823
FXUS65 KCYS 150519
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1019 PM MST Thu Nov 14 2024

.KEY MESSAGES...

- Mild temperatures expected through Friday.

- Colder temperatures are expected in the long term forecast,
  with an initial modest cold front Saturday followed by a more
  potent cold front with a chance for snow on Monday/Tuesday.

&&

.UPDATE...
Issued at 753 PM MST Thu Nov 14 2024

Latest IR loop was showing quite a bit of high clouds streaming
in from the southwest ahead of the deep trof moving towards
California. The bulk of these clouds will most likely not move
into southeast Wyoming until at least midnight and the Nebraska
panhandle between midnight and daybreak. This will allow for
temperatures to tumble a bit before these clouds move in. As a
result, we lowered temperatures a bit from the previous forecast
due to good radiational cooling already taking place. We also
bumped up wind speeds a bit tomorrow afternoon in Rawlins after
the departure of these high clouds in the afternoon. Later
shifts will need to keep an eye on the potential for high wind
headlines due to the potential for good mixing in the afternoon
with speeds well over 50kts in above 7kft agl.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 241 PM MST Thu Nov 14 2024

Latest upper air analysis depicts the deep trough, which swung
across the CWA 36 hours prior, has continued to track east into the
Great Lakes with an upper level ridge developing across the High
Plains. COnditions throughout the day have been mostly pleasant with
an increase in daytime highs associated with the upper level flow
and hovering in the mid to high 50s for areas in southeast Wyoming
and in the mid 60s for Western Nebraska. Not expecting much weather
throughout the day today and tomorrow with 700mb temperatures
remaining well above 0C through 03z Saturday. As a result, another
couple of days of above average temperatures and persistent dry
weather, with the NAEFS mean 700mb temperatures in the
climatological 90th percentile through Friday. Kept with the trends
of increasing temperatures with daytime highs in the mid to high 50s
across the majority of zones. Main concern through Friday deals with
some gusty to stronger winds possibly across the I-25 and I-80
corridors in response to the tightening pressure gradients with a
developing upper level trough pushing eastward from the Western
Seaboard. However, local in-house model guidance keeps winds well
below criteria with 700mb winds struggling to climb above 45 knots,
and only a few isolated areas near KBRX having brief gusts up to 52
knots after 02z. Therefore, kept holding off on issuing any
headlines with any high wind event appearing marginal at best.

Into the early portion of the weekend, the aforementioned trough
will continue swinging eastward through the Intermountain West,
before developing into split flow with a weaker shortwave to the
north and a developing closed low south of the Four Corners Saturday
night. As a result, will see a bit weaker system as the shortwave
lifts north and keeps most snow confined across the higher terrains
off to the west. Main impacts will be the much colder temperatures
associated with the cold front, dragging daytime highs 10F lower
from the previous days, in addition to continued gusty to stronger
winds along and behind the frontal boundary. Otherwise, minor snow
accumulations are possible for the Sierra Madres and Snowy range
around 1 inch or so, mostly due to the split flow decreasing
moisture advection across the zone.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 241 PM MST Thu Nov 14 2024

The weather is expected to become more active in the extended
period across se WY and w NE, with increased precipitation chances
and a more significant cooldown. Starting on Sunday, split flow will
be present over the region. A closed low will be traversing east
along the US/Mexico border, and very subtle shortwave ridging will
take place over the northern high plains as a shortwave exits north
of the Great Lakes, and the next trough digs into the Pacific
Northwest. As a result, the weather will be relatively tame on
Sunday with highs in the upper 40s to mid 50s across the plains and
dry conditions.

The weather starts to get more interesting starting on Monday,
Ensemble and deterministic model guidance is in agreement on
pivoting the southern low northward out of the southern plains and
into the midwest by early Tuesday. At the same time the Pacific
Northwest trough continues to dig south and east toward Wyoming.
This is where models begin to diverge, as the EC  digs the trough
quicker into the 4 Corners, while the GFS and Canadian keep it
further north and drive it east quicker. This pattern is also
evident in the WPC Ensemble Clusters. Both scenarios bring
precipitation in the form of snow showers, accumulating to only a few
inches, into the western part of the forecast area, Mon-Tues, with
the EC pattern being slightly wetter and with weaker flow aloft. The
eastern low could bring some precipitation to the NE panhandle Mon-
Tues, starting as rain and switching to snow, but it is looking more
and more likely the bulk of precipitation will stay east. The
pattern will also send a strong cold front south down the high
plains Mon/Tues as a surface low deepens to the east. The result
will be significantly cooler temperatures on Tuesday, with highs
only in the to the 30s across the lower elevations. Winds will also
be breezy on Tuesday in the wake of the front, gusting to at least
30 knots across eastern WY and the NE PH.

The two systems merge and deepen into an impressive low somewhere
over the mid-MS River valley. Models vary on the exact position;
further west, like with the EC, brings a prolonged period of potent
northerly flow to the area, and gusty surface winds as a result Wed-
Thurs , along with slight precip chances over the NE PH. The
Canadian is the furthest east, resulting in calmer and dry
conditions. The GFS currently lies somewhere between those two. West
of the low, a ridge begins to reestablish itself over the Rockies.
High temps on Wed remain similar to those on Tuesday, while Thursday
should see rebounding temps as the ridge builds. Tuesday night and
Wednesday night lows will be the coldest, with temps falling into
the teens across most areas. In fact, NAEFS Mean 700 mb Temps on
Tuesday night fall to the 10th percentile of climatology, signifying
a considerable cold.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1016 PM MST Thu Nov 14 2024

VFR conditions through the next 24 hours with scattered to
broken high clouds moving over the area as high pressure
remains in control of the weather. May see some fairly strong
winds out by KRWL and possibly KLAR Friday afternoon.
Otherwise...no weather impacts to aviation assets expected.

&&

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

&&

$$

UPDATE...REC
SHORT TERM...MRD
LONG TERM...BL
AVIATION...GCC