Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 171724

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1024 AM MST Wed Jan 17 2018

.SHORT TERM...(Today through Thursday)
Issued at 239 AM MST Wed Jan 17 2018

A weak disturbance will ride through the persistent Great Basin
ridge and bring widely isolated snow showers to the highest
elevations of the northern mountains today. The rest of the area
will see only middle and high cloudiness and continued dry

The Great Basin ridge will move east and over western CO Thursday
afternoon. Following passage of the ridgeline, southwest winds
will gradually increase aloft by sunset Thursday.

.LONG TERM...(Thursday night through Tuesday)
Issued at 239 AM MST Wed Jan 17 2018

The ridge of high pressure will slide east of the region Thursday
night as a trough of low pressure enters the Pacific Northwest and
moves into the Great Basin Friday afternoon and evening. As this
happens, the pressure gradient will tighten with southwest flow
increasing across the area Friday afternoon. This trough will be
accompanied by a 130 kt upper level jet, with H7 winds in the realm
of 20 kts down south to 40 kts up north. This means a breezy to
windy and warm day across the region as these pre-frontal southwest
winds mix to the surface. Daytime temperatures on Friday could reach
well into the 50s in many lower valleys.

All eyes are on the storm system impacting the region this weekend.
The latest models remain consistent on the strength of this system
bringing good moisture and much colder air. The timing is where
discrepancies lie with the GFS being the more progressive and the
ECMWF about 6 hours slower. History would tend to favor the slower,
less progressive solution, with the Canadian somewhere in between
but a little closer to the GFS. The GFS has precipitation beginning
over the eastern Utah mountains Friday night and becoming more
widespread into western Colorado by Saturday morning, whereas the EC
starts precip Saturday morning, becoming more widespread over
western Colorado by Saturday afternoon. Moisture is sufficient with
specific humidity values reaching 3 to 4 g/kg pre-frontal and 2 to 3
g/kg post-frontal.  The cold front appears to move through somewhere
in the late Saturday afternoon or Saturday evening timeframe. H7
temps in the pre-frontal environment when precipitation begins are
around -3C which would mean higher snow levels around 9kft, but it
appears like the timing of the best precipitation and cold air are
mostly in sync which is good news for snow. H7 temps lower to -10C
to -15C across the board once the front passes late Saturday
afternoon into the evening. The mountains have potential to see
significant snowfall with the valleys potentially seeing some snow
as well. Details still need to be worked out with timing and amounts
but it is consistently looking like a good storm system. Snow will
continue through Sunday morning in northwest flow, with orographics
taking over and some showers lingering through Sunday afternoon
before winding down by the evening.

The models are not in great agreement beyond Sunday with the timing
of subsequent shortwaves bringing some snow to the northern
mountains in northwest flow.  Regardless, still looks unsettled
heading into next week with H7 temps staying in that -8 to -14C
range through Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1009 AM MST Wed Jan 17 2018

VFR will prevail through the day. Calm and dry overnight through
the morning on Thursday.




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