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000
FXUS65 KGJT 272335
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
535 PM MDT Sat Apr 27 2024

.KEY MESSAGES...

- Showers and isolated thunderstorms continue this afternoon and
  evening with another round expected on Sunday.

- Additional mountain snow through tonight can leave high
  mountain passes snow-covered and slick. Winter Weather
  Advisories remain in effect through 6 AM MDT Sunday.

- Drier and warmer weather returns next week, but additional
  disturbances can bring more showers across the northern tier.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 332 PM MDT Sat Apr 27 2024

GOES-East water vapor imagery shows a large sprawling closed
mid-level low pressure system spinning over the Four Corners
this afternoon. Underneath the low, plenty of clouds and
widespread showers with counter-clockwise large scale motion are
being observed across eastern Utah and western Colorado via
visible/IR satellite and the KGJX WSR-88D, respectively. As
expected, the clouds and showers have largely kept surface based
instability to a minimum with temperatures several degrees
below normal. The only exceptions to that are across the fringes
of the CWA in extreme northwest Colorado, northeast Utah,
southeast Utah, and southwest Colorado where less clouds and
more sun have resulted in a bit more instability.
Unsurprisingly, it`s those locations that will be favored for
any stronger shower or thunderstorm activity this afternoon and
evening. In fact, we`re already seeing several lightning strikes
in northeast Utah near Vernal where storms have tapped into the
higher instability. With those stronger cores, gusty outflow
winds and small hail are a possibility in addition to the
lightning threat. Elsewhere, light and intermittent stratiform
showers will be the rule, with plain rain falling below 7000 to
8000 feet and snow falling above. In terms of accumulating snow,
that will mainly be confined to above 9000 feet, primarily in
the eastern Uintas and along the Continental Divide mountains
where Winter Weather Advisories remain in effect. Latest webcams
reveal roads that are largely free of snow, which makes sense
given the time of day and time of year. That being said, high
mountain passes could become snow-covered and slick again
towards and after sunset with the loss of daytime heating and
any additional snow that falls. Winter Weather Advisories will
expire at 12Z Sunday morning as our storm system lifts out to
the north and east. Most showers will diminish by late tonight,
but a few could linger into the morning hours on Sunday.

In the wake of today`s system, a weak trailing shortwave
embedded within northwesterly flow will interact with residual
moisture and daytime heating to kick off another round of
showers and possibly a few storms late Sunday morning into
Sunday afternoon. This wave will be battling dry air advection
and a lack of large scale forcing for ascent, so showers won`t
be quite as numerous as the last few days. Most showers will be
tied to the terrain with the aid of orographic lift, but some
showers may drift off into the lower adjacent valleys. QPF will
mostly be light and add up to around a tenth of an inch... a bit
more or a bit less depending on elevation. Given a smaller
footprint of showers, expect less clouds, and a little more sun,
allowing for temperatures to bump back up closer to seasonal
norms. With the loss of daytime heating, showers are expected to
diminish fairly rapidly after sunset, giving way to a drier and
warmer day to start the work week on Monday.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 332 PM MDT Sat Apr 27 2024

Flow becomes zonal on Monday as this weekend`s storm moves to
the Upper Midwest, forced east by a mid-level short wave trough
ejected from a closed low off the coast of British Columbia. The
regional airmass will be largely drier in the westerlies
promising quiet weather Monday morning while temperatures climb
several degrees above normal during the day. However, model
consensus indicated the potential for convective showers over
the northern mountains in the afternoon as modest moisture
moving ahead of the previously mentioned short wave filters in
throughout the day.

The short wave trough moves eastward Monday night driving a
cold front across the northern half of the forecast area.
Meanwhile, moisture and lift along and north of the front is
expected to bring another round of precipitation to the northern
mountains and northwest Colorado plateau with a chance for
showers over the central Colorado mountains and the eastern
Uinta Mountains. A bit of a lull in activity is expected Tuesday
as flow again becomes zonal in the wake of the disturbance,
though scattered instability showers are possible, mainly over
the Elkhead, Park and Flat Top Mountains. Despite the passage of
the cold front, temperatures are expected to be near, or only a
few degrees cooler than on Monday across northeast Utah and
northwest Colorado and a few degrees warmer along the I-70
corridor and south.

On Wednesday, models were in good agreement showing a positive
tilt trough moving over the Intermountain West and Great Basin
causing flow aloft to shift to the southwest. As this plays out,
moisture ahead of the trough overruns the stalled front over
the northern portion of the forecast area resulting in a good
chance for showers, especially for the northern and central
mountains of Colorado. Meanwhile, a tightening of the pressure
gradient ahead of the approaching disturbance will bring breezy
conditions to the northern zones Wednesday afternoon and
evening. Cloud cover and showers should bring a few additional
degrees of cooling to the north while areas to the south can
expect little change in temperature and little chance for
precipitation.

The forecast is less clear for the remainder of the week as the
ECMWF slows the eastward progress of the mid-level trough as
compared to the Canadian and GFS solutions which were more
progressive. The latter two models suggested little chance for
additional showers Thursday and Friday while the ECMWF depicted
active weather Thursday and Thursday night and lingering Friday
with the north again favored. Model blends indicated chance
precipitation for the Continental Divide, and particularly for
the northern Colorado mountains Thursday and Friday and this
seemed to be the appropriate forecast for now. Given trough
passage sometime at the end of the week it stands to reason
Thursday, and to a lesser extent Friday, will be cooler.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 529 PM MDT Sat Apr 27 2024

Rain and mountain snow showers continue to impact all
terminals. Some thunder has occurred this afternoon, but hasn`t
had much impact and is diminishing at this hour. KASE, KEGE, and
KRIL are expected to remain below ILS breakpoints through the
next 12 hours, with improvement expected after 12z tomorrow
morning. For lower elevation terminals, VFR conditions will
prevail, with drops to MVFR/IFR conditions likely as showers
pass overhead. Higher elevation terminals will see VFR/MVFR
conditions prevail with drops to IFR/LIFR expected. Most
terminals will also see conditions drop below ILS breakpoints
occasionally with passing showers. Winds will be gusty and
erratic with passing showers.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 6 AM MDT Sunday for COZ004-009-
     010-012-013-018-019.
UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ023.

&&

$$

SHORT TERM...MDM
LONG TERM...NL
AVIATION...TGJT