Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 140532
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1132 PM MDT Sun Jun 13 2021

.SHORT TERM...(Tonight through Monday night)
Issued at 245 PM MDT Sun Jun 13 2021

The anomalously strong ridge over the West increases in magnitude
Monday while the air beneath remains extremely dry. Consequently,
there will be few clouds over the next 36 hours which will result
in maximized solar insolation Monday. Given the summer solstice is
only a week away, we are close to experiencing the longest days of
the year. Surface dryness, combined with unmitigated sunshine and
almost 15 hours of sunshine essentially makes the region a source
region for heat. Therefore, when combined with weak warm air
advection it`s hardly surprising that large swaths of the forecast
area will experience record temperatures Monday afternoon. If
there`s any good news in the near term forecast, it`s that clear
skies over the very dry lower levels of the atmosphere will
facilitate strong radiational cooling after sunset tonight and
Monday night.

.LONG TERM...(Tuesday through Sunday)
Issued at 245 PM MDT Sun Jun 13 2021

Much of the Desert Southwest, including eastern Utah and western
Colorado, will remain underneath an exceptionally strong ridge
of high pressure through the long term period. This, in turn,
means that exceptionally hot temperatures will also continue, with
forecast highs for the lower desert valleys remaining above the
century mark through the work week and into next weekend. Peak
heat is still forecast to occur Tuesday and Wednesday, with highs
forecast to challenge Grand Junction`s all time record highest
temperature of 106F, set in 2005. Even if the all time record high
isn`t broken during this hot streak, daily high temperature
records likely will be. Overnight low temperatures will also creep
upward through the week, reaching the upper 60s to low 70s in the
desert valleys by midweek. This could cause additional heat
stress, especially among vulnerable populations. Given the
magnitude of these temperatures, Excessive Heat Warnings are in
effect from Monday afternoon through Friday evening.

While the main story here is definitely the heat, another topic of
note is an infusion of sub-tropical moisture under the ridge.
Ensemble forecasts begin to increase PWAT values starting
Wednesday and continuing into the weekend, with anomalies
climbing above climatological norms. The deepest moisture will be
confined to the Four Corners region, as well as the San Juans. Of
course, there is still quite a bit of uncertainty with this
forecast. Models are sometimes too ambitions with moisture return,
especially for the lower atmosphere after a long hot and dry
period. Additionally, the exact placement of the center of the
high pressure will affect the trajectory of the moisture plume,
potentially steering the best moisture away from the forecast
area. With the forecast as it stands, the lower atmosphere will
likely still be too dry for any rainfall to reach the ground.
Instead, gusty outflow winds and dry lightning will be the main
threats with any terrain driven convection that develops. The
upcoming very hot and dry stretch will lead to tremendous stress
on vegetation, setting the stage for any lightning to possibly
produce new fire starts. Summing it all up, the coming week is
shaping up to be very hot and dry, with fire weather concerns
returning toward the end of the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1132 PM MDT Sun Jun 13 2021

VFR conditions will prevail for the next 24 hours. Quiet weather
expected overnight with terrain driven winds. Another sunny day is
in store for Monday with westerly breezes near 20kt developing
during the afternoon. Winds diminish after sunset with another
tranquil night to follow.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Excessive Heat Warning from noon Monday to midnight MDT Friday
     night for COZ006-020.

UT...Excessive Heat Warning from noon Monday to midnight MDT Friday
     night for UTZ024-027-029.

&&

$$

SHORT TERM...NL
LONG TERM...BGB
AVIATION...MDM


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