308
FXUS65 KGJT 111130
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
530 AM MDT Sat May 11 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms are expected today as a
  system moves through the region. Soaking rains are possible at
  lower elevations, and a few inches of accumulating snow are
  expected above 9500 feet. Little in the way of impacts are
  anticipated.

- An unsettled weather pattern remains in place through the
  coming week, with chances of mountain showers and
  thunderstorms each afternoon. More widespread activity returns
  Tuesday into Wednesday

- A gradual warming trend will bring near normal temperatures
  tomorrow, and above normal temperatures from Monday onward.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 241 AM MDT Sat May 11 2024

The cutoff low pressure that has been dominating our weather the
last few days is finally beginning to nudge eastward. This movement
is pushing a corridor of enhanced moisture ahead of it which,
combined with some little wiggles in the flow, has driven showers
and thunderstorms over the San Juans tonight. These showers are
expected to persist well into the morning, becoming more widespread
as the cutoff low continues its trek east and the main vort max
associated with it moves overhead this afternoon. Until that point,
aside from the clouds and showers over the southern mountains, skies
will remain mostly clear with near-normal to slightly below normal
morning low temperatures.

Moisture remains on the higher side as we move into Saturday, with
last night`s 00z sounding showing a PWAT of 0.49 inches, which is
right around the 75th percentile for PWATs at this date and time.
Expect to see this value continue to rise through the day today as
the low pressure tracks overhead. Diurnal heating and the moisture
already present would be plenty to kick off showers and
thunderstorms over the terrain this afternoon, but with the low
pressure moving overhead and adding in some dynamic support as well,
today will see the highest shower coverage we`ve seen so far. The
southern and central mountains will be favored to see the most
activity, but the majority of eastern Utah and western Colorado will
see at least a passing shower or storm today, along with increasing
cloud cover in the afternoon. These showers will be capable of
producing light to moderate rain rates and even some small hail and
lightning. Snow levels are expected to remain between 9000 feet and
9500 feet today, but strong showers will be able to drive that down
briefly, so while the highest elevations will be the only ones to
see accumulating snow, adjacent high valleys will at least have the
potential to see flakes. Snow amounts have come up just a touch for
the San Juans and into the Elks, West Elks, and Sawatch ranges, with
totals now 3-5 inches, with locally higher amounts in the 6-8 inch
range possible. Even still, impacts will be minimal, with just wet
roads expected over the mountain passes. Activity will once again
linger into the evening and overnight hours tonight, as the low
continues east and just a bit of upper level support remains
overhead. The center of the low moves east of the Divide by
midnight, however, so do expect to see a slow tapering of activity
from midnight through sunrise Sunday. Subsidence will move in behind
the low, keeping things generally dry for much of eastern Utah and
western Colorado on Sunday, with the exception of the Divide, where
the influence of the low will remain longest, along with the best
moisture, keeping isolated to scattered showers and storms in the
forecast through Sunday evening.

Increased cloud cover and shower activity today will keep
temperatures 3-5 degrees below normal for much of eastern Utah and
western Colorado, along with near to slightly above normal low
temperatures. Tomorrow, with clearing skies and subsidence moving
in, temperatures are expected to warm to near or a few degrees above
normal, continuing the gradual warming trend we`ve seen over the
last few days.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 241 AM MDT Sat May 11 2024

Any lingering showers from Sunday afternoons convection looks to
come to an end after sunset for a relatively quiet Sunday night as
that pesky low that is having a stronghold over our weather lately
exits further east into the central Plains. Drier air will slowly
advect in as a ridge of high pressure tries to build over the Great
Basin. This ridge is not overly that strong and quickly gives way to
a series of shortwave troughs moving down from the Intermountain
West into the northern Rockies, keeping the weather pattern active
and unsettled through much of the coming week. These shortwaves will
keep the threat for daily afternoon and evening showers and
thunderstorms in the forecast, focused mostly on the higher terrain
Monday. The peak period of moisture and more widespread convection
looks to hone in on the Tuesday and Wednesday time period as a more
robust trough drops southward on Tuesday with its positively tilted
trough axis swinging through the area from northwest to southeast on
Wednesday. Meanwhile, there is a cut off low over the Desert
Southwest during this period but it appears to become a non player
as it is washed out and absorbed by this trough diving out of the
northwest.

Is it too early to be talking about PWAT (Precipitable Water)?  Of
course not! Moisture levels appear to peak on Tuesday as this
initial surge moves out ahead of the trough passage on Wednesday, as
PWAT anomalies rise to 160 to 200 percent of normal for mid May on
Tuesday afternoon. This equates to PWAT near 0.6 to 0.7 inches,
which is sufficient for some potential heavy rainers. Needless to
say, expect showers and thunderstorms to be more widespread to
numerous Tuesday and Wednesday. Storms may linger into Thursday due
to lingering moisture and forcing from the trough as a cut off low
will remain over Arizona by then, but storms should favor the
central and southern mountains and adjacent valleys. Drier air tries
to push in from the north and west on Friday as a ridge of high
pressure tries to build over the western states and expand into the
PacNW and Intermountain West according to the GFS but the ECMWF
seems to have other ideas on the synoptic pattern. Models are not in
the best agreement on what`s going to happen beyond Tuesday so low
confidence in the forecast beyond mid week.

Talking about temperatures, we will see some decent WAA Monday and
perhaps into Tuesday before the moisture increase results in more
widespread development of showers and storms. High temperatures will
be around 5 or so degrees above normal early this week, cooling down
slightly late Tuesday and Wednesday into Thursday with the trough
passage to near to 5 degrees below normal. If the dry air pushes
back in late this week, we are due to see highs creep back up to
above normal levels.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 527 AM MDT Sat May 11 2024

Showers and thunderstorms are already ongoing across the
southern portions of the area. This activity will continue to
move northward through the morning, with increasing coverage
expected. All terminals can expect to see showers or storms at
least in the vicinity today. Higher terrain terminals, such as
KASE and KTEX, are most likely to see showers directly impact
the terminals. Greatest impacts will be moderate precipitation
lowering ceilings and visibility, as well as lightning and gusty
and erratic winds. Some small hail may also be possible. Shower
activity will taper off after sunset, with skies slowly clearing
and winds becoming light and terrain driven. VFR conditions will
prevail, although passing showers will be capable of briefly
reducing conditions to MVFR or IFR. KASE, KRIL, and KEGE will
flirt with ILS breakpoints when showers are nearby.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...BGB
LONG TERM...MDA
AVIATION...TGJT