Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 220554

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1154 PM MDT Fri Jul 21 2017

Issued at 1152 PM MDT Fri Jul 21 2017

Will be allowing the Flash Flood Watch for the southern half of
the forecast to expire at midnight as showers continue to
dissipate. Drier weather moves back into the area on Saturday with
focus for the best convection shifting into our southern zones. No
other changes planned at this time.

UPDATE Issued at 1054 PM MDT Fri Jul 21 2017

Busty evening across eastern Utah and western Colorado with plenty
of reports of minor flooding and few reports of more significant
flooding in and around the Rifle area. See our website for more
details on that.

Dropped the northern zones from the Flash Flood Watch earlier
this evening and cleaned pops up a bit. Now watching a little
meso-low dropping south along the Colorado/Utah state-line with
showers still rolling to the south and east of the circulation.
Overall, activity has been on the decrease, but still could see
another storm or two pop and will hang on to the flash flood watch
for the southern zones until midnight.


.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 06Z TAFS through 06Z Saturday night)
Issued at 1054 PM MDT Fri Jul 21 2017

Showers and isolated thunderstorms will continue to impact areas
south of Interstate 70 through 10Z this morning before ending.
Expect areas of ILS CIGS with local MVFR conds in the vicinity of
stronger showers. The mountains may be obscured at times in low
clouds and showers. After 10Z patch valley fog will be possible,
and may impact KEGE, KRIL and KGJT with any impacts ending after
15Z. Expect isolated to scattered thunderstorms Saturday afternoon
and evening, generally across southeast Utah and southwest
Colorado as drier air sweeps across the northern areas.






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