223
FXUS65 KGJT 151117
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
517 AM MDT Thu Aug 15 2024

.KEY MESSAGES...

- Isolated to widely scattered showers and storms will be
  possible today and tomorrow, mainly along the Northern Divide
  mountains. Gusty outflow winds, frequent lightning, and small
  hail will be the main threats.

- Temperatures will run near normal this afternoon, and climb
  around 5 degrees above normal to round out the work week.

- Returning moisture late in the weekend will bring increased coverage
  of clouds, showers, and storms, as well as a return to near
  or slightly below normal temperatures.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 251 AM MDT Thu Aug 15 2024

With one exception, shower and storm activity has come to an end
across eastern Utah and western Colorado, with mostly clear skies in
control. Westerly flow aloft has continued to advect drier air into
the region, with last night`s 00z GJT sounding having a PWAT of 0.68
inches. This is the lowest value recorded on a GJT sounding in over
a week. This shift to a drier pattern for the next several days will
bring a warming trend across the region, with highs this afternoon
climbing to near normal values, and highs tomorrow topping out
around 5 degrees above normal. This will also bring decreasing
coverage of afternoon showers and thunderstorms as the deep dry air
scours out remnant moisture. Isolated to widely scattered showers
and storms will be possible this afternoon, with areas along the
northern Divide most favored. With PWAT values dropping to 50-75% of
normal tomorrow afternoon, coverage will be isolated at best. So
while a stray shower or storm can`t be ruled out, Friday is shaping
up to be generally dry and sunny.

While eastern Utah and western Colorado remains under the influence
of ridging through the end of the week, a deepening trough off the
West Coast will bring strengthening southwest flow aloft. This will
translate to breezier conditions for Friday afternoon and evening.
Typically, this would bring an increased concern for critical fire
weather conditions, but after a week of wetting rains across the
majority of eastern Utah and western Colorado, fuels are currently
too wet to be receptive to fire in many spots. So for now, holding
off on any fire weather highlights.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 251 AM MDT Thu Aug 15 2024

The weekend should start off dry and hot as a high pressure ridge
remains in place. PWATs will average between 0.4 and 0.6 inches
Friday night into Saturday morning to start off the long term
period. Meanwhile, a low pressure trough will approach the Northern
California and Pacific Northwest coastline and be enough to push the
high pressure ridge eastward over eastern New Mexico into the Texas
Panhandle. This will open the door to a southwest monsoonal moisture
tap, thereby increasing storm coverage across much of Utah by
Saturday afternoon. This moisture and resultant storm coverage looks
to spread into western Colorado by Saturday evening, as PWATs
increase to the 0.7 to 0.9 inch range by late Saturday
afternoon/evening. Given the previous few days will have been drier,
this initial surge of moisture looks to result in more of a gusty
outflow wind and lightning threat than heavy or wetting rain. It
will take some time for the atmosphere to moisten in the lower
levels.  By Sunday, PWATs are already climbing over an inch which
will equate to around 150 to 170 percent of normal. It seems like
Sunday into Monday will provide better chances of wetting rain and
locally heavy rain with storms which could result in some localized
flooding especially among steep terrain, areas of training and burn
scars. The southwest flow remains in place at least through Monday
with several embedded shortwaves moving through the flow around the
periphery of the high and ejected out of the low pressure trough off
the PacNW coast.

Beyond Monday, there is some uncertainty and discrepancy on the
placement of the high pressure system and amount of moisture, which
would impact the precipitation forecast. The high looks to meander
back to the west Tuesday and Wednesday and possibly beyond into late
next week, which would steer the moisture plume to our west and/or
take the long way around the high to get to us from the west instead
of the south. Much of the forecast also depends on what happens with
this PacNW low as this can affect the placement of the high and
where this moisture plume sets up. Time will tell as these details
are important as we could remain active into next week or dry out
towards the latter half of the week if this high retrogrades back to
the west and cuts off our moisture tap. Blended guidance still keeps
scattered to widespread PoPs in the forecast as at the very least
this moisture gets recycled as it doesn`t appear to be any system to
help drive the moisture out of here once it arrives this weekend
into early next week.

Temperatures will start off several degrees above normal Saturday
but get knocked back down to near or slightly below normal by Sunday
into early next week as moisture increases, resulting in more clouds
and showers/storms each afternoon/evening.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 514 AM MDT Thu Aug 15 2024

A few scattered showers and storms have lingered through the
night across northeast Utah and northwest Colorado. This
activity will continue to track southeast and gradually
dissipate as it moves into a more unfavorable environment.
Elsewhere, some passing midlevel clouds have developed over
Southeast Utah and portions of southwest Colorado. These clouds
should remain above breakpoints. Showers and storms this
afternoon will be isolated to widely scattered, with minimal
impacts to airports expected. Southwest winds gusting 20-25
knots are expected across the area. VFR conditions will prevail
for the next 24 hours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...BGB
LONG TERM...MDA
AVIATION...TGJT