821
FXUS65 KCYS 041149
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
549 AM MDT Sat May 4 2024

.KEY MESSAGES...

- Mainly dry and warmer conditions are anticipated for the
  weekend.

- Strong winds (60+ mph) return to southeast Wyoming and western
  Nebraska Monday with a prolonged period of elevated winds
  continuing for wind prone locations through midweek.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 247 AM MDT Sat May 4 2024

Today...Transitory shortwave ridging aloft will build overhead and
with plenty of sunshine and 700 mb temperatures near 2 Celsius,
maximum temperatures will reach the upper 50s to mid 60s, with
south low level winds limiting the warmup.

Tonight...Decent moderation in temperatures will occur as southwest
flow aloft strengthens ahead of the approaching trough aloft over
the Great Basin states, inducing increasing south winds and a
thermal ridge over our counties, with low temperatures from the mid
30s to lower 40s.

Sunday...Southwest flow aloft strengthens ahead of the approaching
trough aloft over the Great Basin states, inducing a fairly
significant surface trough along Interstate 25. Surface and low
level gradients support a windy day with brisk south to southeast
winds. Although the atmosphere will be relatively dry, it appears
there will be enough low and mid level moisture to support isolated
afternoon shower and thunderstorm coverage along the surface trough
from Douglas to Laramie. 700 mb temperatures near 8 Celsius support
maximum temperatures from the upper 60s to mid 70s.

Sunday night...The negatively tilted shortwave trough aloft pivots
into western Colorado, sending the leading edge of a potent Pacific
origin cold front into our western counties. Looks like enough low
and mid level moisture, combined with cold frontal lifting and
dynamic forcing associated with the 500-300 mb and 700-500 mb
quasigeostrophic forcing to produce scattered showers and isolated
thunderstorms across our forecast area, with snow showers becoming
widespread across our Snowy and Sierra Madre Ranges.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 247 AM MDT Sat May 4 2024

An upper level low will be traversing the region early next week
with the trough axis of the initial wave passing through the CWA
Monday. While severe storms are expected across the central plains
farther east, strong winds are likely to be the local impact across
southeast WY and western NE with this storm system. Strong cross
barrier winds developing across the Laramie Range with impressive
downward omega fields in the wake of the trough axis passage could
lead to wind gusts 70-75 mph along the I-25 corridor.

Latest NBM probabilities of 55+ mph wind gusts are quite high (>80%)
for most wind-prone areas Monday across southeast WY with areas
covered by 50% probabilities expanding outside of wind-prone
locations onto adjacent foothills and plains. Additionally, in-house
guidance continues to show high probabilities (60-80%) for high
winds. There remains to be some uncertainty with the duration of
this wind event with elevated to potential high winds continuing
through Wednesday morning. However, guidance has been starting to
suggest Monday is the most likely timing of the strongest winds
across much of the area, while wind-prone locations could continue
to see occasional gusts into midweek. 700mb flow climbing over 60 kt
across southeast WY with strong ensemble support for high winds
early next week as the latest NAEFS and EC are showing over
climatological 99th percentile 700mb winds.

Precipitation chances Monday will be best across Carbon Co as well
as over east-central WY extending northward. Surface cyclogenesis
with this upper low track appears more likely in southeast MT and
western SD keeping much of the precipitation shield to the north.
Additionally, this upper level low looks to stall out across the
central CONUS with a potentially retrograding surface low leaving
southeast WY and western NE under a general troughing pattern
through the remainder of the week. This will lead to below average
temperatures for early May with additional chances for light
precipitation through the remainder of the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 541 AM MDT Sat May 4 2024

VFR conditions currently across area terminals with isolated
pockets of low clouds developing near southeast WY terminals.
Expected mostly clear skies to persist throughout the day with
gusty southerly winds around 20-30 kt this afternoon. Gusty
winds will continue into this evening across the NE panhandle
with a nocturnal LLJ setting up.

&&

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

&&

$$

SHORT TERM...RUBIN
LONG TERM...MB
AVIATION...MB