Area Forecast Discussion
Issued by NWS Grand Junction, CO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

000
FXUS65 KGJT 270403
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
903 PM MST Sat Nov 26 2016

.UPDATE...
Issued at 903 PM MST Sat Nov 26 2016

Made some minor adjustments to the forecast to delay the onset of
precipitation by a couple of hours. Upper level moisture is quite
evident in satellite imagery from southwest AZ to northeast CO.
However, a very dry layer between 700 and 500 mb will have to be
overcome before precipitation is realized at the surface. The very
strong upper level jet is currently over lower Colorado River
Valley...but will slide over southern Colorado between 1 and 7 am.
This will be the period of greatest threat for heavy snowfall and
strong winds over the San Juan mountains. Latest short term and
high resolution models do not show a great northward push of the
precipitation early Sunday. Instead, with the progression of the
upper level jet eastward, the precipitation also moves east. It
looks like central and northern mountain areas will have to wait
for the orographic flow to turn westerly later Sunday before
snowfall rates pick up. Another uncertainty continues to be
precipitation amount and type over the towns south of the San
Juans. Thermo profiles suggest a mainly rain or rain/snow mix event
until closer to 5 am when it could change to snow. The challenge
is that the later in the morning we go, the less precipitation
will be falling. Still an unusual amount of uncertainty with the
evolution of this winter storm over some of the lower elevations the
next 18 hours. Will hold all winter hazard highlights in place
though as the table has been set and confidence still high for the
San Juan mountains tonight and other mountains over the next
couple of days.

&&

.SHORT TERM...(Tonight through Sunday night)
Issued at 327 PM MST Sat Nov 26 2016

Clouds will begin to increase from southwest to northeast throughout
the evening as a 130+ kt jet nudges into the Four Corners. Short
term models indicate precipitation will begin over the San Juans
right around midnight tonight with precip becoming widespread by
daybreak as far north as the Tavaputs Plateau and Flattop
Mountains. The heaviest snowfall rates in the San Juans are
expected between midnight tonight and noon Sunday with 2-3"/hr
rates possible. Combined with these snow rates are going to be
some strong winds to 50 or 60 mph above 9000 feet. It won`t be a
good morning to be traveling in the backcountry or driving over
Molas, Coal Bank, and Red Mountain passes with visibilities near
zero with driving snow. The worst time period to travel in the San
Juans will be between about 2am and 8am. Winds will lessen a bit
after 8am as the upper level jet support moves eastward.

Even being 12-24 hours from the start of this storm, the
rain/snow line forecast continues to be a struggle so had to use
a moderate confidence factor in advisory issuances today. In the
SW Colorado valleys including Cortez east to Pagosa Springs, feel
confident that locations above 6000 ft will accumulate 1 to 4
inches overnight into the morning hours, though both Cortez and
Durango city centers will likely see rain to start and potentially
a late switchover to snow (Sun morn). Sounding at DRO at 09z
overnight indicates complete saturation 2000 ft above the sfc,
with below freezing dewpoints all of the way to the sfc. With
strong H5 vorticity in place, think that heavy wet snow is
definitely possible, and areas along Highway 160 and the route to
Mesa Verde may be a big mess as well. The eastern Paradox valley
including Norwood and Nucla will likely see a bit of snow as well.
As Sunday morning progresses, east of New Castle along I-70 is
likely to deteriorate with westerly flow developing and models
continuing precip along the I-70 corridor throughout the next
couple of days. Same with the Craig/Meeker corridor, with a
prolonged accumulating snow event.

A few spots still of concern where my confidence was just not
there for an issuance today - parts of the North Fork Valley
(zone 11) above 5500 ft may see a few inches of snow, namely
Paonia and the mesas around Hotchkiss. The De Beque to New Castle
corridor is another one to watch, and definitely want to watch
Steamboat as this storm transitions from SW flow to W/NW flow
Sunday night. MAV guidance indicating quite a bit of snow at
Steamboat, but this is later in forecast period and thinking the
GFS is overdoing amounts in snow since it is an outlier.

The initial trough and main vort max pushes clear through western
CO by mid afternoon Sunday, then orographic snow in
westerly/northwesterly flow continues throughout the day. By
Sunday night, the northern piece of the trough splits off and
closes off over the Dakotas.

.LONG TERM...(Monday through Saturday)
Issued at 327 PM MST Sat Nov 26 2016

The next well-defined part of this snowstorm will occur overnight
Monday through Tuesday morning as a secondary trough moves into
the region from the NW. The Rabbit Ears to Vail Pass to Aspen corridor
will likely continue to snow during much of the time between these
systems, but snow intensity will pick up again Monday evening.
Elsewhere snow should be over by early Tuesday. Conditions look to
finally improve on Wednesday morning along the Rabbit Ears to
Aspen corridor. Below normal temperatures will persist in the wake
of the storm systems.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 449 PM MST Sat Nov 26 2016

Moisture will be rapidly increasing this evening with areas of
rain and snow developing across southeast Utah and southwest
Colorado around 06z tonight. The rain and snow will spread north
into the Interstate 70 corridor by 12z and continue lifting north
into the northern areas by 15z Sunday. CIGS will be dropping to
ILS breakpoints from south to north overnight and early Sunday
morning with all mountain areas becoming obscured. Areas of
IFR/LIFR CIGS and VSBYS also expected between 07z tonight through
Sunday evening in snow, fog and blowing snow. KASE, KEGE, KTEX,
KDRO and KRIL will all experience poor flight conditions through
Sunday.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory from midnight tonight to 6 AM MST Monday
     for COZ017.

     Winter Storm Warning from midnight tonight to 6 AM MST Monday
     for COZ012-018-019.

     Winter Weather Advisory from 6 AM Sunday to 6 AM MST Monday for
     COZ002-003-008-014.

     Winter Weather Advisory from midnight tonight to noon MST Sunday
     for COZ020>023.

     Winter Storm Warning from 6 AM Sunday to 6 AM MST Tuesday for
     COZ004-009-010-013.

UT...Winter Weather Advisory from midnight tonight to 6 AM MST Monday
     for UTZ023.

     Winter Storm Warning from midnight tonight to 6 AM MST Monday
     for UTZ028.

&&

$$

UPDATE...BEN
SHORT TERM...JAM
LONG TERM...JAM
AVIATION...JDC



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.