092
FXUS65 KGJT 140528
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1128 PM MDT Tue Aug 13 2024

.KEY MESSAGES...

- Numerous showers and scattered thunderstorms continue today
  with coverage decreasing tomorrow. Gusty outflow winds, small
  hail, and frequent lightning are possible.

- Heavy rain rates with storms will bring an enhanced threat of
  flash flooding and debris flows today. Saturated soils and
  steep terrain will be most susceptible to flooding.

- Only isolated mountain storms are expected Thursday and Friday
  with dry weather elsewhere. Moisture begins to increase late
  this weekend.

- Temperatures will remain near to several degrees below normal
  before beginning to rebound.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 245 PM MDT Tue Aug 13 2024

This morning`s cloud cover and lingering showers did the trick,
with a large swath of light to moderate rain continuing to lift
into northwest Colorado. This has helped dampen instability this
afternoon, with only scattered thunderstorms thus far as MUCAPE
maxes out between 500 and 1000 J/kg. Any stronger cells today
have been pretty shallow, indicating heavy rain rather than the
threat of gusty winds or hail. The potential for more than rain
will still be there through the evening as additional storms
begin to fire in the wake of this morning`s activity. CAM models
have initiated fairly well given the active morning, with these
latest cells joining with a cluster of showers and embedded
storms moving into northeast and east-central Utah later this
evening. From sunset onwards this activity will push through
western Colorado before gradually washing out near the Divide
around midnight as the accompanying shortwave aloft exits the
forecast area. While some additional light showers may linger
overnight, mostly dry weather is expected to prevail with the
loss of daytime heating and with the departure of the wave.
Based on how the day has unfolded, confidence has increased that
the potential for flooding and / or debris flows will be more
localized rather than widespread, so opted to not issue any
flood watches with this afternoon`s package. Additionally, lift
provided by the shortwave has resulted in some quicker storm
motion. All the same, be sure to stay tuned this evening for any
short-duration flood advisories or warnings.

A downturn in convection is expected on Wednesday as flow aloft
shifts to the west, advecting drier air into the region. PWATs
on Wednesday afternoon are projected to drop to around 80% of
normal south of I-70 while the northern tier of the forecast
area sits right around normal. The main trough tracking through
the Intermountain West will finally swing east into the Northern
Great Plains on Wednesday. Its base and accompanying 70 to 80
kt jet will skirt the north and, since this will be where the
better moisture resides, the majority of storms will be focused
here. We should see a bit more wind than heavy rain with storms
as the deeper moisture gradually erodes but, regardless, can`t
rule out small hail and brief heavy rain with any convection. A
transitory ridge begins to build on Wednesday night so quiet,
and slightly cooler, conditions can be expected.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 245 PM MDT Tue Aug 13 2024

Desert Southwest high shifts across Arizona and New Mexico on
Thursday, which drapes the ridge axis across the CWA. In addition, a
shortwave rolling atop the ridge will support a southerly drift of a
70-80 kt upper level jet across the northern half of the forecast
area. With dry air mixing in under the ridge, our moisture source
feeding afternoon convection dwindles. Thus, despite support aloft,
afternoon thunderstorms will have much less moisture to feed off of.
Higher terrain across the Unitas and Elkhead/Park Ranges have a
better chance of seeing isolated to scattered storms by the
afternoon/evening. Elsewhere, dry and warming conditions prevail.
Temperatures follow suit, warming through the end of the week. Highs
are projected to climb back above normal by Friday, thanks to the
warmer and dry air mass.

The center of high pressure will continue to nudge east into the
weekend, pushing far enough east to allow eastern AZ and central UT
to fall back under a plume of tropical mositure on Saturday. The
western edge of the CWA appears to fall right along the moisture
gradient, so confidence is low for how much measurable precipitation
will be able to work its way to the surface for our four eastern UT
counties. Nonetheless, the positioning of said high will, at least,
open the gates to recycling tropical moisture around the ridge.
Thus, recycled moisture and/or the monsoon plume sliding overhead
would allude to increasing PoPs though the end of the weekend.

From Monday onward, a Rex Blocking pattern is looking like a
plausible solution, such that, high pressure will be blocked over
the Desert Southwest/Southern Plains for several days. As subtle
waves roll over the top of the ridge, we`ll see some wobble in the
high`s center. These shifts will dictate how much (or if at all) the
CWA falls under the monsoon plume. If the ridge remains offset to
our east, the Western Slope will be more or less trapped under a
southwest regime, maintaining near to slightly above normal
temperatures and precipitation for several days.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1123 PM MDT Tue Aug 13 2024

An area of stronger showers and storms will work through the
central mountains over the next hour or two, bringing reduced
visibility, brief heavy rain, and lightning to KASE, KEGE, and
KGUC. Skies are clearing behind this area of convection.
Scattered showers across the north will bring occasional periods
of light rain to KVEL and KHDN over the next 2-4 hours as well.
Another stronger area of convection is tracking along the CO/NM
border, bringing light to moderate rain and lightning to KCEZ
and KDRO. This area is showing signs of weakening though, and
like the more northerly area, clear skies are building in behind
this area. Winds will remain generally light and terrain driven
over the next 24 hours, although afternoon gusts of 20-25 knots
will be likely, and gusty, erratic winds are possible around
storms. Afternoon convection will be focused across the north
tomorrow, as well as over the higher terrain. VFR conditions
will prevail.

&&

.HYDROLOGY...
Issued at 245 PM MDT Tue Aug 13 2024

Monsoonal moisture will keep showers and thunderstorms over the
region through tomorrow with rainfall rates of 1 to 2 inches
per hour possible with storms. This morning`s cloud cover has
largely limited the intensity of convection thus far, so the
potential for flooding and debris flows remains localized. All
the same, be sure to stay tuned to the latest forecast for any
flood highlights. Flooding potential decreases on Wednesday as
dry air begins to advect into the region, though it`s still
possible. Only isolated showers and storms are expected over the
higher terrain Thursday and Friday with heavy rain becoming less
likely.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...MMS
LONG TERM...ERW
AVIATION...TGJT
HYDROLOGY...TGJT