816
FXUS65 KCYS 060317
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
917 PM MDT Tue Aug 5 2025

.KEY MESSAGES...

- Largely hot and dry conditions are expected across the area
  through Friday. Areas of smoke from Colorado and Arizona
  wildfires may drift through the area.

- An isolated strong to severe thunderstorm cannot be ruled out
  this afternoon and again on Wednesday, mainly in the northern
  NE panhandle and east central WY.

- Red Flag Warnings remain in effect through Friday due to low
  afternoon relative humidity and poor overnight humidity
  recoveries.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 400 PM MDT Tue Aug 5 2025

A strong but stout ridge remains parked over New Mexico this
afternoon with an upper level low moving over the top of it at this
hour. In between, GOES water vapor imagery shows fairly dry air
transported in from the subtropics streaming in along the WY/CO
state line. Dry air mixing down has pushed dewpoints down into the
teens and 20s for most of the I-80 corridor and points southward
with hot temperatures in the upper 80s to 90s. With breezy west to
southwest winds, widespread long duration Red Flag Warnings look
good for today. Further north, there is a little bit more moisture
present, and diurnal cumulus is developing in this area. Surface
moisture remains plentiful in the central/northern Nebraska
panhandle, exhibited by dewpoints in the mid to upper 50s. While
vertical wind shear is not very substantial, the low level moisture
and steep lapse rates are producing good instability in this area. A
weak low level convergence zone near the Pine Ridge is providing the
focus for today`s isolated thunderstorm activity. Isolated large
hail and strong winds cannot be ruled out with today`s activity, but
the weaker shear and presence of a weak cap will make this more
limited than the active last few days.

Overnight moisture return should push back to approximately the I-25
corridor, while those to the west will see poor RH recoveries. While
smoke concentrations have improved since the morning for our area,
two large wildfires burning in northwest Colorado today are putting
out an impressive smoke plume. As this settles into the valleys, we
may see smoke drifting north with nocturnal drainage flow,
leading to thicker smoke in Carbon and Albany counties by
Wednesday morning. Daytime winds for the High Plains are
expected to retain a weak easterly component, which should keep
dewpoints a bit higher than today for far eastern Wyoming and
western Nebraska. The overall environment looks similar, with
plentiful instability, modest shear, steep lapse rates, and a
bit of a cap. The probability for thunderstorm development is
low, but if something manages to break through the cap, it may
be able to strengthen quickly and become strong to severe.

The ridge strength will peak overhead on Thursday. 700-mb
temperatures are expected to crest around +17 to +20C, which will
likely lead to Thursday being the hottest day of the week. Winds
will also turn downslope again for the High Plains, aiding the
warmth and pushing most of the lower elevations above 100F. Most
cities have forecast highs within about 1-3F of the daily record
highs for August 7, but the only record high explicitly forecast at
this time is a tie for Rawlins (92F). Still, the upper end of the
forecast range would easily put numerous additional daily records in
play, so this will need to be monitored over the coming days.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 400 PM MDT Tue Aug 5 2025

Friday through Monday will bring a synoptic pattern change, as mid-
/upper-level ridging and westerly flow give way to a series of
troughs and associated disturbances barreling through the Pacific
Northwest and northern Great Plains. There remain differences
between the global models regarding the timing and strength of these
disturbances, mainly on Sunday and Monday. The GFS even develops
something of a closed low/cut-off low over the region during this
time frame, while the ECMWF transitions the mid-/upper-levels to
northwesterly flow -- both of which could have impacts on coverage
of convection. Given the uncertainty regarding how the synoptic
pattern will evolve over the weekend, PoPs range generally from 20%
to 40% (slight chance to chance). Any disturbances that traverse the
flow may aid in organization/intensification of convection, but for
now, the probability for widespread severe weather is low. Worth
noting is that portions of the County Warning Area (CWA) may not
even receive rain. That may be the case for western portions of the
CWA, where precipitation will have to overcome drier mid-/lower-
level air to reach the ground.

This pattern change should also release the grip that our current
critical fire weather parameters have over western portions of the
CWA. Relative humidity is forecast to gradually rise from Saturday
through Monday, with sustained surface winds relaxing and lower wind
gusts as well (at least, outside of convection). Something of a cool-
down is also expected, with high temperatures transitioning from the
mid-80s to upper 90s on Friday to the lower 80s to mid-80s through
the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 910 PM MDT Tue Aug 5 2025

West flow aloft will prevail.

Wyoming TAFS...Clear skies will continue. Winds will gust to
25 knots from 16Z to 18Z, to 01Z.

Nebraska TAFS...Clear skies will continue, except for occasional
areas of fog at Chadron, Alliance and Scottsbluff from 09Z to
13Z, reducing visibilities to 4 miles and ceilings to 1500 feet.
Winds will be 10 knots or less.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 6 PM MDT Friday for WYZ419>429.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...KM
AVIATION...RUBIN