-- Discussion containing changed information from previous version are highlighted. --
494
FXUS65 KGJT 081723
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1123 AM MDT Wed May 8 2024

.KEY MESSAGES...

- Sub-freezing temperatures for the lower valleys where
  vegetation is susceptible to damage is forecast early this
  morning. Other areas may see frosty conditions.

- Cool and unsettled weather will linger through the remainder
  of the week. Persistent snow over the northern mountains will
  bring some accumulations to the higher elevations today before
  the threat shifts to the south to end out the week.

&&

.UPDATE...
Issued at 754 AM MDT Wed May 8 2024

Temperatures have reached or pushed above freezing in most areas
so the warning has been cancelled. Additional warnings may be
needed tonight again near Rifle and the North Fork/Unco Valleys
so stay tuned.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 406 AM MDT Wed May 8 2024

Cold air continued to filter southward across the forecast area
early this morning as the closed low pressure system remained over
the northern High Plains early this morning. Clearing was late
in coming for a significant portion of the areas where Freeze
Warnings were in place which has buoyed temperatures thus far.
In addition, the surface pressure gradient has proven strong
enough to keep winds moving at KCNY, KBDG, KGJT and KMTJ which
has also helped keep temperatures above freezing so far. That
said, winds have diminished at KRIL and temperatures there were
just above freezing. There`s a good chance that winds will
continue to keep cold surface inversions from forming which
should be good news for local growers.

The Plains low drifts slowly southward today before turning east
late. As this occurs, the westward flowing jet in the northern
quadrant of the low causes mid-level heights to fall over the
Great Basin resulting in an elongated area of low pressure over
the region. Moisture will linger over the northern half of the
forecast area as flow aloft, though weaker, continues to advect
moisture southward. Dynamic forcing will be limited, but the
cold pool at 500 mb creates sufficient instability for mainly
afternoon showers, mainly over the northern mountains and
portions of the central Colorado mountains. Snow accumulations
will be light and fairly localized. Elsewhere, expect partly to
mostly sunny skies and dry weather. Highs are expected to
continue to anomalously cool with most locations 10 to 15
degrees cooler than normal.

The westward flowing jet north of the Plains low turns south
over the western Great Basin tonight causing a low to close off
over southern Utah early Thursday morning. Jet divergence,
instability and orographics will keep light showers going along
the northern border of the forecast area tonight. However, by
Thursday afternoon the focus shifts to the southern half of the
forecast area as difluent flow and jet divergence develops east
of the low west of the Four Corners. However, enough residual
moisture and instability will remain to fuel numerous showers
and a few thunderstorms over the mountains and high valleys
Thursday afternoon. Despite increased clouds and showers,
temperatures will moderate, though highs are still expected to
peak about 5 degrees below normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 406 AM MDT Wed May 8 2024

A low will  become cut off from the main upper level flow and
continue to spin over the Great Basin through at least Friday night
as a Rex Block forms over the west. This will keep moisture
circulating around the low with easterly upslope flow into the San
Juans and Divide mountains. The higher elevations of the San Juans
look to be the most favored for some snow accumulations along with
the spine of the Central Divide through Friday night. Temperatures
throughout this period also look to be warming as well despite the
unsettled conditions which would increase available moisture. Lapse
rates will steepen and instability present. Given day time heating,
this should result in scattered to widespread showers and
thunderstorms, favoring the high terrain during the afternoon with
some drift off the terrain into adjacent valleys from time to time.
Even though these blocking patterns have a tendency to persist, the
models are showing some signals of this Rex Block breaking down by
Saturday with the cut off low finally moving eastward into the
Plains. Models seem to be in better agreement now than they were a
few runs ago. This may be due to more shortwave energy moving across
southern Canada and making its way into the northern High Plains and
eventually northern Rockies by early next week.

So, conditions will remain unsettled through Saturday with some
afternoon storms favoring the high terrain as we transition from the
unsettled weather with the cut off low over the region to a drier
northwest flow as high pressure tries to build in from the west by
Sunday. Additional shortwaves try to drop in from the northern
Rockies into our CWA early next week, resulting in afternoon
convection mainly over the high terrain of western Colorado. High
temperatures during this period will be around 5 degrees below
normal Friday and Saturday, warming up towards near to slightly
above normal by Sunday as the low exits, and return to 5 to 10
degrees above normal by early next week. Even though most lower
elevations will return to drier and warmer conditions Sunday through
early next week, showers and thunderstorms will be around each day
but mostly favor mountains and high valleys. It should start to feel
more like a warm Spring time convection regime.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
-- Changed Discussion --
Issued at 1120 AM MDT Wed May 8 2024

Cool Northwest flow continues to push moisture into the northern
and central mountains creating terrain obscuration and isolated
to scattered light snow showers. As heating and convection
increase through the afternoon these showers will spread and
could impact adjacent TAF sites but probability is low attm so
VCSH has been used. Winds will be less of a problem over the
next 24 hours as well. Precipitation and clouds will expand
through Thursday morning and ILS to MVFR impacts will become
more probable through the day. Until then mainly VFR prevails.
-- End Changed Discussion --

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

UPDATE...15
SHORT TERM...NL
LONG TERM...MDA
AVIATION...NL/TGJT