Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 240959
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
359 AM MDT Sun Mar 24 2024

.KEY MESSAGES...

- 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.

- 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.

&&

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

Beginning to see the first onset of precipitation moving into
portions of SE Wyoming ahead of an approaching cold front
associated with a deepening cyclone currently moving through the
Intermountain West. Even with the event progged to begin later
today, HI-RES models still are having issues with QPF and
coincidentally the forecast accumulations for the Nebraska
Panhandle. The deterministic models are initializing the
placement of the cyclone this evening comparing latest runs to
WV analysis. This cyclone will continue to deepen as it pushes
east in eastern Colorado and western Kansas. A well defined
warm conveyor belt is noted this evening on WV imagery with the
dry slot beginning to punch into the cyclone. A very classic
Norwegian Cyclone model is taking shape with SE Wyoming sitting
in the warm sector currently but this should be quickly replaced
by the incoming cold front. This will force the warm moist to
upglide over the frontal boundary creating a warm nose that will
be deep enough to have the initial surge of precipitation to be
a rain and/or a rain/snow mix for locations east of the Laramie
Range into the Nebraska Panhandle. The arrival of the deep cold
air will with the mid-level front will transition all
precipitation to snow during the evening hours. This will also
be the beginnings of a brief elevated to high wind event for the
I-80 corridor and the North Platte River Valley. The
combination of falling snow and windy conditions will create
areas of blowing snow. With the snow rates not looking all that
impressive will hold off on mentioning Blizzard conditions and
will keep the Winter Weather Advisories in place for the Pine
Ridge in Niobrara, Sioux, and Dawes counties, as well as the
Cheyenne Ridge in far southeast Wyoming and the southern
Nebraska Panhandle. Decided to add Box Butte, Morrill and
Cheyenne counties to a Winter Weather Advisory for the treat of
2-3" of snow and the blowing snow concern.

Heading into Monday, the bulk of the wintry weather will be
coming to and end and the winds will be decreasing. A quick
passing shortwave may initiate some mountain snow showers and
help keep winds somewhat elevated. With temperatures expected to
drop into the teens to low 20s across the region, Monday morning
wind chill values may end up dropping to below 0 in a few
locations. Temperatures aren`t expected to warm much on Monday
with most areas struggling to see temperatures get out of the
20s.

&&

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

Long Range models in reasonable agreement Tuesday through Thursday,
showing a long wave trough anchored over the Great Lakes Region and
south-central Canada, with northwest flow over the northern Front
Range. This pattern will slowly transition to southwest flow aloft
as a shortwave ridge axis quickly moves eastward across the
Intermountain West and Front Range. Therefore, expect a general
warming trend as we head into Wednesday and Thursday with highs
returning to near or slightly above normal. There is a chance for
snow Tuesday as moist WAA aloft begins and a weak disturbance aloft
digs southeast across the area, but accumulations should be minimal
and mainly confined to southeast Wyoming. Otherwise, kept POP below
10 percent outside of the mountains both Wednesday and Thursday.

After this brief break in the current unsettled weather pattern,
another Pacific upper level trough will move onshore by late
Thursday and into Friday. This is where long range deterministic
solutions diverge. Ensemble guidance also shows a lot of variability
once we head into next weekend with large temperature spreads and
large spreads in POP and QPF. Basically, we`ll have to keep an eye
on a stationary polar front which may become stationary somewhere
between the Colorado border and north central Wyoming Saturday
through Sunday. In addition, the 00z GFS shows an impressive storm
system ejecting east from the southern Calif coastline and
redeveloping into a Colorado low late next weekend. At the very
least, it looks like an unsettled weather pattern with colder than
average temperatures for a bulk of the forecast area, which is
dependent on the position of the cold front. Due to the high
variability (40 degree temp spreads between the 5th and 95th
percentile this weekend) in all ensemble forecasts, decided to
gradually lower temperatures through the weekend and keep just above
the ensemble mean. Slowly trended POP higher and trended more
towards the NBM as Consensus blends appear too high, but kept them
below 50 percent outside of the mountains.

&&

.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 this evening through late tonight for
     WYZ117>119.
NE...Winter Weather Advisory from noon today to noon MDT Monday for
     NEZ002-095.
     Winter Weather Advisory from 6 PM this evening to noon MDT
     Monday for NEZ003-021-055.
     High Wind Watch from this evening through late tonight for
     NEZ054-055.

&&

$$

SHORT TERM...AW
LONG TERM...TJT
AVIATION...TJT


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