480
FXUS65 KCYS 290545
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1145 PM MDT Tue May 28 2024

.KEY MESSAGES...

- Strong to severe thunderstorms mainly along and east of I-25
  into the Nebraska Panhandle Wednesday afternoon with large
  hail and strong winds.

- Active weather pattern will continue through the weekend with
  daily chances for showers and thunderstorms.

- Summertime temperatures will be on the horizon next week.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 155 PM MDT Tue May 28 2024

Visible satellite imagery shows clouds developing over the high
terrain early this afternoon. From this, a few isolated showers and
thunderstorms are likely to develop later this afternoon. Per Hi-Res
guidance, any storms that develop will stay confined to the
Interstate 80 corridor in southeast Wyoming. Both surface
observations and model soundings show dry low-levels across the
area, so expect high-based storms with little to no rain and strong,
erratic winds. Could also see a few dry lightning strikes with these
storms as well. Showers and storms will dissipate later this evening.

Overnight, a LLJ will develop over the Nebraska panhandle.
Besides being a bit breezy in the panhandle overnight, south to
southeasterly flow will advect warm moist air into the eastern
half of the CWA. This will steadily increase dewpoints, leading
to the potential for some patchy fog, but will also help set the
stage for severe weather on Wednesday.

A few different dynamics at play will help spark potentially severe
convection across our eastern plains Wednesday afternoon. A strong
shortwave will move into the northern Rockies, increasing PVA across
the the CWA. At the surface, a trough across eastern Wyoming
will keep southerly winds and moisture advection into the
panhandle. This moisture will keep dewpoints in the upper 40s to
potentially low 50s across western Nebraska, favorable for the
development of storms. Most Hi-Res guidance has storms
developing off the high terrain during the early afternoon and
pushing eastward into the plains throughout the afternoon and
evening. Early on, storms will most likely be discrete, leading
to more of a hail threat. Still some model discrepancies
regarding how much MUCAPE will be present, which will likely
affect hail size and how many storms could contain large hail.
But a safe bet, based on the HRRR and GEFS will be roughly 1200
to 2000 J/kg of MUCAPE. This could lead to hail up to ping pong
ball size. As storms push further east, they will become
clusters, and lead to more of a wind and strong outflow threat,
with possibly a few embedded hailers. By the evening, most of
the storms will have pushed out of the CWA.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 155 PM MDT Tue May 28 2024

The main concern with this portion of the forecast is when the
best chances of convection will be through the remainder of the
week into the weekend.

After an active day on Wednesday, we are looking at a frontal
boundary moving through the forecast area late Wednesday night
into Thursday morning. This front will bring breezy and drier
conditions to the area on Thursday which will limit our
convection chances compared to Wednesday. Some locations such as
Arlington and I-80 summit may even see some 45 to 50 mph wind
gusts Thursday morning into the early afternoon after the front
passes through due to some decent winds aloft combined with
downward vertical motion. Still cannot rule out a few isolated
showers and thunderstorms developing along the southern Laramie
Range on Thursday afternoon, and affect parts of the I-25
corridor during the late afternoon. However, we are not
confident that this convection will hold on past sunset
especially if anything that does develop closer to the I-80
corridor may peel off to the southeast in response to the
steering flow turning northwest and weak instability. Although,
still cannot rule some potential for strong wind gust due to
inverted V soundings. The GFS/ECMWF and NBM are showing some
signs of isentropic lift around 300k early Friday morning
across Nebraska panhandle in response to the low level jet and
moisture advection. Therefore, we are keeping some small
precipitation chances in that region.

On Friday, the deterministic solutions are still showing a
subtle shortwave moving through the eastern half of Wyoming.
As this shortwave moves across Laramie Range, we may see more
convection initiate and shift east of the I-25 corridor during
the late afternoon and evening. Cannot rule the potential for
more strong to severe storms especially in the southern Nebraska
panhandle where the shear and instability will be the greatest.

Saturday-Tuesday:
Quasi-linear upper level flow will be the main theme this
weekend. This will set the stage for daily afternoon showers and
thunderstorms especially along and east of the I-25 corridor.
Not confident about the severe potential at this point, but the
GFS/ECMWF are showing some signs of subtle shortwaves moving
through, but the exact timing of these shortwaves is uncertain
at this time. WPC clusters are still showing signs of the upper
level ridge building over the area next week. If this continues
to pan out, we will mostly likely see a switch to summertime
temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1136 PM MDT Tue May 28 2024

Thunderstorm activity has ended across the area, but a modest
low-level jet is kicking up over the plains that will bring
occasionally gusty southerly winds. This flow in a fairly moist
environment may allow for some low clouds and/or fog to form
near KCYS or KSNY. The probability is too low to add as a
prevailing group, but there is about a 30% probability of IFR at
KCYS and 15% at KSNY between now and 12-13z.

Another round of thunderstorms is expected Wednesday afternoon.
this is expected to start in WY around 20z and move into the NE
panhandle around 21-22z. Most of this activity should be
concluded by around 02z. The highest confidence in t-storm
impacts is at KSNY, but have VCTS in for most other terminals.
Storms will have the potential to produce gusty winds, brief
MVFR/IFR with heavy rainfall, and hail.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM...REC
AVIATION...MN