Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 061025

Area Forecast Discussion
National Weather Service Grand Junction CO
425 AM MDT Thu Aug 6 2020

.SHORT TERM...(Today through Friday)
Issued at 425 AM MDT Thu Aug 6 2020

The 00Z sounding last evening indicated 0.72 inches of
precipitable water (PW), but looking at the profile, this moisture
is mostly at the mid levels with really dry air in the low levels.
This was evident by the increased coverage of shower activity
yesterday, although clouds helped put a damper on lightning
potential and even temperatures to an extent. Some isolated
showers have developed across northwest Colorado from about Aspen
northward. The NAMNest appears to be the only model that has
picked up on this, showing this activity quickly moving out by

Southwest flow will be increasing quite a bit today as the
pressure gradient tightens ahead of a deeper trough out west. This
trough will be pulling in a much drier air mass from the Desert
Southwest, as PW values quickly drop to well below 0.5 inches
across much of the CWA, with values as low as 0.25 inches and
below across northern and central sections of the forecast area.
More widespread critical fire weather conditions will occur under
this dry and windy southwest flow with gusts as high as 35 mph.
Any existing wildfires have potential for rapid spread and growth
under these conditions, so a Red Flag Warning remains in effect
and in fact has been expanded to include a couple more zones. More
details in the Fire Weather section below. As far as storm
potential today, most model guidance keeps precipitation east and
south of the area as this drier southwest flow seems to be a major
player today, pushing this moisture east. The NAMNest is still
picking up on some convective development over the southern and
central Colorado divide, although isolated at best. Felt given the
underperformance of most models on convection last few days,
enough moisture will linger along the divide to help spark some
storms during the afternoon. Expect more wind than rain given very
dry low levels and inverted V soundings.

On Friday, the gradient will relax some as a low pressure system
over the Pacific Northwest breaks off the main trough and scoots
into Canada, leaving behind a low trying to split from the main
trough over California. The best potential for critical fire
weather conditions will be across portions of northwest and west-
central Colorado as well as east-central Utah due to gustier winds
here. So, Red Flag Warning in effect for those areas as well
Friday. Hot and dry conditions will continue and with deeper
mixing and less cloud cover expected, thinking that max
temperatures could be a few degrees above forecast guidance with
lower desert valleys, including Grand Junction, getting fairly
close to triple digits. Therefore, bumped up max temps a bit for
today and a little less so for Friday. Isolated storms still look
possible over the San Juans and possibly central divide on Friday
as some moisture gets recycled and rotates around the high
pressure centered over Texas and New Mexico. Expect continued hazy
to smoky skies each evening and morning as smoke from wildfires
across the southwest US and local to the western slope get
transported in this southwest flow.

.LONG TERM...(Friday night through Wednesday)
Issued at 425 AM MDT Thu Aug 6 2020

Southwest flow will continue through the weekend with hot and dry
conditions remaining with a cutoff low over California associated
with the main trough and high pressure to the southeast. This
cutoff low will continue to split and drift off the California
coast by early next week, allowing the flow to turn over to the
west. This will force the high pressure center further west over
the Arizona, New Mexico and Mexico triple point. Some weak subtle
shortwaves will move through the area as they rotate moisture
around the high pressure center to our south. At this time, really
still expecting mostly dry conditions with high temperatures some
5 degrees above normal and near normal lows. Isolated storms are
possible each afternoon over mainly the higher terrain. By mid to
late next week, the cutoff low gets absorbed by the main trough
and moves onshore and further inland, allowing this high pressure
to shift subtly to the east. This could mean an increase in storm
activity as a shortwave ejects across the area from this low, but
the ECMWF remains dry unlike its distant GFS cousin. Time will
tell, but low confidence this far out...have to say that we have
seen this before. At this time, would have to lean towards the
drier solution until better model consistency is seen.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1143 PM MDT Wed Aug 5 2020

VFR conditions will prevail over the next 24 hours with some areas
possibly affected by smoke/haze in the morning hours with MVFR
temporarily. Winds will be main concern by the early afternoon
hours as gusts in the 25 to 35 mph will be possible at most TAF
sites through sunset. Storm formation will be very isolated and
confidence too low to put into forecast attm.


Issued at 425 AM MDT Thu Aug 6 2020

Southwest winds will increase today in combination with a very
dry air mass, leading to critical fire weather conditions across
much of the area with wind gusts 25 to 35 mph. Latest model
guidance indicates critical fire weather conditions to be a bit
more widespread to include the Glenwood Springs to Eagle-Vail
corridor, where another wildfire started last evening. Added Utah
485 and Colorado 205 to the Red Flag Warning for today. The
Gunnison Basin (Colorado 293) is close but winds look a bit less
in Gunnison and coverage and duration are borderline, so decided
to hold off on including Colorado 293. Day shift may need to look
closer here to see if this also needs to be included.

Critical fire weather conditions are also likely Friday for
portions of east-central Utah to northwest and west-central
Colorado based on latest model guidance, so upgraded the Fire
Weather Watch for Colorado 200 and 202 to a Red Flag Warning and
also expanded this to include Colorado 203 and Utah 487 and 490.
Temperatures will continue to run well above normal through next
week with mainly dry conditions and isolated storms possible each
afternoon over higher terrain.


CO...Red Flag Warning from 11 AM this morning to 8 PM MDT this
     evening for COZ200-202-203-205-290-292.

     Red Flag Warning from 11 AM to 8 PM MDT Friday for COZ200-202-

UT...Red Flag Warning from 11 AM this morning to 8 PM MDT this
     evening for UTZ485>487-490-491.

     Red Flag Warning from 11 AM to 8 PM MDT Friday for UTZ487-490.



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