Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 130000
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
600 PM MDT Tue Mar 12 2024

.KEY MESSAGES...

- A strong cold front will move through tonight through
  Wednesday, bringing widespread precipitation to Utah and
  Colorado.

- Winter Weather Advisories remain in effect for 6 to 12 inches
  over the Colorado mountains beginning this evening through
  Thursday.

- Precipitation will shift to southern regions Thursday and
  Friday as a closed low brings more substantial moisture in
  from the south. Winter Storm Watches have been issued for the
  San Juan Mountains and the La Sal/Abajo Mountains.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 401 PM MDT Tue Mar 12 2024

GOES-16 satellite imagery shows an expansive cloud shield
pushing into eastern Utah and western Colorado this afternoon.
These clouds are associated with a trough of low pressure that
is currently digging into the Great Basin and will move through
our region tonight through tomorrow. Associated with this trough
will be a fairly strong cold front, as evidenced by the many
lightning strikes currently being detected upstream across
Nevada. Increasing moisture and forcing for ascent along and
ahead of the trough/front will support the development of
widespread precipitation later this evening and overnight with
the western Colorado mountains favored. Snow levels will be mild
initially and hover between 6500 and 7000 feet this evening
before falling to between 5000 and 6500 feet by daybreak. Thus,
most snow will be confined to the higher elevations with just
plain rain for the lower valleys below. The higher valleys in
between will likely be a mix of rain and snow. Hi-res guidance
hints there may be a break in precipitation from the pre-dawn
hours through about mid-morning Wednesday from roughly I-70
southward before another round moves in late morning into the
afternoon. It`s during this time that the cold front gains
enough momentum to push through at least the San Juans before
possibly hanging up north of the 160 corridor in the southwest
Colorado. Precipitation rates will increase across the mountains
during the frontal passage and snowfall will likely accumulate
at an inch per hour clip at times. Warm antecedent conditions
may prevent much accumulation on roadways during the middle of
the day, but brief intense rates can sometimes be enough to
overcome marginal pavement temperatures. Something to keep an
eye on.

By Wednesday night, the focus for precipitation shifts in
response to a rapidly deepening closed low that will dig
southward through the Great Basin and into the Desert Southwest.
Wrap around moisture may favor another swath of snow mainly
north of I-70 through the early morning hours Thursday. This
will particularly impact the eastern Uinta Mountains, so in
coordination with WFO SLC and WFO RIW, decided to issue a Winter
Weather Advisory to cover the heightened snow potential there.
Overall, the current forecast for part one of this extended
storm remains on track so no changes to the other Winter Weather
Advisories issued on prior shifts were made. Total snowfall
accumulations for part one through 12Z Thursday morning still
remains at 6 to 12 inches for most of our mountain ranges. After
part 1 departs, the focus then turns towards southeast Utah and
southwest Colorado... more on that below.

Clouds and precipitation will keep overnight temperatures
tonight fairly mild compared to normal, but will be much colder
than average during the day on Wednesday.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 401 PM MDT Tue Mar 12 2024

Part one of this unsettled weather pattern wraps up Thursday
morning, with a subtle break between punches of moisture. By
Thursday afternoon, the upper level low retrogrades over the
Southern Great Basin and pinches off as a closed low. As the
system as a whole shifts to the southwest, moisture wrapped
around the northeast periphery of the low will be pulled back to
the southwest, too. As a result, some of the available moisture
slamming against the Front Range will spill back west. Should
expect an increase in PoPs throughout the day Thursday, and
shift concentration from our northern zones to the southern
mountains. Then, by Thursday evening, the system stalls.
Deterministic guidance is in relatively good agreement with the
center of the low wobbling around the CA/NV/AZ triple point. The
next 24 to 48 hours look promising for the deliverance of an
abundance of moisture across the Four Corners region. By Friday
morning, an upper level jet wraps around the belly of the low,
which will increase the pull of Pacific moisture across the
Desert Southwest. Model consensus places the San Juans in
southwest CO and Abajos in southeast UT directly in the line of
fire in terms of vorticity and moisture advection for nearly 48
hours. So, as long as we`re not plagued with a swath of dry air,
these ranges could see another 1 to 2 feet of snow Thursday
night through Saturday. Due to the model agreement, enhanced
snow totals, and collaboration with neighboring offices/WPC
we`ve decided to include a Winter Storm Watch for UT zone 28 and
CO zone 19 to capture the second round of mountain snow. Snow
totals dwindle as you travel north of said ranges, though the
Swatch, Elks and West Elks are still progged to accumulate
another 3 to 6 inches.

Lingering snow showers may persist into Saturday night, even
though the bulk of the storm and energy associated with it seem
to weaken by Saturday afternoon. Despite weakening, the low
doesn`t budge much over the weekend. As a result, recycled
moisture may continue to flare light snow showers over the San
Juans into early next week. Long term guidance illustrates a
variety of scenarios absorbing the closed low next week, though,
model consensus is breaking down the cyclone by mid week. As
this happens, showers will likely spread back across the region.
Confidence in how this plays out remains low at this time, but,
it appears unsettle weather remains in the 7-Day forecast.

Temperatures for the remainder of the week and into the weekend
will stick 5 to 10 degrees below normal for early Spring. Once
the low begins to breakdown, then we`ll start to see
temperatures on the rise. Note, for areas socked under clouds
overnight, low temperatures may actually stay relative
warm...even a few degrees above normal.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 600 PM MDT Tue Mar 12 2024

Mid and high clouds will increase from the west with some VCSH
and gusty winds. Snow will develop over the mountain TAF sites
around midnight, dropping to MVFR/IFR criteria at times.
Precipitation with rain or a rain/snow mix will have a better
chance of reaching valley TAF sites late Wednesday morning into
the afternoon as a cold front moves through. Mountains are
expected to remain obscured at least through Wednesday night.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until midnight MDT Wednesday night for
     COZ004-013-017.
     Winter Weather Advisory until 6 AM MDT Thursday for COZ009-010-
     012.
     Winter Weather Advisory from midnight tonight to midnight MDT
     Wednesday night for COZ018-019.
     Winter Storm Watch from Thursday afternoon through late Friday
     night for COZ019.
UT...Winter Weather Advisory until midnight MDT Wednesday night for
     UTZ028.
     Winter Storm Watch from Thursday afternoon through late Friday
     night for UTZ028.
     Winter Weather Advisory from 6 PM Wednesday to 6 PM MDT
     Thursday for UTZ023.

&&

$$

SHORT TERM...MDM
LONG TERM...ERW
AVIATION...TGJT


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