Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 291045
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
445 AM MDT THU SEP 29 2016

.SHORT TERM...(Today through Friday)
Issued at 445 AM MDT Thu Sep 29 2016

The forecast area was sandwiched between a high pressure ridge
over the High Plains and a trough of low pressure off the West
Coast. This has opened the door to the latest monsoonal surge
which began Wednesday and will impact the region through the end
of the week. Moisture levels have already risen significantly in
the past 24 hours as measured by dew points at observation points
across the forecast area. As of 10Z/Thu, dew point values were up
by 8 to 13 deg F over eastern Utah and all but the eastern most
zones of western Colorado. Expect these values to continue to
climb as southerly flow continues during the day and remnant
moisture from Roslyn peaks.

The latest radar imagery showed light showers moving northward
across southwest Colorado and southeast and east-central Utah.
This activity appeared to be sustained by 50 kt jet flowing
northeastward across central Utah. Daytime heating combined with
increasing moisture and a weak coupled jet over southeast Utah and
southwest Colorado will lead to increased coverage and intensity
of showers with thunderstorms developing around midday. As
precipitable water levels approach the 1 inch mark over the Four
Corners region storms will become more efficient rain producers
raising the threat of excessive rainfall from the stronger cells.
Storms should move along at a decent clip (15 to 20 MPH) so expect
any flooding issues will be localized.

Waning dynamic forcing and diurnal cooling will result in
decreased showers and thunderstorms tonight...however its
unlikely that moist convection will completely diminish. Showers
and thunderstorms will increase again from late Friday morning
through the afternoon in response to diurnal warming. However, a
shift in flow to a more southwesterly fetch will result in a
decrease in precipitable water values.

Increased clouds and showers will result in more seasonable high
temperatures today and Friday. In contrast, clouds and increased
atmospheric moisture will buoy overnight lows.

.LONG TERM...(Friday night through Wednesday)
Issued at 445 AM MDT Thu Sep 29 2016

Deep tropical moisture transitions to windy and cold early next
week.

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 12Z TAFS through 12Z Friday morning)
Issued at 445 AM MDT Thu Sep 29 2016

Tropical moisture will continue to spread northward across the
region today. Ceilings at mid-levels south of the I-70 corridor
will spread north and lower. Meanwhile, shower coverage will
increase over eastern Utah and southwest Colorado becoming
widespread by midday, with heavy rain possible. KCNY, KTEX, KDRO
and KVEL are likely to see CIGS fall below ILS breakpoints in
heavy showers. Beyond 00z/Friday, TAF sites in east-central Utah
and west-Central Colorado may also be impacted at times. Chances
for rain at sites to the north will be more limited.

&&

.GJT Watches/Warnings/Advisories...

CO...None.
UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...JOE
AVIATION...TGJT



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