Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 241024

Area Forecast Discussion
National Weather Service Grand Junction CO
424 AM MDT Mon Oct 24 2016

.SHORT TERM...(Today through Tuesday)
Issued at 424 AM MDT Mon Oct 24 2016

As mentioned in previous discussions, the ridge which brought
warm, dry weather to the area over the past several days has
shifted to the east. The change in pattern was driven by a trough
off the West Coast which continued to track toward land during the
night. In response, subtropical moisture has begun moving
northward across Utah ahead of the approaching system. So far this
morning, only scant moisture had entered the GJT CWFA at mid and
high levels resulting in partly cloudy skies.

For today, moisture will continue to deepen over Utah west of the
Green River while clouds increase over eastern Utah and western
Colorado. A shortwave ejected from the eastern Pacific trough
combined with rising temperatures will begin to generate showers
over the higher terrain of eastern Utah toward noon and over
extreme western Colorado this afternoon. The subcloud layer in
Colorado will limit the amount of moisture reaching the ground and
expect more virga than rain producing cells. Isolated
thunderstorms are possible over the Four Corners region late this
afternoon. Increased clouds will result in slightly cooler
temperatures as southwest flow aloft continues to bring mild air
to the region.

Shower chances increase markedly tonight as the shortwave trough
tracks over the area. Concurrently, moisture deepens as southwest
flow carries subtropical moisture over the area from Utah causing
precipitable water values to rise from below 0.4 of an inch at
GJT, to around 0.8 of an inch during the night. As a result,
precipitation is likely to be widespread across the forecast
area. The mild airmass will limit snowfall accumulations to areas
above 10000 feet, though flakes are possible below that level.
Overnight lows will be pretty mild due to the insulating affects
of cloud cover.

Showers linger into Tuesday, primarily due to orographic forcing
and instability working on residual moisture. However, showers
will become more scattered in nature as the day progresses.
Snowfall accumulations will remain confined to areas above 10000
feet as mild temperatures persist. Though afternoon highs will be
a bit cooler than those forecast for today, readings are still
expected to peak around 5 degrees above seasonal norms.

.LONG TERM...(Tuesday night through Sunday)
Issued at 424 AM MDT Mon Oct 24 2016

As the shortwave trough continues to push east of the area
Tuesday night, the flow aloft becomes more westerly and begins to
dry. Westerly orographics should become a stronger player in the
location of precipitation Tuesday evening.

Overnight the next big ridge begins to build west of the forecast
area. The flow over the CO and UT mountains will become more
northwesterly and moisture will continue to decrease. The system
will be rather warm with snow levels hovering around 9000 feet
Tuesday, so snow accumulations will be very localized and at high

Wednesday and Thursday will be dry with another strong ridge
dominating the western U.S with a deep trough off the west coast.
On Friday a strong closed low over the California coast fills and
slides northeast. The tail of this trough is projected to cross
the area late Friday night and Saturday, with the bulk of its
energy traveling around the northern periphery of the ridge.
Sunday should be dry with the ridge dominating.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 424 AM MDT Mon Oct 24 2016

VFR conditions will prevail through 00Z/Tuesday though clouds will
be increasing over the region ahead of an approaching Pacific
trough system. Showers are expected to develop over the higher
terrain of northeast Utah late this morning before spreading into
the mountain zones of western Colorado this afternoon. Showers
will be high based initially so expect strong and unpredictable
outflow winds in the vicinity of buildups during the day.

A disturbance in the southwesterly flow aloft combined with
increased moisture is expected to bring widespread showers to
eastern Utah and western Colorado after 00Z/Tuesday. This activity
is likely to cause ceilings to lower below ILS breakpoints for
some sites, especially KASE, KEGE and KRIL. Periods of MVFR
VSBY/CIGS are also possible.






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