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313
FXUS65 KGJT 241136
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
536 AM MDT Mon Jun 24 2024

.KEY MESSAGES...

- A rinse and repeat pattern will continue this week, with
  temperatures 5-10 degrees above normal and afternoon mainly
  afternoon/evening showers and thunderstorms over higher
  terrain.

- A push of deep subtropical moisture is expected to move in at
  mid week, bringing a return to widespread thunderstorms with
  an increasing flash flood threat. Drying will follow for the
  weekend.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 414 AM MDT Mon Jun 24 2024

Showers and thunderstorms have dissipated over the forecast area
in the early morning hours. However, a disturbance moving
through the northern Wasatch has caused showers and a few
thunderstorms to redevelop. It`s unclear at this point whether
this activity will hold together as the disturbance pushes
across the Green River toward sunrise.

Precipitable water (PW) in the 00Z/Mon sounding at KGJT dipped
to 0.67" from 0.94" Sunday morning finally bringing the drying
models had been touting over the past several runs. HREF
indicated that PW will remain largely unchanged today and
Tuesday as the broad area of high pressure stretching from the
Gulf States to southern California will inhibit moisture from
infiltrating the area early this week. Consequently, isolated to
scattered showers and thunderstorms are expected from late
morning through early evening today and Tuesday, mainly
impacting higher terrain. Reduced moisture in the column limits
the potential for heavy rain while drying in the subcloud layer
shifts storm characteristics toward stronger downbursts/outflow
winds. Meanwhile, increased solar insolation will result in
increased temperatures today with even warmer highs on Tuesday.
Diurnal cooling in the absence of upward forcing tonight will
cause moist convection to dissipate early this evening.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
-- Changed Discussion --
Issued at 414 AM MDT Mon Jun 24 2024

With the high pressure having moved a bit northward over
Colorado, the weak circulation around the high begins pulling
the deep moisture over southern Arizona north into Utah and
northern Colorado with IVT`s of 414-300 kg/m/s Tuesday night
into Wednesday peaking around 500 kg/m/s Wednesday night into
Thursday. With the weak flow around the high, this would say
that there must be a lot of water in this stream, hence pwat`s
jump back to over an inch Wednesday peaking at about 1.5 inches
early Thursday. Look for widely scattered showers and
thunderstorms initiating late Wednesday morning becoming
widespread through the afternoon. CAPE looks to run 500 to 1000
J/kg indicating deep convection with possible isolated large
hail. With the weak flow aloft, flash flooding concerns across
the region return with slow moving/training showers and
thunderstorms through the afternoon and overnight Wednesday.

At the same time, the deep cold low that has been spinning off
the Pacific Northwest Coast finally moves inland to track
across Montana and the Dakotas late Thursday into Friday with
the trough brushing the northern boundary of eastern Utah and
Western Colorado. With the pressure gradient increasing aloft,
look for increased shear generally along and north of the I-70
corridor Thursday afternoon and evening spawning the potential
for severe thunderstorms across the northern areas with large
hail, damaging winds the primary threats. It`s really too soon
to make the call, but this is something to watch. Can`t rule out
this area of severe weather spreading south into the central
areas overnight.

Models were showing a dryline pushing through early Friday
sweeping the moisture out of the region, but don`t show a
thermal gradient/cool front one would expect with this boundary.
Likely this is just the models wanting to dry out the region
like they`ve been doing the past couple weeks. More probable,
the moisture will linger with scattered afternoon and evening
showers and thunderstorms Friday through the weekend. With the
heavy cloud cover limiting diurnal heating, temperatures will
fall to near normal to a little below normal Thursday and
Friday. As the skies clear out over the weekend, temperatures
climbing back to five to ten degrees above normal by Sunday.

The question on everyones mind is whether this weather has
anything to do with "the M-word." Some are asking if we`ve
been in it now for a week or so since we have had tropical
moisture move up, but it`s been blamed on remnants of a tropical
storm and not "the M-word." Models show the high pressure
setting up strong over Texas and troughing/low pressure off
Baja, which looks like... Well, if it walks like a duck and
talks like a duck...
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&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
-- Changed Discussion --
Issued at 536 AM MDT Mon Jun 24 2024

Scattered showers and thunderstorms redevelop over higher
terrain late this morning and will continue through early
evening. The main threat from this activity to TAF sites across
eastern Utah and western Colorado is gusty outflow winds.
Otherwise, VFR conditions will persist through the next 24
hours.
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&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...NL
LONG TERM...DB
AVIATION...NL