765
FXUS65 KCYS 262101
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
301 PM MDT Fri Jul 26 2024

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms are developing this
  afternoon and again Saturday afternoon/evening. Some storms
  may produce gusty winds and locally heavy rainfall.

- Drier air aloft will move overhead for Sunday into midweek, limiting
  shower and thunderstorm chances and producing a warming and
  drying trend through Tuesday, then slightly cooler
  temperatures for Wednesday and Thursday.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 300 PM MDT Fri Jul 26 2024

A plume of monsoon moisture moving through the area is giving parts
of the area a temporary break in the hot and dry pattern for the
next 36 hours or so. Satellite water vapor imagery shows the
moisture plume centered over our area stretched out ahead of a
longwave trough in western Canada. A weak shortwave is moving across
the area this afternoon, providing a little extra lift to shower and
thunderstorm activity. This shortwave trough axis is located more or
less from Rawlins to Denver. Ahead of this, a weak stalled frontal
boundary is positioned roughly from Cheyenne to Chadron, which is
providing the focus for precipitation activity. This axis along the
front is where we have the least CIN also at this time, whereas
storms are struggling both to the northwest and southeast of this
corridor. Convective parameters are fairly modest with MLCAPE around
250 J/kg and weak shear, though this is a little more appreciable
across the northern portions of the forecast area. Expect additional
rounds of showers and thunderstorms over the next several hours.
While an isolated strong wind gust or small hail report is possible,
this looks like mostly moderate to briefly heavy rainfall and
occasional lightning today. Storm coverage should decrease with
skies trending clearer behind the shortwave trough axis which should
clear the area late this evening. A few HiRes models show some
thunderstorms lingering behind this, so do have some low end PoPs
continuing through the evening to account for this possibility.

Heading into Saturday, we will see some mid to upper level drying
behind today`s shortwave but PW values will remain above average for
this time of year. However, instability and flow aloft will be on
the increase tomorrow as a more vigorous shortwave approaches from
the southwest. While parameters will be marginal for severe weather,
it does look like a better chance than today for a few organized
strong to severe storms. Strong winds will be the main challenge for
storms tomorrow, as well as the continuing chance for locally heavy
rainfall and lightning.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 300 PM MDT Fri Jul 26 2024

On Sunday, the last-gasp of a weak longwave trough over the northern
Rockies will pivot through the northern high plains. This system and
attendant vort max may be just close enough to our CWA to help
initiate a few afternoon showers and thunderstorms, primarily in far
east-central Wyoming and into the NE panhandle. A potent dry push of
air behind this system will be rapidly transitioning eastward
through the day. Model guidance is still mixed as to whether there
will be enough surface moisture in place to generate any notable
showers and thunderstorms on Sunday, as the fast and dry westerly
flow just off the surface layer may be enough to eradicate any
useful boundary layer moisture/instability by peak heating.
Regardless, have increased PoPs just slightly on Sunday afternoon to
account for the low but non-zero thunderstorm threat anywhere east
of I-25 if enough surface moisture can remain in place.

Beyond Sunday, zonal flow and weak ridging will develop over the
central Rockies into the central high plains. This pattern will
result in a long period of hot weather with highs 10-15 degrees
above average likely for each day from Monday through next Friday.
Light westerly flow will help enhance a slight downslope component,
giving a boost to afternoon high temps east of the Rockies in what
would normally be not as ideal a height-based setup for extreme
heat. Ensemble guidance becomes a bit less confident by the middle
and end of next week as several different iterations of a fresh
plume of monsoonal moisture from the southwest approach southeast
Wyoming. If this monsoonal moisture can make it this far north,
temps may relax somewhat by late week. However, there are still
quite a bit of ensemble solutions (over 40%) that favor a generally
dry and hot pattern for most of next week and beyond.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1108 AM MDT Fri Jul 26 2024

Showers and thunderstorms will develop this afternoon affecting
LAR, CYS, BFF and possibly CDR. The strongest storms may be
capable of briefly lowering Vis and Cig into the MVFR category
at CYS and LAR, but will quickly move off to the northeast. Less
confidence is present with storms at BFF and CDR where only
light rain and some outflow winds from the west may be present
later this afternoon. Expect VFR at remaining terminals and
partly cloudy skies area-wide overnight.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...MAC
AVIATION...MAC