939
FXUS65 KCYS 171141
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
541 AM MDT Sat May 17 2025

.KEY MESSAGES...

- Seasonable temperatures into this weekend with isolated
  thunderstorms returning on Saturday.

- Active weather pattern late this weekend and possibly early
  next week as another Pacific storm system impacts the region.
  There is a chance for strong to severe thunderstorms on Sunday
  across the eastern plains.

- Drier weather with a slow warming trend for mid to late next
  week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 237 PM MDT Fri May 16 2025

Afternoon visible satellite reveals a broad deck of flat cumulus
cloud cover over much of the CWA as transient ridging and cool
air aloft continue over the CWA. This cloud cover has kept
afternoon high temperatures somewhat cooler than expected by a
few degrees. Gusty northwest flow also remains in place along
the backside of the departing low pressure to the east, with
some obs sites along and east of the Laramie Range reporting
wind gusts upwards of 45 mph. As this low pressure center
continues to pull away and daytime heating and surface mixing is
lost, winds will diminish overnight and a majority of the
convective-based cloud cover will dissipate. Expect another cool
overnight with lows generally at or slightly below average for
mid-May.

On Saturday the transient ridge will slide east into the high
plains as a deep trough dives into the Great Basin/Four Corners
region. While heights aloft will continue to rise a bit through
the day, surface flow will quickly change to southeasterly
upslope throughout the afternoon with typical terrain-based
convergence patterns setting up. With a bit of mid-level
moisture increases noted after 21z and strong daytime heating, a
few very high-based convective showers and possibly some
thunder are possible along and east of the Laramie Range,
despite surface dewpoints generally progged to only reach the
upper 30s by late afternoon. Farther west, some additional
showers and weak thunderstorms will likely form off of the
higher terrain of the Sierra Madre and Snowy Ranges. Later in
the evening/overnight period, there is some concern for low
stratus/fog in the NE panhandle and Southeast Wyoming as deeper
moist upslope flow returns ahead of the trough. Forecast
confidence remains high throughout the short-term with minimal
adjustments made to forecast grids.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 237 PM MDT Fri May 16 2025

Sunday begins with low pressure at the surface in the
Central/Southern Plains and a secondary system moving into the
Wyoming area while at the upper levels a stout Pacific trough
will progress towards the Plains and split off into a closed
low. Once again the environment will be mostly marginal for
severe activity, but a modestly unstable environment including
MUCAPE anywhere between 750-1500 J/kg alongside Effective Shear
values of 20-40 knots should be enough to fuel stronger
thunderstorm activity, primarily impacting the southeastern
corner of Wyoming and the southern and central Panhandle of
Nebraska. Some stout capping and CIN will need to be overcome
however, precluding a stronger threat for severe activity, but
any storms that can get going will have the potential for all
severe hazards with the strongest risk in Cheyenne County, NE.
Plentiful moisture alongside this expected activity could also
bring widespread wetting rains, with 0.5-1.5 inches possible
from I-25 eastwards, but amounts could be locally heavier or
lighter depending on where the strongest storms form and how the
evolve.

Moving ahead to the start of the week, on the backside of this
system another day of precipitation for most of the region is
likely but this time only rain and some mountain snow is likely,
with amounts around 0.2-0.75 inch expected from the days
precipitation. Some light precipitation may linger into Tuesday
as this system slowly evolves eastwards across the Mississippi
River Valley, but by the middle of the week a flat ridging
pattern should evolve, allowing us to warm back into the 70s by
Thursday. An isolated shower or storm daily may occur from some
weaker embedded systems progressing through the region, but
analysis of the ensemble clusters shows that the ridge will
continue to build through Thursday and may continue into next
weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 537 AM MDT Sat May 17 2025

VFR will likely continue through the forecast period for
southeast Wyo and western Neb terminals, although there are a
couple aviation weather hazards. The first deals with gusty
south/southeast winds during the afternoon and evening with
speeds approaching 25 kts at times. The second concerns
scattered shower and thunderstorm activity, mainly during the
early and mid evening hours. Gusty erratic winds are anticipated
invof any shower, while brief ceiling drops to around 5kft are
possible. Gusty southeast winds may continue through the
overnight hours tonight in the Neb panhandle.

&&

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

&&

$$

SHORT TERM...MAC
LONG TERM...CG
AVIATION...DS