Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 142218

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
318 PM MST Thu Dec 14 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 318 PM MST Thu Dec 14 2017

Some light snow and clouds are still lingering along the divide
with mostly sunny skies to the west and improving conditions in
most areas. Expect this light snow and cloud cover to clear late
this afternoon into the evening as a drier, northerly flow
continues to move in behind this disturbance. The ridge of high
pressure still sits firmly to the west but shows signs of breaking
down this weekend into the coming week. More on that in the Long
Term section. A trough of low pressure crashes into the ridge on
Friday over the Pacific Northwest and will cause the ridge to
slide eastward, as this system dives into the Great Basin.
Inversions are expected to return in the valleys on Friday as this
ridge slides back over the area, resulting in slightly cooler, yet
still above normal temperatures.

.LONG TERM...(Saturday through Thursday)
Issued at 318 PM MST Thu Dec 14 2017

The aforementioned trough will move through the region Saturday
evening through Sunday, with jet energy diving south of the Four
Corners. This will keep the better precipitation across Arizona
and New Mexico, but the mountains and high valleys of eastern Utah
and western Colorado still stand a chance to see some snowfall in
the realm of 2 to 4 inches as this system moves through fairly
quick and doesn`t bring a lot of moisture with it. The NAM12
appears the wettest solution, whereas the GFS, EC and Canadian are
a bit drier. Leaning more towards the drier and more progressive
solution. Northwest flow behind this system looks to continue
light orographic snow over the Elkheads and northern Park range
Monday and Tuesday, so kept slight chance in there.

A more progressive pattern looks to finally take shape as yet
another trough of low pressure moves into the Pacific Northwest
late Tuesday and across the northern Rockies by Wednesday. The
models are in general agreement on timing with this system moving
through our area Wednesday evening through Thursday. The
differences lie in the details beyond Thursday morning, where the
EC and Canadian favor a more progressive solution with a 110 kt
jet oriented NW to SE, helping to push this system through fairly
quickly and bring much drier air in by Thursday afternoon,
effectively shutting down precipitation. The GFS seems to be the
outlier with the jet energy diving north to south down to Mexico,
which causes the system to form a closed low over southern
California and keep our area in a deformation zone, which keeps
precipitation ongoing through Friday morning. Despite these
differences, the models are in agreement on much colder air
arriving with this system, in the realm of -12C (south) to -20C
(north)...cold enough to snow in all areas. Just how much snow
remains to be seen depending on how the details work themselves
out. High confidence remains through Wednesday but takes a
nosedive to low confidence by Thursday due to model


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1021 AM MST Thu Dec 14 2017

As expected, KEGE and KASE have been down in the IFR category most
of the morning thanks to low ceilings and visbilities from fog and
snow showers. Still thinking that warming of the atmosphere will
cause some of the clouds to burn off in the next hour or two for
those areas and TAF follows suit. Will amend as necessary if low
level moisture overcomes warming and keeps clouds in the picture.
KMTJ also reporting low clouds at this hour but just to the north
of the airport, clearing conditions can be found. Also anticipate
they`ll go VFR in the next hour or so. Once the clouds lift, some
fog will be possible for KEGE overnight but confidence not high
enough yet to include in TAF.




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