Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 270813
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
213 AM MDT Wed Mar 27 2024

.KEY MESSAGES...

- Isolated to scattered showers will remain in place through the
  late morning before a brief drying trend moves in through
  early Thursday.

- An unsettled pattern will bring mountain snowfall and a mix of
  rain and snow to the valleys beginning Thursday...persisting
  well into next week.

- Travel will be impacted at times through the mountain
  corridors...especially during the overnight hours when snow
  is more likely to accumulate on roadways.

- 1 to 2 week outlooks suggest the odds favor this cooler and
  wetter pattern staying in place.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 213 AM MDT Wed Mar 27 2024

It is looking like our radar will get about a 12-18 hour break
beginning late this afternoon...otherwise for the next week
there will likely be something for it to sample. The 27/00Z
H500 hand analysis map is showing an anomalous gyre of low
pressure sitting over the Canadian Prairies. This is resulting
in lower than normal heights over most of the CONUS...the
exception being the upstream coast where transitory ridging is
building onshore out of the EPac. The feature to watch early
today is the elongated area of clearing in water vapor
extending from the N.Rockies past the 4 Corners early this AM.
This area of channelized vorticity in the back of the trough is
delineating upstream WAA and more stable conditons with the
unstable CAA regime we are sitting under. The threat of isolated
to scattered convection and enhanced orographics with high SLR
will not end until this channel shifts East of the Divide early
this afternoon. Several more inches of snow could fall over some
peaks before this happens. We get our short break as the
transitory ridge moves through overnight and into early Thursday
afternoon as Pacific moisture streams back in without much
upper support. By late tomorrow afternoon weak ascent from a
zonal jet nosing in will combine with instability and diffuse
mid-level thermal forcing to produce showers over the northern
CWA. The stronger frontal forcing will remain just upstream
through sunset and it`s progressing will be slowing due to the
persistent moderately strong SW flow aloft. Orographics over the
high Uintas will also bring some light precipitation by
Thursday morning prior to any organized forcing aloft. Lowering
heights upstream will also bring an increase to mid level SW
winds which afternoon mixing should tap into for a breezy
afternoon. This will allow temperatures to warm up about 10
degrees compared to today...but still remain below seasonable
norms.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 213 AM MDT Wed Mar 27 2024

By Thursday night, a 120 kt upper level jet will set up from
southwest to northeast from the Desert Southwest through the Four
Corners into western Colorado. This is all ahead of a deep closed
low that will drop southward along the California coast, allowing
moisture to advect in off the Pacific. Weak ripples in the flow
along this moisture and jet boundary will allow showers to develop
in the left exit region of the jet, which happens to be across
northeast Utah and northwest Colorado Thursday night. Specific
humidity levels reach upwards of 4 g/kg. These showers will continue
through Saturday periodically as the dynamics for this remain in
place with the closed low dropping southward towards central and
southern California Saturday night before tracking inland.  South of
the left exit region of the jet, central and southern areas look to
remain mostly dry with WAA taking place under this increasing
southwest flow. Given the influence of the jet, afternoon winds look
to remain breezy at times, picking up more this weekend ahead of
this strong closed low as the winds from the jet rounding the base
of the trough increase to 160 kts over the Baja and Arizona,
translating to about 130 kts over our neck of the woods. WAA will
help raise snow levels up to above 7000 to 8000 ft MSL across the
north and upwards of 8500 ft MSL across the south. Northern and
central mountains will be more favored in this southwest flow given
the influence of the jet and moisture axis, with roughly 2 to 6
inches of snow here for each 24 hr period Thursday through Saturday.
High March sun angle should limit impacts to the highest elevations
with mostly wet roads, except during overnight periods. These
showers look to be convective as well during the afternoon with
isolated thunderstorms possible. Speaking of WAA, high temperatures
look to be warming closer to normal or a few degrees above for the
central and southern valleys...not quite as warm as earlier depicted
as the moisture stream coming off this closed Pacific low is a bit
more robust and infiltrating our ridge to produce more cloud cover
which will have an impact on how much warmth we will see. Highs on
Friday and Saturday will still push into the low and mid 60s for the
lower central and southern valleys with potential for low 70s among
the southeast Utah canyon country.

This closed low looks to move ashore Saturday night into Sunday,
bringing more widespread precipitation into the region with the
trough axis potentially moving across on Monday. The word
"potentially" is used because there has been some discrepancies
regarding the strength, timing and track of this system. While
models are showing this trough being somewhat progressive, moving
into the Plains by Tuesday with lingering northerly flow but high
pressure trying to build back in behind it...there are some hints
that another low tries to form in the deep recesses of this
elongated trough over the Desert Southwest and close off! Yes, the
closed cut off low! That would mean precipitation could linger
longer for some areas across the south but this is still a ways off
so time will tell. As the previous discussion indicated, the cluster
analysis and ensembles were "hinting" at this possibility and it
appears the latest deterministic GFS is grasping onto this possible
scenario. The Euro hasn`t quite grabbed onto this yet. The bottom
line is that after a warming period late this week into Saturday,
the weather looks to turn unsettled again Sunday into early next
week with a potent storm affecting the area, bringing more mountain
snow and lower valley rain. How much snow and impacts though remain
to be seen just yet as these details are still being refined. It`s
always tricky in these transition periods as we head further into
Spring as many factors can complicate the forecast and impacts.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1113 PM MDT Tue Mar 26 2024

Until the wave passes this afternoon...isolated to scattered
snow showers will continue to impact TAF forecast with VFR/ILS
quickly dropping to MVFR/IFR by a passing shower. Behind this
wave the VFR should then prevail with a few afternoon breezes
approaching 25 mph.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...15
LONG TERM...MDA
AVIATION...TGJT


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