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000
FXUS65 KCYS 201739
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1139 AM MDT Sat Apr 20 2024

.KEY MESSAGES...

- Freezing drizzle and freezing fog will be the main concerns
  today around the Cheyenne Ridge, South Laramie Range, and
  South Laramie Range foothills. Ice accumulations up to one
  tenth of an inch on elevated surfaces, bridges, and overpasses
  will be possible. Slick road conditions can be expected.

- Snow will be more favorable in the southern Nebraska panhandle
  with accumulations around 1 inch possible.

- Much warmer temperatures are expected for Sunday through
  Thursday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 445 AM MDT Sat Apr 20 2024

Pretty quiet across the CWA as much of the action remains south of
the Wyoming/Colorado border. Dense freezing fog has developed across
much of the South Laramie Range early this morning as expected with
the moist low-levels and southeasterly winds. Models like the HRRR
and HREF keep the fog here throughout much of the day, as well as
expanding it into the foothills and central Laramie County this
morning as surface winds become more easterly. A webcam just south
of the Wyoming/Colorado state line does show light snow, however,
per Hi-Res guidance, snow likely won`t move into the CWA until
around daybreak.

The forecast for today remains tricky regarding precipitation types.
Strong 700 mb southerly flow will advect warmer air aloft into the
CWA this morning. Before this warmer air arrives, precipitation will
likely fall as snow as multiple model soundings show a saturated
layer colder than -10C. As this warmer air pushes northward, the
saturated layer will warm into the -10C to 0C range. This is when
precipitation will transition to freezing drizzle. Most likely area
for freezing drizzle will be the Cheyenne Ridge and the South
Laramie Range and foothills. The strongest warm air advection will
be in these locations, with the transition to freezing drizzle
possible by mid-morning, if not a bit sooner. Accumulation of ice is
possible on elevated surfaces, as well as bridges and overpasses.
This will lead to slick and slippery road conditions. Ice
accumulations up to one-tenth of an inch are possible in these
areas. The advancement of warmer air looks to be a bit more delayed
in the southern Nebraska panhandle. Most precipitation this morning
should fall as snow, with accumulations generally around an inch or
less. The warmer air looks to arrive by the afternoon, which could
lead to a brief period of freezing drizzle, although the bulk of
precipitation will be done by then. Winter Weather Advisories remain
in place for the South Laramie Range, foothills, and central Laramie
County for snow, fog, and freezing drizzle. These Advisories run
through noon today, but could need an extension if precipitation
continues into the afternoon. But, the worst of the winter weather
will likely occur during the morning hours. Precipitation will taper
off by the evening.

Model soundings do show the potential for fog developing from the
South Laramie Range eastward into Sidney Saturday night. Low-levels
will be sufficiently moist due to the precipitation during the day
Saturday with calm winds. Conditions aloft also look to dry out and
clear, leading to radiation fog. Models like the HRRR are also
hinting at fog with surface visibility drops. However, lingering
clouds in the southern Nebraska panhandle may limit the fog
potential.

Looking like a much nicer day on Sunday as weak ridging builds over
the CWA, allowing warmer and drier air to infiltrate the area.
Precipitation chances will be minimal with sunnier skies
expected. High temperatures will warm up about 20 degrees
compared to Saturday`s highs. High temperatures will be around
average to slightly above average for late April.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 204 AM MDT Sat Apr 20 2024

Mainly dry cold front moves through the CWA Monday bringing
breezy conditions to the forecast area. GFS advertising 700mb
winds across Carbon and Albany Counties up near 40kts out ahead
of the front. Local WRKHGT wind guidance showing Craig to Casper
850/700mb height gradients near 35mtrs...so for now...wind
headlines are not anticipated. Could see critical fire weather
conditions out by Rawlins Monday afternoon though. But with
fuels rated NO at this time out there...fire weather headlines
are not expected either. ECMWF paints some light QPF for the
mountains Monday afternoon and evening behind the front.

Warming trend for Tuesday and Wednesday as a ridge of high
pressure dominates the weather. GFS 700mb temperatures climb
from -4 to +4C Monday...to +4 to +10C Wednesday. Expecting to
see afternoon highs in the 70s Wednesday.

Next chance for any appreciable precipitation looks to be
Thursday when a low tracks across northeast Colorado. Low draws
a frontal system south across the Laramie Range with 700mb
temperatures falling to around +2C. Would think most of this
precipitation will fall as rain. Unsettled weather continues
through Friday into the weekend as we see another low pressure
system tracking across Colorado. For now...still too warm for
outside the mountains.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1122 AM MDT Sat Apr 20 2024

Surface high pressure and localized upslope will keep low
clouds, snow and fog across portions of southeast Wyoming and
the southern Nebraska Panhandle through much of tonight. A
passing shortwave trough aloft will help clear out the low
clouds Sunday morning.

Wyoming TAFS...At Rawlins, scattered clouds from 12000 to
15000 feet will prevail.

At Laramie, ceilings will range from 800 to 2300 feet until 21Z,
then scattered to broken clouds from 10000 to 15000 will occur
until 06Z, then skies will be clear.

At Cheyenne, visibilities will range from 1 to 4 miles in snow
and fog until 00Z, with ceilings from 500 to 1200 feet, then
ceilings will be near 1200 feet until 06Z, then visibilities in
fog will be near 1 mile with ceilings around 800 feet until 12Z,
then clear skies will occur.

Nebraska TAFS...At Chadron and Alliance, expect scattered to
broken clouds from 5000 to 8000 feet until tonight, then skies
will become clear.

At Scottsbluff, ceilings will be near 5000 feet until 06Z, with
occasional visibilities near 3 miles in snow and ceilings near
2500 feet until 20Z, then clear skies will prevail after 06Z.

At Sidney, ceilings will range from 2500 to 4500 feet until 21Z,
with occasional visibilities near 2 miles in light snow, then
ceilings will be around 4000 feet from 21Z to 06Z, then
visibilities in fog will be near 1 mile with ceilings near
1500 feet until 14Z, then skies will be clear.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until noon MDT today for WYZ116>118.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...GCC
AVIATION...RUBIN