335
FXUS65 KGJT 192115
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
315 PM MDT Sun May 19 2024

.KEY MESSAGES...

- Isolated to scattered showers and storms are expected again on
  Monday, mainly north of I-70. Gusty outflow winds and hail
  will be the main risks from any stronger storm.

- Dry, warm, and breezy weather will continue across the
  southern half of the CWA on Monday. Gusty winds of 35 to 45
  mph will be common, especially in the higher elevations.

- A larger system moves through Monday night into Tuesday,
  bringing fairly widespread precipitation and much cooler
  temperatures. Drier weather returns on Wednesday before
  another system approaches late in the week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 315 PM MDT Sun May 19 2024

Scattered showers and storms have fired across northeast Utah
and northwest Colorado as expected this afternoon, all in the
vicinity of a stalled nearby surface boundary and a subtle
shortwave aloft. These showers and storms are also taking
advantage of a moist and unstable environment, characterized by
a belt of PWs near 150 percent of normal and SBCAPE of 250 to
500 J/kg. Rounding out the parameter space is roughly 20 to 30
kts of effective shear, which is helping to loosely organize
updrafts. As a result, showers and storms have become fairly
sporty this afternoon, producing gusty outflow winds of 45 to 55
mph and some small hail in spots. Despite the above normal
moisture across the entire column, the very lowest part of the
atmosphere is still pretty dry... as evidenced by inverted V
profiles on forecast soundings. This will only make outflow wind
gusts more efficient at reaching the ground through the
afternoon and early evening hours.

The stalled surface boundary is not expected to move much over
the next 24 hours, and additional shortwaves out ahead of the
main trough digging southward across the Pacific Northwest will
allow additional rounds of showers and storms to develop this
evening, overnight, and into the day on Monday. By Monday
afternoon, the deepening trough to our northwest will begin to
phase with a potent positively tilted shortwave over Baja
California, which will extend a very strong upper speed max
northward across the Four Corners states. Combined with daytime
heating and strong boundary layer mixing, a very breezy day is
in store across most of the CWA, especially in southeast Utah,
southwest Colorado, and the higher elevations. Gusts of 35 to 45
will be common Monday afternoon and evening. While we did
consider a Wind Advisory, ultimately decided to hold off for now
given winds should mostly top out just below criteria. Later
shifts can re-evaluate as necessary. The winds will also lead to
near critical fire weather, especially with relative humidities
in the single digits and teens from the I-70 corridor
southward. Fuels have not been deemed critical though, so no
fire weather highlights have been issued. The boundary
separating the moist air across northeast Utah and northwest
Colorado and the dry air southward will again be the focus for
additional scattered showers and storms Monday afternoon and
evening. Forecast soundings and CAM guidance are hinting at
storms potentially becoming strong to borderline severe along
and north of the US-40 corridor towards the CO/UT and CO/WY
state lines given adequate instability and more deep layer shear
to work with. Strong and gusty winds would still be the main
threat with any stronger storm, but plenty of CAPE in the hail
growth zone and fairly low wet bulb zero heights could result in
more of a hail threat as well. Certainly something to keep an
eye on.

By Monday night, the cold front will start pushing into
northeast Utah and northwest Colorado as the deep parent trough
now over the northern Rockies begins to swing eastward. This
will result in the development of more widespread precipitation,
and a push of much colder air into Tuesday. For more on that,
continue on to the long term discussion below.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 315 PM MDT Sun May 19 2024

On Tuesday a closed low pressure clips northern portions of the
forecast area as it swings eastward. With moisture still in
place this should result in another round of showers and storms
across the region. This system should force any lingering
boundaries out of here leaving us with northwest flow. Cold air,
cloud cover, and showers will see afternoon highs Tuesday some
15 degrees cooler than previous days. Due to this cold air aloft
snow levels drop to about 8-9 kft. Accumulating snow will
battle the high sun angle, but there could be a few inches in
the high country on Tuesday. Impacts if any should be confined
to the mountain passes. Conditions start to dry out Tuesday
night as the low pressure proceeds over the Plains. Flow shifts
back to the southwest on Wednesday as another system approaches
from the Pacific Northwest. For the most part Wednesday will be
dry, but could see enough lingering moisture for showers along
the Divide. There is still minor disagreement about this next
low pressure, but most of the models keep the track north of us
over Wyoming. None the less this system should push another cold
front into our area. Showers and storms associated with this
front will favor the northern half of the forecast area through
Thursday night. The end of the week looks to remain active with
multiple waves diving into the persistent western CONUS trough.
The solutions diverge at this point, but it appears this pattern
could continue to keep us away from the summer heat and bring
us occasional cold fronts with some rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1147 AM MDT Sun May 19 2024

A stalled frontal boundary has kicked off another round of
isolated to scattered showers and thunderstorms north of I-70.
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 this afternoon. Some showers will linger near the
Wyoming border tonight with dry weather / VFR conditions
elsewhere into Monday morning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...MDM
LONG TERM...KJS
AVIATION...TGJT