468
FXUS65 KCYS 031150
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
550 AM MDT Thu Jul 3 2025

.KEY MESSAGES...

- Warm temperatures and daily chances for PM showers and
  thunderstorms will continue late this week and into the
  weekend.

- Temperatures drop back down closer to near normal for
  Independence Day but afternoon showers or thunderstorms could
  impact festivities.

- High pressure to the south could drive daily shower and
  thunderstorm chances in the long term while keeping us close
  to near seasonable for temperatures.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 345 AM MDT Thu Jul 3 2025

Current IR Satellite loop shows mostly clear skies across much
of the area with remnant clouds and showers well north of the
I-80 corridor early this morning. Further west, a band of
showers is moving northeast across Utah with increasing moisture
and dewpoints in the 50s. This is the leading edge of the next
Pacific system which is forecast to lift northeast today. Models
continue to show this Pacific trough moving into the Rocky
Mountain area this afternoon, with scattered to numerous
thunderstorms and widespread showers forecast to develop this
afternoon. Subtropical moisture will push over the area from the
southwest United States as PWATs increase over 1.00 to 1.50
inches. Can`t rule out some training heavy rain showers with
this feature. WPC continues to indicate a marginal risk for
excessive rainfall west of the I-25 corridor. Kept POP between
50 to 70 percent through the evening hours. Further east, lower
confidence when these showers and thunderstorms will make it to
the eastern high plains with most high res guidance holding off
until late Thursday night and Friday morning. Getting some
indication that nocturnal convection will initiate just before
sunrise early Friday morning for areas along and east of the
I-25 corridor. The most unstable airmass will be located in this
area with a cap inversion suppressing convection early in the
evening. However, the 700-500mb layer is expected to gradually
cool as the trough axis lifts over the area...with ample
elevated MUCAPE through the morning hours. Current run of the
HRRR shows widespread showers and thunderstorms along and east
of I-25 through early Friday afternoon. Models have trended even
slower with the upper level trough axis and are not showing it
exiting the area until later Friday afternoon. Another line of
showers and thunderstorms may develop and push into the high
plains Friday evening, disrupting July 4th festivities. It will
be a little cooler on Friday, but daytime temperatures will be
near normal for this time of the year and generally in the 80s.

For Saturday, models now show a flattened ridge axis across the
Intermountain West as another Pacific shortwave clips northern
and central Wyoming. With low level convergence along the
mountains due to westerly winds behind the shortwave, but
upslope easterly winds ahead of it...and ample moisture across
the area, showers and thunderstorms are expected to develop in
the afternoon. These thunderstorms may become strong or severe
across western Nebraska with current MLCAPE between 1500 to 2500
j/kg and 0-6km shear of 30 to 40 knots.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Issued at 400 AM MDT Thu Jul 3 2025

Little change in the long term as a typical summer pattern sets
up over the western United States. Will be monitoring the
position and movement of a developing 595 dm to 600 dm upper
level high across the southwest United States during this
period. The position and movement of this high will greatly
influence conditions here over Wyoming and western Nebraska. If
the high is centered closer to the Four Corners region with a
northward extending ridge axis, as the current 00z GFS
indicates, then hotter temperatures and a lower chance for
thunderstorms are expected. However, if this upper level high is
further west across the Great Basin, like the 00z ECMWF shows,
then cooler temperatures under northwest flow aloft is expected
with a much better chance for showers and thunderstorms. Will
also have to watch for shortwave energy ejecting eastward over
the northern periphery of the upper level ridge, since these
tend to produce strong and severe thunderstorms. Ensemble
guidance favors a blend of these two extremes, so kept high
temperatures in the mid 80s to mid 90s with a 20 to 40 percent
chance for showers and thunderstorms each day. Not expecting
this pattern to change too much through late next week.


&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 550 AM MDT Thu Jul 3 2025

Upper level ridge axis will continue to lift northeast into the
Great Plains as a broad Pacific trough moves into Utah and western
Colorado this morning. A round of showers and thunderstorms are
forecast to develop west of the I-25 corridor Thursday afternoon
through late Thursday evening with some heavy rainfall possible.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail through 21z this
afternoon. Showers and thunderstorms will develop and push northeast
over central Wyoming, mainly impacting KLAR and KRWL initially this
afternoon and this evening. A period of steady mod/heavy rainfall
may impact these terminals between 00z to 06z Friday with MVFR
conditions possible. Further east, models have trended later with
precipitation development, so will hold off on mentioning shower and
tstorm activity until after 12z Friday for western Nebraska.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...TJT/CG
AVIATION...TJT