Area Forecast Discussion
Issued by NWS Grand Junction, CO

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827
FXUS65 KGJT 091113
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
413 AM MST Fri Dec 9 2016

.SHORT TERM...(Today through Saturday)
Issued at 413 AM MST Fri Dec 9 2016

Moisture continued to sweep southeastward across the northern
two-thirds of the forecast area early this morning. Orographic
lift over the northern and central mountains has resulted in a bit
more snow than earlier anticipated. The snowboard at Steamboat
Mountain has a solid 8+ inches and the Whiskey Park snotel on the
CO/WY border in the Elkhead Mountains has recorded upwards of 1
inch of liquid which translates to roughly a foot and a half of
new snow. Elsewhere, the cold pool which settled over the Gunnison
basin resulted in steady overrunning snowfall across the area
beginning around sunset last evening which prompted the issuance
of a Winter Weather Advisory.

Latest models indicated moisture stream will continue to flow
during the day and orographic lift will likely milk another 4 to
8 inches of additional snow over the northern Colorado mountains.
Therefore, in coordination with WFO BOU and WFO CYS, upgraded the
Winter Weather Advisories for CO zones 4, 10 and 13 to Winter
Storm Warnings. Meanwhile, continued snow over the Grand Mesa and
the Elk, West Elk and Sawatch Mountains should push totals into
the low end advisory range, so hoisted advisories for those areas
until noon. Finally, though snow has decreased over the Gunnison
basin, will hold onto the advisory there through 15Z this morning
as models indicate moisture to begin diminishing along the
southern edge of the stream during the latter part of the
morning, a trend that will continue into the afternoon.

Models suggest that snow will diminish across the central Colorado
mountains late in the afternoon, but will linger over the Park
Range and Elkhead mountains into the evening and, according to GFS
and NAM through the night and into Saturday morning. Given mixed
model output (ECMWF is dry during this period), don`t believe
extension of highlights in the northern mountains is warranted,
but can`t entirely rule it out either.

What models are more consistent with is the increase in mountain
snowfall across the northern and central high country beginning
Friday afternoon. This surge of moisture appears deeper than the
system currently impacting the area and is delivered on the nose
of a 130 knot jet which should enhance orographic lift. As
described in the long term section which follows, snow will
continue for the higher elevations for some time and could bring
significant snowfall accumulations. However, will defer decision
on watch to the day crew.

.LONG TERM...(Saturday night through Thursday)
Issued at 413 AM MST Fri Dec 9 2016

Strong warm air advection will be occurring with the moisture
increase over the next few days, with H7 temps rising from -15C
(latest) to around -1C by Saturday evening. This will make for an
interesting forecast period with snow levels changing and dynamic
processes occurring due to warm air overrunning. The one thing
which appears almost certain is that the setup beginning Saturday
afternoon and going through the weekend should dump a lot of
precipitation across eastern UT and western CO...mainly in the
form of snow.

Latest forecast models are bringing the incoming weather system
farther south than previous runs which impacts all of western
Colorado Saturday night into Sunday morning. Appears snow levels
will be around 6500 to 7000 ft, but not confident as these levels
seem high, but in a warm air advective environment models may be
right. During the late Saturday night into Sunday time period the
120 kt upper level jet drapes southward across UT and CO, which
will further enhance the orographic component to the snowfall in
the mountains. As it stands, forecast models indicate a break by
Sunday afternoon before the next system moves into the area on
Tuesday. This active pattern of successive snow makers will
continue according to latest forecast output, so snow lovers
rejoice, but travelers beware and be ready for winter driving
conditions.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1050 PM MST Thu Dec 8 2016

Main forecast challenges overnight include timing of brief
precipitation in TEX, as well as whether or not any snow makes it
into valley terminals along the I-70 corridor including RIL and
EGE. Obs from ASE remain offline overnight, however webcams and
other local data indicate snowfall continuing ATTM. This will
remain the case through the mid-morning until snow diminishes in
intensity and ceilings rise above IFR levels. Elsewhere, VFR
conditions are expected with light winds turning southwesterly on
Friday.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until noon MST today for COZ009-012.

     Winter Weather Advisory until 8 AM MST this morning for COZ014.

     Winter Storm Warning until 6 PM MST this evening for COZ004-010-
     013.

UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...JAM
AVIATION...MAC



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