277
FXUS65 KGJT 150838
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
238 AM MDT Wed May 15 2024

.KEY MESSAGES...

- Scattered to widespread showers and thunderstorms are expected
  again this afternoon, with gusty outflows, brief heavy rain,
  and small hail the main threats.

- Drier and warmer conditions move in for tomorrow onward, with
  temperatures running around 5 degrees above normal.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 237 AM MDT Wed May 15 2024

The few light showers lingering over the Continental Divide and into
southeast Utah will slowly dissipate as we head toward daybreak this
morning as the shortwave driving this activity shifts to the east.
Behind this wave, some drier air and weak subsidence are trying to
push in, leading to clearing skies across northeast Utah and
portions of northwest Colorado. The next wave will round the base of
the trough around midday, providing some modest dynamic forcing, in
addition to orographic lift and diurnal heating. The question is,
will the drying this morning put a bit of a damper on storm coverage
this afternoon? Models seem to think so, with forecast PoPs really
keeping activity confined to the higher terrain along the Divide.
Although, models do have a habit of drying things out far quicker
than reality, leading to underdone precipitation. That may indeed be
the case today, with activity winding up more widespread that
current guidance would lead us to believe. The best coverage will
likely still be along the Divide, where the best moisture and lift
will be located. But other usual spots for storm genesis, such as
along the Bookcliffs, will likely spawn a shower or two this
afternoon. These showers and storms will be capable of producing
gusty outflow winds, brief heavy rain, small hail, and lightning.


As this trough is moving overhead, the cutoff low that has been
lingering over SoCal will finally begin shifting east. Model
guidance has this cutoff finally phasing with the northern stream
low this evening, leading to a shift in storm focus to the southern
mountains through about midnight tonight, after which activity will
slowly begin to taper off. This now elongated trough of low pressure
will finally shift east of the Divide tomorrow morning, with ridging
and much drier air building in across the northern half of the area.
Moisture will linger longest over the San Juans, although some may
sneak up into the central mountains as well. Daytime heating will
act on this moisture to produce some isolated to widely scattered
showers and thunderstorms tomorrow afternoon, with the usual threats
of gusty winds and brief heavy rain once again anticipated.

Temperatures today will be near normal as some slightly cooler air
is advected in, along with showers and clouds. Temperatures return
to around 5 degrees above normal tomorrow under warm air advection
and clearing skies, with the exception of the southern and central
mountains, which will be a bit cooler.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 237 AM MDT Wed May 15 2024

The high latitudes will once again fold southward into the mid
latitudes as we end out the week with a strong trough arriving to
the N.Rockies by early Friday...shoving the ridge back into the
Pacific. This is a trend that will continue well through this
forecast period and beyond. The CPC outlooks reflect this with
better probability of below normal temperatures across much of the
West over the next 6 to 10 days. The bulk of the stronger QG forcing
remains well to North initially with the cyclonically curved jet
only dropping into central Wyoming. However moisture transport
vectors show Pacific moisture being pulled inland on the fringe of
the jet which arrives during peak heating Friday. There is a hint of
a weak frontal boundary being pushed across the northern CWA for low
level forcing and isolated storms will be the result. By Saturday
the Southern stream arrives to the SW CONUS leading to a downstream
confluence of the split flow over the central Rockies region.
Moisture pooling near the above mentioned boundary and the arrival
of the SubTrop jet to the 4 Corners looks to excite the atmosphere
enough for an uptick in afternoon convection Saturday which will
likely linger into the early morning hours on Sunday. As heights
lower to the West and the split flow pattern merges Southwest flow
increases downstream over our CWA after sunrise on Sunday. This
looks to force in some drier air with the bulk of the thunderstorm
chances lifting to or north of our CWA border with Wyoming. Above
normal temperatures can be expected to persist through the weekend
at least. Models then diverge quite a bit on how the Western trough
absorbs and spits out the high latitude energy with some vast
differences in timing attm. Either way cool and unsettled weather
looks like it will take hold again as we head into next week. This
is probably good news for runoff season with some snow coming off
during the warmer days through the weekend then tapering off next
week. Who knows...depending no how this western trough pattern plays
out we may just add some back before it`s over.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1123 PM MDT Tue May 14 2024

A band of showers and thunderstorms will continue to move across
western Colorado through the early morning hours with little to
no impacts expected besides potential and temporary ILS
conditions. After a quiet morning another round of isolated to
widely scattered storms can be expected by early Wednesday
afternoon. Gusty outflow winds remain the main concern with
these storms. Otherwise VFR prevails the next 24 hours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...BGB
LONG TERM...15
AVIATION...TGJT