Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 081152

Area Forecast Discussion
National Weather Service Grand Junction CO
452 AM MST Thu Dec 8 2016

.SHORT TERM...(Today through Friday)
Issued at 417 AM MST Thu Dec 8 2016

Clouds and moisture originating from a low over the Gulf of Alaska
began streaming over the forecast area overnight . A few sites
have reported mid-level clouds, but cirrus was most prevalent.
While this initial surge of moisture presents little chance for
snow this morning, the increased clouds have slowed the rate of
cooling. Still temperatures were much lower than at the same time
last night with a majority of sites reporting temperatures from 15
to 25 degrees lower. KGJT and KCNY were the exception where
readings were near 10 degrees colder and KVEL was the same as last

Models indicated moisture will deepen across the north during the
day while warm air advection (WAA) at the 7H level weakens the
strong mid-level inversion over the area. Saturation will be
reached in the dendritic growth region this afternoon. In the
absence of dynamic lift, orographics provided by west winds
ranging from 20 to 25 knots should begin to generate light snow
and blowing snow across Colorado`s northern and central mountain
ranges. This scenario as laid out previously will remain in place
tonight through Friday through lapse will steepen to around 6
deg/km bringing advisory level snow to the Elkhead, Park, Flat
Tops and Gore Ranges. Snow and blowing snow will make travel
difficult over Red Mountain and Vail Passes during this time.
Consequently, will continue the Winter Weather Advisories already
in place. However, did move up the start time to account for snow
arriving during the latter part of the afternoon. The San Juan,
Elk, and West Elk Mountains and adjacent valleys will also
experience periods of snow, but accumulations will be lighter for
those areas and seen no reason at this time to expand highlights.

Despite WAA, today`s highs will be slow to rise off colder than
normal overnight lows, especially with increasing clouds limiting
solar insolation. Conversely, overnight will be less cold as the
blanketing effect of cloud cover limits radiational cooling.
Continued WAA and improved vertical mixing should bring
temperatures close to normal Friday.

.LONG TERM...(Friday night through Wednesday)
Issued at 417 AM MST Thu Dec 8 2016

Snow. Probably lots of snow. The moist westerly flow does not
abate through much of the upcoming week which means there will a
prolonged period of at least light snow falling somewhere across
the mountains and even some valleys at times. The tap of moisture
from the Pacific weakens a bit but still keeps our PWAT near to
above normal through the middle of next week. Basically there will
be a large gyre of low pressure circling the northern latitudes of
central and eastern NOAM which will help supply cold air and
transitory upper jet to bring periods of heavier snow to the
intermountain west including our mountains. There will be peaks
and lulls during this time as the upper and lower atmosphere gel
with favorable orographic flow. Timing of these waves are
difficult at best with confidence at this time pointing to early
to mid Saturday for the next passing disturbance. This flow will
help mixing and many of the valley inversions should be washed out
meaning rain could fall at lower elevations at times. By this
time next week, the big winners should be the northern and
central mountains where totals will be measured in feet. The
southern mountains will not be left out totally but this pattern
is not as favorable overall. However, expect the northern San
Juans should see some decent snowfall at times if the jet is able
to dip far enough southward. Stay tuned. Otherwise, temperatures
stay near to below normal as cold air is ushered in behind troughs
and lifts out ahead of the next.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 452 AM MST Thu Dec 8 2016

Clouds will be increasing over the area with snow developing over
the northern and central Colorado mountains this afternoon and
increasing tonight. Most sites will experience VFR conditions
through the next 24 hours, though there are a few exceptions.
Specifically, KASE and KEGE are likely to experience periods of
snow bringing MVFR CIGS and VSBY. Chances are significantly less
for snowfall at KRIL and KMTJ, however there will likely be
periods where CIGS fall below ILS breakpoints after midnight.



CO...Winter Weather Advisory from 3 PM this afternoon to 6 PM MST
     Friday for COZ004-010-013.




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