Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202145

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
345 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 Saturday
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 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, modeled 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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1105 AM MDT Sat May 20 2017

VFR conditions will prevail at all TAF sites the next 24 hours.
Moderate northwest flow aloft at mountaintop level will continue
producing areas of turbulence of the mountains. Along the
mountains of the Continental Divide low to mid clouds and isolated
snow showers will obscure mountain tops at times. These clouds
will also product ILS cigs at KASE through about 02z this evening.




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