Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 201801
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1101 AM MST Mon Nov 20 2017

.SHORT TERM...(Today through Tuesday)
Issued at 325 AM MST Mon Nov 20 2017

Early morning satellite imagery and u/a hand analysis shows a
moderately strong atmospheric river approaching the central coast
of NOAM with a low pressure system just off the left coast of
N.Washington. This system will be quickly driven inland and
sheared apart by the next 150+kt Polar Jet moving into the
northern Rockies over the next 24 hours. Some of the anomalous
moisture to the west get pulled along with the jet and this system
which arrives to our northern CWA late tonight. The problem is
the very dry air in place attm. Top down saturation will need to
occur to get the lower atmosphere primed and the jet will help but
the fast movement of this storm will not leave much time to make
a big snow storm. X-sections suggest mountain top level saturating
by mid evening and orographics will begin. This however will not
be totally efficient as the true dendritic layer stays up near
500mb. So again the high peaks will stand the best chance of
seeing accumulating snow...timberline or above. Pass level could
see a few inches but it will be accompanied by wind as the jet
moves overhead. Overall the Park and Gore Ranges stand the best
chance of snow early on Tuesday with clearing by late tomorrow
afternoon over all but the divide peaks. It will be cold enough
for snow in the lower elevations but accums look to be 2 inches or
less with possibly some sleet mixed in during the pre-dawn hours
as the most convective part of the storm passes through. Winds
should help mix the atmosphere up a bit today and expect the Yampa
Valley should be able to warm a bit. Not so sure about Gunnison
Basin but warming will continue into Tuesday with mainly dry
conditions by afternoon for better holiday travel conditions.

.LONG TERM...(Tuesday night through Sunday)
Issued at 325 AM MST Mon Nov 20 2017

Northwest flow persists across eastern Utah and western Colorado
with the source of this flow being the high pressure system
spinning over Baja California through Wednesday. A closed low
originating in the Gulf of Alaska will weaken to an open trough
and push toward the Pacific Northwest coastline Thursday and give
the current flow regime just enough of a nudge to make light
westerly flow across the eastern Great Basin and Colorado Rockies
through the weekend. A weak feature could bring some cloud cover
and a few flurries to the UT/WY/CO border on Friday but this will
be a marginal and very temporary change.

Long range forecast models agree with the development of a strong
and large closed low in the Gulf of Alaska pushing southward
toward the Pacific Northwest late in the weekend. This could
potentially be the next weather maker, but recent model
spread leave confidence low on this feature at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1101 AM MST Mon Nov 20 2017

Some mid and high clouds will move across the area, increasing in
coverage this evening into Tuesday morning as a disturbance moves
through. The northern and central divide mountains may see some
obscuration in snow showers with ceilings dropping to near MVFR
conditions but light accumulations are anticipated. Winds will be
light and terrain driven at most TAF sites with some breezy
conditions possible at the higher elevation TAF sites. Mountain
turbulence will be seen among the higher peaks and above. Aside
from the northern and central mountain sites, VFR conditions will
prevail.

&&

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

$$

SHORT TERM...15
LONG TERM...JAM
AVIATION...MDA



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