000
FXUS65 KCYS 202019
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
219 PM MDT Sat Apr 20 2024

.KEY MESSAGES...

- Freezing fog and light to moderate snowfall will be the main
  concerns through mid-afternoon across the South Laramie Range,
  Cheyenne Ridge, and southern Nebraska panhandle. Minimal snow
  accumulation expected, mainly on grassy and elevated surfaces.
  Roadways may be slick, especially bridges and overpasses.

- Warming back up to near-normal, mild temperatures Sunday
  through Thursday along with a chance of late day showers and
  thunderstorms for Wednesday and Thursday.

- Cooler and more unsettled weather is likely for Friday and
  Saturday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 216 PM MDT Sat Apr 20 2024

While light snow and areas of dense fog continue from the I-80
Summit through the southern Nebraska panhandle, conditions are
expected to begin clearing later this afternoon. However, these
areas will still likely not see the sun today as the low clouds are
expected to stick around through this evening and overnight. Areas
of fog may return later tonight through early tomorrow morning
across these same areas as easterly, upslope flow and low-level
moisture stick around until they are pushed out by the incoming
ridge. Once the winds turn westerly, the fog will likely dissipate
quite quickly due to drier air moving in and downslope winds warming
and further drying the air. Latest hires guidance overall shows
surface winds starting to turn westerly sometime between 08Z and
12Z. Looking at soundings, the HRRR pushes the fog out the quickest,
and has arguably been known to push fog/low-level moisture out too
quickly, the NAM Nest holds onto it until well into the afternoon.
But, the NAM Nest tends to not handle boundary layer moisture very
well for this area. That being said, the reality will likely be
somewhere in the middle with fog settling back in late tonight and
continuing until early to mid-morning Sunday with some areas along
the Cheyenne Ridge holding onto it longer than others. As the warmer
air moves into southeast Wyoming and western Nebraska Sunday,
afternoon high temperatures are forecast to be in the upper 50s to
60s with the cooler temperatures being between Laramie and Sidney.
Clear skies and mostly light winds are expected Sunday with minimal
weather concerns once the fog clears.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 216 PM MDT Sat Apr 20 2024

Monday...Brisk northwest flow aloft will produce a breezy to windy
day along and west of Interstate 25. Mild temperatures once again
with 700 mb temperatures near 5 Celsius.

Tuesday...Slightly cooler at most locations in the wake of a weak
cold frontal passage under northwest flow aloft.

Wednesday...Ridging aloft builds across the region which will
produce a decent warming trend as 700 mb temperatures rise to near 7
Celsius, yielding maximum temperatures in the upper 60s and lower
70s. Looks like there may be enough low and mid level moisture
combined with easterly upslope winds to spark isolated to scattered
afternoon showers and thunderstorms.

Thursday...The next progressive shortwave trough aloft moves across
Wyoming and Colorado, helping to produce scattered afternoon and
evening showers and thunderstorms. Continued relatively mild based
on the projected 700 mb temperatures.

Friday...Cooler and more unsettled weather expected with adequate
low and mid level moisture, and low level convergence along a cold
front.

Saturday...Cool and unsettled weather looks to continue as a series
of shortwave troughs aloft move overhead under southwest flow aloft.
Scattered showers and a few thunderstorms again possible based on
instability parameters.

&&

.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 3 PM MDT this afternoon for
     WYZ116>118.
NE...None.

&&

$$

SHORT TERM...LEG
LONG TERM...RUBIN
AVIATION...RUBIN