Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 230525
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1125 PM MDT Fri Mar 22 2024

.KEY MESSAGES...

- Mild conditions are expected to persist through Saturday.

- Increasing chances for rain and mountain snow showers on
  Saturday afternoon. Minor snowfall accumulations possible
  above 9000 feet. Showers may produce 45+ MPH wind gusts.

- Trending much colder Sunday afternoon into Monday with
  widespread light snow and areas of blowing snow.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 215 PM MDT Fri Mar 22 2024

1013mb surface low a cross the north Laramie Range early this
afternoon. A stationary boundary extends south southeastward
from this low to Bordeaux to Pine Bluffs into eastern Colorado
this afternoon. East to northeast winds east of this low/front
continues to bring fairly widespread clouds across the northern
Panhandle into Converse and Niobrara Counties. Broad upper ridge
axis located across eastern Uta/western Wyoming and Colorado
this afternoon with gusty west winds west of the frontal
boundary in Carbon and Albany Counties.

Upper ridge axis slides east this evening ahead of a strong low
pressure system moving into the PACNW. ECMWF a tad slower on
ridge moving through the CWA...roughly by 12 hours or so.
Surface boundary does shift eastward into the Nebraska Panhandle
by Saturday morning with westerly winds increasing. It will be
a breezy day across southeast Wyoming Saturday as GFS 700/750mb
winds increase up to 30-35kts.

ECMWF and SREF guidance showing an increase in showers tonight
into Saturday along the front that stays along the east slopes
of the Laramie Range. Preferred this slower solution and used
for PoPs on Saturday. Could have a few thunderstorms with these
showers as MUCAPE values near 400 J/KG out across Carbon County
and 300 J/KG across the southern Panhandle. Did not add
thunderstorms in the forecast...but would not be surprised to
see a few lightning strikes tomorrow afternoon. SPC has a
General Thunder Outlook over much of Wyoming and Nebraska
Panhandle for Saturday.

As upper trough approaches late Saturday afternoon into the
evening hours...look for snow to become fairly widespread across
the Snowy and Sierra Madre Ranges under diffluent flow ahead of
that trough.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 215 PM MDT Fri Mar 22 2024

Big changes are on the way beginning Sunday and lasting into next
week as a strong storm system traverses across the west. On Sunday,
there is good model agreement on a broad, strong long wave trough
positioning itself over the western US, with a potent subtropical
jet stream surging around the south side across the desert SW
states. The upper level low is somewhat fragmented, with the
initially stronger 500-mb low coming in across the northern Rockies,
while a more vigorous and faster moving shortwave races in below
this, and ejects east of the Rockies later on Sunday. With the
northern low initially dominating, our area is expected to be in the
warm sector Sunday morning. While clouds and some precipitation will
be around, substantial amounts of rain or snow are not expected
during the morning. As the day progresses, the southern shortwave
will support a rapid deepening of a surface cyclone over east
central Colorado in the lee of the mountains, which will eventually
help the southern shortwave take over as the baroclinic zone is
drawn further south. The surface front will plow through the area
sometime during the morning or early afternoon, with brisk
northerlies moving in behind. As a result, expect Sunday`s highs to
be reached early in the day, with temperatures dropping through the
afternoon hours.

Overall, precipitation amounts are much lower with this system than
what would typically be expected for a storm taking this track,
primarily due to the northern shortwave preventing lift and moisture
from wrapping around the system until later in the event. The timing
of the secondary low to the south taking over is the main
uncertainty in snowfall totals at this time. The latest guidance has
trended slightly faster with this process, resulting in higher QPF
compared to previous forecast cycles. Models really don`t show much
of a period of solid upslope easterly flow with this system, as
north to even NNW winds take over right as the storm gets going.
This keeps even the isentropic lift off to our northeast, but areas
favored by northerly flow could still do a little better. The most
likely scenario at this time is widespread light snow over the High
Plains. A few areas more favored to get into advisory criteria
include the Pine Ridge, north side of the Cheyenne Ridge, and
possibly the south Laramie range. Areas further east will also be
closer to the TROWAL, so there is more upside potential particularly
in our eastern row of counties. Those areas will also hold onto
precipitation for a little bit later, as most guidance shows dry air
not making it into those areas until perhaps Monday afternoon.
Monday will be a big chance from recent weather, as 700-mb
temperatures plummet close to -15C. Expect highs to struggle to
reach freezing for most of the area, with chilly northerly winds
continuing to blow. This may cause blowing snow concerns to linger
into Monday, depending on how much snow falls in each area.

Beyond the first system, the weather pattern will remain unsettled
through much of next week. Shortly after the system departs, ridging
will try to build back into the west, allowing a fairly moisture
laden jet stream to translate back across the area from southwest to
northeast Tuesday into Wednesday. This should keep light mountain
snow showers going those days, possibly spreading into the nearby
valleys and adjacent plains Tuesday and Wednesday afternoons. We`ll
also see a gradual warming trend this week, but we may not see above
normal high temps again until Thursday when the ridge axis shifts
across the Rockies ahead of the next shortwave.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1125 PM MDT Fri Mar 22 2024

Scattered snow showers possible overnight at southeast Wyoming
terminals and northern Nebraska panhandle sites. Any shower passing
over a terminal could result in IFR conditions due to poor
visibility in falling snow. Winds will be gusty overnight at
Nebraska terminals with the presence of a low-level jet. The
southeasterly winds will also potentially lead to low CIGs Saturday
morning. Another round of more widespread showers will be possible
Saturday afternoon. Cannot rule out a thunderstorm or two.

&&

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

&&

$$

SHORT TERM...GCC
LONG TERM...MN
AVIATION...SF


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