860
FXUS65 KGJT 190551
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1151 PM MDT Sat May 18 2024

.KEY MESSAGES...

- Warm and breezy this weekend with temperatures remaining at
  least 5 to 10 degrees above normal.

- Isolated to scattered showers are storms are expected today
  and Sunday. The higher terrain along the Divide will be
  favored with gusty outflow winds and small hail being the
  primary concerns from storms.

- A larger system moves through early next week resulting in
  cooler and wetter conditions. Drier weather looks to return by
  midweek.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 138 PM MDT Sat May 18 2024

A boundary that went through the area yesterday is beginning to lift
back to the north. This is in part due to a shortwave approaching
from the southwest. The wave is getting absorbed into the main flow
therefore it is fairly weak. Although this has caused midlevel
confluence in the vicinity of the boundary, which is where moisture
is pooled. High based showers and a few storms have already formed
across the southern half of the forecast area. This development will
go into the afternoon as surface heating continues and the boundary
lifts northward. Strong outflow winds will be possible with storms
with gusts of 40 to 50 mph likely. Outside of convection today, we
can expect mostly to partly sunny skies with occasional breezy
conditions as 700mb winds remain in the 20 to 25 kt range. Showers
and perhaps a few storms will continue tonight as the weak shortwave
lifts over the northern half of the forecast area. Not much rainfall
or snowfall is expected with the showers today or tonight. The
boundary will stall across northeast UT and northwest CO
tomorrow as the main trough deepens down the coast. This will
result in showers and storms through out the day mainly along
and north of the I-70. South of that dry air will inhibit any
instability so do not expect any convection there. The wave that
moves through tonight looks to steepen the lapse rates, which
should result in a bit more instability. So some storms tomorrow
may be capable of small hail.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 138 PM MDT Sat May 18 2024

The southwest gradient will tighten on Monday ahead of a trough
dropping southward into the Great Basin from the Intermountain West.
H7 winds out ahead of it increase to 35 kts with H5 winds up to 60
kts. A 120 kt subtropical jet sets up over the Four Corners region,
stretching up through southeast Utah and southwest to west-central
Colorado. Wind gusts of 30 to 45 mph are possible Monday afternoon.
Due to influence from the subtropical jet, deep mixing is expected
with any shower activity confined mostly to northeast Utah and
northwest Colorado as a frontal boundary remains stalled over that
area. Temperatures will remain cooler across the north due to
increased coverage of clouds and showers and due to the stalled
frontal boundary. However, along and south of I-70, temperatures
will remain warm averaging 5 degrees above normal.

The aforementioned trough will drop through the area Monday night
into Tuesday, bringing increasing coverage of showers as well as
much cooler temperatures, with highs on Tuesday falling to as much
as 10 to 15 degrees below normal. The extent of this trough seems to
reach as far south as the San Juans, with a much lesser chance of
precipitation across the southern valleys. Snow levels drop to
around 8000 feet with the passage of this trough Tuesday, but any
accumulating snow seems to remain above 10kft with a couple inches
at best, favoring the northern and central mountains. Although,
impacts are expected to be minimal to non-existent as roads likely
remain wet given the time of day and year that most of the
precipitation is expected to fall. The trough exits into the Central
Plains by Tuesday night and Wednesday morning, taking the
precipitation with it, leaving a drier westerly flow for Wednesday.
Meanwhile, another low pressure trough enters the PacNW and
inconsistencies crop up with regards to what happens to this PacNW
low as it moves further inland. The GFS wants to dig this trough
into the Great Basin, with potential unsettled weather by the end of
the week. On the other hand, the ECMWF takes this trough north of
our area, leaving us drier. The blended approach seems most
reasonable given the differences at this time, with isolated to
scattered showers favoring the northern high terrain for the latter
half of the week. Following the passage of the trough on Tuesday,
temperatures should bounce back from the cooldown with highs
trending towards normal or slightly below normal late this week.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1139 PM MDT Sat May 18 2024

A few scattered showers will linger over northwest CO and
northeast UT tonight along a stalled frontal boundary. Most of
this activity will break up by daybreak. However, the frontal
boundary will remain in place and help with showers and
thunderstorms north of I-70 Sunday afternoon as things warm up.
Winds aloft remain strong and are expected to mix down to the
surface with gusty southwest winds around the region. Terminals
will see winds gusting around 25-35 mph, with a few stronger
bursts from thunderstorm outflows. Small hail remains a concern
as well Sunday afternoon. Showers and winds will quiet down
towards the end of this TAF period Sunday night.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...KJS
LONG TERM...MDA
AVIATION...TGJT