648
FXUS65 KCYS 132357
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
557 PM MDT Mon May 13 2024

.KEY MESSAGES...

- Chances for scattered showers and thunderstorms Monday and
  Tuesday.

- 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 343 PM MDT Mon May 13 2024

Current radar and satellite show showers developing over the high
terrain. As the afternoon progresses, expect these showers to push
eastward into the high plains through the evening. There is some
instability across the area, so thunderstorms with small hail could
be possible, but the main impact with storms will likely be strong,
gusty winds, as the surface and low-levels remain quite dry. A brief
break from storms is likely overnight.

Over the next two days, two shortwaves will move across the CWA,
bringing more rain and storm chances. Models, especially CAM
guidance has really trended precipitation down compared to some of
the global models. As a result, did trend PoPs down on both Tuesday
and Wednesday as the NBM seemed quite aggressive. Focusing in more
on Tuesday, most of the shortwave will pass just north of the CWA.
This will spark convection throughout most of the day for the
northern tier of the CWA. Later in the afternoon, instability will
build, causing convective initiation over the high terrain. Severe
weather looks unlikely as there isn`t enough strong instability
present. However, still could see gusty winds and small hail.
Next shortwave arrives Tuesday night, bringing with it a cold
front and more moisture. Temperatures on Wednesday will be about
10 degrees colder behind the front. Again, more scattered
showers and maybe a thunderstorm or two will be possible. There
is not as much instability present with the cooler temperatures,
so expecting mostly rain showers.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 343 PM MDT Mon May 13 2024

Medium to long range models in better agreement compared to
yesterday with still some large ensemble spreads for later this
weekend. 12z ECMWF is no longer showing a strong cold front pushing
across the high plains into southeast Wyoming on Thursday as the
trough axis is much further north near the United States/Canadian
border. Models show northwest flow aloft initially early on Thursday
before it transitions to westerly flow by Friday. Expect another
warming trend to end the week as afternoon temperatures climb into
the 70s across most areas of southeast Wyoming. Western Nebraska
will likely climb well into the 80s Friday afternoon. With drier
westerly flow expected, kept minimal POP outside of the mountains
with a few sprinkles possible.

Warm than average temperatures will likely continue into next
weekend with all models showing a flat upper level ridge quickly
progressing eastward over the Great Plains and zonal flow over
the western third of the country. Another cold front will quickly
move across Wyoming, but models are in considerable disagreement on
when this may be. The 12Z ECMWF and Canadian are a full 24 hours
behind the 12z GFS and show FROPA on early on Sunday instead of
Saturday. GEFS and ENS ensemble forecasts show a large spread in
temperatures, but this time later in the weekend/early next week
compared to yesterday. Gradually decreased temperatures late this
weekend and into next Monday with increasing cloud cover and chances
for showers/thunderstorms in the afternoon. Chances for strong to
severe thunderstorms appears very low at this time.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 553 PM MDT Mon May 13 2024

Scattered showers and thunderstorms are drifting from northwest
to southeast across the area this evening. Most of the lightning
activity should be in the next few hours, but showers may
continue until after midnight. Brief gusty winds are possible
with this activity.

A frontal boundary will push through the area Tuesday morning,
bringing gusty northwest winds for much of the area through the
afternoon. Another round of showers and thunderstorms will
develop Tuesday afternoon, but this may just be near KCDR and
KAIA early on. Showers and storms may then spread towards other
terminals near the end of the TAF period.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...SF
AVIATION...MN