769
FXUS65 KCYS 070031
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
631 PM MDT Thu Jun 6 2024

.KEY MESSAGES...

- Warm weather will continue through late week, with widespread
  highs in the 80s and lower 90s on Thursday and Friday.

- Saturday through Monday will see increasing chances for
  afternoon and evening showers and weak thunderstorms.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 400 PM MDT Thu Jun 6 2024

Pleasant weather this afternoon with hardly a cloud in the sky.
Temperatures are on track and currently in the 80s with a few
locations across western Nebraska approaching 90 degrees.
Shortwave upper level ridge axis is currently moving eastward
across Wyoming and Colorado and is expected to move east of the
forecast area tonight as the 700mb thermal ridge moves into the
area. This will keep overnight lows on the mild side with
readings in the 50s.

One more very warm day forecast for Friday with highs quickly
climbing into the 80s to low 90s. We may see the low to mid 80s
by the late morning hours ahead of the next cold front. Models
have delayed the timing of this cold front by a few more hours
compared to yesterday...with FROPA along highway 18 and 20 over
east central Wyoming late Friday afternoon and not across the
I-80 corridor until late Friday evening. With this in mind,
increased high temperatures a few more degrees due to the delay
in the cooler airmass. Kept POP between 15 to 30 percent for
widely scattered showers and thunderstorms later in the day and
Friday night. Thunderstorms look sub-severe at this time with
maybe some gusty winds possible. Northwest winds will become
north and become gusty on Friday ahead/near the cold front, but
high winds (gusts >58 mph) are not expected at this time.

For this weekend, models show the upper level flow shifting into
the northwest with east and southeast winds at this surface.
Cold front will stall across the mountains and provide
additional convergence across the high plains. Kept POP pretty
high with numerous showers and scattered thunderstorms expected.
Not seeing strong signals for strong to severe thunderstorms as
thermodynamic profiles and model soundings are less than
impressive with limited CAPE, poor lapse rates, and a cooler
boundary layer. Moisture will definitely be in place with the
NAEFS showing mean Precipitable Water in the 95th to 99th
percentile for this time of the year over most of southeast
Wyoming and western Nebraska Saturday afternoon. Will continue
to keep an eye on this, but as of right now, the boundary layer
looks a bit too stable with too much cooler air near the surface
and a warm layer around 700mb, capping any surface based
convection. High temperatures on Saturday will be tricky since
any amount of limited sunshine this time of the year will
rapidly warm the lower atmosphere. However, cloud cover and
persistent upslope flow should keep max temperatures in the 70s
or upper 60s for much of the day. The warmest location will
likely be Carbon County and Rawlins with highs in the low 80s.
Areas near the Carbon county/Albany county border, including
Rawlins and Laramie, may have the best chance to see some strong
to severe storms as they`ll be warmer with mostly sunny or
partly sunny skies...resulting in more instability compared to
areas further east.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 400 PM MDT Thu Jun 6 2024

Unsettled weather will carry into the early part of next week, but
conditions will turn drier and hotter by mid-week.

A messy weather pattern will continue across the west on Sunday with
a weakening dirty ridge over the Great Basin area and several
shortwaves on its periphery. The ridge will be fairly moisture-laden
with above normal precipitable water across much of the mountain
west. Our area will be under a stalled stationary frontal boundary
waffling back and forth close to the front range of the Rockies. A
small closed low dropping out of the northern plains on Sunday will
add a bit of extra lift ahead of it, with some overrunning
isentropic lift promoting afternoon showers and thunderstorms. The
severe weather threat looks fairly limited though, as forecast
soundings show cool low level temperatures under fairly warm
temperatures aloft. Thus, lapse rates look to remain rather weak.
There will be some instability, so expect there to still be some
thunderstorm activity. Uncertainty exists in high temperatures
because of differences in how far south the upper level shortwave
and associated cold front will get. GEFS members tend to be a little
more aggressive with this, resulting in cool temperatures for Sunday
into Monday with a strong cold front clearing most of the area.
ECWMF members tend to keep this weaker and further north, leading to
warmer temperatures for this time period. Monday looks similar to
Sunday. The closed low from the north will be moving off to the east
by this time, but another shortwave in the northwest flow will
locally enhance lift again.

Tuesday looks like a transition day as the ridge starts to expand
eastward, pushing the stalled frontal boundary responsible for the
period of unsettled weather away from our area. Lingering chances
for showers and thunderstorms will exist across the area Tuesday,
but a warming trend will also begin. Expect strong warm air
advection into Wednesday, as ensemble median 700-mb temperatures
climb up to +16C near KCYS by 00z Wednesday. A few models graze the
area with a shortwave, sparing us from the brunt of the heat for
Thursday, but most ensemble members keep that shortwave far enough
north to bring another very hot day on Thursday, with the potential
for near record highs. The NAEFS mean shows 700 and 500-mb
temperatures over the 90th percentile of climatology on Wednesday
and Thursday even at a 6-7 day lead time.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 623 PM MDT Thu Jun 6 2024

VFR conditions expected across area terminals through the
forecast period. Increasing northwest winds and cloud cover
expected starting Friday morning with a frontal passage. Friday
afternoon wind gusts around 30 kt for southeast WY terminals and
approaching 25 kt for NE panhandle terminals. Decided to
introduce VCTS Friday afternoon for southeast WY terminals,
especially KCYS and KLAR, with gusty outflow winds looking to
be the most likely hazard in the vicinity of any storms after
21z.

&&

.HYDROLOGY...
Issued at 400 PM MDT Thu Jun 6 2024

Several days of above normal temperatures have accelerated snowmelt
runoff in the North Platte and Laramie River basins. Temperatures
for the next several days are forecast to remain high enough to
sustain rapid snowmelt and the subsequent high flows including minor
flooding through Saturday. Snowmelt from the Sierra Madre and
Snowy Ranges has driven the Encampment and North Platte Rivers
to bankfull stages. The Encampment River is forecast to crest
above flood stage on Saturday morning. Emergency management has
reported minor flooding along the Little Laramie River. This
flooding is expected to continue through the weekend.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...MN
AVIATION...MB
HYDROLOGY...AJA