Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 192336
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
436 PM MST Mon Nov 19 2018

.SHORT TERM...(Tonight through Tuesday night)
Issued at 330 PM MST Mon Nov 19 2018

Clear skies dominate the weather picture over the central Rockies
this Tuesday afternoon. Overnight temperatures are once again
expected to drop below guidance averages given clear skies and
calm winds, and temps have been adjusted toward MET guidance both
tonight and Tuesday night. With dry northwest flow in place, not
much to talk to in the short term. Moving along...

.LONG TERM...(Wednesday through Monday)
Issued at 330 PM MST Mon Nov 19 2018

All focus remains on the potential for two storm systems in rapid
succession from Thanksgiving Day through this coming weekend.
Overall forecast confidence has increased today regarding the
chances for snow in the mountains (and possibly the valleys),
however several key details still need to be ironed out.

The first forecast question is exactly how much precipitation will
fall on Thursday afternoon through Friday morning with the first
storm. Forecast timing has slowed somewhat across the board today,
with all major models waiting to bring snow into the mountains
until after noon on Thanksgiving Day. This storm is now coming
into the range of the NAM, which is (not surprisingly) the wettest
model on Thursday evening. While the 12z GFS and ECMWF were fairly
consistent on around 3-6 inches of snow across all mountain ranges
(more possible above 11kft), the 18z GFS has backed off somewhat
on QPF totals. We now have a rather notable spread between the GFS
(low), ECMWF (middle) and NAM (highest) in terms of snowfall
potential. As this storm will largely be driven by faster flow
aloft and residual moisture from the west/northwest, we will favor
the middle/lower end of the spectrum for now. Much of the Pacific
moisture stream could be gobbled up over the hungry Sierra and
Wasatch ranges on Thanksgiving Day...

Precipitation will come to an end by sunrise Friday and a mainly
dry day is expected through the morning and afternoon hours. The
next storm system moves into the northern portions of Utah and
Colorado by Friday evening. All major global models agree that
this storm will be much more potent than the first, with a better
Pacific moisture tap and much stronger dynamics aloft. As with
the first storm, timing once again is fairly consistent across
forecast guidance. The ECMWF has trended northward somewhat today,
and the GFS has inched southward with regard to QPF totals. Both
models now indicate a relatively similar outcome with regard to
snowfall - at least 6 to 12 inches will likely fall across all
major mountain ranges in Utah and Colorado.

Two main forecast questions remain with this system. The first is
exactly how cold temperatures will get before precipitation ends
on Saturday evening. With 700mb temperatures in the -6 to -8
range, it is quite possible that accumulating snow could reach the
valley floors across all of western Colorado and much of eastern
Utah. Grand Junction often sees its best chances for snow with low
level flow out of the west-northwest, and it appears as though
this setup could occur before the atmosphere drys out on Saturday
night. Will have to watch this closely over the next several model
cycles. The other question is with regard to the southern extent
of precipitation. The ECMWF has been the most southern model with
this system over the past few days, supporting the idea of rain
and snow all the way to the valleys near the Four Corners.
However, the northward trend today casts some doubt on higher
precipitation totals in the south, especially given the
consistently more northern track of the GFS. The San Juan
Mountains may not see quite as much snow as areas to the north,
and precipitation may be more limited in the valleys to the south
of the San Juans on Saturday.

Overall, the main takeaways in the long term are centered around
the threat of significant winter weather in the mountains from
Friday evening through Saturday night, and possible snow in the
valleys on Saturday. Given that these systems will move through
during one of the busiest travel weekends of the year, extra care
should be taken for those headed out from Thanksgiving afternoon
through Sunday morning. The latest SPSGJT product details
potential travel impacts throughout the holiday weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 434 PM MST Mon Nov 19 2018

Clear skies and light winds will keep VFR conditions in place the
next 24 hours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...MAC
LONG TERM...MAC
AVIATION...TGJT


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