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000
FXUS65 KCYS 091138
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
538 AM MDT Tue Apr 9 2024

.KEY MESSAGES...

- A slow warming trend is expected by mid to late week. A weak
  weather disturbance and its associated cold front will bring
  cooler temperatures and a chance of precipitation for
  Wednesday.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 255 AM MDT Tue Apr 9 2024

Models continue to show quieter weather through the middle
portion of the week, with the only minor forecast concern
Tuesday night and Wednesday in the form of the next Pacific cold
front quickly moving across the area. For today (Tuesday), northwest
flow aloft will continue over the area, but 700mb will
increase back to the 0c to -5c range, which translates to
surface temperatures in the mid 40s (north) to mid 50s/low 60s
across far southeast Wyoming and most of western Nebraska. Kept
POP near zero with a drier airmass in place and hardly any low
level instability present. This will change later tonight as the
Pacific cold front and associated progressive upper level trough
axis slides southeast into Montana and Wyoming. The upper level
trough will then dig south and slow down through the day,
allowing scattered showers to continuously develop through the
day and into the early evening hours. Not much forcing with this
system, but there is some terrain-induced convergence along the
mountains and particularly the Laramie Range with some low
level instability present as LI`s lower to around 0c to -2c.
Model sounds are indeed showing decent mixing to around 500mb
with CAPE values between 100 to 300 j/kg. The environment
appears sufficient for scattered to numerous rain/snow showers
with mainly snow above 7500 feet. Can`t rule out a few lightning
strikes and rumbles of thunder, but kept out of the forecast
for now due to very low coverage and low confidence. Expect
these showers to produce some graupel as they push southeast
over the area before dissipating around sunset Wednesday
evening.

For Thursday, all models show the high amplitude ridge axis off
the west coast of the United States finally pushing east into
the Front Range. The actual warming trend will begin on Thursday
as 700mb temperatures climb well above 0c. Expect high
temperatures in the mid 50s to low 60s across most of southeast
Wyoming and western Nebraska. Areas that have a lingering
snowpack from last weekend`s system might struggle to reach 50
during the day, but most of the snow should melt by Thursday
afternoon.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 235 AM MDT Tue Apr 9 2024

By late this week, the 500mb ridge axis will begin to shift overhead
with the continuation of above average temperatures for mid-April,
while an upper level low approaches the Pacific Coast. Latest NBM
MaxT interquartile ranges across the area are quite small with
afternoon highs expected in the upper 60s to mid-70s. Precipitation
chances appear rather minimal with a few weak disturbances in the
flow leading to the possibility of widely scattered showers
Saturday, mainly in the mountains. Expect this warmth to continue
into the weekend, however forecast uncertainty begins to grow late
in the weekend and early next week.

Latest deterministic guidance progresses this upper level low over
the western CONUS from the four corners region towards northeast CO
with lee cyclogenesis occurring along the Front Range. Right now,
the GFS is a little deeper with a upper level low over the northeast
CONUS leading to a more northeast, slower track with with a stronger
blocking pattern over the central US. The EC is a little deeper with
a upper level low over the northwest CONUS propagating this system
through our area a little bit quicker. Latest cluster analysis shows
ensemble members from both systems sitting in these two pots with
the former (stronger omega block over central US) making up of ~70%
GEFS and ~45% of EC members leading to higher QPF totals across our
area.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 533 AM MDT Tue Apr 9 2024

VFR conditions expected across area terminals through the
forecast period. Breezy conditions possible at times this
afternoon with gusts around 20 kt out of the west before winds
shift more northwesterly late this afternoon into the evening.
Latest GOES imagery shows SCT-BKN high clouds moving southeast
out of MT that will move overhead starting this afternoon.
Forecast soundings suggest ceilings could drop to 5-8 kft, but
should remain at VFR levels at least through 06z Wednesday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...MB
AVIATION...MB