200
FXUS65 KGJT 241959
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
159 PM MDT Mon Jun 24 2024

.KEY MESSAGES...

- Residual moisture will continue to fire isolated afternoon
  showers and storms this afternoon and again on Tuesday.

- A push of deep subtropical moisture moves in by Wednesday,
  returning widespread showers and storms through Thursday.

- Mid-week moisture content, exceeding 200% of normal, also
  returns the threat of flash flooding due to periods of heavy
  rain and/or training storms.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 101 PM MDT Mon Jun 24 2024

Afternoon showers and storms have already triggered atop the
high country. While last week`s mositure surge has displaced to
our southwest, anomalously high precipitable water values have
been slow to exit the region. PWATs still range from 120 to
200%, equating to dew points in the upper 40`s. Nothing to
scream about, but still sufficient moisture to see isolated
pockets of heavy rainfall. SBCAPE ranges from 1000 to 1500 J/kg
across the Western Slope, along with DCAPE values in excess of
1000 J/kg, this afternoon. Thus, as storms drift off high
terrain, collapsing cells will be capable of producing small
hail and strong outflow winds, 40 to 50 mph. Though most
activity wanes around sunset, elevated CAPE should support
storms surviving through late night hours again this evening.

Rinse and repeat for Tuesday...not much changes synoptically,
thus, expect another warm day with isolated storms triggering
off mountainous terrain in the afternoon. This lingering pool
of moisture overhead is slightly shifting to the southwest, so
terrain across northwest Colorado may be less active Tuesday
afternoon in comparison to today (i.e. Routt County and
portions of east Moffat County).

Aside from storms, high pressure overhead has maintained warm
temperatures for late June. Highs and lows will continue to run
5 to 10 degrees above normal tonight and tomorrow.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 101 PM MDT Mon Jun 24 2024

A trough that has been lurking off the Pacific Northwest finally
moves inland on Wednesday. This will nudge the subtropical high
sitting over the Desert Southwest eastward, allowing the clockwise
flow around the high to begin advecting deeper tropical moisture
into eastern portions of the Great Basin, including eastern Utah and
western Colorado. This plume of moisture is forecast to be richer
than normal for late June, with ensemble guidance indicating values
of 200-250% of normal by Thursday, with some guidance even
suggesting near-record values for the period. As it stands, a wide
area of eastern Utah and western Colorado will see PWAT values of
over an inch of moisture. This will mean that, in addition to
widespread shower and thunderstorm activity Wednesday and
Thursday, the threat for heavy rain and flash flooding will make
a return. Thursday remains forecast to be the big day this
week, with the deepest moisture in combination with multiple
little waves in the flow and a tightening pressure gradient
aloft adding in a bit of enhanced shear. So in addition to
frequent lightning and heavy rains, some stronger storms are
likely and will be able to produce hail and strong, gusty winds.

As the upper level trough continues tracking across the northern
tier of the country, the subtropical high will continue to be swept
eastward, eventually cutting eastern Utah and western Colorado from
that deep moisture plume. In addition, model guidance wants to sweep
a punch of dry air in behind the trough axis on Friday, leading to a
rapid dry-out of the atmosphere. Now, Friday will most likely see a
decrease in available moisture aloft, but surface moisture is more
stubborn and could hold on longer. So the potential is there for a
continuation of widespread showers and thunderstorms bringing heavy
rain on Friday afternoon. Look for decreasing storm coverage through
the weekend as another ridge builds in and convection becomes tied
primarily to the higher terrain.

Wednesday will see the last day of above normal temperatures this
week, as the increasing moisture and storms will keep things cooler
for Thursday and Friday, with highs near normal. Heat will rebuild
for the weekend as ridging returns, with highs forecast around 5
degrees above normal. Lows will remain mild and 5-10 degrees above
normal through the period.


&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1118 AM MDT Mon Jun 24 2024

Afternoon showers and thunderstorms are expected over the next
3-6 hours across the higher terrain of eastern Utah and western
Colorado. These should mainly impact higher terrain terminals,
but even lower elevation terminals may see showers or storms in
the vicinity at some point. Main threats will be gusty winds,
brief heavy rain, and lightning. These should diminish after
sunset, with skies clearing and typical terrain driven winds
kicking in. Tomorrow is expected to be very much the same, with
a clear and quiet morning giving way to afternoon showers and
storms. VFR conditions will prevail for the next 24 hours, but
impacts from showers or storms passing over a terminal will lead
to the potential for brief drops to MVFR conditions and possibly
drops below ILS breakpoints.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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