Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 201743

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1143 AM MDT Fri Oct 20 2017

Issued at 932 AM MDT Fri Oct 20 2017

Expanded the wind advisory area to include the Grand Valley, Moab
and Canyonlands areas of southeast Utah, the Paradox Valley and
Roan Plateau including Douglas Pass based on latest model
guidance. These areas along with the valleys of northwest Colorado
plateau will be more prone to reaching wind advisory criteria
with gusts to 50 mph in the valley zones and gusts to 60 mph over
Douglas Pass due to prefrontal southwest flow and a 90 kt upper
level jet over southeast Utah through northwest Colorado. This
will result in sufficient mixing of stronger winds to the surface
this afternoon due to a mostly cloud free sky with a few cirrus
passing overhead. The cold front associated with this upper level
trough is forecast to move through this evening with gusty winds
continuing until sunset. Therefore, also decided to start the wind
advisory earlier at 11 am and extend it until 8 pm instead when
the winds are expected to decouple after sunset and behind the
cold front. See the Wind Advisory product for details on the areas


.SHORT TERM...(Today through Saturday)
Issued at 230 AM MDT Fri Oct 20 2017

Some clouds and a few returns are showing up on radar but with
cloud bases hovering around 10,000 feet, don`t expect much
precipitation to be hitting the ground. Clearing skies can be
found just to the west of our forecast area and by daybreak, the
clearing will be entering western Colorado. The main concern today
will be some gusty surface winds thanks to the jet stream,
approaching from the northwest, and a tightening pressure
gradient. Winds will start picking up around noon, if not a bit
before, and will gust between 25 to 35 mph at times. Our northern
valleys will see some stronger gusts, bordering on 45 mph at
times, as deep mixing taps into some stronger winds aloft. Not a
slam dunk by any means but still close enough to issue a wind
advisory for those two zones from noon through 6PM.

As far as the cold front is concerned, timing and intensity
remains the same with the front moving through after 6PM up north,
9PM for the I-70 corridor, and the rest of the CWA between
midnight and 3AM. Precipitation should start around 9PM with the
best coverage from midnight through 6AM Saturday. Temperatures
will drop quickly as the front moves through allowing snow to fall
as it does so. In fact, a quick 1 to 3 inches will occur along and
just behind the front for the northern and central mountains. Snow
levels will start off at 10,000 feet but will drop to mountains
floors by Saturday morning. The NAM is showing some banding
setting up and may cause some snow to fall for zone 2 and will
need to be watched Friday night.

By daybreak Saturday, the front will have scooted off to the east
and with northwesterly flow setting up, expect high temps to be
anywhere from 5 to 10 degrees below normal. Plenty of sunshine is
also expected.

.LONG TERM...(Saturday night through Thursday)
Issued at 245 PM MDT Thu Oct 19 2017

Since the cold front pushed through, lows Saturday night into
Sunday morning will be on the chilly side with much of the area
seeing below freezing temperatures through the early morning
hours prior to sunrise.

Temperatures will start a warming trend Sunday as high pressure
builds in from the west. Ridging aloft will continue to strengthen
through the week as a few shortwave troughs slide around the
periphery. Monday and Tuesday, a stronger trough should flatten the
ridge somewhat as upper level flow turns more northerly. A dry cold
front is expected to move through early Tuesday dropping
temperatures a degree or two behind the front.

Global models begin to diverge on timing and amplitude beginning on
day 6 as an upper level trough is progged to move down from the NW.
The GFS is considerably further east with a closed low dropping due
south out of Saskatchewan and Manitoba into the Ohio Valley, as a
west coast ridge intensifies. The ridging further west keeps some of
the colder polar air out. The ECMWF shows a secondary shortwave
feature moving over the area dragging the colder polar air further
south. Regardless of the disagreement, some potential for mountain
snow and a cool down appears possible in the very long range period.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1119 AM MDT Fri Oct 20 2017

VFR conditions are expected through the day. Gusty winds out of
the west and eventually northwest will be the primary aviation
hazard through the evening hours affecting all terminals. Some
higher-elevation shower activity may reach the ground at EGE, RIL,
ASE and TEX, otherwise most terminals will only see light vicinity
precip and mostly Virga nearby. CIG heights may briefly drop to
MVFR levels after sunset but any categorical conditions will be
short lived as the frontal system passes overnight.


CO...Wind Advisory until 8 PM MDT this evening for COZ001>003-006-020.

UT...Wind Advisory until 8 PM MDT this evening for UTZ027-029.



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