881
FXUS65 KGJT 141138
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
538 AM MDT Wed Aug 14 2024

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms will occur
  today mainly for areas along and north of I-70 as coverage
  begins to decrease with drier air moving in from the west.
  Gusty outflow winds, small hail, and frequent lightning are
  possible in addition to brief moderate to heavy rain.

- Flooding threat will be reduced today given the drier air mass
  moving in, but still remains possible, especially with heavier
  rain rates in any stronger storms and in case of training.
  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 a few degrees below normal today
  before beginning to rebound towards near and slightly above
  normal levels late this week into the weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 354 AM MDT Wed Aug 14 2024

Isolated to scattered showers are continuing across the north
early this morning behind yesterday evening`s shortwave trough.
Drier air is beginning to work into the area from the west as
skies are starting to clear out south of I-70. Even though drier
air is beginning to advect in from the west, scattered to
numerous showers and thunderstorms are expected to favor areas
along and north of I-70 as the Pacific Northwest trough moves
east across the Northern Rockies today. A 95 kt jet streak will
accompany this trough passage as it lays across the northern
areas, providing ample forcing for ascent for convection. We
could see some stronger storms given the clash between the
remnant moisture and incoming dry air as it tries to push this
moisture out of the region, with more sun resulting in more
surface heating to fuel the instability and act on the moisture
in place. Some shear also will remain present across the north.
So, storms today will be capable of strong gusty winds, small
hail and frequent lightning in addition to brief moderate to
heavy rain. SPC does have portions of northeast Utah and
northwest Colorado, mainly north of I-70, under a marginal risk
for severe storms, mainly due to the strong wind threat. Storm
coverage will be noticably less for areas south of I-70 though
as this drier air pushes in and this area is not in the favored
area for ascent and forcing.

Regarding the flooding threat, it will be reduced today given
the drier airmass advecting in as well as reduced storm
coverage. However, given the saturated soils from the last few
days, especially yesterday, any storms that form will be capable
of heavy rain rates where this moisture remains and if any
storms exhibit training, this could lead to localized flooding
especially in areas of steep terrain. So, something to keep an
eye on today but it doesn`t appear widespread enough to warrant
any Flood Watches. It is still important to remain vigilant and
up to date on the latest developments as some storms could be
stronger today given more surface heating to act on this
moisture. CAPE values will range from 500 to 1000 J/kg along and
north of I-70 with much less instability across southeast Utah
and southwest Colorado. Mixing ratios also will be lower than
yesterday but still in a modest 6 to 7 g/kg mainly across the
northern and central areas with drier air at the mid levels
across the south. Instability appears to peak late this morning
into the early afternoon before stabilizing by this evening, but
early morning showers and cloud cover across the north could
result in a later start. Hi-res CAMs appear to favor convective
initiation between 1 pm and 2 pm MDT with a reduction in storm
coverage shortly after sunset, so the overnight period tonight
is looking a bit quieter for once.

Drier air mass will be fully entrenched across the area by
Thursday with high pressure expanding to our south over Arizona
and New Mexico and stretching across the Desert Southwest as
most of the moisture exits to the east. The jet lifts north of
the region so expect a sharp reduction in storm potential and
coverage on Thursday. Only isolated storms remain possible
Thursday afternoon over the high terrain, mainly across the
north where the better forcing and moisture remains but overall,
not anticipating much with mostly sunny skies across the
region. Temperatures will be a few degrees below normal today
but warmer than yesterday given more sunshine. We will see
temperatures moderate to near normal by Thursday as this drier
air mass takes over for the latter half of the week.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 354 AM MDT Wed Aug 14 2024

With limited moisture in place by Thursday night and high
pressure in control, afternoon convection will begin to taper
off not long after sunset and a generally quiet night should
follow. These dry conditions will continue through Friday and
into Saturday as the subtropical high remains centered directly
to our south and eastern Utah and western Colorado remain cutoff
from the monsoonal moisture plume. That said, waves passing
through the flow around the high and a 60-70 knot jet to our
north will provide enough dynamic support to see a few isolated
to widely scattered showers or thunderstorms Friday afternoon.
Areas north of I-70, particularly the higher terrain, will be
most favored. The increased sunshine and decreased moisture
during this period will also result in near to a few degrees
above normal temperatures across the majority of the forecast
area.

By Saturday afternoon, the center of the high will have shifted
east of the Divide, allowing flow to turn southwesterly across
Arizona and Utah, dragging up some deep monsoonal moisture. The
edge of this plume is forecast to be over eastern Utah, where
some increased showers or thunderstorms will be possible during
the afternoon and evening hours. After a few days of dry
conditions, it`s likely that the main threats with these storms
will be gusty outflow winds and lightning, rather than heavy
rain, although a brief heavy downpour is not out of the
question. As we move into the coming work week, we remain in a
blocky, amplified pattern, with high pressure dominating the
center of the country. Under this scenario, our sensible weather
relies on where exactly the center of the high sets up on a
day-by-day basis. A bit to the east, and the entire Western
Slope winds up under the moisture plume. A bit to the west, and
the moisture plume sets up over western Utah and we see sunny
skies. Passing waves in the flow around the high will also have
a hand in how widespread showers and thunderstorms are on any
given day. As of now, deterministic and ensemble model guidance
does keep above normal moisture in the area, with blended
guidance reflecting this with higher PoPs through early next
week. Temperatures look to remain near to a few degrees above
normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 538 AM MDT Wed Aug 14 2024

Light rain showers will continue across the north through 14Z or
so with VCSH across KVEL and KHDN, possibly KRIL. Elsewhere,
clearing skies are evident with potential clearing behind these
showers across the north after sunrise. Expect redevelopment of
showers and thunderstorms mainly along and north of I-70, with
VCTS more probable at KVEL, KHDN, KRIL, KEGE as well as higher
terrain sites like KASE and KTEX this afternoon into the early
evening. Elsewhere, mostly to partly sunny skies remain with
drier conditions expected. VFR will prevail with brief MVFR or
ILS conditions in any storms (mainly across the north) with
strong gusty winds and brief heavy rain possible. Showers come
to an end and skies should clear shortly after sunset.

&&

.HYDROLOGY...
Issued at 354 AM MDT Wed Aug 14 2024

Monsoonal moisture will keep showers and thunderstorms over the
region today mainly focused on areas along and north of I-70
with rainfall rates of 1 to 2 inches per hour possible with
storms. Flooding potential decreases today as dry air begins to
advect into the region, though it`s still possible given the
remnant moisture and forcing. 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...MDA
LONG TERM...BGB
AVIATION...MDA
HYDROLOGY...TGJT