Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 252325
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
425 PM MST Fri Nov 25 2016

.SHORT TERM...(Tonight through Saturday night)
Issued at 245 PM MST Fri Nov 25 2016

A ridge of high pressure over the Rockies will hold on for another
24 hours then exit to the east late Saturday and not return for
the foreseeable future. One more clear and calm night with cold
overnight lows will occur tonight followed by a pleasant late
November day Saturday. Some high clouds will increase late in the
day over the Four Corners region.

Southwest flow aloft increases Saturday night in advance of a sharp
upper level trough moving from Southern California to the Four
Corners. Moisture will quickly increase and precipitation will
begin falling by late evening...enhanced by southwest flow
orographics and a left exit region of 170+ kt upper level jet. The
San Juan mtns look to receive the brunt of this storm between
midnight and 8 am Sunday. Very heavy snowfall and strong winds
will lead to potentially non-existent travel conditions during
this time over the passes. Precipitatin will spread north into the
central mountains by Sunday morning. Precip type is still a bit
uncertain for the lower elevations. Enough warm air may be in
place ahead of the cold front to keep precip as rain for areas
south of the San Juans. On the other hand...dynamical cooling
could be enough to turn precip over to snow. Areas from the Four
Corners to Pagosa Springs will have to be monitored carefully for
further forecast adjustments.

.LONG TERM...(Sunday through Friday)
Issued at 245 PM MST Fri Nov 25 2016

Precipitation associated with this initial trough passage will be
advancing northeastward Sunday morning...reaching the northern
mountains by noon. Thermodynamic profiles suggest the potential
for snow or rain/snow mix for valley locations such as the Grand
Valley Sunday morning, but any appreciable accumulations are not
likely with temperatures hovering at or just above freezing.

As the initial trough exits northeast Sunday afternoon, the worst
of the heavy snow and wind will be over. However, a second trough
will drop through UT and head over NM Sunday night. Weak lift but
northwest orographic flow will persist over the region continuing
periods of light snow that will impact mainly the mountains and
adjacent windward high valleys. Colder air will filter in as well
setting the stage for a prolonged period of more winter-like
temperatures. Snowfall amounts for the Colorado mountains and
mountains of southeast Utah will likely be fairly hefty...1 to 2
feet through Monday. This combined with the expected impacts from
strong winds and blowing snow further supported the issuance of a
Winter Storm Watch. Blizzard conditions certainly possible in the
San Juan mountains above 9000 feet with travel over mountain
passes seriously impacted if not temporarily shut down. Will be
messaging this potential for those traveling home from the holiday
festivities.

A third shortwave trough in the northwest flow aloft will move
over the region Monday night...followed by yet another weaker
trough Tuesday night. Again...this keeps the unsettled showery
weather pattern over the region going...affecting mainly the
favored northwest-facing terrain and high peaks.

Models showing some differences by late next week with northern
stream trough potentially digging south and cutting off over the
Great Basin or Desert Southwest. However there is good agreement
all week on the general upper level trough pattern over the
western CONUS. This favors below normal temperatures so have
hedged toward the colder side of the model guidance.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 425 PM MST Fri Nov 25 2016

Clear skies will leave VFR conditions in place through this
forecast. High clouds will be increasing across southern Utah and
Colorado late as the next storm approaches.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...     Winter Storm Watch from Saturday evening through late Sunday
     night for COZ012-018-019.

     Winter Storm Watch from Sunday morning through late Monday night
     for COZ004-009-010-013.

UT...Winter Storm Watch from Saturday evening through late Sunday
     night for UTZ028.

&&

$$

SHORT TERM...BEN
LONG TERM...BEN
AVIATION...TGJT



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