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047
FXUS65 KGJT 281653
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1053 AM MDT WED SEP 28 2016

.SHORT TERM...(Today through Thursday)
Issued at 347 AM MDT Wed Sep 28 2016

A digging low pressure trough off the coast of British Columbia
will continue to drive the high pressure ridge, which brought
mild and sunny conditions over the past few days, to the east.
Concurrently, a closed low pressure system centered over southern
California will continue to drift northward moving over Las Vegas
late in the day.

The pattern change described will result in a shift in flow to
the south bringing a return of sub-tropical moisture to the area.
The initial moisture surge will be high based favoring showers
and thunderstorms over the higher terrain surrounding the Four
Corners region beginning late this morning. As the day progresses
moisture will spread into east-central Utah and west-central
Colorado fueling isolated thunderstorms over those areas during
the afternoon.

A 50 kt jet nosing into the Four Corners combined with deepening
moisture (precipitable water (PW) over southeast Utah rises to
near 0.90 of an inch) will sustain showers overnight, especially
over the south. On Thursday, remnants of T.S. Roslyn reach the
forecast area which will cause thunderstorms to increase in both
intensity and coverage. PW levels climb to near 1 inch across
southeast Utah raising the potential for heavy rain and localized
flooding.

Above normal warmth will continue today and tonight before
increased clouds and showers return temperatures to near normal
levels Thursday.

.LONG TERM...(Thursday night through Tuesday)
Issued at 347 AM MDT Wed Sep 28 2016

Thursday night and Friday: Showers and thunderstorms stand a
better chance to continue through the overnight hours Thursday
night into Friday morning as a few embedded disturbances move
through. The Pacific Northwest low strengthens and deepens a
trough over the western states on Friday, which will allow
moisture to increase even more compared to Thursday with showers
and storms continuing with heavy rain likely in any showers and
storms that form. Temperatures will be fairly mild yet cooler
under clouds and showers with highs near seasonal. Snow levels
remain high as well with snow levels around 12,500 feet.

Saturday and Sunday: A bit of a downturn is expected on Saturday as
drier southwest flow pushes into the region as the trough of low
pressure over the Pacific Northwest pushes inland.  Still enough
moisture remains for scattered storms to develop Saturday afternoon,
mainly over the higher terrain with a few drifting into adjacent
valleys. The latest 12Z GFS pushes this trough across the area
quicker than earlier runs. This faster push is all driven by a 130kt
upper level jet upstream punching into the Pacific Northwest and
across the northern Rockies. The upper level trough becomes
negatively tilted by Sunday evening with a cold front moving through
the area Sunday evening through Monday morning. Showers and storms
will develop out ahead of this system in southwest flow Sunday
afternoon with snow levels starting off near 12kft. Snow levels will
lower throughout the evening and overnight, dropping to around 9000
ft Sunday evening and as low as 7500 ft across the north overnight
through Monday morning.  The heaviest precip is expected along the
cold front and could cause impacts for the northern and central
mountains and passes if this forecast holds true.  This will be
something for future shifts to consider.

Monday and Tuesday: Drier air moves in by Monday but continued west
to east flow will allow orographics to take hold over the northwest
Colorado mountains and possibly Steamboat Springs being affected as
this flow tends to favor them. This continues into Tuesday as this
100kt upper level jet nudges into the NW Colorado mountains. Enough
moisture and cold air exists for orographic snowfall mainly above
8000 ft. However, unsure of snow amts as moisture does appear
limited. The rest of the CWA looks to be fairly dry with
cooler, below seasonal temperatures.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1053 AM MDT Wed Sep 28 2016

A tap of tropical moisture will be pushed across eastern Utah to
the Colorado border late this afternoon through the overnight
hours. This moisture will allow for isolated to scattered mountain
showers to develop through the afternoon. High to mid level
cloudiness will becoming more widespread...thickening and lowering
through the evening hours. Precipitation is expected to become
more probable over the eastern Utah counties through the night
with some heavy rainfall possible. As a result KCNY and KVEL may
see some impacts to flight levels overnight and terrain
obscuration may become more widespread as well. Otherwise over the
first six hours of the 28/18z forecast limited impacts are
expected.

&&

.GJT Watches/Warnings/Advisories...
CO...None.
UT...None.
&&

$$

SHORT TERM...NL
LONG TERM...MDA
AVIATION...TGJT