402
FXUS65 KCYS 121109
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
508 AM MDT Sat Jul 12 2025

.KEY MESSAGES...

- Temperatures will be warming Sunday through Monday, before a
  potent cold front brings cooler temperatures for Tuesday and
  Wednesday, with another warming trend for Thursday and Friday.
  Shower and thunderstorm chances will be greatest for Tuesday
  and Wednesday.

- Elevated fire weather conditions expected late this weekend
  and early next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 1222 PM MDT Fri Jul 11 2025

Cumulus field and some showers are already developing across
the area as we expect thunderstorm initiation shortly in Albany
County. Storms will form around the frontal boundary just over
the border in Colorado and continue to evolve eastwards through
the afternoon and evening primarily along the I-80 corridor,
though a few stragglers just north of this could be possible.
Low to mid level flow is quite slow, so any storms that do form
should slowly propagate eastwards bringing a heavy rainfall
threat with them alongside supportive PWAT values peaking around
125-150% of normal. Widespread QPF values are forecast around
0.5-1 inch which should keep us just outside of flooding, but if
we get clustered storms to train over a location some localized
flooding can`t be ruled out. Meanwhile for the severe threat,
mesoanalysis shows instability rising with widespread MUCAPE
around 1000-2000 J/kg and surface to 3km wind shear 25-30 knots,
supportive of isolated initial stronger storms capable of large
hail and damaging wind gusts. That being said, LCL heights are
still sitting at around 1500-2000 feet, so storms will struggle
to reach the surface and should keep the tornado threat limited
(but can`t be fully ruled out). With the slow motion, storms
will likely congeal into clusters quickly and we should see the
hail threat begin to wane while the wind threat remains enhanced
as activity continues eastwards through Nebraska. The bulk of
the strongest storm activity should vacate the CWA by around 9
to 10 PM, with a few lingering showers or weak storms possible
after that time but most precipitation should be fully out of
our area by midnight.

Overnight soundings are supportive of low clouds and possible
fog for our usual problematic spots (Laramie Summit through
western Cheyenne and also along I-80 into Sidney) with this
clearing out as the sun rises. High pressure builds and brings a
clearing and warming trend, though a few isolated terrain
driven showers or weak storms can`t be fully ruled out on
Saturday. These will be brief and mostly inconsequential, and
should quickly dissipate as the sun sets. Otherwise a pleasant
summer day is on tap with highs beginning to rebound back into
the upper 70`s to mid 80`s as warming returns, continuing into
Sunday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 1222 PM MDT Fri Jul 11 2025

Sunday...Ridging aloft builds overhead with 500 mb heights nearing
5920 meters. Warm temperatures aloft should limit convective chances
and produce a dry day. Decent warming trend with maximum
temperatures in the mid 80s to mid 90s with 700 mb temperatures near
17 Celsius.

Monday...Another hot day expected with 700 mb temperatures near 16
Celsius. Looks like enough low and mid level moisture for isolated
to widely scattered afternoon and evening showers and thunderstorms.

Tuesday...A progressive shortwave trough aloft moving across Montana
and North Dakota will send a fairly strong cold front southward
across our counties, dropping high temperatures into the upper 70s
and 80s. With decent low level upslope winds and plenty of low and
mid level moisture, we expect to see scattered afternoon and evening
showers and thunderstorms.

Wednesday...Another relatively cool day for mid July with low level
upslope, plenty of cloud cover and high temperatures in the 70s to
lower 80s. Adequate moisture for scattered afternoon and evening
showers and thunderstorms, most numerous near the Colorado state
line where the moisture will be the deepest.

Thursday...GFS shows a relatively strong cold front moving southward
across our counties in response to a shortwave trough aloft moving
over the Dakotas. However, this solution may be too fast, and thus
will continue to show maximum temperatures in the upper 70s to mid
80s, which matches well with our neighboring offices. Adequate
moisture for isolated to scattered afternoon and evening
thunderstorms.

Friday...Ridging aloft builds overhead, producing another warming
trend. 700 mb temperatures near 15 Celsius yield high temperatures
from the mid 80s to lower 90s. Despite the ridge and warm
temperatures aloft, it looks like enough low and mid level moisture
for isolated to widely scattered thunderstorms focused near the
southern Laramie Range.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 508 AM MDT Sat Jul 12 2025

Low clouds remain around KCYS, KLAR, KRWL, KSNY, and to a lesser
extent KAIA. MVFR to LIFR ceilings remain possible for these
locations to start the TAF period. These low clouds/fog should begin
to decrease by mid-morning, generally clearing between 15z and 18z.
VFR conditions then prevail for all terminals for the rest of the
period. Diurnal winds occur this afternoon, with gusts to around 20
knots, decreasing in the evening.

A few hi-res models are producing showers/thunderstorms between 19z
and 00z around KCYS and KLAR, with a lesser extent eastwards.
Chances for these locations are about 15% to 20% at this time, so
have left out mention in TAFs due to the lower confidence.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Dense Fog Advisory until 6 AM MDT Saturday for WYZ116-117.
NE...None.

&&

$$

SHORT TERM...CG
LONG TERM...RUBIN
AVIATION...RIW