Area Forecast Discussion
Issued by NWS Grand Junction, CO

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441
FXUS65 KGJT 191743
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1143 AM MDT Thu Oct 19 2017

Updated aviation section

.SHORT TERM...(Today through Friday)
Issued at 253 AM MDT Thu Oct 19 2017

Plenty of clouds are showing up on IR satellite imagery this
morning and are heading our way thanks to a relatively weak
shortwave. Upstream observations over Utah are indicating some
cloud cover, generally above 10K feet, but no precipitation at
this time. In fact, the atmosphere looks to be so dry that it may
take some time to get any precipitation to reach the ground. With
that in mind, forecast calls for some showers to start around
noon, give or take, with chances increasing towards the late
afternoon and evening hours. As the shortwave will remain to our
south, the San Juans will be favored today. A few rumbles of
thunder are also possible this afternoon due to some limited
instability but coverage looks to be fairly minimal. Those areas
not seeing any precip can still expect partly cloudy skies
becoming mostly cloudy towards the evening hours. For the
overnight hours, a few stray shower will be possible but any
appreciable qpf is not anticipated.

Friday, the jet stream begins to affect the area supporting an
upper level trough and surface cold front. Thanks to the jet, the
pressure gradient will tighten which will allow some gusty surface
winds (25 to 35 mph...maybe a bit stronger up north) to
materialize around the noon timeframe. The cold front will start
moving into northeastern Utah Friday evening and should reach the
I-70 corridor by about midnight.

.LONG TERM...(Friday night through Wednesday)
Issued at 240 PM MDT Wed Oct 18 2017

The upper level trough swinging in over Northern California and
Southern Oregon will continue pushing into the area late Friday
and early Saturday. As the h5 height gradient tightens and the 80
kt jet nose moves over, gradient surface winds will strengthen
from the west southwest. As mentioned above, some stronger gusts
near 25-30 kts may mix down to the surface late Friday afternoon.
Fire weather is not a concern given the lack of widespread Red
Flag Conditions in the forecast area. A few showers and high
mountain snow will develop late Friday and into Saturday across
the northern and Central Divide areas as the cold front comes
through. Wide Spread precip is not expected with this dry system
as it moves through. The cold front will usher in a much cooler
airmass as H7 temps plummet from 5-6 C to -9 C by early Saturday
morning. Some light snow on the order of 1-3 inches is possible in
the central divide but, again, wide spread snow is not expected.

Skies will begin to clear behind the front Saturday and Sunday as
high pressure builds back in from the West. West northwesterly flow
will dominate the rest of the extended as the ridge fluctuates
intensity. Temperatures behind the front will be cooler before
recovering early next week under clear and sunny skies.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1140 AM MDT Thu Oct 19 2017

An incoming trough will increase winds this evening, first aloft,
then down to affect downslope and downvalley winds tonight. Winds
will become breezy just before 18z Friday at many TAF sites, but
LLWS will be localized to areas mainly north of KVEL over the
eastern Uintas. ILS breakpoints are not expected to be reached
over the next 18 hours, but could be reached toward 18z on Friday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...TGR
LONG TERM...ADL
AVIATION...JAM



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