432
FXUS65 KCYS 192058
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
258 PM MDT Sat Oct 19 2024

.KEY MESSAGES...

- Areas of fog are expected tonight into Sunday morning over the
  High Plains, particularly along the Cheyenne ridge.

- Strong winds are possible Monday and Monday night, with warm
  and dry weather taking over for the remainder of the week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 300 PM MDT Sat Oct 19 2024

The morning fog and low clouds have cleared out, leaving our area
with pleasant fall-like weather and mostly sunny skies. Yesterday`s
storm system has dropped well to the south, currently visible on
satellite imagery spinning over southern Arizona. Its cloud
shield extends almost up to the CO/WY border, but the broad
ridge is rebounding around the closed low, returning mild
temperatures to the area. Despite feeling chilly relative to
recent weather, highs today are still a few degrees above
average for mid October. Surface dewpoints remain fairly high
across the area today, generally in the 30s and 40s, which will
set the stage for another round of low clouds/fog across the
area. Light south to southeast flow will support some fairly
widespread upslope fog and/or low clouds over the High Plains
and possibly the Laramie Valley. Dense fog advisories will
likely be needed by morning, but the confidence in this coming
in as fog vs. low clouds is not high enough to issue any
products just yet. The most likely area to see fog will be the
higher spots along the Cheyenne ridge where the low cloud deck
will intersect the ground. Expect a fairly heavy frost in the
valleys of Carbon, Albany, Converse, and Niobrara counties, but
no products were issued since all of these areas have already
seen a season- ending freeze.

Fog and low clouds will gradually clear through the morning, and
should be mostly gone by noon as the closed low to the south begins
to spin back northward. Expect partly cloudy skies as some mid to
high level cloud cover ahead of the closed low works its way back to
the north. Highs will rebound quickly back to values around 10F
above average for this time of year. Vorticity advection aloft
collocated with very marginal instability over our western zones
should be enough to kick off a few isolated showers mainly in
southern Carbon/Albany counties. This may continue into the
evening/overnight hours as more synoptically driven lift comes into
play, but there is some uncertainty if this will make it north of
the border into Wyoming. Another area of lift will be present in the
southerly flow over the Plains in advance of the lifting upper level
low. However, best estimates currently indicate this lift will be
just south and east of our area, which means that our Plains areas
will most likely miss out on the second phase of this system just as
they missed the first phase. Through Sunday afternoon/evening, the
upper level low will support the development of a modest lee trough
along the I-25 corridor as surface pressure simultaneously
increases over the inter-mountain region. This will increase
wind speeds Sunday night, mainly just in the wind prone areas to
start, but spreading across the plains Monday once the trough
axis moves to the east of the area. Probabilities for high wind
remain fairly low through the daytime hours Monday, but breezy
conditions gusting to 40 or perhaps occasionally 50 MPH look
like a good bet. The best window for high winds will be Monday
evening and overnight with a brief period of stronger 700-mb
flow behind the exiting trough with probabilities of about 30 to
50% for the wind prone areas. With 700- mb flow peaking around
45 knots and a marginal cross-barrier pressure gradient,
confidence is not very high at this time, but the gridded
forecast reflects winds slightly below high wind criteria Monday
night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Issued at 300 PM MDT Sat Oct 19 2024

Long term forecast will focus on the return to above normal
temperatures with models trending towards quasi-zonal flow aloft and
potentially weak upper level ridging leading to above average
temperatures for the majority of the week. Tuesday and Wednesday
will be the coldest/wettest of the period, with the clipper system
tracking north across Montana and far northern Wyoming with it a
chance for precipitation across our northern zones and a backdoor
cold front dropping temperatures into the mid-60s. Expected to be
relatively shortlived with weak upper level ridging expected to
build back into the region Thursday and Friday, with a semi-omega
block pattern attempting to build across the CONUS. NAEFS mean 700mb
temperatures have begun locking onto this model solution with 700mb
temperatures in the climatological 90th percentile for the majority
of areas across southeast Wyoming and the Nebraska Panhandle both
Thursday and Friday. As been the trend over the last month, will
need to continue blending in higher NBM percentiles to the current
long term model blends to slowly increasing daytime highs to account
for this most recent model solution. Could see this upper level
pattern break up pretty quickly into the weekend, with the next
shortwave expected to push east of the Western Seaboard, dropping
daytime highs a few degrees, in addition to some increased winds for
zone. Will need to monitor for any precipitation associated with
this wave, as PWATs indicate the system is mostly dry with westerly
winds keeping the area under a dry downsloping flow and prolonged
fire weather concerns into late October.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1138 AM MDT Sat Oct 19 2024

Conditions beginning to clear across the CWA, with IFR CIGs and
Visibility lifting across the majority of terminals, outside of
KRWL with some lingering IFR ceilings. Latest satellite imagery
has showed continual clearing for areas surrounding KRWL, with
KRWL expected to lift by 19z. Next main concerns over the next
24 hours will focus on IFR conditions for areas east of the I-25
corridor beginning tonight for KCYS and the early morning hours
for the Nebraska Panhandle. Easterly components to the wind
will be enough tonight to bring upslope flow and IFR conditions
for KCYS, KAIA, KSNY, and KBFF. See TAFs for timing.

&&

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

&&

$$

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