Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240537
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1135 PM MDT Sat Mar 23 2024

.KEY MESSAGES...

- Rain and mountain snow showers this afternoon and evening.
  Minor snowfall accumulations possible above 9000 feet. Showers
  may produce 45+ MPH wind gusts. A couple of lightning strikes
  are also possible.

- A winter storm will bring much colder temperatures, strong
  winds, and the potential for accumulating snowfall to portions
  of the area from Sunday through Tuesday. The most likely areas
  for impactful snow and blowing snow will be over the Pine
  Ridge in Niobrara, Sioux, and Dawes counties, as well as the
  Cheyenne Ridge in far southeast Wyoming and the southern
  Nebraska Panhandle. A Winter Storm Watch has been posted for
  Dawes and northern Sioux counties.

- Strong wind gusts are possible Sunday evening into early
  Monday as a strong surface low pressure intensifies over the
  Central Plains. Wind gusts in excess of 50mph along the
  Interstate 80 corridor from the I-80 Summit toward the NE
  Panhandle are possible.

&&

.UPDATE...
Issued at 806 PM MDT Sat Mar 23 2024

Went ahead and adjusted PoPs through Sunday night to account
for newer Hi-Res guidance. Overall, trended PoPs tonight through
Sunday morning down as Hi-Res shows decreasing shower activity
through this time. Did add a slight chance of thunder in the
forecast for tomorrow afternoon for far southeast Wyoming and
the southern Nebraska panhandle. Model soundings do show non-
zero CAPE values which could lead to a few rumbles of thunder
and/or a brief, weak thunderstorm.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 300 PM MDT Sat Mar 23 2024

Light rain showers are beginning to occur early this afternoon
across southeast WY, as a weak semi-stationary frontal boundary
lingers across the area. The Nebraska Panhandle saw persistent
upslope flow this morning, which resulted in cloud cover
lingering much longer than anticipated. As a result, chilly
temperatures in the 30s and 40s have been the main story instead
of daytime highs creeping into the 60s as originally forecast
for Saturday. As the rain showers propagate into the western NE
Panhandle, we can expect a gradual weakening. However, gusty
winds from the rain shower activity will still be a possibility
in excess of 40mph through the early evening hours. The threat
of a couple rumbles of thunder has dissipated slightly due to
the cloud cover sticking around longer.

The main weather story that will take hold of the region in the
coming 24-48 hours will be the approaching cold frontal passage
coupled with an potent mid-latitude cyclone developing further
downstream from our cwa. The higher resolution guidance coupled
with medium range guidance continues to provide a myriad of
deterministic outcomes for weather guidance, which unfortunately
means we have a low confidence forecast going into the eve of
big event. Higher confidence exists for much colder temperatures
to sweep across the forecast region on Sunday, and strong winds
in its wake along the I-80 corridor as a sub-980mb surface low
is progged to evolve across the eastern CO Plains into western
KS. With a deep warm layer of air that will have to
evaporational cool behind the cold FROPA, we can expect a long
window of rain showers on Sunday afternoon east of the Laramie
Range. By sunset, wind gusts trending upward, and a rain
changeover to snow is anticipated by Sunday evening for the cwa.
Have decided on a High Wind Watch for the I-80 corridor from
the South Laramie Range Foothills to Cheyenne County in western
NE for Sunday evening into early Monday due to the potential of
50+ mph winds being possible. Continued the Winter Storm Watch
for the Pine Ridge area of the NE Panhandle. We will have a
challenging forecast to pin down in the coming 24-36 hours due
to exactly when rain changes to snow Sunday afternoon, and how
much it may impact visibility due to blowing snow. At this time
of inspection, the strongest wind gusts are not co-located with
where the higher snowfall rates may reside along the Pine Ridge.
This is favored to prevent any mention of blizzard conditions
for the NE Panhandle forecast, but it may change when we get
within 12 hours of the onset of the event, and additional
wind/winter headlines may be prudent. 12z and 18z model guidance
has a large spread with deterministic outcomes, but the general
consensus is that the majority of winter impacts from snowfall
remain to our east for the most part.

By Monday morning, the stronger wind gusts and snow showers will
wind down from west to east. Considerations for high winds
persisting into 18z and onwards are possible for the next
forecast update. Temperatures will struggle to get out of the
20s as it will feel like winter again for most of the cwa. The
cold temperatures coupled with wind gusts will make some areas
see sub-zero wind chills for a large portion of the morning
hours on Monday. With clearing skies east of the Laramie Range
by Monday evening, temperatures will drop quickly. Areas that
see accumulating snowfall east of the Laramie Range will likely
have overnight lows in the single digits. Another shortwave
disturbance will trek toward the region late Monday night into
Tuesday morning. This will bring another round of snow showers
to the mountain zones. Stay tuned for forecast updates as
changes are expected in the coming 24 hours.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 300 PM MDT Sat Mar 23 2024

Minimal changes made from the previous forecast package. The primary
forecast concern in the long term forecast period will be the
generally unsettled pattern as shortwave passages and brief ridging
move through the forecast area, resulting in limited to low impacts.

Due to the brief shortwave passages, isolated, weak rain/snow
showers cannot be ruled out daily across southeast Wyoming and
western Nebraska. The mountains may continue to receive light snow
showers through this period as well, but overall accumulations will
be minimal. As brief ridging takes over Wednesday into Thursday, CAG
to CPR pressure gradients jump up to near 50 meters, so gusty to
strong winds are possible, mainly in wind prone areas of southeast
Wyoming. During this time frame, temperatures will gradually
increase each day starting in the 30s to 40s Tuesday, increasing
Wednesday to 40s and 50s, then 50s and 60s Thursday and Friday. The
next system is forecast to start making its way into southeast
Wyoming and western Nebraska Saturday into Sunday, so cooler
temperatures and increasing precipitation chances are likely.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1135 PM MDT Sat Mar 23 2024

A stationary front remains along the I-25 corridor tonight and is
not expected to move much for the rest of tonight with any remnant
showers and thunder showers moving eastward into central Nebraska. A
surge of cold air is forecast to push this front into Colorado by
late Sunday morning, as a storm system develops along the front.
Cloudy conditions with some fog this morning around 12z will
gradually transition to widespread snowfall and IFR conditions after
21z this afternoon and into Sunday evening.

HAZARDS/WEATHER TRENDS:

VFR conditions will prevail through tonight until about 10-14z early
Sunday morning. MVFR to IFR CIGS and patchy fog will develop just
before sunrise for KCDR, KAIA, and KSNY as the colder air sweeps
south across the area. Dense fog is possible, with the best chance
at KAIA between 11z and 17z.

Fog and LIFR CIGS will lift briefly Sunday afternoon before
widespread snow and IFR conditions develop at all terminals between
21z Sunday and 00z Monday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Sunday evening through late Sunday night
     for WYZ117>119.
NE...Winter Storm Watch from Sunday afternoon through Monday
     morning for NEZ002-095.
     High Wind Watch from Sunday evening through late Sunday night
     for NEZ054-055.

&&

$$

UPDATE...SF
SHORT TERM...BW
LONG TERM...LEG
AVIATION...TJT


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