Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 150438

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
938 PM MST Tue Nov 14 2017

.SHORT TERM...(Tonight through Wednesday night)
Issued at 337 PM MST Tue Nov 14 2017

A shortwave ridge will develop over the area tonight in the wake
of the fast moving short-wave trough which brushed northwest
Colorado this afternoon. Some cirrus will continue to sweep
overhead during the night, but a lot less than we`ve seen this
afternoon. Overnight lows are expected to be near persistence or a
bit lower given reduced cirrus coverage.

Another mild day in store Wednesday as 7h flow begins to shift to
the southwest ahead of a developing Pacific storm. Mostly sunny
skies will help temperatures climb to several degrees above
normal again at midweek. Models indicated mid-level moisture will
be increasing Wednesday night which, when combined with weak warm
air advection, is expected to bring milder overnight lows.

.LONG TERM...(Thursday through Tuesday)
Issued at 337 PM MST Tue Nov 14 2017

...Winter like weather returns to the mountains and portions of
northwest Colorado late this week...

Southwesterly flow continues across the area on Thursday as the
Pacific storm moves toward the West Coast. Increasing winds
aloft mix to the surface ahead of the storm during the afternoon
resulting in breezy conditions, especially across northwest
Colorado. Clouds will be increasing as mid-level moisture
increases ahead of the system. Some showers can be expected for
northeast Utah and northwest Colorado during the afternoon.
Only the GFS supported precipitation outside of the eastern Uinta
Mountains, so pared back PoP values over the Flat Tops and
central Colorado mountains during the early phase of this storm.

The most active period of the storm begins Thursday evening and
is expected to continue to impact the area into Friday night.
Model differences, most notably with the ECMWF and the other
production models reduces confidence somewhat, especially with
regard to the latter stages of this event as the ECMWF appeared to
be 6 to 12 hours slower than the others. Therefore, the remainder
of the discussion will be based on the faster GFS solution.

Moisture increases Thursday night beneath a 125+ KT jet over
northwest Colorado. In response, showers increase and spread into
the central mountains as strong west-southwest winds provide
orographic lift which will be enhanced by jet let divergence.
Snow levels will remain above 8500 feet during the night as 7H
temperatures in the warm phase of the storm will be close to 0
deg C.

The Pacific trough sweeps eastward across the Great Basin on
Friday driving the cold front associated with this system south-
southeast across northeast Utah and northwest Colorado during the
day. This will cause snow levels to lower to valley floors as 7h
temperatures fall to near -8 deg C by the end of the day.
Meanwhile, snow continues in the northern and central mountains
with lighter snow and higher snow levels in the south where 7H
temperatures remain at or above freezing. Colder air does spread
south Friday night as the trough pushes eastward over the region
driving the cold front south of the border by sunrise. However,
subsidence and drying behind the trough should bring showers to an
end by sunrise. Preliminary snowfall output suggests 6 to 12
inches of snow in the northern and central mountains with lesser
amounts in the San Juan`s by Saturday morning.

Dry northwest flow settles over the area Saturday, then shifts to
west on Sunday. By Monday, the EC, Canadian and GFS are out of
phase, but still dry. The forecast for Monday night and Tuesday
is problematic given model differences. Will defer to the more
consistent Canadian/GFS solutions which indicated moisture moving
over a ridge to the west will bring showers to northwest Colorado
early next week.

Warmer than normal temperatures will continue Thursday ahead of
the cold front, but become much cooler Friday and Saturday behind
the Cold front. By Sunday however, temperatures will moderate to
near normal in response to weak warm air advection.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 933 PM MST Tue Nov 14 2017

Dry conditions persist through this period with a gradual increase
in west to southwest winds across the region. Wind speeds may
exceed 40 kts near mountain tops by midday Wednesday. High clouds
will also be on the increase with some mid-level cloudiness
arriving after 00Z/Thu, mainly north of Interstate 70.




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