414
FXUS65 KGJT 252103
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
303 PM MDT Tue Jun 25 2024

.KEY MESSAGES...

- Isolated showers and storms thrive for another evening, before
  the mid-week moisture surge returns...

- Showers become widespread Wednesday/Wednesday night thanks to
  a plume of deep subtropical moisture.

- Flooding and Flash Flood potential ramps up during this
  anomalously moist period.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 300 PM MDT Tue Jun 25 2024

Like clockwork, storms are firing off high terrain, feeding off
abnormally moist atmospheric conditions. Despite PWAT anomalies
running over 150%, this morning`s inverted V sounding suggests
high based storms this afternoon with potential for some
impressive outflow winds (i.e. in excess of 50 mph). In
addition, current mesoanalyses indicate DCAPE contours over
1500 J/kg for much of the Western Slope, also supporting strong
downward momentum and thus, strong surface winds. While small
hail is still possible, heavy rainfall and training storms favor
flooding and flash flooding threats, too, rather than severe
hail.

Satellite imagery already illustrates the plume of deep
subtropical mositure creeping back into the southwest corner of
the forecast area. Said progression will only continue
overnight, thanks to the PacNW low nudging inland and pushing
the broad ridge of high pressure eastward. By Wednesday morning,
moisture content is progged to run in excess of 200% of normal,
peaking around 250% of normal by Wednesday night. Surplus
moisture will support orographic showers Wednesday morning;
however, perturbations rippling along synoptic flow will boost
lifting mechanisms and may support longer lasting thunderstorms
Wednesday afternoon. WPC has eastern Utah and western Colorado
under a marginal risk for excessive rainfall, which favors the
potential for flash flooding across the Western Slope. One
caveat, though, may be the longevity of those early morning
showers and whether or not we see lingering cloud cover. If
clouds do hold, surface temperatures will be hindered, as well
as instability for storms to feed off of. Thus, in this case,
widespread showers are still possible, but storm intensities
decrease, resulting in a dampened threat for flash flooding. I
have held off on any flood watch highlights for tomorrow due to
said uncertainty.

Regardless, winds ramp up aloft Wednesday night into Thursday as
pressure gradients are squeezed between the broad trough to the
northwest and ridge (now) to the southeast. Jet dynamics and the
approaching trough may support more organized convection by
Thursday afternoon. We don`t see too many days with defined
helicity swaths draped across the CWA. That, along with CAPE
values ranging from 1500 to 2000 J/kg, suggest strong
thunderstorm development, especially along a frontal boundary
dipping in from the northwest Thursday evening. A Flash Flood
Watch may be warranted for Thursday`s convection, so stay tuned
as high resolution guidance trickles in. Thursday looks like the
most active day this week, and best potential for severe
thunderstorms, so stay tuned for updated watches and warnings.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 300 PM MDT Tue Jun 25 2024

The trough responsible for providing an extra punch of synoptic lift
on Thursday pushes off to the east Friday morning. This will help
scatter out some of the remaining convection, but the northern half
of the forecast area will likely see continued convection through
Friday evening (45-75% chance) with pulses of shortwave energy
continue to advect through the mid-level flow. Even though the
forcing becomes less organized after Thursday night, PWAT values
remain elevated at 120-200% of normal until early next week. Daytime
heating and orographic lift will lead to scattered showers and
storms in the high terrain each afternoon/evening, with coverage
increasing on Sunday evening as more moisture surges into the
region. Recent model runs are trending towards stronger moisture
advection (especially the GEFS) so we will have to keep an eye on
this period in the coming days. Otherwise expect seasonal
temperatures with some fluctuations depending on cloud cover and
coverage of precipitation.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1058 AM MDT Tue Jun 25 2024

VFR conditions are forecast through the TAF period with light
westerly breezes today. Isolated to scattered showers and
thunderstorms will develop over the higher terrain this
afternoon with brief periods of MVFR near the storms. Winds
become light drainage winds this evening as the showers die
down.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...ERW
LONG TERM...KAA
AVIATION...TGJT