425
FXUS65 KGJT 031150
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
550 AM MDT Mon Jun 3 2024

.KEY MESSAGES...

- Mostly cloudy skies expected today with showers increasing
  late this afternoon and evening as a cold front moves through,
  particularly across northern and central areas with the Park
  Range and Flattops favored. Gusty outflow winds and embedded
  thunderstorms remain possible with better chance of wetting
  rain at higher elevations.

- Temperatures will remain above normal into the coming week.
  The warmest temperatures of the season thus far will be
  Thursday and Friday at 10 to 15 degrees above normal.

- Major stem rivers will continue to show rises over the coming
  days thanks to warm surface temperatures.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 418 AM MDT Mon Jun 3 2024

Moisture is already starting to advect into the region from the
west as an early June Atmospheric River brings in moisture aloft
at the mid and high levels. The low levels still remain dry for
much of this afternoon, as evident based on inverted V
soundings. This is resulting in quite the increase in mid and
high level cloud cover this morning, especially across the
north but also extending into the central mountains according to
nighttime satellite imagery. While the IVT moisture is fairly
strong as it hits the Pacific Northwest and northern California
coast, as it tracks further inland, IVT values lessen quite a
bit as moisture gets wrung out over the western upstream ranges
and translates to a modest 300 km/m/s across areas north of
I-70 by the time it reaches us. The hi res CAMs and even the
deterministic models are finally starting to pick up on this
moisture in the form of increasing precipitation potential
across the area, especially this evening as the upper level
trough and associated cold front move through.

The fly in the ointment on how much storm activity gets
generated really is the early morning cloud cover and its impact
on diurnal heating to act on the moisture and get storms going,
which we have seen in the past. If you go based on satellite
trends, it would appear like the cloud cover would be too much
in the morning and stick with us much of the day to really
prevent diurnal heating from kicking off stronger storms. The
DESI is indicating the best chances of precipitation occurring
after 00Z (6 pm MDT) and occurring with the front across the
northern and central mountains with isolated to scattered
activity possible in the lower elevations as well. While
moisture is there as mixing ratios rise to 5 to 6 g/kg ahead of
and along the front, the instability is lacking as CAPE doesn`t
really go much above 100 J/kg and enough CIN is present to
prevent stronger storms from developing. That`s not to say there
won`t be thunderstorms, just they may be more isolated with a
lot of the precipitation along the front being stratiform in
nature. Also, the dry low levels still need to be overcome, so
gusty outflow winds seem like a better bet in the lower
elevations with best chances of wetting rain across the northern
high elevations. Increased PoPs as a result to blend more in
line with much of the hi res CAMs, which favors the northern
areas as well as down to the Grand Mesa and West Elks for the
best potential for showers. Some showers may linger through the
overnight given the forcing from the trough. Behind the front,
much drier air pushes in from the northwest, which should sweep
out most of this moisture by Tuesday morning, with a few showers
lingering over the northern high terrain.

On Tuesday, drier northwest flow moves into the region with some
lingering moisture along the central and southern Divide where
some isolated storms are possible and cannot be ruled out
completely. We should see plenty of sunshine Tuesday afternoon
allowing for diurnal heating to act on whatever moisture may be
left behind, which isn`t expected to be much but might be
enough to kick off some convection. Most models are indicating a
dry day with very little in the way of storm activity, but
could see a scenario where we see some storms popping over the
high terrain.

Temperatures will be warm today (about five degrees above
normal) but cloud cover may inhibit some of the warming as
mentioned earlier, so forecast highs may be a tad too warm. It
all depends on the amount of cloud cover with the increasing
moisture aloft as we are currently seeing this morning. By
Tuesday, temperatures will still be warm but cooler by about
five degrees post frontal, ending up near normal on average.
Temperatures will heat up quite a bit though over the mid to
late week timeframe, so this brief "cooldown" won`t last long.
More on this in the Long Term discussion.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 418 AM MDT Mon Jun 3 2024

In the long term synoptic pattern, models agree on high
pressure sliding in over the Western States and building north
out of Mexico by Wednesday with troughing over the Eastern Conus
and a cutoff low off Baja forming an omega-ish block that stays
in place through the rest of the week. They want to lift the
cutoff low north along the West Coast or into the Great Basin
going into early next week, but the models struggle to handle
cutoff lows, so that solution is questionable. There is also
indications that some models want to drop a deep low south out
of the Gulf of Alaska to knock the top off the ridge mid next
week (GFS and European ensemble), but there is not much
confidence in this either. A reasonable solution concurs with
GEFS suggesting the omega block stays in place pretty much
centered on the Rocky Mountains going into next week, but there
isn`t a lot of confidence in this either. What can be said is
that a strong ridge will build in over the West mid week into
the weekend bringing high temperatures flirting with records in
many locations that may pose hazardous heat risks generally
Thursday onward. The fly in the ointment that puts this in
question will be the moisture, remnants of the AR, that lingers
in the Great Basin sliding in under the ridge to generate
afternoon clouds with diurnal heating that will temper the high
temperatures and even produce widely scattered showers and
thunderstorms through the latter half of the week.

With that being said, as the ridge builds in over the region
Wednesday, the skies should clear out under the subsidence, but
persistence says the moisture will still linger in the area to
combine with diurnal heating to spawn isolated to scattered
afternoon showers and thunderstorms over the higher terrain favoring
the northern mountains. This scenario will likely repeat Thursday
into the weekend with PoP`s increasing to the south as subtropical
moisture moves moves up from the south under the ridge. With the
ridge in place, eastern Utah and Western Colorado will see
temperatures five to ten degrees above normal for the first week of
June Wednesday, climbing to ten to 15 degrees above normal Thursday
through Saturday. Currently record highs are forecast for Friday in
many locations across the region with near record temperatures the
other days. This isn`t absolute based on the above discussion of
lingering/advecting moisture in the region. For this reason, holding
off on excessive heat headlines for late in the week to get a better
handle on the forecast. Stay tuned on this one.

Of interest on the advection of subtropical moisture north, the
Madden-Julian Oscillation says activity has returned to the Indian
Ocean, but satellite imagery shows the convective activity in the
Eastern Pacific is still going strong and could be a source for
moisture to advect north. Activity over Sonora and Chihuahua has
been very quiet this year likely due to the cool Spring and a more
westerly flow keeping the region dry. This ridge may be the key to
open the southern door to kick off the subtropical moisture
flow into northern Mexico. If this happens, we`ll see hints of
MCS`s initiating south of the border priming the pump for later
this Summer.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 550 AM MDT Mon Jun 3 2024

Clouds will increase across the area this morning into the
afternoon, especially for northern and central areas. Winds will
remain light and terrain driven until 18Z when winds pick up
from the west, gusting 25 to 35 mph. Showers will develop over
the high terrain late this afternoon with embedded thunderstorms
along a cold front expected to move through this evening. KHDN,
KASE and KEGE stand the best chance to see showers/storms
impacting the terminals with brief MVFR conditions with
conditions below ILS breakpoints during showers, with a lesser
chance at KRIL. Some shower activity could linger overnight
across the north. Elsewhere and outside of shower activity, VFR
conditions should prevail.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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