Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 132120

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
220 PM MST Mon Nov 13 2017

.SHORT TERM...(Tonight through Tuesday night)
Issued at 220 PM MST Mon Nov 13 2017

Primarily zonal flow is prevailing under a flat ridge of high
pressure, with warmer temperatures than seen yesterday due to
lack of dense cloud cover. Some high thin cirrus is moving through
southeast Utah and southwest Colorado but still resulting in
mostly sunny skies with no impact to temperatures. Some breezy
conditions will occur in some areas today and Tuesday, as H7 winds
remain between 20 and 30 kts but overall expect light terrain
driven winds. A weak shortwave will brush by the north as it moves
through Wyoming on Tuesday, fairly dry with not much in the way
of precipitation. Could see a few flurries in the extreme northern
mountains but otherwise some passing high cloud cover is expected.
Temperatures will remain about 10 degrees or so above normal with
cooler overnight lows near or slightly above normal.

.LONG TERM...(Wednesday through Monday)
Issued at 220 PM MST Mon Nov 13 2017

Breezy southwest winds will prevail Wednesday with mild, above
normal temperatures continuing into Thursday afternoon. The
gradient will tighten Thursday as a trough of low pressure
approaches, with windier conditions as H7 winds increase up to 40
kts. A 140 kt jet will also move into the area, with convective
showers developing in the pre-frontal southwest flow, which should
help drive some of those gustier winds to the surface. The
limiting factor in all of that will be the increasing cloud cover

The forecast models are still at odds with the timing of trough
and cold front passage with the more progressive GFS bringing the
trough through Thursday evening into Friday afternoon, with the
cold front moving through Friday morning. The slower ECMWF brings
the trough through Friday morning into Saturday morning with the
cold front moving through Friday evening. This ECMWF timing is 12
hours behind the GFS, which makes for a tricky forecast. The
Canadian on the other hand is right in between the two, which
provides a good middle of the road approach to this forecast. So
expecting the showers to develop over the higher terrain Thursday
afternoon with the best chance of precipitation Thursday evening
through Friday afternoon. Some showers may linger into Friday
evening along the divide but overall a drying trend from the west
should be seen by Friday night into the weekend. Snow levels will
start fairly high aoa 9000 feet MSL and drop with the cold air
that arrives sometime Friday morning into Friday afternoon
depending on which model solution wins out, with snow levels
lowering to mountain bases and possibly some higher valley floors
around 5000 feet up north and 7000 feet down south with an average
around 6000 feet MSL. The models all agree on the depth of the
cold air with H7 temps as low as -6C down south and -12C up north.
This storm provides some good moisture ahead of it and along the
cold front with specific humidity values in the 4 to 5 g/kg range.
Drier air moves in with the cold air behind the cold front but
still should be enough to continue snow for the mountains, where
the valleys may not see too much accumulation by this point.
Details still need to be ironed out but still looks like the
northern and central mountains will be favored for any significant
accumulations and impacts due to snow.

A ridge of high pressure builds into the area by the weekend into
early next week with some high clouds infiltrating the ridge as
more Pacific moisture slams the west coast and into the Pacific
Northwest. We will remain dry with cooler temperatures near or
slightly above normal, although the nights will be quite cold
following trough passage.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 954 AM MST Mon Nov 13 2017

VFR for all terminals through the forecast period. A few high
clouds will drift through the Four Corners through the evening.




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