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000
FXUS65 KCYS 192129
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
329 PM MDT Fri Apr 19 2024

.KEY MESSAGES...

- Freezing Drizzle and Dense Fog will be the main concerns
  tonight especially between Cheyenne and the I-80 Summit.

- Snow will be more favorable in the southern panhandle tonight
  where accumulation will range from 1 to 2 inches.

- Much warmer temperatures are expected for Sunday through
  Thursday.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 254 PM MDT Fri Apr 19 2024

A very tricky forecast is expected tonight especially with the
models now showing the higher QPF shifting south of the border
into northern Colorado. This will be setting the stage for the
potential of more freezing drizzle/ice accumulation/fog across
the I-80 corridor from the I-80 summit to Cheyenne. The latest
NAMNEST soundings seems to have the best handle on the current
satellite trends with the thicker cloud deck in place. The
models have also been shifting the entrance region of the upper
level jet currently over the northern Nebraska panhandle
further south into the southern panhandle this evening and
overnight. As a result, we are looking at the best synoptic
scale forcing across northern Colorado which is the area that
has the best potential for lift to reach the dendritic growth
zone. The latest water vapor loop is also showing some higher
clouds starting to move in from southwest Wyoming. This may
induce some seeder feeder light snow showers this evening.
However, the best low level warm air advection appears to be
overnight and tomorrow morning which will most likely moisten up
the saturated boundary layer and start the freezing drizzle and
fog again. The better synoptic scale forcing does appear to
enter the I-80 corridor between Pine Bluffs Wyoming and Sidney
tomorrow morning as the shortwave pushes off to the east, but it
should be fairly shortlived with amounts generally less than 2
inches. Since we are looking at a greater potential for freezing
drizzle/fog tonight between the Cheyenne and the I-80 summit we
did issue and Winter Weather Advisory for that area since
temperatures will be well below freezing overnight along with
colder ground temperatures, but ground temperatures should warm
quickly by mid morning on Saturday as the higher sun angle kicks
in.

The snow, fog and freezing drizzle should be tapering
by early afternoon, but would not be surprised to see some
dense fog develop Saturday night with continued response to
upslope flow.




&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 254 PM MDT Fri Apr 19 2024

An active pattern through early next week will keep near daily
chances for rain/snow showers and warmer temperatures. Sunday warmer
air quickly makes its way into southeast Wyoming and western
Nebraska as upper-level ridging makes its way back into the area.
However, Monday a quick shortwave ejects eastward along the northern
fringes of the forecast area, dropping temperatures a few degrees as
a boundary drops to near the WY-CO state line. This boundary is then
pushed eastward Tuesday into Wednesday, resulting in increased
precipitation chances, particularly along the I-80 corridor between
Laramie and Sidney. Wednesday afternoon a boundary develops along
the Laramie Range before moving eastward. With increased moisture
moving up the Central Plains from the Gulf and a few hundred J/kg of
CAPE, thunderstorms are not out of question Wednesday afternoon and
evening. Thursday is where long range models begin to really differ
significantly in their solutions with the ECMWF bringing a weak
shortwave embedded in the flow, while the GFS brings a much more
potent shortwave in ahead of the main low pressure system. Overall
the end of the week looks to bring cooler temperatures with higher
precipitation chances, starting as rain and potentially
transitioning to snow over the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1123 AM MDT Fri Apr 19 2024

IFR conditions persist at KCYS with freezing drizzle continuing
for the next few hours before lifting with MVFR to VFR
conditions briefly anticipated before dropping once again to IFR
with snow showers late tonight into early tomorrow. KLAR and
KSNY may also experience light rain/snow showers late tonight
into early tomorrow. Elsewhere across southeast Wyoming and
western Nebraska will remain VFR with CIGS near 5kft
sticking around until later this afternoon/early evening.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 8 PM this evening to noon MDT
     Saturday for WYZ116.
     Winter Weather Advisory from 11 PM this evening to noon MDT
     Saturday for WYZ117-118.
NE...None.

&&

$$

SHORT TERM...REC
LONG TERM...GCC/LEG
AVIATION...LEG