293
FXUS65 KGJT 041119
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
519 AM MDT Tue Jun 4 2024

.KEY MESSAGES...

- A few light showers will be possible over the northern and
  central mountians through about midday today, but will taper
  off this afternoon as high pressure and drier air builds in.

- Some of the hottest temperatures of the year so far are
  expected late week, with highs running 10-15 degrees above
  normal, and triple digits likely for the lower desert valleys.

- Chances of mountain showers and storms will return for the
  weekend into early next week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 300 AM MDT Tue Jun 4 2024

With the surface front just about through the area, shower activity
has decreased quite sharply across the area. Generally, only areas
along the Divide are still seeing rain showers, and these are
expected to come to an end over the next few hours. With 700-500 mb
mixing ratio guidance indicating a lingering pool of moisture over
the northern and central Colorado Divide mountains, as well as some
modest CAPE thanks to steepening mid-level lapse rates in the post-
frontal regime, chances for isolated to scattered showers will be
possible over this area through the mid-morning hours. Northwesterly
flow aloft will quickly bring in some drier midlevel air that will
erode these lingering pockets of moisture through the day, tapering
off any shower activity by the afternoon hours and bringing gradual
clearing from west to east through the day. High temperatures will
run near to maybe a degree or two below highs yesterday...but still
remaining 5 or so degrees above normal for early June. Clear skies
and light winds tonight will allow radiational cooling to do its job
and drop low temperatures to near normal values.

Ridging building into the Desert Southwest starting tonight will
kick off a warming trend, with high temperatures tomorrow running a
good 10 degrees above normal. Parts of southeast Utah will likely
see their first triple digit day of the year, with the rest of the
desert valleys seeing mid to upper 90s. Higher elevation valleys
will see highs in the 80s, while mountain towns are looking at upper
60s to 70s. A shortwave passing by across Wyoming may tighten the
gradient aloft enough to bring some increased gusts up to 30 mph
across northeast Utah and northwest Colorado, but otherwise, look
for clear skies and light winds to characterize the day
Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 300 AM MDT Tue Jun 4 2024

The big story in the Long Term is the heat that will make it feel
like Summer already across the Western Slope for the first full week
of June. A ridge of high pressure builds across the area with its
axis sliding overhead by Thursday. The flow will turn southerly by
Friday ushering in strong WAA and some of the hottest temperatures
of the year thus far. Basically from Thursday through Saturday, high
temperatures across the area will exceed 10 to 15 degrees above
normal with triple digit heat seeming more like a near certainty for
the lower valleys of west-central Colorado (Grand Valley) as well as
east-central and southeast Utah. High temperatures seem to peak on
Friday as there is potential for some subtropical moisture to advect
northward heading into the weekend and early next week. Mid to upper
90s will be felt across the Uinta Basin, Delta and Uncompahgre River
Basin, up through Debeque Canyon to Rifle and the valleys across
southwest Colorado. So, all in all, it will get hot quickly making
it all the more important to stay hydrated and take it easy in this
heat, whether doing work or recreating outdoors or even trying to
stay cool indoors. The latest NBM probabilities of exceeding 99
degrees (so basically reaching 100 or more) is near 100% for Moab
and portions of east-central and southeast Utah with most of that
area greater than 90%, while the Grand Valley is over 80% and Delta
to Hotchkiss is around 60 to 80% depending on where you are.

While higher confidence exists for the heat, what is less certain is
the eventual advection of subtropical moisture and how that impacts
our area. It all has to do with the evolution of a cut off low that
will be sitting over the Baja Peninsula underneath this high
pressure ridge. The ridge axis largely remains firmly in place over
the spine of the Rockies this weekend with a trough moving into the
Pacific Northwest and the cut off low either remaining over the
Baja/SoCal region or getting absorbed in the flow and pulling
through our neck of the woods by late this weekend into early next
week by this PacNW trough as it tracks inland. It does appear like
Thursday and Friday will remain dry. There might be some isolated
storms Friday afternoon over the western Colorado mountains along
the Divide or at the very least cumulus buildups as this subtropical
moisture tries to work its way northward. It seems like guidance is
honing in on the development of afternoon convection at least over
the high terrain this weekend, potentially expanding in coverage
Sunday into Monday, depending on if this cut off low is absorbed and
tracks across with the embedded shortwaves from the PacNW trough.
There is lots of uncertainty this weekend into early next week as
models are not in great agreement on how this plays out with the
different scenarios listed above. At the very least, afternoon
convection favoring the high terrain seems like a good compromise
with the lower valleys remaining drier, given the drier low levels
and lower confidence. If this wave tracks across the area, the lower
valleys could see some storms and precipitation but gusty outflow
winds seem like the better bet and more probable outcome.

The heat remains through this weekend with near record heat
possible, although could turn slightly cooler early next week if it
becomes more unsettled (and by cooler I mean 90s for the lower
desert valleys instead of 100s and 80s for the rest of the valleys
instead of 90s...still 5 degrees above normal for early June).
Projections beyond the uncertainty this weekend into early next week
seem to indicate potential for a strong ridge to build back over the
west and into our area for mid June, as is more typical this time of
year...meaning drier and hot (warmer than normal). The CPC outlooks
would seem to agree with this scenario.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 517 AM MDT Tue Jun 4 2024

Shower activity has generally come to an end across eastern Utah
and western Colorado, although a few showers may linger across
the northern and central Divide. Ceilings near ILS breakpoints
at KASE and KEGE will continue through 15z before improving.
Aside from passing high clouds this morning, look for generally
clear skies across the area. Winds will be northwesterly today,
with gusts up to 30 knots possible this afternoon. VFR
conditions will prevail for the next 24 hours.

&&

.HYDROLOGY...
Issued at 530 PM MDT Mon Jun 3 2024

High pressure building overhead through the end of the week will
result in an unseasonably warm period across the Western Slope.
Simultaneously, as those temperatures rise, so will the rate of
snowmelt across our high terrain. Even though low to mid elevations
have already melted out, there`s still an abnormally high amount of
snow left over basins generally at and above 11,000 ft. As a result,
we`ll see creeks, streams and major tributaries along the Upper
Colorado River Basin rise. Seasonal peak flows are expected over the
next 10 days, with the Upper Gunnison, Upper Yampa and Colorado
Headwaters basins potentially peaking this weekend. Current
guidance oscillates diurnal peaks cresting the Action Stage for
portions of Gore Creek and Eagle River in Eagle County and the
Elk River in Routt County Colorado. We will continue to monitor
these evolving forecasts to see if any Flood products are
warranted. But for now, we just want to pass on the message:

As scorching temperatures lure folks to the water, please
remember the potential hazards associated with high flows during
the snowmelt season. Fast flows are not just dangerous for
those choosing to float the rivers. In addition, high diurnal
swings may drastically change the depth and flow for normally
small creeks and streams. Swift currents and cold water
temperatures can catch you off guard, so please be vigilant with
current conditions and look for forecast updates when
recreating or working near the water`s edge.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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