Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 231026
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
426 AM MDT Sat Mar 23 2024

.KEY MESSAGES...

- Breezy to windy conditions will occur this afternoon with
  warm, above normal temperatures ahead of a potent cold front
  and storm system arriving tonight. Isolated to scattered
  showers and thunderstorms possible this afternoon.

- Showers become more widespread this evening through Sunday as
  colder air arrives and brings temperatures and snow levels
  down.

- Significant mountain snow is likely through Monday morning
  with travel impacts over the passes increasing during the
  overnight hours.

- Unsettled weather continues through the coming week with
  additional disturbances bringing scattered showers.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 426 AM MDT Sat Mar 23 2024

Some light showers were moving across northeast Utah and
northwest Colorado earlier this morning and are seen tracking
across the western Colorado divide mountains at this time. Upper
level soundings indicate inverted V signature with plenty of dry
air at the surface so showers may be producing more virga than
anything as breezy conditions are being seen underneath these
showers. Southwest winds will increase today as an upper level
trough pushes into the Great Basin with a strong 170 kt upper
level jet rounding the base of the trough through the Desert
Southwest. These stronger winds remain south of the Four Corners
and with increasing cloud cover expected today, the winds may
not be as strong as indicated a few days ago. Still expect
breezy conditions with gusts in the 20 to 35 mph range across
the area this afternoon. High temperatures will be 4 to 8
degrees above normal for most areas today but take a tumble on
Sunday by about 12 to 18 degrees compared to today, ending up
about 8 to 15 degrees below normal.

Ahead of this trough, moisture will increase off the Pacific
with the jet driving much of this moisture through the Desert
Southwest and into the Four Corners. While IVT values remain
higher across Arizona and New Mexico, we will still see a modest
150 to 200 kg/ms IVT values across southeast Utah into western
Colorado this afternoon through Sunday morning. Lapse rates
steepen to 9 C/km and CAPE values increase to a modest 200 J/kg,
so enough instability remains for isolated to scattered showers
and thunderstorms to develop this afternoon. Large scale ascent
is maximized this evening through Sunday afternoon as indicated
by the QG dynamics. This will be the period of more steady
precipitation and moderate to heavy snowfall rates in the
mountains. Snow levels remain high AOA 8kft this evening,
lowering to 7kft by Sunday morning and ending up AOA 5500 to
6000 ft by Sunday afternoon after the cold front passes through
Sunday morning. The lower elevations look to see primarily rain
with best chance of more widespread and steady precipitation
occurring tonight through Sunday morning before becoming more
scattered and convective by late Sunday afternoon. Of particular
concern is potential banding and convection during the day on
Sunday which could lead to locally higher amounts or heavier
rates at times and temporarily lowering snow levels. The high
March sun angle during the afternoon also will tend to lead to
less impacts on the roads, keeping them mostly wet to slushy in
spots. Given these concerns, snowfall accumulations in the
mountains still look to be in the 6 to 12 inch range with
locally higher amounts possible. Decided to issue Winter Weather
Advisories for all western Colorado mountains and the southeast
Utah mountains beginning this evening and continuing through
midnight Sunday night for the Tavaputs (elevations above 7000
feet), Uncompahgre Plateau and La Sals and Abajos (elevations
above 8000 feet)...with the remaining western Colorado
mountains continuing through 6 am Monday morning given the
lingering northwest orographics.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 426 AM MDT Sat Mar 23 2024

Models show good agreement with the trough moving east of the Divide
Sunday evening putting eastern Utah and Western Colorado under a
weak northwesterly flow with cold air advection (CAA) aloft
over the region into Wednesday keeping atmospheric conditions
unstable. With generally light winds through this period, there
is nothing to move the lingering moisture in the lower levels
out of the area, scattered light orographic showers will
continue through the mountains, becoming more widespread each
afternoon with the springtime stronger diurnal heating. Weak
shortwave disturbances in the northwesterly flow Monday evening
and again Tuesday night will keep many of the showers going well
into the evening hours. With snow levels running 5-6,000 feet
through this period, most of these showers will be snow, but
little if any snow will accumulate with at most only a few
inches falling on the higher mountains. The CAA will keep
temperatures Monday and Tuesday ten degrees below the seasonal
average for late March. Wednesday will see a temporary end to
the unsettled weather, clearing skies and temperatures warming
about five degrees as a transitory ridge starts pushing into the
region from the west.

Models show continued agreement Thursday having the ridge move east
onto the Plains by Thursday afternoon and a southwesterly flow
return ahead of the next low pressure system that will have
descended from the Aleutian Islands into the Pacific Northwest.
Remnants of a weak to nonexistent AR does pump moisture northeast
over eastern Utah and western Colorado Thursday on this
southwesterly flow. From Thursday onward, the models diverge in
their solutions, though the ensembles tend to follow the
corresponding deterministic models, i.e., the European ensemble
keeps a tight grouping that runs behind the GFS/GEFS solutions
and generally tracks the low down over the Desert Southwest
Saturday. The GFS seems to treat this next system similar to how
it handled the last system, splitting off a leading shortwave
that takes a more northerly track early in the period while the
remaining low tracks south to the Desert Southwest. The GEFS
also indicates this bimodal solution with a shortwave passing to
the north of the region Thursday evening and a second grouping
dropping into the Desert Southwest Saturday. The NBM guidance
looks to be favoring the GEFS solution bringing widespread
orographic showers to the region Thursday afternoon with the
showers intensifying overnight as the shortwave passes to the
north. Different from the last system, the models are wanting to
keep the low over the Desert Southwest into the following week
with high pressure building over the Pacific Northwest forming
a Rex block like we had two weeks ago. This would provide
another steady stream of moisture into the southern and central
mountains for an extended period. Of course, this far out there
is little confidence in this forecast of the Rex Block, but it
gives us something to anticipate. Stay tuned to see how this
plays out.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1153 PM MDT Fri Mar 22 2024

A weak disturbance is moving west to east through the region
currently with light rain showers over northeastern Utah and
northwestern Colorado. These showers will move over KHDN, KEGE
and KASE by about 10Z and last for a few hours before passing
east of the divide. Expect brief periods below ILS breakpoints
at KEGE and KASE. Southwest winds pick up in the late morning
across the region gusting 25-35 kts and continue into the early
evening hours. Ceilings will drop through the afternoon as deep
moisture advects into the region from the southwest with
widespread showers developing after about 21Z, intensify after
00Z and continue overnight into Sunday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from midnight tonight to midnight MDT
     Sunday night for COZ003.
     Winter Weather Advisory from 6 PM this evening to 6 AM MDT
     Monday for COZ004-009-010-012-013-018-019.
     Winter Weather Advisory from 6 PM this evening to midnight MDT
     Sunday night for COZ017.
UT...Winter Weather Advisory from 6 PM this evening to midnight MDT
     Sunday night for UTZ028.

&&

$$

SHORT TERM...MDA
LONG TERM...DB
AVIATION...DB


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