Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202255
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
455 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 00Z TAFS through 00Z Friday evening)
Issued at 452 PM MDT Thu Jul 20 2017

Scattered showers and thunderstorms will continue for another 24
hours with storms most numerous during the afternoon and evening
hours. Heavy rain, small hail, gusty winds to 30 kts and dangerous
lightning will occur with the storms. CIGS will drop below ILS
breakpoints with local MVFR CIGS/VIS in the vicinity of the
strongest storms. Mountain tops may be obscured at times. Away
from showers and thunderstorms, VFR conditions will be present.

&&

.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...JDC


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