899
FXUS65 KGJT 162223 CCA
AFDGJT

Area Forecast Discussion...CORRECTED
National Weather Service Grand Junction CO
423 PM MDT Fri Aug 16 2024

.KEY MESSAGES...

- Weak monsoon moisture will bring isolated to scattered showers
  and storms on Saturday, favoring the mountains and eastern Utah.

- More robust monsoonal moisture will impact the region Sunday
  and beyond. Showers and thunderstorms will bring back the
  threat of localized flooding Sunday and into the new work
  week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 423 PM MDT Fri Aug 16 2024

Winds in the mountains were gusting at 20 to 30 mph this afternoon
with temperatures running a few degrees above normal. There are
some areas of near critical fire weather conditions this afternoon
with low relative humidity in the lower valleys and across
northwestern Colorado. A deep low dropping into the Pacific
Northwest and a second low shifting east across the Great Lakes
were driving the high over the Southwest eastward into west
Texas. This shift in the pattern opens the door to deep monsoonal
moisture which is expected to move north through Arizona into
eastern Utah and western Colorado Saturday. The return of
subtropical moisture will fuel isolated to scattered afternoon
showers and thunderstorms over higher terrain. Storms strengthen
going into the evening as a shortwave passes to the northwest. The
HRRR continued to be more bullish with this system than the other
models indicating a strong line of storms moving over the
northern two-thirds of the region between 5 PM and midnight. With
the southern edge of the jet overhead and IVT`s in excess of 500
kg/ms over eastern Utah and northwest Colorado driving PWAT`s
above 1", there will be an increased risk for flash flooding due
to localized heavy rain and/or training storms. Not enough
confidence to issue headlines at this time, but this is something
to watch with the next couple runs of the models.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 423 PM MDT Fri Aug 16 2024

Models continue to return consistent agreement on a blocking high
taking up residence over the Rockies this coming week. Despite
several pushes from the northeast Pacific, the ridge remains the
dominant feature here on the West Slope. This regime will set the
stage for monsoonal moisture to work its way under the ridge each
day, producing areas of showers and thunderstorms Sunday afternoon
and beyond. Model agreement remains high that this regime will stay
in place through the extended period. PWAT values 140 to 150 percent
of normal are progged for Sunday across much of the CWA. Ensemble
forecasts are in agreement that precipitable water values stay up
through the week, with some minor deviations thanks to the center of
the high wobbling a bit. Some nocturnal activity is expected to
linger beyond the afternoon into the late evening/early overnight
hours as well. Light steering flow will extend residence time of
storms on their source terrain and thereby increase risks for flash
flooding. Morning lows will trend warm through the period thanks to
elevated dewpoints, while afternoon highs will stick around normal
to 5 degrees warmer than climatology. Some hints are cropping up
that this pattern will shift by Saturday, but likely not enough for
a meaningful break in unsettled conditions.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1130 AM MDT Fri Aug 16 2024

VFR conditions will prevail at terminals this TAF period. Winds
will pick up this afternoon, westerly at around 20 mph around
the region, then subside this evening. A few scattered mid level
clouds will crop up on some terrain features this afternoon, but
skies should remain mostly clear around the region. Terrain
influenced, light winds return for the overnight period into
Saturday morning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...DB
LONG TERM...LTB
AVIATION...TGJT