501
FXUS65 KCYS 121038
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
438 AM MDT Sun Oct 12 2025

.KEY MESSAGES...

- Widespread strong winds are expected through this afternoon.
  Fire weather conditions will be elevated over the High Plains.

- Chilly temperatures will lead to frost and areas of sub-
  freezing temperatures tonight into Monday morning.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 430 AM MDT Sun Oct 12 2025

A potent frontal boundary is currently about halfway through its
trek across the forecast area. A powerful upper level low is
apparent on GOES satellite imagery circulating over roughly
south central Montana. A narrow tongue of increased mid to upper
level moisture content is apparent stretching to the south,
currently over Carbon County. Earlier this morning, rain changed
over to brief light snow at Rawlins before getting chocked off
by dry air. Strong, moist southwest flow is continuing to
produce precipitation (likely mostly snow by now) in the
mountains of southeast Wyoming, but this will likely come to a
close by around sunrise as the dry air pushes into the
mountains. While I-80 is likely seeing some light snow, nothing
more than a dusting is anticipated below about 8000`.

The main concern with this system remains the expected strong winds.
Several gusts of 60 to 65 mph have already occurred along the
frontal passage in Carbon county, and we are in somewhat of a lull
right now. Surface pressure is expected to continue to build over
the inter-mountain region through the day today. The pressure
gradient will maximize around 9am. Indicators still look good for
the existing High Wind Warnings, but confidence remains fairly low
in the I-25 wind prone areas actually reaching criteria due to a
consistent model signal for the surface trough setting up very close
to the crest of the Laramie Range, west of I-25. The strong winds
aloft (likely exceeding 55 knots and approaching 60 knots at 700-mb
this morning) combined with good synoptic descent and potential for
breaking mountain waves is sufficient to lean towards I-25 seeing
the stronger winds. Outside of the wind prone areas, there is
potential for a brief gust exceeding 60 mph, especially in Converse
County and the southern Nebraska panhandle. However, this is
expected to be brief if it occurs, and its probability is too low to
warrant an expansion of the High Wind Warning. Regardless, a very
windy day can be expected for nearly the entire area with widespread
gusts of 40 to 55 mph on track. With RH dropping to between 15 and
20%, fire weather conditions will be elevated.

Winds will die down quickly around sunset as the surface high
pressure settles in over the High Plains. With clear skies and a
fairly dry airmass in place, the stage will be set for excellent
radiative cooling and chilly temperatures into Monday morning.
However, recent model guidance has trended faster in evacuating the
surface high pressure to the east. Once this occurs, winds are
expected to begin again, mainly out of the south to southeast. This
may prevent a widespread killing freeze over the High Plains. Still,
localized freezing temperatures are very likely. Therefore, it seems
that a Frost Advisory may better represent the potential hazard, and
we can save the Freeze Warning for the first widespread hard freeze.
The caveat here is that dewpoints will probably be too low to see
frost develop over Laramie County, but areas to the north and east
will be slightly more humid and thus can expect actual frost
formation early Monday morning.

The southerly winds will increase Monday as the strong surface high
moves off to the east. Winds are expected to be unusually strong for
a southerly wind event. Widespread gusts of 35 to 45 mph can
expected for the Laramie Valley and points eastward, and we could
even see some isolated gusts exceeding 50 mph, mainly in the
southern Laramie Valley, around Chugwater, and along the Pine Ridge.
Meanwhile, a powerful closed low will dive into the West Coast on
Monday, amplifying the downstream ridge over the southern plains. As
the flow aloft turns more southerly again, deep moisture will be
pulled north once again in a resurgence of the pseudo-monsoonal
weather pattern. Cloud cover and shower activity will increase
from the south once again beginning Monday morning. The best
chance for rainfall will again be in Carbon county where
orographic lift will assist, but there does appear to be
sufficient positive theta-e advection aloft to produce a few
showers over the High Plains Monday and Monday night.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 430 AM MDT Sun Oct 12 2025

Mild and unsettled weather will continue through Wednesday as the
unseasonable monsoon-like pattern continues. Precipitable water will
remain well above climatological norms keeping low-end shower
chances in the forecast. 700-mb temperatures will peak on Wednesday
which should be the warmest day of the week with highs around 10F
above average. The powerful closed low over the West Coast will
begin to lift off to the northeast midweek, and will bring a better
potential for widespread precipitation late Wednesday into early
Friday. While the details are still somewhat uncertain, there is now
better ensemble agreement in the upper level low tracking off
to our northwest once again, which puts the area in the warm
sector of the system. Still, snow showers mixing in will be
possible west of the Laramie Range, but those to the east will
probably need to wait a bit longer for the first flakes of the
season. As the trough axis moves through, westerly winds are
likely to increase once again. A period of high winds is
certainly possible, but the timing and details are still highly
uncertain at this lead time.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1134 PM MDT Sat Oct 11 2025

A strong cold front is beginning its trip across the area
currently. KRWL is on the only terminal expected to receive
precipitation along the front. Showers with some embedded
thunder are expected nearby for the next 2-3 hours or so, after
which time there is a 30% chance for a brief period of snow
which could lead to a VIS/CIG drop to MVFR. IFR cannot be ruled
out. Expect drier air to work in after 10z.

Further east, shallow fog is developing in the NE panhandle.
KSNY has improved to VFR, and could hold on to light westerly
winds long enough to maintain VFR, but a dip back to IFR over
the next few hours is certainly possible. KAIA (and later, KBFF)
are expected to be in IFR to LIFR more consistently. All should
quickly improve with the frontal passage between 10 and 13z.

Attention shifts to strong winds for Sunday. Marginal LLWS is
possible through early Sunday morning ahead of the surface
front. Expect westerly winds to jump up quickly along the front.
Speeds will increase around 15z across the board with widespread
gusts of 35 to 45 knots through early afternoon. Winds will
begin to weaken mid-afternoon, and then drop off quickly around
00z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Frost Advisory from midnight tonight to 9 AM MDT Monday for
     WYZ106>108-117>119.
     High Wind Warning until 6 PM MDT this evening for WYZ106-110-
     116.
     High Wind Warning until 6 PM MDT this evening for WYZ107-117.
NE...Frost Advisory from midnight tonight to 9 AM MDT Monday for
     NEZ002-003-019>021-054-055-095-096.

&&

$$

SHORT TERM...MN
LONG TERM...MN
AVIATION...MN