 182018

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
118 PM MST Mon Dec 18 2017

.SHORT TERM...(Tonight through Tuesday night)
Issued at 1230 PM MST Mon Dec 18 2017

High pressure will nose over the area from the southwest tonight
and Tuesday. A closed upper low will pass through southern New
Mexico tonight and Tuesday placing the forecast area under the col
created between this low center and zonal flow over the northern
Rockies. Winds aloft will gradually shift from light northwesterly
overnight to westerly by late Tuesday afternoon, then strengthening
and becoming more southwesterly by late Tuesday night. The short
term will remain dry but high clouds will ride over the top of the
ridge so variable higher clouds are expected. These will begin
thickening Tuesday night and temper the cold overnight
temperatures a bit.

.LONG TERM...(Wednesday through Monday)
Issued at 1230 PM MST Mon Dec 18 2017

The forecast guidance remains in good agreement about winter
weather returning to the area Wednesday through Thursday. A
strengthening storm will move from the Pacific Northwest to the
Great Basin Wednesday afternoon with its cold front reaching NE
Utah and NW Colorado by late Wednesday evening. The front will
progress southeast through Thursday and exit the forecast area
by sunset Thursday. The 700 mb and 500 mb troughs will close off
over western CO and eastern UT respectively, with the area of good
dynamic uplift between the two troughlines over the area
throughout Thursday. Precipitation will become widespread late
Wednesday night and continue through Thursday. The precipitation
area should exit eastern UT before sunset Thursday, then exit east
of the CO portion of the forecast area by sunrise Friday. At this
time it looks like advisory level snowfall is expected in the all
the mountains, meaning snow accumulation less than one foot, with
half an inch to a few inches possible in the valleys. The NW CO
Plateau area has the potential for the highest amounts for the
lower elevations with about 2-4 inches possible. Much colder air
will move in behind the cold front which will help produce the
higher snow accumulations and lower density snow Thursday morning.

The other main story to tell will be plummeting temperatures
later this week. Colder air will move into the area Thursday then
very cold conditions are expected this weekend and early next
week. Saturday and Sunday nights single digit low temperatures
will be common at lower elevations of central and southern CO and
UT, with negative single digits in higher valleys and negative
teens possible over the Northwest CO Plateau.

By Saturday a huge longwave trough will cover much of the
Continental U.S. and a reinforcing shortwave trough will plow
through the area from north to south. This will keep cold
conditions in place. Precipitation with this feature should be
focused along the Continental Divide through Sunday. Monday should
be dry.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1230 PM MST Mon Dec 18 2017

VFR conditions will prevail at all TAF sites for the next 24
hours. Winds will be light and terrain driven and only variable
high clouds are expected.




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