Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 241052
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
452 AM MDT Thu Jun 24 2021

.SHORT TERM...(Today through Friday)
Issued at 452 AM MDT Thu Jun 24 2021

There`s a void of shower activity across the region early this
morning. Looking upstream though, scattered nocturnal showers
continue to thrive across Arizona. This moist air mass is on the
move, and heading in our direction. Precipitable water values
nearing an inch cover a vast majority of the Western Slope, which
will help prime the atmospheric column for rain reaching the
ground later today. Terrain induced storms will start firing
around noon, however, increased instability and upper level
dynamic support will enhance scattered thunderstorms to develop by
mid-day. The combination of increased moisture and dynamic
forcing may finally allow measurable precip to reach the ground
across valley floors! CAM guidance is still a "scatter plot" with
regard to where those stronger storms will form and which valleys
will win the rain lottery. But, general consensus favors southern
to central ranges early afternoon, shifting northward by late
evening hours. Activity generally wanes overnight, though a few
lingering showers may drop some light precipitation across the
central and northern mountains along the Divide.

By Friday, our source of moisture and dynamic forcing shift gears
as a deepening trough drags a weak cold front across the area.
Expect the boundary to dip into northeast Utah and northern
Colorado by late morning and continue trudging southward through
evening hours. Storm activity will favor this surface boundary
with increasing coverage expected after noon. Diurnal convection
will still flourish ahead of the front, however, the juicy storms
forming along this boundary have a higher chance of dropping
heavier precipitation rates, in excess of 0.5 in/hr possible.
Brief periods of intense rainfall may become of concern over burn
scars...So, in addition to keeping an eye on wind shifts and
storm tracks for ongoing wildfires, heavy rain rates may threaten
recent burn scars as well.

As for temperatures, we`ll be running 5 to 10 degrees cooler this
afternoon, thanks to increased cloud cover and shower activity.
Friday`s cold front will bring noticeably cooler temps across the
northern half of the forecast area, while regions across the south
will actually bump up a degree or two.

.LONG TERM...(Friday night through Wednesday)
Issued at 452 AM MDT Thu Jun 24 2021

A very large area of high pressure will develop over the
northwest portion of the country this weekend, with our CWA on the
eastern side of this high pressure in a somewhat drier northerly
flow. We will be right on the fringes of the better moisture as
several shortwaves drop through the eastern portion of this ridge
and down the Front Range. The high will shunt much of this
moisture south and east, with the western Colorado divide
mountains seeing the best chance of afternoon thunderstorms. Some
moisture will linger behind so coverage may be a bit more Saturday
than models indicate as we transition back to a drier air mass.
PW values come down quite a bit on Sunday with less than 0.5 inch
across much of the area and some pockets of 0.75, mainly down
south. The high pressure expands further east early next week,
with still a few shortwaves potentially generating some storm
activity over the San Juans and southern foothills. Models are not
in the best agreement on the placement of this closed off area of
high pressure with lows trying to undercut the ridge to the
south. PW values still remain less than 0.5 inch across much of
the area with 0.75 near the Four Corners and southern border.

Friday`s cooler temperature trend will carry into the weekend,
with highs about 10 degrees below normal...15 degrees below normal
depending on what model guidance you look at. Anyway, the cooler
and wetter weather will be a welcome change from the record heat
and dry period we recently experienced. Highs return to near
normal values by early next week with above normal highs by mid
next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1207 AM MDT Thu Jun 24 2021

Scattered showers will continue to affect ASE, EGE, and possibly
GUC through the overnight period. Expect brief periods of MVFR if
heavy rain does move over the airport and lowers CIGs, however
this will be brief and short lived. VFR likely at all terminals on
Thursday with scattered showers in the afternoon in the higher
terrain.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...ERW
LONG TERM...MDA
AVIATION...MAC


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