Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 070531

Area Forecast Discussion
National Weather Service Grand Junction CO
1131 PM MDT Tue Jun 6 2023

.SHORT TERM...(Tonight through Wednesday night)
Issued at 214 PM MDT Tue Jun 6 2023

The broad area of low pressure spinning over SoCal will slowly
shift into the Southern Great Basin during the short term period.
Right now, the CWA remains under a southern transport of tropical
moisture which has supported an early onset of daily convection
atop all mountain ranges. However, as the afternoon and evening
progress, a short wave rippling around the cyclonic circulation
will start to tilt upper level winds back to the southeast. In
addition, pressure gradients squeezed overhead support the
strengthening of an upper level jet, with the right entrance
region tilting over the Four Corners region tonight. Looking
further down the atmospheric column, a dry slot at 700 mb will
begin to lift across the Desert Southwest, wrapping around the
deepening low. Adding all these ingredients together, the Four
Corners region becomes a focal point of decent 0-6km shear,
greater than 40 kts, along a pseudo dry-line nudging into the
forecast area. Moisture ahead of the dry air, measures from about
0.6 to 0.9 inches of precipitable water, which tips over 150% of
normal for early June. Now all that`s left is instability...well,
based on mesoscale trends and HiRes guidance, areas across
southwest Colorado and southeast to eastern Utah indicate SBCAPE
exceeding 1000 to 1500 J/kg through the evening. As a result,
expect these areas to see an uptick in thunderstorm strength and
coverage later this afternoon/evening. A tilted line of storms
from about Moab through Telluride is progged to form around 5 to 7
PM MDT. Anticipate embedded thunderstorms with small hail, bursts
of heavy rain and lightning possible along this line. Once the
shortwave lifts across the Divide this evening, storms along said
line will loose their juice; and, remaining terrain driven
convection will, too, after sunset. Rain on the northwest end
fizzle over the Grand Valley to Tavaputs region by 9 PM MDT,
though a region of stratiform precipitation may linger along the
San Juans until midnight.

The low will continue to shift east overnight, so that by
Wednesday afternoon, the 70+ kt jet is draped overhead and
another shortwave ripples across. Expect very similar storm
activity forming along the pseudo dry-line. However, initiation
will have shifted northeast. Actually, HiRes models indicate
this line redeveloping about in the same spot it falls apart
tonight. Dry air nosing into the Four Corners will minimize storm
coverage along the southern zones. Meanwhile, the central and
northern mountains along the Divide may see over 0.5 inches of
precipitation in localized areas, depending on how quickly the
line moves.

Due to active weather and shifting low, temperatures will continue
to run around, or just below normal (depending on where cloud cover
and precipitation end up).

.LONG TERM...(Thursday through Tuesday)
Issued at 214 PM MDT Tue Jun 6 2023

On Thursday morning, the resident low will be absorbed back into
the jet...moving north through the Great Basin and toward the
Pacific Northwest. Meanwhile, another low will take hold once
again along the central California coast by Saturday night. In the
wake of the current low, drier air will move in from the
southwest, easily dropping dew point temperatures by 10 to 20
degrees across much of the forecast area. This leaves the moisture
gradient roughly arcing through the Tavaputs to the Grand Mesa
and San Juans (with the moist surface air mass to the north). As
such, if storms can get going, this general area will be the place
to watch for strong downdrafts. By Friday, the dry air spreads
across the forecast area and this will continue through the
weekend, leading to at least 3 days of a reprieve from convection.

The aformentioned low will move inland, through the Great Basin on
Monday and likely through our CWA by next Tuesday. Before this
occurs, the pressure gradient tightens and leads to gusty winds on
Sunday afternoon over portions of the four corners region.  As the
low nears the area, wind speeds increase slightly and gusty
conditions become more widespread. On Monday afternoon, gusts
above 25 mph spread across all of eastern Utah and around 50 miles
east of the state line. On Tuesday, winds relax slightly as the
system moves overhead and flow becomes more northerly on the back
side of the low. Along with the winds early next week, increasing
chances for precipitation can be expected (especially favoring the
high elevations along the Continental Divide) with the, albeit
meager, moisture content and lift associated with the passing

Temperatures during much of the long term forecast period remain
below normal by a few degrees thanks to elevated (surface) moisture
and cloud cover.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1128 PM MDT Tue Jun 6 2023

Broken to overcast skies will be common overnight for much of the
CWA as isolated precip comes to an end. Tomorrow, similar
conditions are expected as seen today with VCSH and VCTS included
in all CO TAF sites. Convection will fire around 18Z and continue
through the early evening hours. Gusty outflow winds, some heavy
rain, and small hail will be possible under and near the stronger
storms. ILS breakpoints will likely be met from time to time for
the mountain TAF sites. Mechanical turbulence will also be found
throughout the CWA.


Issued at 214 PM MDT Tue Jun 6 2023

Potential for localized areas of excessive rain and continued
snowmelt have influenced forecast hydrographs to rise again. In
general, rivers, streams and creeks are receding, though
localized heavy rainfall over the next two days may result in a
secondary spike. Most regions are, fortunately, projected to stay
at or below peaks already experienced this year. However, one
area, to keep an eye on will be the Green River downstream the
Yampa confluence. Releases from Flaming Gorge, in addition to
rainfall/snowmelt runoff over the Yampa River Basin, may result in
levels exceeding peaks previously experienced this year near the
town of Jensen, Utah. Other reservoirs with planned releases may
have timed their delay for higher releases just right as other
large tributaries are starting to decline.

That being said, water is still running fast and high this year,
so receding conditions may not necessarily mean it`s safe to
play. Please plan trips and activities accordingly, accounting for
diurnal fluctuations in each reach, as well as a rise or fall in
reservoir releases. In addition, all this storm activity has made
flashy conditions much more frequent in rivers/streams, but these
are still very difficult to predict which drainage will see the
heaviest precipitation and how high water spikes will be. Rapidly
changing river conditions remain a concern across the West Slope.




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