660
FXUS65 KCYS 050530
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1130 PM MDT Fri Oct 4 2024

.KEY MESSAGES...

- Red Flag Warnings and High Wind Warnings now in effect for
  portions of today through Saturday.

- Very dry conditions to continue for the foreseeable future.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 125 PM MDT Fri Oct 4 2024

Clear, sunny skies persist across southeast Wyoming and western
Nebraska. Temperatures have warmed nicely across the region with
temperatures currently in the mid-70s to low-80s. Breezy winds are
ongoing west of I-25 with winds gusting to around 30mph as of 19Z.
The High Wind Watches have been upgraded to High Wind Warnings and
expanded to include the I-80 Summit and runs from midnight tonight
through 6pm Saturday. Additionally, the Fire Weather Watch has been
upgraded to a Red Flag Warning as humidity values will be well into
critical levels across the entire region. However, the timing
remains the same, with the newest portions of the Red Flag Warning
only running from 6am Saturday through 8pm Saturday, rather than
overnight Saturday like the majority of the Red Flag Warning.

With already dry conditions across the region, no precipitation
since early September, and dry downsloping winds across the higher
terrain, decreased dewpoints around two degrees across the entire
area. Previous forecasts have been slightly too high on the dewpoint
values, so decreasing the values a couple of degrees should better
represent the very dry conditions. With this decrease, relative
humidity values across the Fire Weather Watch zones tanked to 10 to
15 percent, so included these areas into the Red Flag Warning. Gusty
winds will continue throughout the day Saturday as a 700mb shortwave
trough traverses to the north across Montana, leading to tightened
height gradients across the mountain ranges and increased 700mb.
700mb winds around 60 to 65kts, leading to very strong winds at the
surface. GFS Omega fields suggest a strong upward/downward couplet
across the Laramie and Snowy Ranges. Therefore, high wind criteria
winds are expected in the typical wind prone regions across
southeast Wyoming. Did decrease winds slightly in the Laramie Valley
due to GFS Omega suggesting strong rising motion with the mountain
wave pattern setting up across the ranges. With the strong upward
Omegas over the Laramie Valley, surface winds will be elevated, but
should remain below high wind criteria. The mountain wave looks to
break near the I-80 Summit, evident by the strong downward Omegas
across the region. With this mountain wave breaking, included the I-
80 Summit into the High Wind Warning as strong surface winds are
expected. High winds should remain west of Cheyenne and portions of
the Panhandle, but expecting elevated winds to continue. With these
downsloping winds across the region, increased over night low
temperatures a little, as the dry, adiabatic warming associated with
downsloping winds should keep the adjacent locations warmer than
previous nights.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 232 AM MDT Fri Oct 4 2024

The GFS/ECMWF/GEM are showing various differences in the
amplitude of the upper level ridge over the Rockies next week.
The GEM shows a more zonal pattern while the ECMWF has more
amplitude while the GFS is somewhere in the middle. Meanwhile,
the ensembles and clusters continue to support the upper level
ridge keeping its grip over the Rockies and leans more towards
an amplified ridge solution. With this in mind, we decided to
do a blend of the models for max temperatures with a little
more emphasis in the bias corrected data which keeps us a tad
warmer than the National Blend of Models. We are also leaning
towards minimal chances of high wind headlines due to the jet
staying mostly north of the forecast area.

The GFS is getting a little excited about a strong upper level
trof approaching the west coast this weekend and closing off
somewhere over the Intermountain West. This solution would bring
a good shot of drawing some moisture and precipitation to the
area next weekend. At this point, this solution is an outlier
compared to the rest of the models. However, the NBM is showing
a glimmer of hope with about a 20 to 30 percent probability of
>.01. Certainly not a drought buster. We will see how things
pan out with later runs. For now, we are looking at mild and dry
weather continuing through the week with near critical fire
weather conditions.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1123 PM MDT Fri Oct 4 2024

A fast moving weather disturbance aloft and its associated cold
front will sweep across the terminals today, producing windy
conditions.

Wyoming TAFS...Mostly clear skies will prevail. Winds will gust
to 50 knots at Rawlins until 00Z, then to 30 knots until 03Z.
Winds will gust to 40 knots at Laramie and Cheyenne until 02Z.
Expect low level wind shear at Laramie until 11Z.

Nebraska TAFS...Mostly clear skies will prevail. Winds will gust
to 35 knots at Chadron until 01Z, to 35 knots at Alliance from
14Z to 03Z, and to 35 knots at Scottsbluff and Sidney from
16Z to 23Z. Expect low level wind shear at Chadron, Alliance
and Scottsbluff from 09Z to 18Z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 7 PM MDT Saturday for WYZ417>429-432.
     Red Flag Warning from 6 AM to 7 PM MDT Saturday for WYZ430-431-
     433.
     High Wind Warning until 6 PM MDT Saturday for WYZ104-106-107-
     109-110-116.
NE...Red Flag Warning until 7 PM MDT Saturday for NEZ434-435.
     Red Flag Warning from 6 AM to 7 PM MDT Saturday for NEZ436-437.

&&

$$

SHORT TERM...AM
LONG TERM...REC
AVIATION...RUBIN