Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 181721
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1021 AM MST Sat Feb 18 2017

.UPDATE...
Issued at 1016 AM MST Sat Feb 18 2017

Updated to increase areal coverage of showers over eastern UT as a
more active area of showers moves through.

&&

.SHORT TERM...(Today through Sunday)
Issued at 354 AM MST Sat Feb 18 2017

The first surge of moisture and energy began working through the
area beginning Friday afternoon and continued to bring
precipitation to the region during the night. Snow was recorded
down to 9000 ft as recorded at KTEX which fits in with what models
have shown over the past several runs.

The Pacific trough responsible for this activity was just moving
ashore along the Baja/California coast early this morning. Models
carry the splitting and negatively tilted trough system eastward
over extreme southwest Arizona during the day. This places the
forecast area beneath a broad area of difluence/divergence which
should sustain precipitation throughout the day with the southern
mountains favored. Mild temperatures will persist today as flow
continues out of the south. As a result, expect the snow level to
rise above 9000 ft with accumulating snow above 9500 feet this
afternoon.

Moisture will continue to surge over the area ahead of the southern
branch of the split low as it lifts northeastward across Arizona
tonight. The dynamic forcing begins to wane later in the evening,
but steepening lapse rates and orographic lift should keep showers
going, especially across the south. Falling temperatures and
advection of colder mid-level air will bring snow levels down as
the night progresses with snow lowering to near 6500 feet by
sunrise Sunday morning. However, expect accumulations will be
limited to areas several hundred feet upslope with best amounts
above the 9000 foot mark.

Sunday looks like the most favorable period for mountain snow
across the San Juan`s and to a lesser degree the Abajo and La Sal
Mountains as the southern branch closes off and passes just south
of Colorado`s southwest border. Temperatures, though cooler, will
still be too warm for accumulations across the lower elevations of
southwest Colorado. Meanwhile, as cold air sweeps in from the west
then northwest on the backside of this system snow becomes more
favorable across the northern and central mountains.

Given the warmth of this system, expect snow impacts will be
largely confined to areas above the 9000 foot mark. While the
southwest San Juan`s remain the most favored, expect some of that
snow to spill over onto the northwest side of the range. In
addition, the La Sal and Abajo Mountains should do well with this
system this weekend. As a result, I expanded the Winter Weather
Advisory into CO forecast zone 18 and UT zone 28. The duration of
the event was also extended as it was difficult to find a lull in
the activity over the next 36 hours.

.LONG TERM...(Sunday through Friday)
Issued at 354 AM MST Sat Feb 18 2017

Cold advection behind the trough should lower the snow level to
5000 to 5500 feet by Monday morning. Several inches of snow area
possible in the mountains, with a few inches expected in the
higher valleys and four corners.

After a break in the unsettled weather late Sunday night through
Monday night, another Pacific system will approach the area from
the west and northwest. This system will bring colder air and a
better chance of snow to the forecast area Tuesday through Friday,
with northwest facing slopes and northwest Colorado more favored.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1016 AM MST Sat Feb 18 2017

Rain and snow will increase from SW to NE throughout the next 24
hours as this current moderate winter storm impacts the area. Expect
widespread mountain obscuration, especially across the San Juan
Mountains. All TAF sites will see CIGs lowering below ILS
breakpoints at times. Snow or a rain/snow mix is expected to bring
MVFR VSBY and possibly IFR conditions as well with the highest
probability at KTEX, KASE and KEGE.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 6 PM MST Sunday for COZ018-019.

UT...Winter Weather Advisory until 6 PM MST Sunday for UTZ028.

&&

$$

UPDATE...CC
SHORT TERM...NL
LONG TERM...CC
AVIATION...CC



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