-- Discussion containing changed information from previous version are highlighted. --
058
FXUS65 KGJT 210514
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1114 PM MDT Fri Sep 20 2024

.KEY MESSAGES...

- An early fall storm will bring some mountain snow and rain
  showers to the region Saturday and Sunday. Impacts remain
  mostly above pass level, but a few area roadways can expect
  some wet snow on the road Saturday night.

- Unsettled conditions remain in place through early next week.

- A warmer and drier trend looks to develop by late next week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 253 PM MDT Fri Sep 20 2024

The stacked low situated over SOCAL continues to push a stream of
moisture along a diagonal from the Four Corners to the Nebraska
Panhandle. PWAT values on this morning`s sounding jumped
significantly, but dry boundary layer conditions beneath a modest
capping inversion are keeping things quiet on the West Slope this
afternoon. Temperatures are near 80 degrees around the CWA, a
fitting sendoff for the last day of summer. This all changes
tomorrow with the arrival of the stacked low working across the
Southwest. The surface low lifts into the vicinity of the Four
Corners by lunchtime. A few morning rain showers are expected around
our southern counties near daybreak. As the low lifts north and
eastward, precipitation should spread across much of the CWA south
of the I-70 corridor. Widespread convection develops over the entire
CWA by afternoon. Generous QPF will amplify a few of these showers
into downpours and could lead to some localized flooding concerns.
However, some doubt lingers with regard to surface moisture in the
early stages of this storm. Dry boundary layer conditions could
prove stubborn as much of the moisture from this system tries to
work across the mountains on an easterly wave. This becomes apparent
as we look at storm totals along the Sawatch and eastern shoulders
of the Gore Range. Much of the early cycle of this storm will fall
as cold rain Saturday afternoon, with freezing levels fluctuating
around 11,000 feet. Outdoor recreation enthusiasts and hunters will
want to take note of local forecasts Saturday, given the early
season nature of this event. As temperatures cool under
precipitation processes and sunset approaches, rain will switch over
to snow in the high country. Snow levels still hover around 10,000
feet and higher, which will fluctuate in the heavier showers. Road
level impacts are not expected for the majority of the CWA, but
passes along Highway 550, Independence Pass, and Vail Pass can
expect to see some wet snow and slush accumulating on the road
Saturday evening and into early Sunday morning. Morning lows will
trend downward this weekend, but cloud cover will keep them in check
with desert valleys in the 50s and up the hill in the upper 30s and
40`s. Afternoon highs will vary around the region given the
rain/snow and cloud cover. Low valleys will struggle to reach 80,
while the mountains will hover in the 50`s much of the
afternoon.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 253 PM MDT Fri Sep 20 2024

By Sunday morning, the low will be centered over northeast Colorado,
heading towards central Nebraska by Sunday afternoon. Some light
showers will linger through Sunday morning with some snow at the
higher peaks but this should come to an end by Sunday afternoon as
drier northerly flow follows. Northwest flow sets up Sunday evening
ahead of another disturbance projected to move through the area as
an open wave positively tilted trough on Monday afternoon. Unlike
previous model solutions 24 hours ago, the latest guidance shows a
quick moving weaker wave passing from northwest to southeast as
opposed to a more robust system dropping down the western slope from
north to south. So, expect some scattered showers and unsettled
conditions, but mostly favoring the mountains with little in the way
of accumulation.

My oh my how the models change even after 24 hours. This is why we
cannot hang our hat on one particular solution beyond 3 days as
models have a tendency to change. The latest GFS solution now
indicates drier northwest flow following the quick moving shortwave
by Tuesday with high pressure ridge building out west and moving
overhead by mid to late week. A weak wave brushes the north on
Thursday but even this looks dry. Lo and behold, the ECMWF is fairly
similar in this drier trend. So, temperatures will start off the
week much cooler than we`ve seen with highs 5 to 10 degrees below
normal on Sunday following Saturday`s closed low system. Highs stay
relatively 5 degrees below normal for the early part of next week
with temperatures moderating towards near to slightly above
seasonable by mid to late next week. This could be a tad milder if
the drier solution holds true. Blended model guidance keeps isolated
to scattered PoPs in the forecast through mid week, probably a
carryover from previous solutions but if this drier pattern holds in
future model runs, anticipate these PoP chances will dwindle. Low
confidence exists in PoPs beyond Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
-- Changed Discussion --
Issued at 1113 PM MDT Fri Sep 20 2024

An approaching low pressure system will track northeast across the
Four Corners after 18z reaching the San Juan Mountains by 00Z
Sunday. Expect isolated showers to start after 10Z across
southeastern Utah and spread east into the San Juan Mountains by
about 15Z. Showers and thunderstorms become scattered to widespread
across the southern areas after 18Z spreading north to the I-70
corridor by 21Z and into the northern mountains by 00Z Sunday. These
storms may produce periods of moderate to heavy rain and wind gusts
of 30-40 kts. Snow levels start around 12K feet lowering to 11K feet
by the end of the TAF period resulting in snow showers obscuring the
higher mountain peaks across the region. Expect brief periods of
MVFR conditions below ILS breakpoints at KDRO and KTEX between 15Z
and 00Z, and at KGUC, KASE, KEGE and KRIL after 20Z through the TAF
period.
-- End Changed Discussion --

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...LTB
LONG TERM...MDA
AVIATION...DB