453
FXUS65 KCYS 131045
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
445 AM MDT Mon May 13 2024

.KEY MESSAGES...

- Trending warmer through Monday, but remaining unsettled with
  daily chances for showers and storms through mid-week.

- A cold frontal passage is expected on Wednesday, with much of
  the region returning to below-normal temperatures and
  increased chances for rain and high-elevation snow.

- Warming temperatures through the end of the week with a dry
  start to the weekend expected.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 400 AM MDT Mon May 13 2024

As the low in the southern plains continues to depart eastward,
satellite imagery shows the next shortwave stretching across the
PACNW into ID and MT. Being positioned between the two, southeast
Wyoming is looking mostly dry and breezy. With warmer temperatures
today, there`s a bit more instability out there and 20 to 30 knots
of shear. However, since the better moisture has departed eastward,
we`re still looking at deep inverted-v soundings with a very dry
surface layer. There`s still a chance for isolated to widely
scattered rain showers and thunderstorms, mainly along the higher
terrain, but we can`t rule out a light shower or weak thunderstorm
in the high plains. Afternoon high temperatures Monday are forecast
to be a few degrees warmer than they were Sunday with overnight low
temperatures nearly the same.

Tuesday, a stronger shortwave begins to enter the forecast area,
bringing cooler temperatures and increasing precipitation chances.
HiRes guidance is not too excited about the precipitation chances
Tuesday afternoon, and global models are split between the GFS
keeping shallow ridging across most of southeast Wyoming and western
Nebraska through Tuesday afternoon, not allowing the shortwave to
push through until Tuesday night; and the ECMWF which brings the
shortwave all the way through southeast Wyoming and western Nebraska
Tuesday morning/afternoon, which is a much wetter, cooler signal.
Overall, impacts are not expected to be major with either solution.
For now, opted to keep areas north of the North Platte River Valley
cooler and wetter through Tuesday afternoon, and south of the North
Platte River Valley warmer and drier until Tuesday
evening/night.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 400 AM MDT Mon May 13 2024

A cold front will sag southward as a shortwave trough passes
east through the region on Tuesday evening into Wednesday.
Expect much cooler temperatures on Wednesday on the order of 5-8
degrees below average. Cooler temperatures aloft combined with
daytime heating will result in enough instability for scattered
showers across the area, especially as a secondary weak vort max
pivots through during the afternoon hours. With cooler
temperatures in place, will have to watch for the potential for
snow accumulations in the mountains. Current guidance supports
the potential for a light event in the Snowy and Sierra Madres
of an inch or two or less. However, farther north closer to the
upper level low, favorable upslope flow may result in 3 to 6
inches in the northern Laramie Range if current trends remain on
track.

Following this system, expect a drying and warming trend as
west-northwest flow remains in place. Widespread mid-70s are
likely east of I-25 on Saturday with high confidence of near-80
degree readings in the NE panhandle. By the Saturday night-
Sunday timeframe, differences in ensemble guidance emerge with
the GEFS favoring troughing returning to the west coast and the
EPS suggesting a flatter system. Temperatures look to remain
above average through the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 400 AM MDT Mon May 13 2024

Mainly VFR conditions expected to persist through the 12Z TAF period
across southeast Wyoming and western Nebraska. While a brief period
of light fog is possible near KSNY early this morning, confidence
remains low in its development. Isolated to widely scattered showers
and thunderstorms are possible across far southeast Wyoming and
western Nebraska this afternoon, mainly between 18Z and 03Z.
Confidence is low in any direct TS or SHRA impacts to the
terminals.

&&

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

&&

$$

SHORT TERM...LEG
LONG TERM...MAC
AVIATION...LEG