Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 190958
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
358 AM MDT Thu Sep 19 2019

.SHORT TERM...(Today through Friday)
Issued at 358 AM MDT Thu Sep 19 2019

Southwest winds will increase today ahead of an upper level trough
over the Pacific Northwest that will drop into the northern Great
Basin. A 100 kt jet over western Utah will approach, allowing
deeper mixing to take place. H5 winds of 40 to 50 kts with H7
winds of 25 to 35 kts, will result in surface winds gusting in the
30 to 40 mph range. Precipitable water (PW) values increase to
between 0.5 and 0.75 inches, allowing for some isolated to
scattered storms to form late this afternoon and evening across
western Colorado into northeast Utah. Drier conditions will occur
over southeast Utah due to stronger winds rounding the base of the
trough through the Desert Southwest into the Four Corners region.
Critical fire weather conditions will occur over portions of
southeast Utah as a result. See Fire Weather discussion below for
more details.

Breezy conditions will remain overnight into Friday as this trough
lifts northeast through Wyoming and moves across the area. We look
to stay on the drier southern side of this trough, which may lead
to critical fire weather concerns once again across southeast Utah
and possibly extending into western Colorado. Temperatures will be
warm today due to deeper mixing but take a 10 degree swing
downward on Friday after trough passage. So above normal temps
today will lower to near normal by Friday.

.LONG TERM...(Friday night through Wednesday)
Issued at 358 AM MDT Thu Sep 19 2019

Breezy and cooler temperatures will occur Saturday as another
shortwave on the backside of the upper level trough moves through
our area. Conditions remain dry with this secondary passage and
temperatures look to lower to a few degrees below normal.
Temperatures will rebound to near to slightly above normal by
Sunday as a transitory ridge of high pressure moves across the
area and southwest flow returns by Monday ahead of the next
stronger storm system set to move into the Great Basin and Desert
Southwest. Models diverge with the evolution of this next storm
system. The GFS is the wetter and more aggressive solution
showing a closed low developing just southwest of the Four Corners
Monday and hanging around through mid week before lifting across
the area on Thursday. The ECMWF, on the other hand, is much
further southwest than the GFS, keeping our CWA on the dry side.
Showers and storms still look to favor the Monday afternoon and
evening timeframe as this low drops southward and again returning
Thursday as the system lifts across the southern portion of the
CWA. At it`s core, this closed low carries H7 temps between +2C
and +4C. Depending on the track of this system, we could end up
seeing our first accumulating snow in the high country above 11 to
12kft or we could end up missing out. Still way too early to call
and due to model discrepancies, confidence is low. Still
something to watch. Models tend to struggle with these seasonal
transitions.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 358 AM MDT Thu Sep 19 2019

Southwest winds will increase this afternoon and continue through
early evening ahead of an approaching trough. Surface winds at
many TAF sites could gust in the 20 to 30 kt range with some
higher gusts at times to 35 kts. Some mid level clouds will form
as well as some isolated to scattered storms after 21Z over mainly
western Colorado high terrain. Mountain wave turbulence and wind
shear is possible due to the stronger upper level winds mixing to
the surface.

&&

.FIRE WEATHER...
Issued at 358 AM MDT Thu Sep 19 2019

Southwest winds will increase today ahead of an approaching upper
level trough. Decent mixing of stronger winds aloft will occur
where gusts 30 to 40 mph will be common across much of the area.
Relative humidity remains elevated enough across western Colorado
and northeast Utah to preclude critical fire weather conditions.
However, this is not the case across southeast Utah where gusty
winds will combine with low relative humidity to produce critical
fire weather conditions. Therefore, issued a Red Flag Warning for
Utah fire weather zone 490 (Moab and Grand Flat area). Decided to
leave out Utah 491 (southeast Utah) as only the far western
portion near Lake Powell looks to hit criteria while the majority
of the zone maintains higher relative humidity values. Drier air
will encompass all of southeast Utah on Friday as the trough
passes through, elevating fire weather concerns. Later shifts will
need to reassess whether fire weather highlites are needed for
Friday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...Red Flag Warning from noon today to 9 PM MDT this evening for
     UTZ490.

&&

$$

SHORT TERM...MDA
LONG TERM...MDA
AVIATION...MDA
FIRE WEATHER...MDA


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