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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KCYS 211748
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1148 AM MDT Sun Apr 21 2024

.KEY MESSAGES...

- Patchy fog possible Sunday morning along the Interstate 80
  corridor between Cheyenne and Sidney.

- Elevated to high winds possible for areas west of the Laramie
  Range Monday afternoon.

- Warmer, unsettled weather expected throughout much of the week
  with multiple chance for precipitation.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 400 AM MDT Sun Apr 21 2024

Quiet across much of the CWA early this morning. Clearing skies and
calm winds have lead to effective radiational cooling, so looking at
a chilly morning for most with temperatures in the low 20s and
perhaps a few teens in low lying areas. Low-level moisture from
yesterday`s precipitation has kept some low stratus around Laramie,
Kimball, and Cheyenne Counties based on satellite nighttime
microphysics. The low-level moisture has also lead to the
development of patchy fog in these areas per ASOS and webcam
observations. A few areas of dense fog could also be possible.
Fog and low status will likely burn off pretty quickly after
sunrise with a drier airmass moving in, but, could linger
through mid-morning in a few spots.

As mentioned, a drier and warmer airmass will take hold of the CWA
today as a weak ridge axis passes overhead. 700 mb temperatures will
warm back up over 0C by late afternoon. Sunny skies will also help
surface temperatures warm, with highs near to above average.
Overall, looking like a pleasant warm, dry day compared to the
latter half of this past week.

Winds will pick up Sunday night into Monday as a shortwave passes
north of the CWA. The windy areas will include the usual wind prone
locations, as well as areas west of the Laramie Range. There are no
huge indicators of this being a high wind event. In fact, both
pressure gradients and 700 mb CAG-CPR are pretty unremarkable. The
omega field is fairly average for wind events, but does potentially
indicate mountain wave activity is possible. 700 mb winds only max
out at around 45 to 50 kts. In-house guidance also shows about a 20
percent chance of high winds in the wind prones. So although high
winds may not be possible, it will still be very windy, especially
for areas west of the Laramie Range. Even the NBM shows wind gusts
up to 55 MPH between Laramie and Rawlins. So, for now, will forgo
any high wind headlines in favor of seeing additional model runs as
the event gets closer. The most likely time for seeing high winds
looks to be Monday afternoon.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 300 AM MDT Sun Apr 21 2024

Flat ridging overhead for Tuesday as a 500mb low tracks across
the Dakotas. Ridge more pronounced at 700mb with the axis laying
roughly from central Colorado north to north central Wyoming. A
dry and warmer day expected Tuesday with highs from the mid 50s
across the northern Nebraska Panhandle to the mid 60s in the
Platte River Valley. Overall...a pretty pleasant day.

Going to see unsettled weather returning as a stalled out
frontal boundary that was across central Colorado begins to
make its way back north Wednesday. Best chances for showers will
be along and west of the Laramie Range Wednesday afternoon.

Thursday shows that frontal boundary stalled out across the
Laramie Range. South to southeast low level winds east of the
front. GFS suggesting a good fetch of low level moisture across
the Nebraska Panhandle. Humidity at 850mb around 90-95 percent
would suggest low stratus and fog east of the Laramie Range
Thursday morning. An upper level trough set to move across the
CWA Thursday afternoon for a pretty good chance for showers and
thunderstorms.

Differences in guidance for what will happen Friday. GFS shows upper
low shifting into Kansas Friday morning. Eastern portions of
the CWA remain in high low level moisture...so likely more low
clouds and fog Friday morning as well as light rain in the wrap
around flow around that low. ECMWF however...lifts the low
north into central Nebraska and southern South Dakota. This
would suggest a colder solution for us here in southeast
Wyoming. ECMWF also showing heavy rainfall across the Nebraska
Panhandle with over 3 inches of rain for the day. Will need to
watch this closely as we get closer to the event.

Active weather over the weekend as longwave trough over the west
coast continues to spin off pieces and energy that track across
the area each day.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
-- Changed Discussion --
Issued at 1144 AM MDT Sun Apr 21 2024

Northwest flow aloft will become west overnight and strengthen.

Clear skies will prevail this afternoon, then scattered to
broken clouds near 15000 feet will spread across the terminals
tonight and Monday.

Winds will gust to 26 knots at all terminals except Scottsbluff
until 02Z, then will gust to 30 knots at Rawlins and Laramie
after 15Z Monday.
-- End Changed Discussion --

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

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