633
FXUS65 KGJT 122339
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
539 PM MDT Sun May 12 2024

.KEY MESSAGES...

- Showers and thunderstorms, favoring the northern valleys and
  mountains along the Divide, will continue this afternoon and
  again, tomorrow.

- A disturbance will bring more widespread showers and storms
  Tuesday and Wednesday, then favoring the San Juans on
  Thursday.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 155 PM MDT Sun May 12 2024

The area of low pressure that brought the rain, storms, and
mountain snow has shifted to the Plains where the precip
continues. In our neck of the woods, plenty of mid to upper
level instability remains in the atmosphere as indicated by some
steeper lapse rates and widespread CAPE values around 300 to
600 J/kg. This instability has been realized as radar is showing
plenty of convective cells across the area, favoring the
northern valleys. Cyclonic flow around the low is causing these
cells to move almost directly from north to south. A few
lightning strikes have been noted under the stronger cells and
that will be the biggest concern along with some gusty winds of
35 to 45 mph. Heading towards the evening hours, the atmosphere
will return to more stable conditions as convection ends. A few
clouds will persist as temps drop to the usual mid May values.

For tomorrow, another day of convection but coverage should be
somewhat less than seen today. Forecast Skew-Ts are showing
shallow inverted V profiles so we should see some virga and the
occasional gusty outflow. Cumulus clouds will be common over the
higher peaks as the afternoon wears on. Flow will become more
zonal allowing daytime highs to slowly start increasing. Highs
will be about 4 to 6 degrees warmer than those seen today.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 155 PM MDT Sun May 12 2024

Zonal flow will kick off the long term period as a trough of low
pressure quickly pushes across the Northern Rockies on Tuesday.
Moisture will increase in earnest across the forecast area as the
trough`s axis dives farther south with PWATs jumping to 150 to 200
percent of normal by Tuesday afternoon. Even with the better broad
scale ascent remaining well to our north, the abundance of moisture
paired with daytime heating will result in numerous showers and
storms on Tuesday. We`re not out of the woods yet when it comes to
mountain snow but, with 700mb temperatures remaining in the 4 to 8
degree C range over the higher terrain, snow levels will generally
be above 11kft. Convection could drive these levels locally lower
but little impact or accumulation is expected. The trough undergoes
a bit of a split as the northern wave`s axis slides across the north
on Wednesday while the southerly feature hang back over southeast
Utah and southwest Colorado into Wednesday night. So, after a brief
downturn in shower activity Tuesday night with the loss of daytime
heating, thunderstorms will redevelop for Wednesday with scattered
to numerous coverage expected. An additional couple inches of snow
will fall along the higher terrain favoring the southern and central
Colorado mountains with wetting rain likely elsewhere into Wednesday
evening.

Confidence is lacking going into the latter half of the work week as
there are some discrepancies regarding if the trough exits by
Thursday. Guidance does favor a strong ridge of high pressure
building off the West Coast which would help usher the trough out of
the region. As a result, a shift towards drier weather is favored at
this time, though residual moisture paired with orographics would
lead to daily showers and storms over the higher terrain each
afternoon. Another large trough develops upstream towards the end of
the long term but it`s too early to get excited about such things.

Temperatures will be a grab bag through the long term as various
systems approach and move across the area. Tuesday`s highs will
trend well above normal before dropping back down to slightly below
normal before values become unseasonably warm once more by Friday.
Overnight lows will generally be mild for mid May through the
period.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 539 PM MDT Sun May 12 2024

Scattered showers and thunderstorms will continue this evening
and remain in the vicinity of most northern and central TAF
sites through 03Z. Storms will be capable of producing brief
MVFR conditions in addition to gusty outflow winds of 35 to 45
kts. Activity diminishes tonight as weak ridging slides over-
head with CIGS remaining above ILS breakpoints into Monday
morning. Another round of scattered thunderstorms will develop
after 18Z Monday, favoring the higher terrain along the Divide.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...TGR
LONG TERM...MMS
AVIATION...TGJT