734
FXUS65 KCYS 221735
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1135 AM MDT Tue Apr 22 2025

.KEY MESSAGES...

- Breezy winds and low RH values will bring enhanced fire
  weather concerns on Tuesday with a generally low risk of
  critical conditions expected.

- Moist southeasterly flow alongside a stalled frontal boundary
  between WY/CO will produce a widespread thunderstorm risk on
  Wednesday with a marginal risk of severe activity.

- Adequate low and mid level moisture along with passing weather
  disturbances will help produce scattered afternoon and evening
  showers and thunderstorms nearly every day.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 253 AM MDT Tue Apr 22 2025

The overall upper level pattern will be fairly quiet as flow
turns southwesterly with a few embedded shortwaves passing
across while at the surface we should see weak flow turn more
easterly to southeasterly and begin to bring moisture that will
help fuel a more active pattern for the remainder of the week.

For Tuesday - Conditions should remain relatively quiet for
Tuesday as moisture will be lacking alongside any appreciable
forcing. Breezy winds alongside RH values dropping into the low
20`s to upper teens will bring a risk of some enhanced fire
weather concerns for the day, however the HREF only shows a
greater than 50% probability for gusts 25+ mph and RH values
below 20% between Wheatland and Alliance with the bulk of this
occurring on the Wyoming side of the border where fuels are
still unfavorable for critical fire weather conditions. Looking
like a brief hour, maybe two, could occur on the Nebraska side
near Scottsbluff to Alliance for critical fire weather
conditions before tempering back down for the day. Some of the
high-res guidance also shows the chance of a brief popup shower
from the high terrain eastwards into the Nebraska Panhandle
through the nighttime hours, but most of this activity will be
limited to some lighter rainfall at best if precipitation can
even make it to the surface under dry lower levels.

For Wednesday - That all changes on Wednesday, however, as we
see moist easterly to southeasterly surface flow establish at
the surface with moisture support also establishing in the mid
layers of the atmosphere allowing for a more widespread
likelihood of showers and storms during the afternoon and
evening. A frontal boundary should make its way across and stall
out right along the borders of WY/CO, bringing the ignition
needed to support thunderstorm development for the day. The
strongest axis of instability looks to be from Cheyenne up
through Wheatland and eastwards across the bottom half of the
Nebraska Panhandle. HREF guidance alongside deterministic models
are all pinging around 500-1200 J/kg of CAPE with supportive
surface to 500mb shear around 35-55 knots. This should be enough
to initiate several thunderstorms during the later afternoon
into the early evening hours capable of marginally severe hail
and some strong wind gusts. Activity may persist into the
evening before finally weakening into the nighttime hours,
though pockets of showers with attendant lightning may persist
overnight east of I-25 moving into Thursday morning, but the
severe risk should diminish into the nighttime hours. In any
case, at least favorable moisture should occur, with current
QPF totals for the day between 0.1-0.5 inch east of I-25,
heaviest in the Nebraska Panhandle where showers and storms
should linger longer into the nighttime hours.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 253 AM MDT Tue Apr 22 2025

Thursday...With a relatively moist airmass in the low and mid
levels. upslope northeast winds, and southwest flow aloft with a
shortwave trough passage near peak heating, we anticipate scattered
to numerous showers and scattered thunderstorms in the afternoon and
evening, most numerous across I-25 from Wheatland to Cheyenne.

Friday...Another decent setup for afternoon and evening showers and
thunderstorms, with the flow aloft turning south southwest, and
moist low level southeast winds underneath. Looks like scattered
afternoon and evening showers and thunderstorms once again, with a
bit less coverage than Thursday. With 700 mb temperatures near 7
Celsius and plenty of cloud cover, high temperatures will be in the
upper 40s to lower 60s.

Saturday...Warmer temperatures expected with less cloud cover and
700 mb temperatures near 8 Celsius yielding maximum temperatures
from the mid 60s to lower 70s. With less low and mid level moisture
availability, shower and thunderstorm coverage will be less than
Friday.

Sunday...As the primary trough aloft moves into Utah, southwest flow
aloft strengthens over our counties, helping to produce a surface
lee trough, which will act as a focus for isolated to scattered late
day showers and thunderstorms.

Monday...As a potent shortwave trough aloft and its associated cold
front move across our counties, we expect scattered showers and
isolated thunderstorms, that could be more numerous early in the day
before downslope low level west winds help decrease moisture
availability. Cooler 700 mb temperatures near 2 Celsius will yield
high temperatures in the 50s to mid 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1128 AM MDT Tue Apr 22 2025

VFR conditions will remain through the TAF period. A stalled
boundary may produce some rain showers as early as 21Z for KCYS
and 22z for KBFF and KAIA. KSNY may also be affected by these
showers but that looks to be as early as 23z. Considering that
these clouds would be mid to high based, precipitation may not
reach the ground and end up being virga. However, there is a
slight chance these showers could become thunderstorms strong
enough to produce rain that could penetrate the dry layer below.
Confidence is lower that 30 percent for that scenario thus left
out of the Prob30. There could also be showers tomorrow but
confidence on timing wasn`t strong enough to put it in the TAFS.

&&

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

&&

$$

SHORT TERM...CG
LONG TERM...RUBIN
AVIATION...MM