835
FXUS65 KGJT 010854
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
254 AM MDT Mon Jul 1 2024

.KEY MESSAGES...

- A Flood Watch for southeast Utah and southwest Colorado
  remains in effect through 6 PM this evening. Abundant
  monsoonal moisture will bring the threat for high rainfall
  rates and potential flash flooding through today.

- There is a potential for stronger thunderstorms today, with
  heavy rain, gusty winds, hail, and frequent lightning all
  threats. Activity may linger into the overnight period.

- One more round of mainly terrain based convection is expected
  tomorrow afternoon before drier air finally moves in and
  brings an end to the unsettled period.

- Warmer, drier, and breezier conditions are expected for the
  end of the week, with a return to potential critical fire
  weather conditions.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 253 AM MDT Mon Jul 1 2024

The 00z GJT sounding had a PWAT of over 1 inch, and still indicated
around 1500 J/kg of CAPE still available for use. And use that
instability has gotten, as showers and thunderstorms have been
nearly continuous through the evening and overnight hours. At the
time of writing, nearly 2AM, there are still still pockets of
showers and storms producing lighting and heavy rain. The current
SPC mesoanalysis is still picking out a large pocket of around 1000
J/kg of CAPE over northeast Utah and northwest Colorado, with around
500 J/kg across the remainder of the region. The edge of a jet
across northeast Utah and northwest Colorado, as well as a few
wiggles in the flow and remnant outflows, have act as sources of
lift, and between the high PWAT and 50-60F dew points, there is more
than ample moisture to keep this party going through daybreak.
Things should quieten down after about 7AM, at least for a few hours.

The high remains in place over the Southern Plains this morning,
with the deep subtropical moisture plume continuing to stream into
the Desert Southwest. At the same time, a deep trough is progged to
move through the region this afternoon and evening, dragging a
frontal feature along with it. At the trough and this frontal
feature move through this afternoon and evening, looking for an
increase in activity as the frontal works as a lifting mechanism and
the trough brings steepening midlevel lapse rates. Models are
picking out a corridor of around 1500 J/kg of CAPE in association
with this feature, so the instability will be there, as well as the
moisture and lift. Some modest shear is also forecast during this
period, which will lend itself to producing more organized
convection capable of producing larger hail and stronger winds, in
addition to the heavy rain and lightning threat that will be present
all the way through the day. To account for the continued heavy rain
threat, a Flood Watch remains in effect through 6PM tonight for
southeast Utah and southwest Colorado to account for the increased
threat of flash flooding.

Convection is forecast to shut down fairly quickly behind the front
as the instability is exhausted, with northeast Utah and northwest
Colorado expected to shut down during the early afternoon while the
remainder of the area continues to see activity. However, with
surface moisture expected to remain high and this area expected to
take advantage of peak heating, modest instability will redevelop
through the afternoon and evening. With a wave passing through the
base of the trough tonight to act as a lifting mechanism, look for a
round of nocturnal convection to fire over northeast Utah and
northwest Colorado tonight, even as the frontal convection is still
ongoing over southwest Colorado. The biggest question with all of
this is will we have enough support to maintain organized convection
into the overnight hours, or will we things begin to stratiform out
as tonight turns toward tomorrow morning. In any case, all these
clouds and showers will keep daytime temperatures cooler, running
around 5 degrees below normal, and overnight lows on the milder side.

The trough axis finally swings through around daybreak tomorrow
morning, shunting the subtropical high and its associated moisture
tap to our east. Additionally, drier northwesterly flow will take
control over eastern Utah and western Colorado through the day
Tuesday. Surface based moisture and daytime heating will be
sufficient enough to produce some showers and storms over the
higher terrain, but there will be pronounced decrease in strength
and coverage compared to the previous days. The lingering strong,
dry northwesterly flow aloft is a bit different from the last few
times we`ve done this song and dance, and it is under this setup
that we stand the best chance to see that surface based mositure
scoured out and finally bring an end to this unsettled period for
more than 12-24 hours. Tomorrow will see similar temperatures to
today, but more sun and much more comfortable dew points as the
afternoon wears on.


&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 253 AM MDT Mon Jul 1 2024

The high amplitude pattern that has been anchored over the higher
latitudes will be migrating to the mid latitudes by midweek. It will
look more like a mid-winter triple R pattern with the higher than
normal heights to our West effectively shutting down the monsoon as
the Northwest flow dominates the pattern over the interior West.
PWAT currently 2-4 Std Dev above normal will plunge to below normal
by late week as dry air spreads back into the region. This is good
news for your swamp cooler which will actually push out cold air
again as dew points drop back into the 20s and 30s...but maybe not
so good news on the fire weather front. Low afternoon humidity and
afternoon wind gusts could create pockets of critical fire weather
even with temperatures hovering near to slightly below normal in the
latter half of the week and heading into the weekend. Isolated
afternoon storms may linger in the eastern and southern mountains
Wednesday afternoon before any residual moisture gets wrung out.
Otherwise a mainly dry forecast looks on track to end out the week.
The Western Ridge pattern looks to hold well into next though it
will migrate a bit farther inland. Hence the 6-10 day outlook calls
for good chances of above normal temperatures moving back in and the
drier than normal pattern continuing.


&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1122 PM MDT Sun Jun 30 2024

Moist...unstable conditions will keep a threat of shower and
thunderstorm activity in place over the next 24 hours. For the
most part VFR will prevail but if a shower with heavier rainfall
rates moves over an airfield MVFR conditions could occur mainly
due to restrictions to VSBY. Gusty outflow winds will also
remain a threat from passing storms or larger outflow boundaries
from the storm clusters. Quickly changing conditions are
possible and confidence is low on timing and exact conditions
but will be amending as necessary.

&&

.HYDROLOGY...
Issued at 253 AM MDT Mon Jul 1 2024

With anomalously high moisture continuing to stream into the region
today and widespread showers and thunderstorms in the forecast, the
Flood Watch will continue through 6PM this evening. The Flood Watch
encompasses areas south of the I-70 corridor where moisture will be
maximized and where heavy rains have already saturated the ground in
previous days. This area will see the highest potential flash
flooding. Drier air begins to move in tomorrow, so a reprieve from
the heavy rain and flash flooding threat is on the way.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch through this afternoon for COZ009-011-012-014-
     017>023.
UT...Flood Watch through this afternoon for UTZ022-028-029.

&&

$$

SHORT TERM...BGB
LONG TERM...15
AVIATION...TGJT
HYDROLOGY...TGJT