842
FXUS65 KGJT 231741
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1141 AM MDT Sat Aug 23 2025

.KEY MESSAGES...

- Temperatures will be a few degrees cooler today, though still
  around 5 degrees above normal. Temperatures drop near to
  below normal starting tomorrow.

- Scattered to widespread convection is expected for areas
  along and south of I-70 this afternoon, with more isolated
  convection to the north. Gusty winds, frequent lightning, and
  moderate to heavy rain are all possible.

- Moisture continues to increase over the next several days,
  with widespread shower and storm activity expected. Potential
  for heavy rain and debris flows over burn scars will be
  heightened from Sunday into early next week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 306 AM MDT Sat Aug 23 2025

While high pressure remains dominant, the increasing moisture
is evident just about anywhere you look. Clouds and a few
showers left over from the afternoon`s convection have manage to
linger well into the overnight period. Dew points across the
region have climbed into the upper 40s to low 50s. Last night`s
00z Grand Junction sounding had a PWAT value of 0.90 inches,
which is approaching the 90th percentile for that day and time.
The sounding does still indicate a stubborn surface dry layer,
although even that is gradually getting chipped away...as
evidenced by the moderate to heavy rainfall that fell south of
the I-70 corridor yesterday afternoon, prompting a few flash
flood warnings. For areas south of the I-70 corridor, that trend
will continue today, as another round of widespread showers and
thunderstorms will develop during the afternoon. We may
struggle a bit with lingering cloud cover during the morning,
but hi-res models are indicating CAPE values of 400-800 J/kg
developing over the southern half of the area, as well as up
into northeastern Utah. It`s not an impressive amount of
instability, but with the amount of moisture we have around the
area, it`s more than enough to pop afternoon convection. We can
still expect gusty winds and lightning with any storms, but as
evidenced yesterday, we have saturated the atmosphere enough to
produce heavy rainfall. This means concerns for flash flood and
debris flows in known flashy areas, such as slot canyons or
steep and rocky terrain, as well as over recent burn scars. If
out recreating this afternoon, make sure to stay weather- aware
and have multiple ways of receiving watches, advisories, and
especially warnings.

Areas north of the I-70 corridor will actually see a bit of a
downturn in activity this afternoon. A pocket of drier air is
expected to slide southeasterly out of the Pacific Northwest,
and just clip our northern and eastern counties. In fact, this
pocket of dry air is already evident on satellite imagery,
stretching along a northwest-southeast oriented line through
Idaho and Wyoming and into northwest Colorado. Storms that do
form in this region will be likely to produce gusty winds in
excess of 45 mph and frequent lightning, but will be far less
likely to produce heavy rain. With the increased sunshine across
the northern half of the area today, temperatures will actually
be a degree or two warmer. Meanwhile, temperatures along and
south of I-70, where clouds and showers will be more prominent,
will see temperatures a good 5 degrees cooler compared to
yesterday. Still above normal, but not in the record- setting
territory we`ve seen this past week.

Moisture starts to return with a vengeance tonight, as the high
starts to slip to the east and the deep subtropical moisture
plume moves more directly overhead. This will result in clouds
and showers lingering through the overnight once again, along
with another muggy and mild night. Highs tomorrow will fall to
near-normal values as well, in response to the increasing clouds
and showers. PWATs jump to 150-200% of normal, placing most of
eastern Utah and western Colorado at or above the 1.00 inch
mark. With moisture this deep, and several days of "priming the
pump" we could be looking at a widespread heavy rain event on
Sunday. It all comes down to, how much cloud cover will stick
around during the morning. CAMs are inclined to give us some
clearing, especially south of I-70, allowing those areas to
develop some substantial instability. This would mean a more
convective storm mode, with prolonged periods of heavy rain and
high rainfall rates, in addition to frequent lightning and
possibly some hail. Not great news for sensitive areas,
including slot canyons and recent burn scars. Now, north of I-
70, CAMs aren`t as thrilled with morning clearing, resulting in
less instability and a more stratiform storm mode. This is
better news, especially for the burn scars, where we`d be
looking at a prolonged steady rainfall. This seems like the most
likely scenario at this point, but the monsoon is a tricky
beast. All it takes is a passing wave so subtle that models
can`t pick up on it, and we`ll be socked in the clouds. Or for
overnight convection to die off much sooner, and we see even
more sunshine than expected. So definitely stay tuned to the
latest forecasts, especially if travelling or planning to spend
some time outdoors.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 306 AM MDT Sat Aug 23 2025

The wet pattern is expected to persist well into next week with
most of the week on track to produce widespread precipitation
and QPF up to 0.45 inches. This is owed mostly to the high
pressure centered near the Four Corners beginning to move
eastwards again, pulling the plume of anomalous moisture over
the western CONUS back over our CWA. PWAT anomalies upwards of
175% of normal are thus likely over portions of the region
through Wednesday. It may be a little too early to begin
expecting relief for our extreme drought conditions though as it
remains to be seen how this precipitation may present itself,
be it through a stratiform or convective storm mode. And it is
entirely possible that the storm mode will vary heavily from
day- to-day. Lingering morning cloud cover will play the largest
role in determining daily storm mode. Should cloud cover
struggle to clear past sunrise, lacking surface heating may
result in steadier and more widespread stratiform rain, which
would provide us more in the way of potential drought relief
than a more convective setup. What complicates the setup though
are various shortwaves which will travel through the overhead
ridge. Stronger dynamics during these periods may yield an
environment more favorable for stronger convective storms, which
would limit the overall coverage, yet produce heavier rainfall
in localized areas. With higher resolution guidance from CAM`s
still unavailable, it is still too difficult to determine the
details of this active period. While rain in any capacity would
be a welcome relief for our drought concerns, it is also
important to note that flash flooding should still be considered
a notable risk throughout this wet pattern, particularly over
burn scars, regardless of storm mode.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1138 AM MDT Sat Aug 23 2025

The southern half of western Colorado and most of eastern Utah
will see rounds of showers and thunderstorms this afternoon
with gusty and erratic winds, frequent lightning, and brief
heavy rain all possible. VFR conditions will prevail for most
terminals, but drops to MVFR conditions due to heavy rain are
possible, especially for KTEX and KDRO where shower and storm
activity is most likely to occur.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...BGB
LONG TERM...BW
AVIATION...TGJT