537
FXUS65 KGJT 051035
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
435 AM MDT Sun May 5 2024

.KEY MESSAGES...

- Very strong winds for much of eastern Utah and western
  Colorado today, with gusts up to 65 mph for the valleys and 80
  mph for the mountains.

- A strong spring storm will bring widespread precipitation
  tonight and Monday with significant mountain snow expected
  across the northern Colorado ranges. Light snow accumulations
  are possible for the higher valleys by sunrise Monday.

- Much cooler and unsettled weather will be the rule for the
  rest of the week ahead as several disturbances keep mountain
  showers in the forecast most afternoons.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 435 AM MDT Sun May 5 2024

The deep mid-level closed low which has been the prime topic in
previous discussions was centered over the Oregon-Nevada-Idaho
triple point at 09Z. Ahead of the system the height gradient had
begun to strengthen. Models continued to show anomalously strong
southwest winds of 40 to 50 kts at the 700 mb level shifting
over eastern Utah by sunrise as the low tracks eastward. The
strong winds aloft will spread into western Colorado during the
day as the low moves to extreme northwest Utah by early evening.
Deep mixing will help transfer stronger winds aloft to the
surface resulting in very windy conditions. As pointed out in
the previous discussion, today`s winds stand out
climatologically as occurring only once every ten years or
more, so it doesn`t appear this will be your garden variety
windy day. Wind Warnings and Advisories issued by the day shift
appeared to be on track and made no adjustments. Precipitation
ahead of the cold front will be limited to mainly virga except
for over the eastern Uinta Mountains where showers become likely
during the afternoon.

Showers become widespread tonight as the base of the low tracks
across northern Utah driving the cold front eastward across the
forecast area and onto the high plains by sunrise Monday. Lift
from the surface to jet level will be maximized during this
period and as a result, mountain snow becomes heavy with rates
exceeding an inch an hour for the northern ranges. As the colder
air filters in, snow levels lower below mountain bases and light
snow accumulations are expected in the higher valleys by Monday
morning. Meanwhile, winds shift to the west behind the front and
weaken, but remain brisk.

The low lifts to the northeast over the northern High Plains on
Monday, though lingering moisture, instability and orographics
is expected to keep snowfall going over the northern and central
Colorado Mountains late into the day. QPF values came up with
the latest model runs which seemed reasonable given the strength
of this system. Amounts across the northern Colorado mountains
were solidly in the 5 to 10 inch range with local amounts up to
18 inches indicated over the higher ridges. Meanwhile, though
amounts came up for the central and southern mountains, higher
amounts seemed to be limited to only the highest areas which
limits impacts. Consequently, issued a Winter Weather Advisory
for the Elkhead Mountains, Park Range and Flat Tops from 00Z/Mon
to 00Z/Tues but held off elsewhere. The day shift is encouraged
to consider whether advisories need to be expanded.

Since the area remains in the warm sector of the storm today,
afternoon highs will remain mild, though increased clouds are
expected to shave a couple of degrees off Saturdays max
temperatures. The arrival of colder air tonight will drive
temperatures down across the region with lows Monday morning
expected to run close to 10 degrees below normal while
afternoon highs fall somewhere between 10 to 15 degrees below
normal.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 435 AM MDT Sun May 5 2024

Lingering troughing and favorable orographics will continue to act
on residual moisture and keep the snow showers going across the
northern Colorado mountains Monday night. Any additional
accumulations are expected to be light. Another wave embedded in the
broad westerly to northwesterly flow will dig across the northern
Four Corners states and bring another round of snow showers across
parts of northeast Utah, northwest Colorado, and the northern and
central Colorado mountains on Tuesday. Additional minor
accumulations are a good bet, particularly across the Flat Tops,
Elkheads, and Park Range mountains. Given the time of day and year,
impacts should be low. Most snow showers will come to an end by late
Tuesday evening, but some may linger across the northern mountains
through Tuesday night. Elsewhere, mainly dry weather will prevail
under partly cloudy skies.

The wave will also drag a strong cold front through much of eastern
Utah and western Colorado, ushering in a much colder air mass in its
wake. Latest 00Z model guidance is advertising 700mb temperatures
falling to between -8C and -12C by Wednesday morning, which is quite
cold for this time of year. The unseasonably cold air mass will make
for very chilly overnight lows Tuesday night into Wednesday morning,
with widespread temperatures nearing or dropping below freezing.
Even some lower elevations like the Grand Valley and Uncompahgre
Basin may near 32 degrees, which could be an issue for budding
vegetation. For historical context, the record low temperature at
the Grand Junction Regional Airport for Wednesday morning (May 8th)
is 33F, set back in 1979. With near record cold temperatures
possible, those with agricultural interests will want to pay close
attention to the forecast over the next few days as freeze headlines
may be necessary.

For Wednesday and beyond, the bottom line is that cool and unsettled
weather is likely to persist across the northern tier of eastern
Utah and western Colorado as well as the Continental Divide
mountains... with mainly dry weather and a slow warm up likely
elsewhere. Ensembles are still showing a fairly complicated synoptic
pattern developing later next week with a possible Rex block
featuring a ridge over top a cut-off low setting up over the Western
CONUS. As it stands, it looks like high elevation and mountain
showers are possible almost daily through the end of the long term
period, with the exact position of the Rex block determining how
widespread those showers may become (particularly Thursday and
Friday). For now, will heavily lean on the blended guidance until we
get closer and details become more clear.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1140 PM MDT Sat May 4 2024

Mid and high level clouds will continue to increase overnight
and through the day on Sunday out ahead of an approaching cold
front. Ahead of the front, very strong winds will develop out of
the south and southwest by mid-morning and continue through the
afternoon and evening. Sustained winds of 25 to 35 kts with
gusts of 40 to 50 kts will occur. A few showers may develop
across the higher terrain ahead of the front as well, but the
heaviest and most widespread precipitation will push through
along the front mainly after 00Z Sunday evening. As a result,
reductions in ceilings and visibility are likely Sunday night.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...High Wind Warning from 8 AM this morning to midnight MDT
     tonight for COZ001-006-011-020.
     Wind Advisory from 8 AM this morning to midnight MDT tonight
     for COZ002-007-008-021-022.
     High Wind Warning from 6 AM this morning to midnight MDT
     tonight for COZ003-017.
     Winter Weather Advisory from 6 PM this evening to 6 PM MDT
     Monday for COZ004-013.
UT...High Wind Warning from 8 AM this morning to midnight MDT
     tonight for UTZ022-024-027-029.
     High Wind Warning from 6 AM this morning to midnight MDT
     tonight for UTZ025-028.
     Wind Advisory from 6 AM this morning to midnight MDT tonight
     for UTZ023.

&&

$$

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