495
FXUS65 KCYS 301754
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1154 AM MDT Sat Aug 30 2025

.KEY MESSAGES...

- Scattered precipitation chances continue Saturday, though
  drier conditions are expected to return Sunday and through
  much of next week.

- Warming trend starts Sunday with temperatures closer to, or
  slight above, seasonal averages.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 315 AM MDT Sat Aug 30 2025

Current KCYS radar loop early this morning shows scattered
showers and isolated rumbles of thunder continuing over portions
of eastern Wyoming and western Nebraska. This activity is in
response to a potent upper level trough and associated 85 kt jet
max near the Colorado/Wyoming border. Some pretty heavy rainfall
fell late last night between Scottsbluff, Torrington, and
Kimball with localized amounts around 2 inches...although most
other places received around a half an inch to one inch of
rainfall. Upper level vort max is currently ejecting eastward
into western Nebraska at this hour, with storm motion oriented
northwest to southeast behind the disturbance. Will likely see
additional activity along the I-25 corridor before sunrise.
Otherwise, a brief lull in the precipitation is expected after
sunrise towards noon. As with the last several mornings, can`t
rule out some patchy fog and low stratus...especially where it
clears out briefly.

One last day of unsettled weather and relatively cool
temperatures on Saturday before next week`s drying trend.
Models show another weak disturbance aloft...embedded in the
mean mid to upper level northwest flow. Expect convection
initiation earlier in the day, with models soundings showing
little or no CIN. There could be a few stronger storms, but not
expecting long lived strong to severe thunderstorms through the
day. SBCAPE is decent around 1000 to 1500 j/kg, but shear will
be unidirectional at around 15 to 20 knots. High temperatures
will be around 5 to 10 degrees below average with highs in the
70s. Thunderstorm activity will quickly dissipate or move out of
the area around sunset.

All models show drier conditions as we head into Sunday and
Monday. Upper level high and associated ridge axis will
strengthen over the four corners region and nudge eastward, with
weakening northwest flow into early next week. High temperatures
are expected to return to the upper 70s to middle 80s on Monday,
which is near average for this time of the year. Kept POP and
Prob thunder below 10 percent Sunday and Monday afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Issued at 330 AM MDT Sat Aug 30 2025

Not many changes to the previous long term forecast package.
Uncertainty remains with the westward extent of the relatively
strong fall cold front moving into the Great Plains late Tuesday
and Wednesday. Models show an impressive 545-555 dm upper level
low dragging southeast across the Great Lakes Region, with a
strong cold front extending south and southwest into the high
plains. Ensemble spreads are the highest on Wednesday, with
interquartile range in the upper 60s to low 70s...but as low as
the upper 50s to mid 60s for the 10th to 20th percentile. With a
much drier airmass, overnight lows are expected to return to the
40s, and even some 30s in the more sheltered valleys, mainly
Tuesday night through Thursday night. Precipitation is looking
more likely along and behind the front Wednesday and Wednesday
night, but kept POP below 40 percent due to considerable
ensemble spreads during this period.


Previous discussion...

Model guidance diverges somewhat for Wednesday onward. There is good
agreement that an unseasonably strong upper level low will dive into
the central and eastern CONUS around the middle of the week, but
there is a bit of a discrepancy between ensemble systems in how far
west the edge of the cool airmass will end up. The ECMWF ensemble is
strongly clustered on a more westward position of the trough, which
would bring a noticeable hint of fall into the area for Wednesday
and Thursday. The GEFS system is mostly clustered on a more eastward
position of the trough, which would keep temperatures generally near
seasonal average through the middle of the week ahead. However, both
scenarios bring some limited chances for rainfall back into the
forecast, just from entirely different mechanisms. The westward
solution may allow for some stratiform rainfall due to modest
shortwaves rotating around the flank of the broad upper level low.
The eastward solution would allow for some limited monsoon moisture
to return to the area by Thursday or Friday, coming more in the form
of afternoon convective activity.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1148 AM MDT Sat Aug 30 2025

A mix of flight categories expected through tomorrow. Primarily
all sites will have a low risk of a passing shower or storm
which could briefly lower CIGs or VIS, but not expecting a long
duration event at any site. Otherwise, expecting a deck of low
clouds and possibly some BR at KCDR/KAIA tomorrow morning much
like this morning. Otherwise CIGs will be generally mid level,
around 8-10k feet. Winds around 5 to 15 knots, with some
occasional stronger gusts possible, particularly if a storm or
shower moves near or over a site. Storms expected through this
evening, weakening after the sun sets.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...MN
AVIATION...CG