894
FXUS65 KCYS 072356
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
556 PM MDT Fri Jun 7 2024

.KEY MESSAGES...

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

- Threat for strong downburst winds this afternoon and evening
  from high based thunderstorm development.

- Monday and Tuesday will see the greatest coverage of late day
  showers and thunderstorms, while Wednesday and Thursday will
  be warmer with a general decrease in shower and thunderstorm
  coverage.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 405 PM MDT Fri Jun 7 2024

Pretty nice weather this afternoon with temperatures in the mid
80s to mid 90s, hottest over western Nebraska. Current
observations show the leading edge of the cold front across the
northern Nebraska Panhandle and eastern Niobrara County at this
hour, with winds shifting into the north and slightly cooler
temperatures (95 at Scottsbluff compared to 84 at Chadron). This
front will likely remain stationary through this afternoon as
some afternoon convection continues to develop across the
mountains and slide east-southeast over the area through this
evening. Current KCYS radar loop shows a band of showers and
thunderstorms near the leading edge of the cold front. This
activity is expected to continue moving east while the line
gradually propagates southward along the cold front this
evening. High resolution models show additional development of
thunderstorms along the I-80 corridor later this afternoon into
this evening once the cold front moves into the central high
plains. With high base thunderstorms and showers expected, gusty
winds will be the primary concern...but can`t rule out some
small hail as well. Environmental winds have already been pretty
gusty this afternoon with some gusts between 40 to 50 MPH. Any
additional thunderstorm outflow will likely result in gusts over
60+ MPH. May need to issue a Special Weather Statement later to
cover these gusts, or handle them with individual SVR Tstorm
warnings when necessary.

For this weekend, models continue to show the upper level flow
shifting into the northwest with east and southeast winds at
this surface. The surface cold front will stall across the
mountains Saturday afternoon and provide additional
convergence/lift across the high plains. Increased POP Saturday
with with numerous showers and scattered thunderstorms
likely. Pretty good forcing with this event with event some
moderate jet dynamics within the right entrance region of a
departing weak jet streak aloft. Showers and thunderstorms are
expected to develop over the mountains/near the frontal boundary
and push southeast. Expect several rounds of convection to
impact portions of I-80 and I-25 corridors with some decent (and
much needed) rainfall amounts. Can`t rule out some strong
thunderstorms but any signals for severe weather appear to be
pretty marginal due to limited instability, 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. High
temperatures on Saturday and Sunday will be tricky since any
amount of limited sunshine this time of the year will rapidly
warm the lower atmosphere. However, cloud cover, several chances
for showers, and persistent upslope flow should keep max
temperatures around 70 degrees for much of the day. However, any
additional cloud cover, fog, or stronger upslope winds may
result in highs struggling to warm up out of the low to mid 60s.
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. Sunday will be
similar, but models are now showing a transitory shortwave
ridge axis moving across the Front Range later in the day. Even
lower confidence for Sunday`s temperature forecast with a wider
spread in ensemble solutions. For now, kept temperatures close
to Saturday as winds shift into the south. Also, added fog to
the forecast late Saturday night/early Sunday due to persistent
moist east to southeast winds.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 254 PM MDT Fri Jun 7 2024

Unsettled weather will continue into Monday for our area, but expect
a warm and dry pattern to take hold for the middle part of next
week.

Shower and thunderstorm activity will continue well into the evening
or overnight hours on Sunday, fueled by an approaching shortwave
trough. This feature moving over top the flattened ridge will pass
through the area Monday, and help kick off another round of showers
and thunderstorms. Ensembles are in pretty good agreement that low
level moisture will stay in place east of the Laramie range for
Monday with southerly winds over the plains. The approaching
shortwave trough will start to introduce a slight cooling aloft,
around 500-mb, leading to slightly steeper lapse rates and
instability. High altitude winds are not expected to be that strong,
but veering winds should allow for sufficient shear to get a few
strong to severe storms going across the area. It`s a little early
to dig into specific hazards, but will need to continue monitor this
possibility.

As the upper level shortwave moves off to the east, the persistent
ridge over the southwest will rebound across the area. This is not a
very high amplitude ridge as an active jet stream will remain over
the far northern US. Still, look for temperatures to return to above
normal values over the High Plains as westerly flow pushes the
dryline a little further east. Drier air will also work in from the
west, reducing storm chances for Tuesday. A few showers and storms
will still be possible, but expect this to be quite a bit less
widespread than Friday through Monday. The ridge strengthens further
for Wednesday and Thursday, pushing ensemble mean 700-mb
temperatures to around +15 to +17C. There is some potential for a
weak cold front to slide through Thursday and deliver slightly
cooler temperatures, but other ensemble members actually peak the
heat wave on Thursday. Regardless, expect above normal temperatures
both Wednesday and Thursday. The probability of record heat is low,
but certainly non zero, especially if the stronger ridge scenarios
plays out. A few showers/storms will still be possible mainly over
the higher terrain these days, but they should be very isolated.
Shower and thunderstorm chances return to the area by the end of
next week, as models are in pretty good agreement on a closed low
that will be sitting off of southern California all week getting
pulled back into the flow and across the Four Corners states around
the Friday/Saturday time frame.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 555 PM MDT Fri Jun 7 2024

Showers and thunderstorms continue early this evening with
gusty, erratic winds in the vicinity of storms for southeast WY
terminals. Thunderstorm activity should calm down over the next
few hours, but lingering showers will remain overnight. Moist
northeasterly flow overnight into Saturday morning will give way
to the potential for MVFR conditions with low ceilings. HREF
guidance currently shows low, but non-zero probabilities of
ceilings dropping below 3000 ft continuing through Saturday
midday.

&&

.HYDROLOGY...
Issued at 254 PM MDT Fri Jun 7 2024

Above normal temperatures have resulted in accelerated mountain
snowmelt across the Rocky Mountains this week. Temperatures in
the Snowy and Sierra Madre Ranges are expected to remain
elevated this weekend, even as a cold front stalls across the
mountains. Flood warnings for snowmelt continue for the Little
Laramie River west of Laramie, and the Encampment River south
of Saratoga, mainly due to minor flooding concerns. Emergency
Managers have reported some flooding in these areas today.
Flood Watches continue for the upper North Platte River valley
and Medicine Bow River near Elk Mountain for potential impacts
this weekend. Current forecasts suggests river levels will peak
later this weekend and remain elevated into early next week due
to some slightly cooler air. However, rainfall in and around the
mountains may become an issue this weekend and could lead to
rapid additional rises in creeks and rivers.

&&

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

&&

$$

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