Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202149
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
349 PM MDT Thu Jul 20 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 302 PM MDT Thu Jul 20 2017

Showers and thunderstorms, some producing small hail and heavy rain
started to develop late this morning and early this afternoon.
Better instability, a weak disturbance, and boundaries left from
yesterday all contributed to better and sooner development this
afternoon. Expect showers and thunderstorms to continue through the
evening producing small hail and heavy rain. The heavy rain will
cause flash flooding. This trend will continue through Friday
although the moisture plume will be shifted slightly to the east
with the deepest moisture extending from the four corners through
northwest CO. Precipitable water values remain over an inch. Will
let the current hilites play out and let next shift analysis
models and cloud cover for placement for possible flash flood
hilites.


.LONG TERM...(Saturday through Thursday)
Issued at 302 PM MDT Thu Jul 20 2017

Dryer air moves over into the area from the north affecting
northeast UT and northwest CO first. Expect a downturn in convective
activity over the north. The south should also see less activity
although deeper moisture will linger longer. Current model runs
focus showers and thunderstorms from lingering moisture mainly over
the divide and associated higher terrain. The slight down trend in
storms continues for Sunday. The ridge builds back over the Great
Basin starting this weekend and strengthens into early next week.
The ridge starts to slide east as a trof enters the moves inland
over OR and northern CA allowing an opening for another surge of
moisture to move toward eastern UT and western CO. Differences in
models means confidence is lower with timing and placement of the
moisture plume. Temperatures will increase again as the ridge builds.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1216 PM MDT Thu Jul 20 2017

Scattered to numerous showers and thunderstorms expected through
this evening, some with heavy rainfall and small hail that will
obscure mountain tops and reduce ceilings and visibilities to MVFR
category, including reaching ILS breakpoints. Showers and
thunderstorms will largely diminish after 06Z tonight, though some
will continue overnight and into the morning hours at a lesser
intensity.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Flash Flood Watch until midnight MDT tonight for COZ003-006>009-
     011-017-020>022.

UT...Flash Flood Watch until midnight MDT tonight for UTZ022-025-
     027>029.

&&

$$

SHORT TERM...AS
LONG TERM...AS
AVIATION...JRP



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