Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 211800
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1200 PM MDT Mon May 21 2018

.SHORT TERM...(Today through Tuesday)
Issued at 304 AM MDT Mon May 21 2018

Satellite imagery clearly shows some circulation over southern
California at this hour which matches up nicely with guidance
closing off a low over the same area. Circulation around this low
will cause flow to be generally south today and this flow will
advect some moisture into southern regions of the forecast area.
Once the sun starts heating things up and favorable orographics
kick in, enough instability will exist to allow some showers and
storms to form this afternoon. The main difference today will be
that most of the convection will stay south of I-70 (a stray
shower or storm certainly possible up north). Favored areas will
be the San Juans and central mountains from the late morning
through sunset. Medium confidence that Durango will see some
showers/storms but increasing as you heads towards Pagosa Springs
where chances look pretty good for some convection today. The rest
of the CWA will see partly cloudy skies becoming cloudier as the
day goes on. High temperatures will run at or just above normal
today. A few spots over extreme southwestern Colorado will see
increased winds and low humidities but any critical fire weather
conditions will be very limited in scope and length so saw no need
to issue any highlights.

On Tuesday, the low pressure will continue to encroach on the CWA
with the center of low pressure over Las Vegas. Flow will continue
to be from the south while weak disturbances will rotate around
the low. These minor perturbations will tap into some instability
causing another round of showers and storms though coverage will
increase thanks to the presence of the low pressure and increased
vertical motions. Variable cloudiness will be the rule as the day
progresses with most higher terrain seeing convection in the
afternoon. Temperatures will be similar to today, if not a bit
cooler.

.LONG TERM...(Tuesday night through Sunday)
Issued at 304 AM MDT Mon May 21 2018

The closed low will begin its transition to an open wave late
Tuesday/early Wednesday and slowly lift to the northeast. This will
subsequently shut down most of the shower and thunderstorm activity
across eastern Utah and western Colorado during the overnight hours
and allow for the heavier cloud cover to lift. Wednesday should
be a fairly quiet day, though some isolated convection could fire
off over the higher terrain during the afternoon hours. A ridge of
high pressure will begin to build over the western CONUS late
Wednesday and only continue to amplify Thursday, Friday and
Saturday. The weather for the end of the work week and throughout
the weekend will be fairly quiet with temperatures rebounding back
to well above normal levels, even creeping back into the low 90s
for some valleys by Saturday. Drying beneath the ridge will limit,
but not entirely put an end to afternoon/evening showers and
thunderstorms which will favor the mountains of the Continental
Divide each day.

Saturday night a Pacific trough of low pressure will push into the
west coast. The arrival of this trough will usher the ridge of high
pressure east into the Plains with upper level flow once again
becoming southwesterly across eastern Utah and western Colorado.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1200 PM MDT Mon May 21 2018

Showers and thunderstorms will develop over the higher terrain
early this afternoon and will continue into the evening with the
San Juan Mountains and adjacent valleys favored. Showers and/or
thunderstorms are likely to impact KDRO, KGUC after 20Z,
continuing through 02Z. Those sites can expect outflow winds up
to 40 MPH, but visibility and ceilings are expected to remain in
the VFR range. Showers/thunderstorms in the vicinity of KEGE,
KRIL, KASE and KTEX may see similarly strong outflow winds as
those mentioned previously. Elsewhere, VFR conditions will
continue through the next 24 hours with no threat of CIGS falling
below ILS breakpoints.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...TGR
LONG TERM...MMS
AVIATION...NL



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