Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 220953

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
353 AM MDT Tue Aug 22 2017

.SHORT TERM...(Today through Wednesday)
Issued at 353 AM MDT Tue Aug 22 2017

High pressure remained overhead early this morning while low
pressure continued to circulate over southern California early
this morning. Clouds lingered over the southern half of the
forecast area where difluence aloft prevalent.

As mentioned in previous discussions, models carry a shortwave
trough northward along the eastern edge of the SoCal low. This
disturbance will move across southeast Utah and southwest Colorado
this morning bringing increased clouds and light showers before
noon. Thunderstorms will likely hold off until the latter part of
the morning. The disturbance continues to lift northward, pushing
over the central portion of the forecast area this afternoon
which will combine with daytime heating to generate more showers
and thunderstorms than seen over the past several days. Soundings
from around the area indicated an increase in moisture and the
00Z/Tues KGJT sounding recorded 0.75 inches of liquid in the
airmass. Therefore, expect some of these storms will become heavy
rain producers.

The shortwave moves into the north tonight which should sustain
showers and thunderstorms later into the evening, especially
across northwest Colorado and northeast Utah. Some lighter
nocturnal activity is possible after midnight. This disturbance
remains a player in weather conditions Wednesday as it moves
slowly east northeastward over the north during the day.
Consequently, expect showers and thunderstorms will get an earlier
start there with greater coverage during the afternoon. Meanwhile,
to the south residual moisture is expected to fuel another round
of diurnally driven showers and thunderstorms, mainly over the
higher terrain.

High temperatures will be cooler today in response to increased
cloud cover and showers/thunderstorms, most noticeably across the
south. In the wake of the shortwave trough described above, highs
in the south will rebound to near normal. In contrast, highs
across the north will be suppressed Wednesday as the disturbance
moves overhead.

.LONG TERM...(Wednesday night through Monday)
Issued at 353 AM MDT Tue Aug 22 2017

Upper level low in the Gulf of Alaska finally making a push
southeastward toward the Lower 48 on Wednesday and Thursday. This
will allow the southern closed low over SoCal to dissolve into
high pressure over the southern US. A weather disturbance progged
to push through eastern UT and western CO Wednesday night into
Thursday morning potentially bringing some nocturnal showers and

Drier conditions are expected to develop beginning Friday as high
pressure amplifies over the Southwest and filters drier air into
the region from the northwest. Temperatures will run a few degrees
above normal over the weekend and into early next week. Afternoon
convection should remain focused over the highest terrain with
valleys remaining dry.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 353 AM MDT Tue Aug 22 2017

Daytime heating, increased moisture and a disturbance approaching
from the southwest will bring increased showers and thunderstorms,
mainly to the higher terrain during the afternoon and evening.
This activity poses some threat to TAF sites, but those chances
are pretty minimal except at KASE, KMTJ, KTEX, KGUC and KDRO where
there is a a 40 to 50 percent chance for thunderstorm activity.
Moisture levels are close to a point where MVFR visibility is
possible in heavy rain and ILS breakpoints could be reached at
KASE. A few showers are possible later tonight, mainly north of
the I-70 Corridor as the disturbance continues to lift to the
north. However, rain intensity will be light and VFR conditions
should prevail during the latter part of the night.






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