014
FXUS65 KCYS 222352
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
550 PM MDT Thu May 22 2025

.KEY MESSAGES...

- Marginal Risk (Level 1 of 5) for severe weather today across
  portions of southeast Wyoming along the Nebraska border into
  the Panhandle. Primary threats are hail and wind.

- Slight Risk (Level 2 of 5) for severe weather Friday across
  portions of the Nebraska Panhandle. All threats are possible.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 332 PM MDT Thu May 22 2025

Mostly sunny conditions ongoing across much of the CWA as of 21Z.
Some low-level cumulus have begun to develop out west and across the
Panhandle. Mountain showers are ongoing at this time, but mostly
quiet weather is present in the lower elevations. Gusty southeast
winds continue this afternoon as temperatures have risen into the
mid-60s to mid-70s area-wide. Dewpoints across the Panhandle and the
locations under a Marginal Risk are in the mid- to upper-30s at this
time, however these values should increase into the afternoon with
continued southeasterly flow.

Broad upper-level ridging is overhead today and will continue to
remain over head through Friday. With the broad ridging, broad, weak
subsidence is ongoing. However, multiple 500mb vorticity maxima and a
subtle shortwave trough are leading to enough lift to get clouds and
some showers developing across western portions of the CWA.
Vorticity maxima will continue to push through well into the evening
and overnight hours, keeping synoptic support ongoing for showers
and storms. 700mb ridging will slowly breakdown this afternoon into
the evening hours as a 700mb low develops over central Montana by
06Z Friday. As this low develops, warm air advection will dominate
across the region at 700mb, further supporting additional lift for
any nocturnal storms this evening. Precipitation chances ramp up
around 03Z tonight and continue through the overnight hours as the
700mb low develops and matures overnight. Most CAMs are coming in
quite low for CAPE values this afternoon and evening, keeping most
of the CAPE capped and/or only around 200 to 500 J. While this is
enough instability to get storms going, there is the possibility
that the cap with hold and little to no severe weather will occur.
However, forecast soundings from the RAP suggest steep low-level
lapse rates with excellent low-level turning, resulting in 0-1km SRH
values around 60 and 0-3km value around 200 to 250. Bulk shear
values climb into the 50 to 60kt range, leading to a low-CAPE, high
shear set up once again across portions of the CWA. SPC has included
portions of the area in a Marginal Risk (Level 1 of 5) for the
evening into the overnight hours. Primary threats currently look to
be damaging, downburst winds and some larger hail in the strongest
storms. Storm initiation looks to be fairly late, around 03Z, with
some showers developing within the next hours or two.

Broad ridging will continue Friday ahead of an upper-level trough
moving in from the West Coast. Once again, this broad ridging will
promote weak subsidence across the region, but 500mb vorticity lobe
ejecting out ahead of the approaching trough and another shortwave
will overpower the subsidence and lead to storm development once
more. Similarly, a couple 700mb shortwaves will push through the
region Friday afternoon and evening, further supporting low-level
lifting for showers and storms. Strong 700mb WAA is expected in the
afternoon towards evening hours before a cold front pushes through
from the low over Montana, dropping 700mb temperature back towards
5C. Surface winds turn easterly to southeasterly Saturday afternoon
and evening leading to broad upsloping across eastern portions of
the CWA due to a backdoor cold front. This front will be the main
forcing mechanism for storms Friday afternoon and evening. CAPE
values look to be higher than today, with NAM forecast soundings
suggesting upwards of 1500 J. Inverted-V soundings are not present,
with more of a loaded gun sounding across the southern Panhandle.
SPC has a small portion of the region under a Slight Risk (Level 2
of 5) for severe weather, with a Marginal Risk (Level 1 of 5)
expanded further into the CWA. All hazards are possible Friday with
hail and wind being the primary hazards, but an isolated tornado
cannot be ruled out.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 332 PM MDT Thu May 22 2025

An active long term is expected with near-daily chances for rain
across the CWA. A slow moving trough entering the Rockies on
Saturday will lead to a soggy holiday weekend for most. Another
shortwave at its heels will lead to continued storminess through at
least mid-week.

The sluggish upper-level trough will lead to a prolonged period of
moisture advection into the CWA before it eventually swings into
the Rockies. Moist southerly flow on both Saturday and Sunday will
cause PWATs to increase into the 90th percentile for NAEFS
climatology. This combined with the vorticity maxes aloft will spark
widespread storms in southeast Wyoming and western Nebraska on both
days. Model soundings over the weekend are fairly modest, showing at
most 1000 J/kg of MUCAPE in a few isolated spots. Cannot rule out a
few isolated strong storms, but the environment will likely be a
fair bit stable due to cooler temperatures in place. Similar
condiitons are likely headed into Memorial Day, with widely
scattered storms potentially putting a damper on holiday festivities.

As this weekend trough exits eastward, another shortwave will take
its place on Tuesday. Moisture will be a bit harder to come by with
this shortwave as there will be no moisture advection out of the
Gulf. However, decent mid-level moisture will exist with forcing
from vorticity aloft. This could spark additional storms Tuesday
through Thursday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 550 PM MDT Thu May 22 2025

An upper level disturbance and jet max will push across the area
tonight. This will result in showers and thunderstorms developing
around sunset with storms pushing eastward over the western Nebraska
terminals through 06z tonight.

HAZARDS/WEATHER TRENDS: Tricky Aviation forecast for the next 18
hours. Although aviation concerns are pretty limited through 00z,
thunderstorms are forecast to develop near KLAR and KCYS between 00z
and 03z and then push eastward into western Nebraska after 03z.
Based on recent high res guidance, confident enough to include VCTS
for the western Nebraska terminals. Brief strong gusty winds, some
moderate to heavy rainfall, and frequent lightning are expected.
Storms should push east of KCDR, KAIA, and KSNY after 07z. Will then
have to worry about low CIGS and IFR conditions developing due to
low stratus at KAIA, KSNY, and KBFF towards 12z early Friday
morning.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...SF
AVIATION...TJT