080
FXUS65 KCYS 182013
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
213 PM MDT Fri Apr 18 2025

.KEY MESSAGES...

- Winter Storm Warnings and Winter Weather Advisories remain in
  effect through this evening. Continued snowfall expected
  through the day.

- Warmer and slightly drier Sunday through Tuesday. Windy
  conditions possible Sunday night and Monday.

- Another period of  unsettled weather expected mid to late
  week with numerous showers and widely scattered thunderstorms.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 210 PM MDT Fri Apr 18 2025

Radar returns show precipitation slowly decreasing across the area
this afternoon. Many of the Winter Storm Warnings were able to come
down earlier in the day, but a few Warnings and Winter Weather
Advisories remain in place until this evening to account for areas
of blowing snow and some lingering snow. These remaining headlines
look on track to come down on time as Hi-Res guidance shows shower
activity dying down by this evening. Some lingering snow showers and
potentially fog will be possible overnight along the Interstate 80
corridor in Wyoming.

Heading into Saturday, the upper-level trough will still be in place
over the CWA. This means that the cold, below average temperatures
will also stay in place. Low temperatures Saturday morning will be
quite cold as 700 mb temperatures sit in the 10th percentile of
NAEFS climatology. This anomalously cold air will lead to low
temperatures early Saturday morning in the teens and 20s.
Temperatures in western Nebraska will heat up quickly into the 50s
due to mostly sunny skies and minimal snow cover. Southeast Wyoming
will remain on the chillier side with 40s along the Interstate
25 corridor, and upper 30s along the Interstate 80 corridor.
Temperatures out west will be particularly cold due to snow
cover. Although chances are slim, cannot rule out a few snow
showers in the high terrain during the day Saturday as a
vorticity max hangs over the CWA with some leftover mid-level
moisture. Any showers that do develop are not expected to be
impactful. The precipitation threat will taper off Saturday
night as winds become stronger and more westerly.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 210 PM MDT Fri Apr 18 2025

An area of surface high pressure moves into the
intermountain west following the trough responsible for the mountain
precipitation on Saturday. This results in a weak upper level ridge
that isn`t very amplified and easily flattened.  Another shortwave
starts to push into our region Monday morning. This shortwave is
pretty weak and not likely to overcome the downsloping westerly
flow. Looking at model soundings, there is a little bit of
saturation in the mid levels and a stout dry layer in the lower
levels. Virga seems the more likely result of this shortwave given
the environment. However, the rain chances may not really occur until
Monday night into Tuesday morning as it will be easier to saturate
in the overnight period and in the morning. Tuesday throughout the
day looks rather dry as the dry lower layer remains in the model
soundings. Wednesday becomes very muddled in the long term. The
deterministic models have reached an agreement of the possibility of
showers forming along this southern boundary. However, it seems like
the moisture advection doesn`t reach our area until late Wednesday
morning with the stronger forcing to the north of our forecast area.
NAEFS places PWAT values between 0.25 and 0.35 inches across the
state of Wyoming and 0.35 to 0.50 values for the Nebraska Panhandle
around 18z Wed. So its more likely if showers do occur Wednesday
they would be more likely in the afternoon during the strongest
moisture content and peak heating for some possible afternoon garden
variety thunderstorms. The global models look to throw in a couple
hundred joules of CAPE in the afternoon and evening.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1123 AM MDT Fri Apr 18 2025

IFR to LIFR conditions through the afternoon then MVFR to VFR
in the evening to overnight hours. Looking at Satellite and
observation cloud decks upstream float between 2,500 to 3,500
and a couple places have 5,000ft as their ceiling. So ceilings
aren`t expected to rise above 5,000ft even though the models
have us clearing out. Snow will be intermittent throughout this
afternoon and gradually tapering off through the evening.
Between 00z and 06z snow should be ending at most TAF site with
all sites having snow showers complete by 06z. Due to recent
snowfall and saturated lower levels, light to dense fog may
develop overnight at all terminals.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until 6 PM MDT this evening for WYZ106-
     109-110-116-117.
     Winter Weather Advisory until 6 PM MDT this evening for WYZ107-
     108-113-115-118-119.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...MM
AVIATION...MM