Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 071115
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
415 AM MST Wed Dec 7 2016

.SHORT TERM...(Today through Thursday)
Issued at 415 AM MST Wed Dec 7 2016

The latest shortwave trough continued to bring snow to west-
central and southwest Colorado early this morning. The axis of the
trough was just reaching the Continental Divide at 10Z, but a
weaker secondary wave combined with divergence on the nose of a
120 knot jet sustained snowfall. Of course, the orographic
component was also a factor. Meanwhile, to the north skies were
clearing in the subsident region behind the shortwave, though a
few light showers continued off and on from KCAG eastward.

With the main trough east of the forecast area by 12Z, subsidence
and drying begin. However, the weak secondary perturbation,
mentioned previously, combined with residual moisture will
continue to bring isolated to scattered showers over the divide
mountains this morning, and a few may continue into the afternoon.
Additional accumulations will be minor however, so will allow
current highlights to expire at 12Z as scheduled. The reinforcing
shot of Arctic air that came with last night`s system has 7h
temperatures ranging from -20 C along Colorado`s northern border
and near -12 C at the southern border. This will translate into
afternoon highs near 20 degrees below normal in the north and
around 10 degrees colder than normal in the south.

Expect snow showers to diminish early this evening as mid-level
warm air advection (WAA) stabilizes the drier post-trough
environment. Reduced clouds will allow for good radiational
cooling and frigid overnight lows. Temperatures are expected to be
well below normal across northwest Colorado and in the northern
and central mountains. Single digits will be common across the
remainder of the region with the exception of southeast Utah where
readings are expected to ranged from 10 and 15 degrees F.

WAA will continue Thursday which should help moderate the cold
airmass over the forecast area. However, clouds will be increasing
during the day as moisture tops the ridge to the west. This will
reduce solar insolation thereby hindering warming to a degree...
pun intended. EC and GFS both indicated mid-level moisture may be
sufficient for some light snowfall over the northern and central
mountains but only bringing up to an inch across the higher peaks
and ridges.

.LONG TERM...(Thursday night through Tuesday)
Issued at 415 AM MST Wed Dec 7 2016

Temperatures will be closer to seasonal by Friday as H7 temps
increase to 0C near the Four Corners and -5C up north. A southwest
flow will shift to westerly and draw in some moisture off the
Pacific as specific humidities increase between 3 and 4 g/kg. Snow
looks to begin again over the western Colorado mountains by
Thursday evening and continue on and off again through Saturday
night into Sunday morning as embedded disturbances move through
this moist, westerly flow. Some favored upslope mountain areas
could see a prolonged snow event but timing these waves appears
problematic given model differences unable to resolve those
details with great accuracy. Regardless, looks like an unsettled
period with snow in the mountains and milder temperatures in the
valleys closer to or a little above seasonal. Colder air moves in
again Saturday evening into Sunday morning as a more distinct
trough moves through the area. Drier conditions expected after
this trough passage with the moist, westerly flow returning Monday
afternoon into early next week. This moist, westerly flow off the
Pacific looks to have the makings of an atmospheric river event.
Keep an eye on the forecast for changes in this active weather
pattern as details come into better focus.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 946 PM MST Tue Dec 6 2016

As of 05z, a cold front was draped across western Colorado along
and just south of the I-70 corridor. A wind shift from the west-
southwest to west-northwest was been noted in GJT VAD wind
profile below 12kft over the past few hours as the front crossed
the Grand Mesa. The wind shift will slowly progress to the surface
at valley locations over the next 6 hours. IFR to LIFR ceilings
and visibility will continue at ASE through the overnight.
Elsewhere, MVFR to at times IFR conditions are possible in central
and northern terminals with a snow shower or two possible. From
MTJ southward, IFR conditions are unlikely. Gusty westerly winds
will affect TEX through 12z this morning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 6 AM MST early this morning for
     COZ004-008>010-012-013.

UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...TGJT
AVIATION...MAC



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