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fxus65 kgjt 090843 
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Area forecast discussion
National Weather Service Grand Junction Colorado
143 am MST Fri Dec 9 2016

Update...
issued at 143 am MST Fri Dec 9 2016

Made some changes to current highlights which are detailed in the
watch/warnings/advisories section below. Basically, this storm has
outperformed model guidance with higher amounts than expected
indicated on Steamboat Mountain where the snowboard indicated 8
inches or more of snowfall. Meanwhile, just east of The Divide the
Whiskey Park snotel indicated in excess of 1 inch of liquid water
which equates to over a foot of snow. Models suggesting another 4
to 8 inches over the area. Therefore, in agreement with the bou
and cys offices, upgraded the advisories at 4, 13 and 10 to
winter storm warnings. Bear in mind most significant impacts in
Colorado 10 will be fair areas around Vail Pass. Finally, added winter
weather advisories for Colorado zones 9 and 12 until noon today where a
total of 4 to 8 inches are likely.

Update issued at 1142 PM MST Thu Dec 8 2016

Updated to add a Winter Weather Advisory for snow across the
Gunnison basin through 15z/Fri. Received a report from just north
of town which indicated 2 inches of new snow. Bear in mind, models
and numerical guidance were poo-pooing chances for snow over the
valley which was at first a bit puzzling. However, after a moments
thought realized models were not picking up the cold dome over the
valley. Given moisture upstream and overrunning mechanism believe
the snow will continue through the remainder of the night bringing
totals of 2 to 5 inches with higher amounts near Cerro Summit.
Left mountains to the north of the Gunnison Valley out of the
advisory as snow criteria higher, though similar amounts are
expected there as well.

Update issued at 1050 PM MST Thu Dec 8 2016

Have upped snow totals to 4 to 8 inches in the Winter Weather
Advisory for the park, Flat Top, and Gore mountains including the
Vail Pass area. Observational data indicate that the highest
elevations in these locations have already seen as much as 5
inches of snow since this morning. Snowfall will continue
overnight before decreasing in intensity during the afternoon on
Friday.

&&

Short term...(tonight through Friday night)
issued at 342 PM MST Thu Dec 8 2016

An active zonal flow pattern will continue over the region for
the next 7 to 10 days. Atmospheric moisture has begun to deepen
across the higher elevations of northwest Colorado but will be become more
widespread and bring dewpoints up across all of eastern Utah and
western Colorado throughout the next 24 hours. Snow is expected to
remain light across most of western Colorado this evening, but
accumulate about 5 to 8 inches from the Steamboat Springs mountain
area south to Vail Pass and the Maroon Bells with lesser amounts
at Aspen. Forecast models indicate this snowfall will lighten if
not stop completely by Friday afternoon.

Long term...(saturday through thursday)
issued at 342 PM MST Thu Dec 8 2016

Strong warm air advection will be occurring with the moisture
increase over the next few days, with 700 mb temps increasing from
-15c (now) 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 we know for sure is that the setup beginning Saturday and
going through the weekend looks to dump a lot of moisture across
eastern Utah and western Colorado. The forecast models today are bringing
the incoming weather system further south than previous runs which
impacts all of western Colorado overnight Saturday night into
Sunday morning. It's looking at this time that snow level will be
around 6500 to 7000 ft, but i'm not feeling super confident on
this as these levels do seem high and we are dealing with a warm air advection
case during the overnight hours. During this late Saturday night
into Sunday time period the 120 kt upper level jet drapes
southward across Utah and co, which will further enhance the
orographic component to the snowfall in the mountains. Right now
the forecast models indicate a break by Sunday afternoon before an
additional system moves in on Tuesday bringing even more snow.
This pattern with snow makers every few days will continue, 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 at this time. 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...

Colorado...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.

Utah...none.

&&

$$

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