Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 190544

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1044 PM MST Thu Jan 18 2018

.SHORT TERM...(Tonight through Friday night)
Issued at 357 PM MST Thu Jan 18 2018

The warm part of this forecast will come in the short term as we
are downstream of the next approaching storm system. Currently
this storm is crashing on shore in the PacNW region. Strong
southwest flow ahead of this storm is transporting moisture well
inland with precipitation over the Northwest transitioning to just
high cloudiness over our CWA. This cloud cover will create a light
blanket tonight and lows should not be quite as cold. Tomorrow the
trough will be slowly digging along the Left Coast as another core
of stronger winds aloft drops in upstream. Southwest gradients
tighten aloft from the Baja to the Wyoming Rockies. This presents
another a prolonged opportunity for moisture to be transported
into the trough...however a good chunk of it will be used for
producing precipitation upstream of us. The warm advection flow
tomorrow looks to push temperatures up several degrees. The
outliers may continue to be the Gunnison Basin and Upper Yampa
Valley where the colder air is deeper. Warm advective winds stay
strong on Saturday as our storm stalls a bit just upstream. Plenty
of cloud cover will be in place and even a few light snow showers
may develop on the some of the higher peaks in the pre-dawn hours
in this gusty warm advective flow. Lows will be milder as a

.LONG TERM...(Saturday through Thursday)
Issued at 357 PM MST Thu Jan 18 2018

The most challenging part of the forecast comes for the weekend as
our system arrives then deepens as it moves onto the Eastern
Plains. Forecasting often relies on pattern recognition and
relating the current storm to one of the past. Sometimes with good
results sometimes not. This storm has a familiar pattern in that
is continues to slow down and the front which looked to arrive as
early as Saturday morning not long ago...should be held out of
most of our CWA until Saturday afternoon. The models often
produce prefrontal WAA precipitation in this strong SW flow that
is not realistic. Feel this is happening with this storm and snow
and precipitation levels will stay quite high on Saturday as we
wait for the main ascent and colder air to work it`s magic. The
one exception is in SW Colorado where the dry conveyor belt will
be wrapping into the storm Saturday afternoon before the push of
the front. This will add a good bit of instability and besides the
possibility of the some isolated thunderstorms...some of the
precipitation could be enhanced across the San Juans with lower
snow levels as a result. Overall the best precipitation will be
coming Saturday evening through Sunday morning with the push of
all the favorable features from the surface front to the upper jet
aloft. Snow levels will be crashing to the valley floors with the
passage of the front. Most valley floors outside of the 4 Corners
should see some light to moderate accumulations by sunrise on
Sunday...with the highest amounts across the Yampa and White River
Basins. Cold...yes cold...advection and orographics then should
keep snow going on favored north facing slopes through the
afternoon hours on Sunday. Hopefully this high SLR precipitation
will bring some better snow amounts to some areas and there will
be isolated spots we will need to watch on the backside...again
pattern recognition. Much cooler conditions fill in behind this
system and we settle back near normal for mid to late January as
far as temperatures go. There is promise in the late model runs
for additional storm to filter into the region as the Western
ridge will be pushed out to sea and more troughs able to drop into
the Great Basin. A promising pattern.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1044 PM MST Thu Jan 18 2018

High clouds will continue to sweep over the area during the next
24 hours as Pacific moisture streams over the collapsing ridge.
However, this will not impact TAF sites and VFR conditions with
CIGS above ILS breakpoints are expected to hold through Friday




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