Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 071439 AAC

Area Forecast Discussion...UPDATED
National Weather Service Grand Junction CO
739 AM MST Wed Dec 7 2016

Issued at 736 AM MST Wed Dec 7 2016

Received reports of visibility down to less than quarter mile in
the Redlands and areas along the river. This dense fog seems to be
localized along the river as the top of the fog layer/low stratus
deck is visibile from the airport to the south. Issued a Dense Fog
Advisory for the Grand Valley (COZ006) until 10 am MST when fog is
expected to burn off and lift with improving visibility.

UPDATE Issued at 716 AM MST Wed Dec 7 2016

Added mention of fog to the Grand Valley this morning in the
forecast grids for rest of this morning until 9 am. Visibility
briefly went down to 3/4 mile at the Grand Junction airport with
the fog retreating towards the river. Visibility has improved as
the sun came up so not widespread enough for a dense fog advisory
although some areas near the river may experience visibility down
to 1/2 mile.

UPDATE Issued at 600 AM MST Wed Dec 7 2016

Have allowed the Winter Weather Advisory for the northern and
central Colorado mountains and the upper Colorado River basin to
expire. The trough axis has pushed east of the Continental Divide
and drier air was filling in behind the system. Isolated to
scattered snow showers are expected to continue today, however
additional accumulations will be light.


.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 12Z TAFS through 12Z Thursday morning)
Issued at 451 AM MST Wed Dec 7 2016

The latest upper level disturbance will be largely east of the
Continental Divide by 12Z. However, isolated to scattered snow
showers are expected to continue over western Colorado`s
mountains this morning before gradually diminishing this
afternoon resulting in areas of obscuration. In addition, KTEX
and KASE will continue to see snowfall through 14Z resulting in
MVFR conditions. CIGS are likely to remain below ILS breakpoints
for these sites through roughly 16-17Z, along with KVEL, KRIL,
KEGE and KASE. After 18Z, expect VFR conditions and CIGS above ILS
breakpoints through 12Z/Thursday.


CO...Dense Fog Advisory until 10 AM MST this morning for COZ006.



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