Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 210434

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1034 PM MDT Sat May 20 2017

.SHORT TERM...(Tonight through Sunday night)
Issued at 221 PM MDT Sat May 20 2017

Northwesterly flow has returned to the western slope this afternoon
as low pressure that affected the region earlier this week
continues to head eastward in the high plains. Sufficient moisture
has lingered behind this system to aid in afternoon convective
development over the central and northern mountains. Not expecting
much in the way of precipitation accumulations this afternoon and
evening, however, a few wet roadways should be expected along the
US40 Corridor.

Overnight, a weak shortwave trough and associated vort max will
slide southward from the northern Rockies and into northern Utah.
This trough will zip eastward across the UT/CO border on Sunday
resulting in a better chance for more widespread convection during
the day. While the higher terrain should see showers and perhaps
a rumble or thunder first, some of these showers will likely move
off higher elevations and affect some valleys as well. PoPs still
remain low in valleys in this forecast package, but are non- zero
to address this possibility. A general northwest to southeast
drift is expected for any stronger cells that manage to develop.
High temperatures will continue their slow recovery and will run
only around 5 degrees below seasonal averages. Overnight, expect
shower activity to wane after sunset. Clouds should linger at
least through the first half of the night so not expecting much
of a fog impact early Monday morning.

.LONG TERM...(Monday through Saturday)
Issued at 221 PM MDT Sat May 20 2017

Heights will finally begin to rise in earnest over the region by
Monday as the shortwave trough pulls away to the east. Guidance is
indicating yet another weak trough sliding down from the northwest
by Monday afternoon, however nearly all guidance keeps any impact
from this system to our east. An isolated afternoon shower may
affect the Parks and Elks otherwise a dry afternoon with partly
sunny skies is in the forecast with temperatures continuing to
recover to near late-May averages.

The Four Corners region will be on the eastern fringes of an
advancing ridge of high pressure on Tuesday. Afternoon convective
activity will be minimal, even over the highest terrain. By
Wednesday, this ridge passes through the western slope with
widespread 80+ degree readings returning to the valleys.

The longer-range forecast has shifted somewhat over the past few
model cycles. Wednesday`s ridge was, for a while, modelled to
build over the region and last several days. Now, guidance has
trended away from that idea showing a more potent trough at 500mb
diving southward into the pacific northwest early on Thursday.
Flow turns southwesterly over the Four Corners with a few
afternoon showers and thunderstorms modeled as heights fall
slightly during the afternoon. Afternoon high temperatures will be
at their maximum for the week on Wednesday with low to mid-80s
possible in the typically warmer valley locations in eastern Utah
and far western Colorado. By Friday, differences in the strength
of this trough become apparent depending on what model you prefer.
The GFS implies a sharper trough passing Friday night into
Saturday while the ECMWF is flatter and more progressive. Both
models keep the associated vorticity maximum to our north however,
so the best dynamics for possible thunderstorm development over
the central Rockies may remain above the Colorado border. PoPs in
this forecast package reflect a drier solution...for now. Trends
in the timing and location of this next system will be monitored
over the next several days.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1034 PM MDT Sat May 20 2017

Mostly dry and VFR conditions can be expected through at least 18Z
before clouds and the chance for showers increases as a weak wave
moves overhead. Precipitation will be favor the northern
mountains with activity dying down after midnight. Some VCSH are
possible for TAF sites but do not expect anything too widespread.




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