Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 212244
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
444 PM MDT Fri Jul 21 2017

.SHORT TERM...(Tonight through Saturday night)
Issued at 343 PM MDT Fri Jul 21 2017

Showers and thunderstorms got an early start today as deep
subtropical moisture continued to stream northeastward across the
region. Expect this activity to continue into the evening as
diurnal instability lingers. Meanwhile, high pressure rebuilds to
the west in response to a shortwave trough moving eastward over
the northern Rockies during the night. This will cause flow to
shift to the north allowing drier air to filter across the
northern most portions of the forecast area. Convergence where the
northerly flow encounters remnant southwest flow may yield
persistent shower/thunderstorm activity over Colorado`s central
mountains and valleys late into the night.

Models were consistent in spreading drier air south of the I-70
Corridor Saturday. Residual moisture farther south will continue
to fuel diurnal showers and thunderstorms with just a few storms
possible over the northern mountains. Some storms will remain
capable of producing heavy rain. Diurnal cooling will bring
showers/thunderstorms to an end for most areas during the latter
part of the evening, though some activity may linger past midnight
in the San Juan Mountains.

.LONG TERM...(Sunday through Friday)
Issued at 343 PM MDT Fri Jul 21 2017

Drying will continue to spread south on Sunday, but models suggest
enough moisture will hang over the San Juan`s to fuel another
round of showers and thunderstorms during the afternoon and
evening. Models were divided on when the monsoon pattern returns
with the ECMWF reintroducing moisture Monday while the GFS holds
off until Tuesday. However, from Tuesday onward models in
agreement with afternoon/evening showers each day with nocturnal
activity possible. Temperatures are expected to be near normal
during this period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 444 PM MDT Fri Jul 21 2017

Scattered showers and thunderstorms will persist across the
forecast area this evening with heavy rain, small hail and gusty
winds to 35 kts being the primary threats with storms. Cigs will
drop below ILS breakpoints with local MVFR cigs/vis in the
vicinity of stronger storms. Mountain tops may be obscured at
times. Drier air will begin to work into the region from the north
overnight and into Saturday, decreasing the chance for showers and
storms. Storms will mostly die down after 06Z tonight before
redeveloping over the southern and central mtns after 18Z
Saturday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Flash Flood Watch until midnight MDT tonight for COZ001>014-
     017>023.

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

&&

$$

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



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