Area Forecast Discussion
Issued by NWS Cheyenne, WY

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

000
FXUS65 KCYS 131134
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
534 AM MDT Wed Mar 13 2024

.KEY MESSAGES...

1) Winter Storm Warnings are in effect starting Wednesday
morning for the Snowy and South Laramie Ranges, including the
I-80 Summit between Cheyenne and Laramie.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 406 AM MDT Wed Mar 13 2024

Model and ensemble trends are coming into better agreement early
this morning with most model solutions trending towards less
snowfall outside of the mountains. IR Satellite loop early this
morning shows broad cyclonic flow across the western third of
the United States as the primary upper level trough slides
southeast across the Pacific NW. This trough is forecast to
eventually become a closed low and dig southward into the
eastern Great Basin region today. Ahead of this main system,
current KCYS radar loop shows rain and snow showers with snow
mainly above 6500 feet. These bands of precipitation are in
response to the leading shortwave disturbance ejecting northeast
across the plains today. The primary difference with model
solutions compared to 36+ hours ago is the evolution and
placement of this leading shortwave, which shows the surface low
associated with the shortwave intensifying rapidly this morning
and then weakening late this afternoon and moving quite a bit
faster to the east compared to 36 to 48 hours ago. This
difference will likely result in weaker upslope flow and less
moisture, especially aloft. Model soundings do confirm this with
a drier boundary layer and a drier 700-550mb layer aloft.
Forcing appears to be even weaker than 24 hours ago with any
frontogenesis, enhanced upslope flow, and isentropic lift still
not co-located nor at the same time. High resolution models are
now starting to capture the first part of the event, and are
less than impressive with precipitation rates. Therefore,
continued to lower snowfall totals outside of the mountains
based on high resolution guidance and current GEFS and European
Ensemble output. Current snowfall totals are likely still a bit
too high, but prefer to lower them gradually given the amount of
remaining uncertainty with this storm system. Some of that
uncertainty revolves around convection this afternoon with the
last few runs of the HRRR showing some thunder shower activity
with locally heavy snowfall rates along portions of Interstate
80. Did not add thunder into the forecast quite yet, but will
brief the next shift accordingly. If enough colder air pushes
into the area late this afternoon, some of these snow showers
may produce some very heavy snowfall rates and low visibility.

The better forcing with this event appears to be late Wednesday
night through Thursday night with some jet dynamics and upper
level diffluence coming into play. Low level winds will shift
into the northeast and increase, resulting in better upslope
flow and enhanced low level convergence. This will likely be the
primary window for snow accumulations, but it will be confined
to mainly southeast Wyoming along and west of the I-25
corridor. To complicate things further, western slopes of the
Laramie Range, Snowy Range, and Sierra Madre Range will likely
see downslope winds during this part of the storm with drier
northeast or easterly flow. Winter Storm Warnings still look
good for the Snowy Range, the I-80 Summit, and the Arlington/Elk
Mountain region over the northern foothill of the Snowy Range
due to enhanced upslope northeast winds. Kept the Winter
Weather Advisories for the lower elevations of Carbon and Albany
Counties and replaced the Winter Storm Watches with Winter
Weather Advisories for the Wheatland to Cheyenne area. Periods
of snow are expected in these locations, with most of the snow
likely falling this evening until midnight, and a second round
later Thursday through Friday morning where the best dynamic
forcing occurs. Further east, it`s going to be tough to get much
accumulating snow in these conditions along with the minimal
cold air to work with below 5000 feet. Therefore, kept snow
accumulations around a half an inch for Chadron, Scottsbluff,
and Sidney, with slightly higher amounts along the Pine Ridge,
Cheyenne Ridge, and Wildcat hills southwest of Scottsbluff.
Issued Winter Weather Advisories for Saratoga and southwest
Carbon County with steady snow reported last night and early
this morning in those locations...with additional snow expected
this afternoon through tonight before the downslope easterly
winds increase. Thursday will likely be the coldest day with
highs around 15 degrees below average for this time of the year
with highs in the 30s to low 40s.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 333 AM MDT Wed Mar 13 2024

The low pressure systems responsible for the long duration winter
storm will be long gone by Friday morning as the original Colorado
low will be well off to the east and the upper-level low continues
to spin over the Desert Southwest. Precipitation will have ended
across most of the CWA by Friday morning. Cannot rule out a chance
of freezing drizzle and/or freezing fog around Cheyenne, the
foothills and the south Laramie Range. GFS soundings do show a
saturated profile at the surface and the lowest 100 mbs with
temperatures between 0C and -10C. This is supported by weak
southeasterly flow at the surface which could lead to the
development of drizzle and/or fog. Any lingering precipitation or
clouds will clear out during the afternoon hours.

Looking at mostly dry conditions headed into the weekend as the CWA
is sandwiched between the near stationary upper-level low over the
Desert Southwest and an incoming trough dropping down into the Great
Lakes Region. This trough will dig south on Sunday, but stay just
east of the CWA. This will send some colder 700 mb air into the CWA,
but the coldest air will likely remain far enough east. Highs on
Sunday will be near to slightly below average for mid-March.

The warmth returns Monday as an upper-level ridge builds over
western CONUS. 700 mb temperatures will be above 0C which will allow
surface temperatures to climb well above average. Highs for most
locations will be in the 50s and 60s Monday through mid-week. The
ridge will also lead to continued dryness over the region with ample
sunshine.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 534 AM MDT Wed Mar 13 2024

Conditions will gradually deteriorate throughout the day as the next
winter storm enters the region. Scattered showers are expected at
all terminals during the day. Southeast Wyoming terminals will see
snow showers while western Nebraska terminals will primarily see
rain showers. Low CIGs are likely at most terminals throughout the
day and into the overnight hours. Expect poor visibility in snow
showers with IFR conditions. Rain showers will lead to MVFR
conditions with slight reductions to visibility. Precipitation will
continue this evening and overnight, becoming steadier and more
widespread. Rain will transition to snow in Nebraska later
tonight.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 3 PM this afternoon to 6 AM MDT
     Friday for WYZ101-103>105-109-115.
     Winter Weather Advisory from 6 PM this evening to 6 AM MDT
     Friday for WYZ106-117>119.
     Winter Storm Warning from 3 PM this afternoon to 6 AM MDT
     Friday for WYZ110.
     Winter Weather Advisory until 3 PM MDT Thursday for WYZ111-113.
     Winter Weather Advisory until 6 PM MDT Thursday for WYZ112.
     Winter Storm Warning until 6 AM MDT Friday for WYZ114-116.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...SF
AVIATION...SF


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.