050
FXUS65 KGJT 302101
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
301 PM MDT Sun Jun 30 2024

.KEY MESSAGES...

- A Flood Watch for southeast Utah and southwest Colorado
  remains in effect through Monday afternoon. Abundant monsoonal
  moisture will bring a heavy rainfall rate threat to these
  areas through tomorrow.

- The stonger thunderstorms will be capable of producing gusty
  outflow winds, large hail, and plenty of cloud-to-ground
  lightning.

- Monsoonal moisture gets forced east on Tuesday, and afternoon
  showers will be far more isolated in nature.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 119 PM MDT Sun Jun 30 2024

Another day, another round of storms. It took awhile for
convection to get going today thanks to a fairly strong cap.
The morning sounding showed a strong midlevel inversion from 400
to 500mb so it took some time to break through. Once it did,
convection started going which is exactly what happened. In 2
scans (approximately 8 minutes), radar returns of 20dBZ jumped
to 58dBZ...not too shabby. PWATs remain high and there`s little
change in that regard. Flow around a high situated over Texas
continues to pump in moisture from the south. PWATs hitting 250
to 300% of normal is still in the forecast with models showing
this being 2 to nearly 4 standard deviations above normal. The
deepest moisture is still expected to remain over the southern
half of the forecast area so the Flood Watch will remain in
place. CAPE values as per SPC`s Mesoscale Analysis are forecast
to reach between 1500 to 2000 J/kg from 4PM onwards. The highest
CAPE values currently remain over the San Juans. The stronger
storms will produce some gusty outflow winds, large hail, and
torrential rains that will increase flooding concerns. The 18Z
HRRR guidance is keeping convection in the forecast through this
afternoon and evening and continuing for the overnight. Looks
like a second wave will move through around 9PM and though convection
will die down, some, lightning, gusty winds, and the continued
threat of heavy rain will continue.

Monday morning, some lingering, moderate to occasionally heavy,
showers will be found across the higher terrain of the southern
portion of the CWA. By noon, another round of showers and storms
begins...rinse and repeat. One would think the residual clouds
would inhibit convection but forecast CAPE for tomorrow varies
from 500 to 1500 J/kg while midlevel lapse rates will reach 7 to
9C/km. Yep, there`s plenty of instability that will get worked
on as an upper level trough moves through. Furthermore, a weak
jet streak will also be moving overhead bringing some upper
level divergence that will also aid in lift. All that being
said, look for very similar conditions tomorrow as we`ll see
today.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 119 PM MDT Sun Jun 30 2024

The upper level trough exits the region on Tuesday with dry
northwesterly flow in its wake. This will serve to shunt
monsoonal moisture south and eastward, effectively turning down
the tap we`ve been drinking from the last week. This will spell
out dry conditions over the western half of the CWA, but remnant
moisture hanging on along the terrain will likely get worked on
another day Tuesday for some afternoon showers and
thunderstorms. Temperatures will remain on the mild side behind
this pseudo- frontal passage Tuesday, with only our desert
valleys hitting 90`s. Temperatures quickly surge back upward
Wednesday, as the passing wave flattens into a zonal regime
thanks to a strong northwesterly jet digging into the PACNW.
This will find us in a bit of an ambivalent flow pattern with a
southwest lean to it. Desert valleys will again flirt with
triple digits, both Wednesday and Thursday. The broad cyclonic
flow to our north finally exits Thursday afternoon and northwest
flow returns another downturn in temperatures as well as more
dry air. The drying trend from Wednesday onward proposes some
uncertainty into precipitation forecasts. While shower and storm
coverage will be notably less, it remains risky to commit to a
dry forecast. For now, we`ll stick with isolated showers on the
terrain through the end of the week. The dry surface conditions
in the northwesterly regime should allow for some gusty outflow
winds under collapsing storms. This drying trend continues
through the weekend thanks to an amplifying ridge over the West.
The return of warm, dry conditions will once again turn our
attention back to fire weather late week as well. Wednesday and
Thursday look like the best bets for winds and relative
humidities to coincide for critical fire weather. While RH
values will be there, winds still look pretty marginal. The
arrival of the Fourth of July holiday and return of a dry
pattern after a very wet period will warrant some vigilance.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1141 AM MDT Sun Jun 30 2024

Ample moisture will lead to widespread shower and thunderstorm
activity this afternoon and into Monday morning for the region.
As previously discussed, the best chances for little to no
rainfall remain in the northwest corner of the CWA, where a
sharp moisture gradient exists. Southward, chances for heavy
rainfall get better closer to the subtropical moisture plume
feeding northeastward across the Four Corners. Heavy showers,
small hail, and gusty winds will pose threats to aviation
operations. TEMPO IFR/MVFR conditions are likely at most
terminals. Shower and thunderstorm activity will diminish some
after dark, but low ceilings and stratiform rain will then
become the problem for terminals into the latter hours of this
TAF period.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...TGR
LONG TERM...LTB
AVIATION...TGJT