Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 250607
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1207 AM MDT Tue Jul 25 2017

Updated aviation discussion

.UPDATE...
Issued at 911 PM MDT Mon Jul 24 2017

Short term models are indicating good saturation of the ground
overnight and into the morning hours across NE Utah and NW
Colorado. Decided to issue Flash Flood watches for the rest of the
county warning area with threat of convection firing early and
potentially widespread on Tuesday. Excessive rainfall will enhance
the threat for mudslides, rockslides, and dry washes/arroyos
suddenly becoming raging streams through at least midnight Tuesday
night.

&&

.SHORT TERM...(Tonight through Tuesday night)
Issued at 246 PM MDT Mon Jul 24 2017

Water vapor imagery this afternoon seems to indicate the
circulation of the upper high has now shifted into W.New Mexico.
Moisture is surging northward on the backside of the high with
PWAT doubling at KGJT overnight. Satellite derived imagery and
ground instruments show amounts in excess of 1.25 inches is now
encroaching the SE.Utah border. Orographics are the favored
lifting mechanism for the moisture and convection firing on the
over the hills and trying to survive in the valleys. This changes
later this evening when forcing from a well defined wave in
W.Arizona begins lifting around the periphery of the upper high.
Precipitation is expected to become fairly widespread from SW to
NE through the overnight to morning hours on Tuesday. The forcing
should help release instability overnight and in turn create
conditions favorable for efficient rainfall production. Model
soundings suggest much of E.Utah and far W.Colorado seeing warm
cloud depths at or above 7000 feet. This could produce rainfall
rates near 1 inch per hours in the heavier showers. Flood Watch in
effect is on track though a northward expansion may be necessary
near the CO/UT border counties depending on evolution of the storm
system overnight. Showers will linger into Tuesday night though
the forcing will be accelerating eastward out of the region so the
heavy rain threat should be easing. Temperatures will be fairly
cool on Tuesday with widespread clouds and precipitation in the
picture.

.LONG TERM...(Wednesday through Monday)
Issued at 246 PM MDT Mon Jul 24 2017

A shortwave trough moving across the northern Rockies from Tuesday
night into Wednesday will allow high pressure over the southern
Plains to expand westward, effectively cutting off the direct flow
of moisture into the area. This will begin a drying trend that
will extend from late Wednesday through Saturday. This by no means
will bring an end to diurnal showers and thunderstorms over the
higher terrain during this period, but will result in a decrease
in coverage and rainfall efficiency from day to day. Meanwhile,
valley locations will see a decrease in rain potential.

EC and GFS split on the onset of the next monsoonal surge. Latest
GFS indicated an easterly wave moving northward across Utah on
Sunday bringing an uptick in moist convection Sunday and Monday.
In contrast, EC maintains high pressure center to the west which
would continue to inhibit moisture advection into the area late
this weekend into early next week. As a result, will defer to the
blended solution in the late periods until model consistency
improves.

After being suppressed earlier in the week, temperatures should
climb to above normal levels during the latter part of the week
and into the weekend as the shift in high pressure brings a break
in monsoonal flow.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1207 AM MDT Tue Jul 25 2017

Showers and thunderstorms will work northward through
Tuesday morning and redevelop by afternoon. Expect VCTS for all
TAF sites with periods of heavy rain and gusty outflow winds along
with frequent lightning with showers and storms. CIGS will lower
through Tuesday morning across NE UT and NW CO with this increase
in moisture with heavy rain in showers bringing CIGS and VSBY
below ILS breakpoints at times. Some clearing is possible late
Tuesday morning before thunderstorms redevelop in the afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Flash Flood Watch through this evening for COZ001>014-017>023.

UT...Flash Flood Watch through this evening for UTZ022>025-027>029.

&&

$$

UPDATE...JAM
SHORT TERM...15
LONG TERM...NL
AVIATION...TGJT



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