-- Discussion containing changed information from previous version are highlighted. --
004
FXUS65 KCYS 021128
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
528 AM MDT Thu May 2 2024

.KEY MESSAGES...

- A cold front will move through the region on Friday with
  another round of shower activity and isolated thunderstorms
  over the region. Snow expected above 6500 feet.

- Mainly dry and warmer conditions are anticipated for the
  weekend.

- Breezy to windy, and cooler weather expected for Monday
  through Wednesday, with isolated to scattered late day showers
  and thunderstorms.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 300 AM MDT Thu May 2 2024

Early morning IR Satellite loop across the Front Range shows
decreasing cloudiness across the area as a very dry airmass
settles in. Lingering moisture across western Nebraska has
resulted in patchy fog early this morning, but it has not been
dense and visibilities have remained above 2 miles. Added some
fog in the forecast for the Sidney, Alliance, Chadron, and
Scottsbluff areas over the next few hours until sunrise. For the
rest of today (Thursday), cool but quiet weather is expected
behind the cold front. It will be windy across most of the area
with westerly winds between 15 to 30 MPH and gusts up to 40 MPH.
High temperatures should be a few degrees cooler compared to
yesterday with highs generally in the upper 40s to upper 50s.

For tonight and Friday, models show the next progressive upper
level trough pushing east out of the eastern Pacific with an
associated cold front ahead of the trough axis. All models are
struggling with run-to-run consistency with this system and are
now showing it further north compared to yesterday...with the
highest coverage of showers/most precipitation mainly in the
mountains and north of I-80. Again, the upper level trough axis
will move pretty fast across the area, which should limit
overall impacts. Previous model runs showed the precipitation
beginning just before midnight early Friday morning, but with
the amount of dry air in place do not expect any precipitation
to hit the ground this early. Kept low POP until midday Friday
as the trough axis moves into central Wyoming. Models indicate
pretty good lift associated with this system with a period of
enhanced 700mb frontogenesis increasing as the front moves east
into the high plains. All models also show a 100 kt jet streak
rounding the base of the trough during this time period with it
ejecting east into the high plains during the afternoon hours
with a broad area of strong upper level diffluence in the left
exit region. Will need to monitor this trend as a higher
coverage of precipitation is possible which may lead to higher
POP compared to the official forecast across most of the area
on Friday. Increased POP along the I-80 corridor and most of
western Nebraska for now, but didn`t go too high due to the lack
of model consistency. Believe it will be too warm for snow
earlier in the day with some thunderstorm activity possible. A
few models, such as the GFS, are showing higher snowfall amounts
in the mountains (6+ inches)...so may need a Winter Weather
Advisory in the Sierra Madre Range and Snowy Range if this trend
continues. Friday will likely be the coolest day of the week
with highs in the mid 40s to mid 50s across the area, coolest
west of I-25 where some snow is possible down to the valley
floors. Thankfully, this system will move fast with clearing
skies Friday night and cold overnight lows in the upper teens to
upper 20s.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 220 AM MDT Thu May 2 2024

Saturday...Warming and drying expected as a transitory low amplitude
shortwave ridge aloft builds overhead. 700 mb temperatures near
2 Celsius will yield maximum temperatures in the lower to mid 60s.

Sunday...Continued mainly dry, though with isolated showers and
thunderstorms, as the flow aloft transitions to southwest and there
is minimal low and mid level moisture. This day looks like the
warmest day of the period as a low level thermal ridge develops with
700 mb temperatures near 9 Celsius yielding maximum temperatures
mainly in the 70s.

Monday...Cooler temperatures expected as the next progressive
shortwave trough aloft moves across the region. It looks like there
will be adequate low and mid level moisture to produce scattered
afternoon and evening showers, and a few thunderstorms.

Tuesday...Looks like a windy and mild day as a wound up trough aloft
and its associated surface low pressure pivots across eastern
Montana, producing decent low level pressure gradients for our
forecast area. With cyclonic curvature aloft and some low and mid
level moisture, we anticipate isolated to scattered afternoon
showers and a few thunderstorms despite the drying westerly low
level downslope winds.

Wednesday...The trough aloft pivots across the Dakotas, keeping
cyclonic northwest flow aloft over our counties, and with adequate
low and mid level moisture, we anticipate isolated late day showers.
Continued breezy with decent low level pressure gradients and low
level winds.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
-- Changed Discussion --
Issued at 524 AM MDT Thu May 2 2024

A weather disturbance and its associated cold front have moved
across the terminals overnight, ushering in drier conditions.

Clear skies will prevail until this evening, then ceilings
around 10000 feet will occur. Winds will gust to 35 knots until
02Z.
-- End Changed Discussion --

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...RUBIN