Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 290444

Area Forecast Discussion
National Weather Service Grand Junction CO
1044 PM MDT WED SEP 28 2016

.SHORT TERM...(Tonight through Thursday night)
Issued at 340 PM MDT Wed Sep 28 2016

A tropical moisture surge dominates these periods and into Friday.
The main threat is heavy rainfall with potential runoff problems.

A weakening upper low over southern California this afternoon
weakens and lifts NE through Nevada tonight. A 40kt jet nose
scrapes eastern Utah this evening and moisture from the remnants
of T.S. Rosyln deepens to near 1.0 inch in SE Utah by Thursday
morning while the upper low lifts through NW Utah. Instability is
limited so only isolated thunderstorms are expected overnight
with showers favoring the higher terrain. Storm motion will be to
the NNE at 15-20 mph.

Thursday-Thursday night, the deeper moisture spreads into much of
western Colorado with precip Water values of 1.0 south and up to
0.7 inch north. Persistent showers will begin to saturate soils
over eastern Utah and SW Colorado of the forecast area beginning
the potential for localized runoff issues/flooding.

.LONG TERM...(Friday through Wednesday)
Issued at 340 PM MDT Wed Sep 28 2016

Deep tropical moisture transitions to windy and cold early next

Friday-Friday evening, the sheared dynamics of Rosyln work
through the region. The NAM is further north producing the best
deformation over NE Utah-NW Colorado while the GFS and EC track it
further south through the Four Corners then NE through western
Colorado. The deep moisture will remain in place so these like
the favored period for western Colorado flooding potential while
eastern Utah begins to dry out. Due to the tropical origin of this
moisture, snow levels remain above tree line, between 12k and

Behind the dynamical remnants of Rosyln, late Friday night into
Sunday will still see some, mainly diurnal, showers and
thunderstorms. A colder and stronger West Coast low develops along
the OR-CA coast. Sunday, a strong vort max digs down the west side
of the trough progressing it into the Great Basin on Monday.
Strong SW winds develop early Monday as the cold front passes.
Storms along the front will favor the northern half of the
forecast area. These storms may be strong with increasing
instability and a veering and speed shear environment.

Monday afternoon-Tuesday, the upper low lifts through western
Wyoming and onto the northern plains. A cold but drier NW flow
will lower snow levels to around 6kft that will bring potentially
significant snowfall to the NW Colorado mtns from Vail Pass
northward. The GFS has more energy dropping into the backside of
the trough that could continue snow over the northern mtns into
Wednesday. The EC is faster and dries out by Wednesday. Elsewhere
expect below normal temperatures and freezing Tuesday night
temperatures into most areas above roughly 5500 ft.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1044 PM MDT Wed Sep 28 2016

Tropical moisture will continue to spread from south to north
across the region overnight. Mid level ceilings south of the I-70
corridor will spread north and lower. Shower coverage will
increase over eastern Utah and southwest Colorado overnight.
Showers will increase on Thursday becoming more widespread by
midday, with heavy rain possible. KCNY, KTEX, KDRO and KVEL may
see some impacts to flight levels with MVFR ceilings and mountain
tops obscured in the heavier showers. The chance for thunderstorms
will also increase during the afternoon. After 00z Thursday other
Taf sites may also be impacted at times.


.GJT Watches/Warnings/Advisories...


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