Weather Service Report

FXUS65 KGJT 201533

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
933 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 12Z TAFS through 12Z Saturday morning)
Issued at 230 AM MDT Fri Oct 20 2017

Cloud bases between 8k to 10k feet are still being reported at
this hour but will lift by daybreak giving way to mostly clear
skies. Winds will start picking up around 18Z and continue through
00Z. Gusts from the I-70 corridor south will range from 25 to 35
mph while winds north will gust from 30 to 40 mph with higher
gusts possible. Clouds will increase from the northwest after 00Z
as a cold front moves through bringing rain and snowshowers. As
the front moves through, KASE and KEGE, and maybe KRIL, may see 
some MVFR under rain and snow showers. Expect flight conditions to
be affected by the front from 00Z through 12Z.


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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