-- Discussion containing changed information from previous version are highlighted. --
079
FXUS65 KCYS 151001
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
401 AM MDT Sat Jun 15 2024

.KEY MESSAGES...

-- Changed Discussion --
- Scattered high-based showers and thunderstorms will develop
  this afternoon. Primary concern with these storms will be wind
  gusts over 60 MPH and the potential for dry lightning.
-- End Changed Discussion --

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
Issued at 355 AM MDT Sat Jun 15 2024

Southwesterly flow will dominate this morning as the shortwave
responsible for Friday`s storms pushes eastward and a strong upper-
level ridge builds over eastern CONUS. This southwesterly flow will
advect warm air into the CWA and rapidly warm surface temperatures.
700 mb temperatures will range from +12C to +16C by the afternoon,
leading to highs in the upper 80s to mid 90s. Winds will shift more
westerly during the afternoon hours as a weak disturbance passes
overhead. This will lead to a quick drying out of the low-levels as
the dryline is pushed further east into Nebraska. Winds, especially
west of the Laramie Range will also ramp up as 700 mb winds increase
up to 45 kts. Because of this, cannot rule out elevated wind gusts
above 50 MPH for the western zones. This disturbance will also spark
scattered convection by mid-afternoon. Thunderstorms will be high-
based since the low-levels will be very dry. Model soundings show
prominent inverted-V profiles with DCAPE values across the CWA over
1000 J/kg. This will primarily lead to a strong wind threat in and
around storms. With the already elevated wind gusts expected
out west, winds in these storms could gust over 60 MPH. Because
the low-levels will also be so dry, its possible that little to
no precipitation will make it to the ground, leading to an
elevated risk for dry lightning strikes. Storms will not linger
around long, with convection wrapping up by early evening.

Looking at quieter weather on Sunday as a trough begins to dig
southeastward out of the Pacific Northwest. This will push cooler
700 mb air into the northern portion of the CWA, dropping high
temperatures by about 10 degrees for areas north of the North
Platte River Valley. Most Hi-Res guidance is in agreement with
limited shower and storm activity during the day. But a frontal
boundary sagging into the far northern zones Sunday evening will
increase moisture and potentially lead to thunderstorms
developing.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Issued at 355 AM MDT Sat Jun 15 2024

Medium to long range models in better agreement as we head into
early to mid next week. Deterministic models and ensembles
continue to show southwest flow aloft through most of next week
with several disturbance bringing a daily round of showers and
thunderstorms...mainly to the eastern plains and the mountains.
A long wave upper level trough across the eastern Pacific is
forecast to remain anchored near the Pac NW through Tuesday,
with the primary shortwave trough forecast to push across the
northern Front Range Monday night and early Tuesday. At the
surface, upslope east to southeast winds will continue nearly
every day this week as surface high pressure will fluctuate from
southern Canada and the northern plains. Expect a continuation
of isolated to widely scattered (10 to 30 percent coverage)
thunderstorms in the late afternoon through the late evening
hours Monday and Wednesday, with Tuesday appearing the only
"dry" day so far behind a surface Pacific cold front. Temperatures
should remain near or slightly above average with highs in the
80s for most locations along I-80 and west of I-25. Continued to
lower temperatures further north towards Niobrara County and the
northern Nebraska Panhandle (Alliance, Chadron) as a backdoor
cool front stalls just north of the North Platte River valley on
Monday.

For Tuesday and Wednesday, Models are in much better agreement
with some late-season cooler air moving across the forecast area
with low temperatures likely in the upper 30s to mid 40s both
Tuesday and Wednesday morning. Hesitated to lower temperatures
towards MOS guidance and the 10th to 20th percentile of
ensemble spreads due to forecast cloud cover. Will continue to
keep an eye on this as some guidance suggests a near freeze for
the colder high valleys. Newest 00z model runs are now showing
700mb temperatures lowering to -2c across central and eastern
Wyoming, which is a little colder compared to yesterday. Kept
high temperatures in the mid 60s to mid 70s on Tuesday and
Wednesday although some guidance remains about 5 to 10 degrees
cooler due to cloudy skies and upslope winds. Probability for strong
to severe thunderstorms is very low both of these days due to
cooler air near the surface but relatively warmer air
aloft...resulting in stable thermodynamic profiles.

For later in the week, models indicate a general warming trend
as we head into Thursday and Friday with a more favorable
environment for afternoon and evening thunderstorms due to
Pacific shortwave energy and a more active subtropical jet
stream.
-- End Changed Discussion --

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1040 PM MDT Fri Jun 14 2024

Concerns with the 06Z TAFs will be fog/stratus in the Panhandle
overnight. Some areas received significant rainfall this
afternoon and evening...especially across northern Cheyenne
County into southern Morrill County. Lots of low level moisture
tonight that could aid in low cloud/fog development. Primary
airports of concerns will be KBFF and KAIA where the latest HRRR
guidance shows widespread IFR/LIFR conditions. Followed its
guidance on timing. As for KSNY...need to keep an eye on
observations overnight as they got over a half inch of rain as
well. Improving conditions after sunrise Saturday with VFR
conditions returning to all airports.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM...TJT
AVIATION...GCC