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Area forecast discussion
National Weather Service Grand Junction Colorado
1057 am MDT Fri Sep 20 2019

Update...
issued at 927 am MDT Fri Sep 20 2019

Update includes a red flag warning for Colorado fire weather
zones 203 and 292 this afternoon and evening until 9 PM MDT. This
morning's sounding shows a very dry atmosphere with dry air
advection still on track for this afternoon. Expect stronger winds
and drier conditions capable of mixing to the surface this
afternoon compared to yesterday. Enhanced wind gusts combined with
lower relative humidity values have spread critical fire weather conditions
across a wider portion of southwest Colorado.

&&

Short term...(today through saturday)
issued at 242 am MDT Fri Sep 20 2019

A few showers and storms continue at this hour but coverage is
minimal at best thanks to a weak wiggle in the mean flow. The main
weather concern today will, again, be the winds. A trough
approaching from the west has decent upper level support in a 100
kt jet that will be almost directly overhead this afternoon. Deep
mixing will tap into some of these winds not to mention a tight
surface pressure gradient thanks to the location of the trough.
Like yesterday, we can expect gusty winds reaching 25 to 35 mph
across the area with some spots, looking at you eastern Utah,
seeing winds a bit higher than that. Water vapor imagery also
showing some drier air moving up from the south so fire weather
concerns have also increased. More on that in the fire weather
section below. As the day progresses, the jet stream will shift
northward causing the trough and area of low pressure to follow
suit. The best lift will remain where the cold pool aloft is
located and this will be around the low pressure. Models highlight
the best chance for precip over the eastern uintas as the low
pressure clips that area as it moves to the north. South to
southwesterly flow should also favor some lift over the San Juans,
central and northern mountains so isolated chances for a quick
shower or storm looks reasonable too. Having said that, most areas
will remain dry, windy, and a bit cooler than seen yesterday.

Speaking of cooler, thickness values show a definite decrease by
Saturday morning as cooler air advects in from the northwest.
Latest model runs not as cold especially with regard to hard
freeze temperatures (<28f) but even so, our northern valleys are
notorious for dropping to sub-freezing temperatures, especially
the Craig area, after frontal/trough passages so the freeze watch
will remain in effect for Friday night/Saturday morning.

For Saturday, the upper level trough will slowly push through but
with all support moving to the plains, minimal moisture and lift,
we'll remain dry. The only thing we'll notice is that high temps
will be 5 to 10 degrees cooler than those seen today. It also
won't be as windy as we've seen lately.

Long term...(saturday night through thursday)
issued at 242 am MDT Fri Sep 20 2019

A transitory ridge of high pressure builds in Sunday but will only
last through Monday as the next trough digs down from the
northwest. The ec and GFS are finally getting into better
agreement, sort of, and both now show said trough moving through
Utah and then closing off a low south of The Four Corners by
Tuesday morning. Both models keep US relatively dry thanks to the
trajectory of the low pressure. Differences pop up with the
evolution of the low as the GFS solution keeps the low tracking to
the southeast through Arizona into New Mexico and finally Texas.
This trajectory keeps almost all the associated precipitation to
our south and west though extreme southern Colorado and
southeastern Utah may see a passing shower or storm. The ec drops
the low into Arizona where it gets cutoff and then opens up and
shifts to the northeast bringing more widespread precip to our County Warning Area
towards the end of the week. Either way, most of the long term
period will be dry, mostly sunny, as high temps run right around
normal, give or take a few degrees here and there.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1052 am MDT Fri Sep 20 2019

Winds are gusty and could reach 30-35 kt at times this afternoon.
Clouds are building across the area and may result in isolated to
scattered showers and thunderstorms mainly in the higher terrain
this afternoon. Precipitation comes to an end this as well as the
wind gusts.

&&

Fire weather...
issued at 242 am MDT Fri Sep 20 2019

Gusty conditions will materialize again today as an approaching
upper level trough will mix strong southwest winds to the surface.
The combination of gusty winds with low relative humidities and
dry fuels will result in critical fire weather conditions across
southeast Utah and southwestern Colorado. Therefore, a red flag
warning is in effect for this afternoon and evening until 9 PM MDT
for winds, low relative humidity, and dry fuels.

&&

Gjt watches/warnings/advisories...
Colorado...red flag warning until 9 PM MDT this evening for coz203-207-290-
292.

Freeze watch from late tonight through Saturday morning for
coz002-005.

Utah...red flag warning until 9 PM MDT this evening for utz490-491.

&&

$$

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