Area Forecast Discussion
Issued by NWS Grand Junction, CO

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707
FXUS65 KGJT 242046
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
246 PM MDT Mon Jul 24 2017

.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 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1156 AM MDT Mon Jul 24 2017

Scattered showers and thunderstorms will continue to erupt early
this afternoon, mainly over the higher terrain of the central and
southern mountains. This activity will begin moving off of the
higher terrain and could impact KTEX and KDRO as early as 19Z.
Heavy rain from these cells may bring brief MVFR VSBY and CIGS
near ILS breakpoints. TAF sites to the north face little chance
for direct impacts from thunderstorms until later tonight as an
upper level disturbance moves over the area.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Flash Flood Watch through Tuesday evening for COZ003-006>014-
     017>023.

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

&&

$$

SHORT TERM...15
LONG TERM...NL
AVIATION...NL



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