Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 211736
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1136 AM MDT Thu Sep 21 2017

.UPDATE...
Issued at 1019 AM MDT Thu Sep 21 2017

Updated to increase winds based on latest guidance and decided to
include the Paradox Valley (COZ020) in a wind advisory as well for
today.

&&

.SHORT TERM...(Today through Friday)
Issued at 336 AM MDT Thu Sep 21 2017

A strong upper level trough and surface cold front will move into
the Great Basin today. A 120 kt jet core will stretch from
southwest to northeast across west and central UT and gradually
move east through Friday. By 15Z Friday, the jet core is
projected over the Utah and Colorado border, and move very little
east throughout the day. The forecast area will be in the dry slot
ahead of the Great Basin low through most of the period. In NAM12
forecast soundings, the 700 mb winds start the day at 25 kts and
increase to 30 kts at noon and 35 kts at 6 pm. Mixing should go
all the way up to about 550 mb which will tap into 50 kt winds
available to mix down to the surface. The strongest winds aloft
actually don`t pass over the area until 06z when winds have
decoupled somewhat. At 06z, 700 mb winds are projected to be 50
kts with 60 kts at 500 mb.

Surface winds will be strong enough to warrant continuing the
wind advisory in effect from 12 pm to 9 pm and will have fire
weather impacts.

.LONG TERM...(Friday night through Wednesday)
Issued at 336 AM MDT Thu Sep 21 2017

Models were consistent in moving the deep trough of low pressure
eastward on Saturday driving a cold front to the Green River/Lake
Powell late in the day while a stalled front hovers along the
CO/WY border. Still in the warm sector, expect scattered to
numerous showers and thunderstorms, mainly over Colorado`s
mountains. Relatively mild temperatures will limit snow to areas
above 10,000 feet, though convection will drive levels lower at
times. The low slowly eases eastward Sunday pushing the cold
front across the forecast area ahead of it while the boundary to
the north remains stalled. As the colder air fills in snow levels
will lower. The low finally lifts to the northeast late in the
day Monday allowing the stationary front to push southward across
the forecast area on Monday. With further cooling snow levels
could drop to near 7000 feet across the north early Monday
morning. Too early to say anything unequivocal with regard to snow
accumulations, but latest model guidance not very impressive.
However, colder temperatures are likely with season ending
freezing temperatures very possible across the north with highs on
the order of 15 degrees below normal for this time of year.

A secondary trough sweeps in behind the first maintaining a large
scale trough over the area for the remainder of the week. However,
little moisture associated with this system and no reinforcing
colder air, so drier weather with few clouds in store which
should help temperatures moderate toward midweek. That said, highs
will still top out 5 to 10 degrees below normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1133 AM MDT Thu Sep 21 2017

South to southwesterly winds will be gusting across the region
today thanks to a strong jet moving overhead and slowly
approaching cold front. Winds will gust anywhere from 30 to 45 MPH
for most areas though eastern portions of the forecast area should
see lighter gusts. Plenty of sunny skies will keep VFR conditions
in the picture through tomorrow.

&&

.FIRE WEATHER...
Issued at 336 AM MDT Thu Sep 21 2017

Winds will be very gusty ahead of an approaching storm system in
the Great Basin. Southerly winds gusting 35 to 45 mph will be
common over much of eastern Utah and western Colorado this
afternoon and evening. Afternoon humidity in the lower teens will
also occur over many of the lower elevations of southwest
Colorado where fuels are critically dry. Therefore the combination
of wind and low humidity will create Red Flag conditions over far
SW Colorado. Winds look to remain strong through the weekend
before this system moves eastward. Southeast UT will avoid
critical conditions due to non- critical fuel conditions. Still,
with such strong winds some control problems are anticipated on
any existing or new fires.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Wind Advisory until 9 PM MDT this evening for COZ001>003-006>008-
     020.

     Red Flag Warning until 7 PM MDT this evening for COZ207-290.

UT...Wind Advisory until 9 PM MDT this evening for UTZ022-025-027-029.

&&

$$

UPDATE...MDA
SHORT TERM...CC
LONG TERM...NL
AVIATION...TGR
FIRE WEATHER...CC



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