961
FXUS65 KCYS 130316
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
916 PM MDT Tue Aug 12 2025

.KEY MESSAGES...

- Hot temperatures and critical fire weather conditions are
  expected to return for Wednesday and Thursday.

- Isolated to widely scattered PM showers and thunderstorms will
  return for Thursday onward.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 300 PM MDT Tue Aug 12 2025

Dry and fairly calm conditions prevail over the area this afternoon
with mostly sunny skies aside from typical diurnal cumulus mainly
concentrated over and near the mountains and elevated ridges.
Temperatures this afternoon are reaching highs just a touch below
average for mid August. Westerly flow aloft dominates overhead while
the stout ridge has been suppressed into the desert southwest.
Overnight tonight, we will see pressure falling along the I-25
corridor, while higher pressure remains fairly steady to the east.
This will increase the pressure gradient over the High Plains and
lead to a modest low-level jet event late this evening into
Wednesday morning. Look for gusty southerly winds over much of the
High Plains, particularly on the higher/windier portions of the Pine
and Cheyenne Ridges.

Rapid warm air advection will take place aloft over the next 24
hours as the ridge axis shifts eastward. This will also be enhanced
ahead of a very subtle shortwave trough moving over the top of the
ridge. By Wednesday evening, the NAEFS mean has 700-mb temperatures
pushing +16 to +18C, which will be up around the 90th to event
97.5th percentile of climatology. The surface trough will end up
somewhere around the WY/NE state line, allowing westerly downslope
winds to aid warming for all of southeast Wyoming. Look for a hot
day with highs reaching into the 90s to lower 100s for most. Even
Laramie and Rawlins will likely be close to 90F. The aforementioned
weak shortwave aloft will provide some modest synoptic lift as it
moves north of the area Wednesday afternoon and evening. While the
boundary layer looks very deep and very dry, some decent mid-level
moisture may allow for a few high based showers and thunderstorms,
mainly for the northern portions of the forecast area. Most of this
will be virga, possibly bringing gusty and erratic winds to the
area. Low level moisture will be most appreciable for our far
eastern zones, which stand a slight chance for producing a more
organized thunderstorm and actually receiving rainfall. PoPs were
added to account for this activity. A Marginal Risk for severe
weather has been introduced by the Storm Prediction Center, mainly
just around Dawes County.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 300 PM MDT Tue Aug 12 2025

An upper level ridge starts to slowly break down on
Thursday and push off to the east as an upper level system tracks
eastward across the Canadian providences. Westerly flow continues to
be the dominant pattern as a stout dry air layer continues to hold
firm near the surface. Between Thursday and Saturday some weak
disturbances will provide some isolated to scattered thunderstorm
chances. With the firm hold that the dry air has near the surface,
there`s some uncertainty as to how much rain will make it to the
ground. This dry layer also presents a fire weather concern as some
areas may experience dry lightning those days as well. Any area with
cured fuels may also be at risk for wildfires to occur if dry
lightning were to struck these areas. Saturday looks to be the best
day out of the three days for rain chances as we switch from
westerly flow to a more southerly flow. The moisture advection is
slightly stronger allowing some moisture to infiltrate the lower
levels for scattered thunderstorms to have rain reach the ground.
Sunday through the next work week that ridge retrogrades back to the
four corners region to give us back our westerly flow pattern. LREF
cluster analysis shows a ridge building next week as all the global
ensembles have reached a consensus in that aspect. There is some
disagreement as to the amplification of the ridge and how warm we
will get. This mainly has to do with a low pressure system moving
through the Pacific Northwest during this time. Depending on how far
this system digs into the Pacific Northwest will directly influence
how amplified the ridge will be over us. This will be a monitoring
point for trends and see how models handle this upcoming system.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 913 PM MDT Tue Aug 12 2025

Northwest flow aloft prevails. Skies will be mostly clear. Low
level wind shear occurs at Chadron and Scottsbluff until 13Z to
14Z. Winds will gust to 25 knots at Chadron until 13Z, and to
27 knots at the Wyoming terminals, Sidney and Alliance from 14Z
to 01Z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from noon to 8 PM MDT Wednesday for
     WYZ418>422-427.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...MM
AVIATION...RUBIN