394
FXUS65 KGJT 071732
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1132 AM MDT Tue May 7 2024

.KEY MESSAGES...

- Windy conditions return today with gusts of 40 to 50 mph
  likely across the region. Several Wind Advisories are in
  effect through 9 PM this evening.

- Clearing skies tonight, combined with much colder air, brings
  the potential for sub-freezing temperatures for the lower
  valleys where vegetation is susceptible to damage. Freeze
  Watches remain in effect for those areas.

- Cool and unsettled weather will linger through the remainder
  of the week, with a series of disturbances keeping chances of
  light mountain showers in the forecast most afternoons.

&&

.UPDATE...
Issued at 950 AM MDT Tue May 7 2024

It`s been one of those days all before 1000. Perfect combination
of conditional/symmetrical instability being released by jet
dynamics and frontogenetical forcing making some intense
precipitation bands over the central CWA. Definitely some
snowfall rates in excess of an inch per hour occurring and we`ll
likely see some thunder added to the mix the next few hours.
Decreased temperatures and increased precip/snow amounts in many
areas going into the afternoon. There may be more to do but for
now leaving advisories in place but conditions not looking to
good for travel over Vail Pass. This convective banding will
continue well through the afternoon and let`s not forget winds
will begin to get cranking as we continue to mix up the next
hour or so.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 327 AM MDT Tue May 7 2024

Monday`s storm lifted to the western Dakotas during the night,
but moisture wrapping around the system has continued to
generate snow over the northern mountains. The system stalls
today while a short wave on its western flank approaches the
region from the northwest. Consequently, snowfall is expected to
persist largely unabated for the Elkhead, Park, Flat Tops, Gore
and a portion of the Elks today. Latest models indicated an
additional 3 to 6 inches, so Winter Weather Advisories will
continue for those areas. Meanwhile, the height gradient
strengthens slightly which means more windy conditions across
the forecast area today and current Wind Advisories appeared to
be on track, so made no changes there. Expect afternoon highs to
be close to 10 degrees below seasonal norms.

Light showers will continue for the northern mountains, but
additional accumulations are expected to be light. Meanwhile,
the short wave trough mentioned previously pushes southeastward
across the forecast area tonight and begins advecting colder air
across the region. Combined with clearing skies for most of the
region outside of the north, this is expected to yield markedly
colder lows by Wednesday morning. In fact, models continued to
indicated the potential for freezing temperatures in the lower
valleys where vegetation is susceptible to freeze damage.
Forecast numbers remain borderline, so will leave the Freeze
Watch in place for now.

Conditions improve on Wednesday as the gradient aloft relaxes
and flow weakens in response. As mentioned in previous
discussions, the polar jet wraps around the northern quadrant of
the Dakotas low causing a low pressure aloft to expand back
westward over the area. As a result, moisture is expected to
remain entrenched over the northernmost portion of the forecast
area. This moisture, combined with instability resulting from
the 500 mb cold pool being in close proximity, is expected to
continue to generate showers over the northern mountains, the
Steamboat Basin and portions of the northwest Colorado plateau.
Elsewhere, skies will be partly/mostly sunny with no real chance
for showers. Temperatures will continue to run 10 degrees or
more below normal.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 327 AM MDT Tue May 7 2024

Wednesday night into Thursday, models are in agreement that a piece
of energy breaks off from the closed mid-level low over the northern
Plains and retrogrades westward before closing itself off over the
Great Basin. This is all thanks to an anticyclonic wave breaking
event with a large sprawling ridge off the West Coast spilling over
top across southwest Canada and the Pacific Northwest. This synoptic
evolution and configuration creates a blocking pattern known as a
Rex Block. This type of blocking pattern is often a precursor to
stagnant and repeatable weather patterns which can last for several
days or even weeks. Unsurprisingly, models show a fairly unsettled
and active pattern setting up through the weekend and into next week
given the cut-off low nearby.

The exact placement of synoptic features will dictate where showers
set up the most frequently, but right now, all signs point towards
the high elevations and adjacent high valleys for the most
persistent and widespread activity each day. Adding confidence to
that is the fact that a slow warm up is expected through the end of
the long term period. Warming temperatures combined with residual
surface moisture from previous days showers will only increase the
instability from day to day... which then increases the QPF output
from showers... which increases the moisture even more... and then
the cycle repeats. This process is most prevalent in the high
terrain given steeper lapse rates, though showers can and often do
drift off the terrain and into the adjacent valleys below. So the
bottom line is that while not everyone will see showers the rest of
this week, the weekend, and early next week, chances are high that
they will at least be around, with the highest odds in the mountains
and high valleys.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1131 AM MDT Tue May 7 2024

A band of heavy precipitation with embedded convection including
thunderstorms continues to bring MVFR to IFR conditions at KRIL
KEGE and KASE late this morning. This will be slow to improve
and conditions here will are likely to fluctuate between VFR and
IFR as showers continue through the afternoon with rain and/or
snow possible. Most TAF sites along and north of I-70 will be
under this same threat through the evening. Winds will be the
bigger story as widespread gusts of 45 to 60 mph will be
possible through mid evening before things begin to taper off.
With precipitation the threat of fog/low clouds may linger over
some of the higher valley TAF sites such as KEGE/KASE through
tomorrow morning. Otherwise VFR will be in control at most sites
overnight into tomorrow morning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 6 PM MDT this evening for COZ004-
     010-013.
     Wind Advisory until 9 PM MDT this evening for COZ006>008-011-
     014-021>023.
     Freeze Watch from 10 PM MDT this evening through Wednesday
     morning for COZ006-007-011.
UT...Wind Advisory until 9 PM MDT this evening for UTZ022-024-027.
     Freeze Watch from 10 PM MDT this evening through Wednesday
     morning for UTZ022-027-029.

&&

$$

UPDATE...15
SHORT TERM...NL
LONG TERM...MDM
AVIATION...TGJT