776
FXUS65 KCYS 120949
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
349 AM MDT Sun May 12 2024

.KEY MESSAGES...

- Trending warmer through Monday, but remaining unsettled with
  daily chances for showers and storms. Severe weather is not
  expected.

- 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.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 251 AM MDT Sun May 12 2024

Sunday is looking like a beautiful spring day across southeast
Wyoming and western Nebraska with high temperatures in the 60s to
low 70s and mostly dry conditions. While another push of moisture
continues to eject northward along the periphery of the low
positioned in south Colorado, model soundings overwhelmingly show
deep inverted-v`s indicating a very dry surface layer. That being
said, there is 400-800 J/kg of CAPE, which is enough instability to
develop some cumulus clouds across southeast Wyoming and western
Nebraska and potentially an isolated thunderstorm or brief rain
shower. The main threats are likely to be gusty winds and lightning.
These thunderstorms are not likely to be strong or severe due to the
lack of shear, and with the dry surface layer, they will likely not
produce much rainfall, if any. The best chances for precipitation
are in the southern Nebraska panhandle. In terms of timing, it looks
like a classic summer day with chances for showers and thunderstorms
between noon and 9 PM.

Monday is nearly a rinse and repeat forecast with temperatures a few
degrees warmer than Sunday and more chances for isolated to widely
scattered showers and thunderstorms in the afternoon. HiRes guidance
is showing very dry surface layer once again in deep inverted-v
soundings, so the main threats are likely to be gusty winds and
lightning.
&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 251 AM MDT Sun May 12 2024

A generally persistent overall northwest flow pattern will be in
place for the long-term period. However, several waves will ride
southeastward in this flow pattern bringing periods of unsettled
weather to southeast Wyoming and western Nebraska. Forecast
guidance is in generally good agreement showing the first
shortwave trough in this northwest flow pattern approaching on
Tuesday and moving through on Wednesday. Warm weather will
persist on Tuesday out ahead of this system, but increasing
clouds and afternoon showers and possibly a rumble of thunder
are possible in the higher terrain as heights begin to fall and
the mid and upper regions of forecast soundings begin to
moisten. By Wednesday, the main vort max swings through during
the early afternoon hours. Accompanying this system will be a
cold front diving southward at the surface from the north. The
most favorable period for showers and a few isolated
thunderstorms will be on Tuesday from noon through sunset over
much of the CWA. Most ensemble guidance supports at least a
tenth of an inch of QPF for most locations, with more in the
northern slopes of the mountain ranges where a fresh shot of
spring snow is expected. Despite some briefly favorable dynamics
and lift, severe weather east of I-25 continues to look unlikely
due to poor moisture return and a lack of upslope flow. Chillier
air is expected over the area on Wednesday and early Thursday
with temperatures running around 5-10 degrees below average.

Expect a quick rebound on Thursday afternoon and especially on
Friday as ridge axis moves through. The next wave of energy will
approach the region later on Saturday in the persistent west to
northwest flow pattern. However, ensemble guidance becomes much
more dispersive by this point with a large cluster of members
favoring dry west-northwest flow and another featuring a more
potent trough by the middle to end of next weekend. Forecast
confidence with regard to precipitation diminishes notably at
this time however near to above average temperatures do appear
the most likely outcome.


&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 251 AM MDT Sun May 12 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. The
highest confidence of direct TS impacts is KSNY, followed by KCYS
and KLAR.

&&

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

&&

$$

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