174
FXUS65 KCYS 300556
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1156 PM MDT Wed May 29 2024

.KEY MESSAGES...

- Strong to severe thunderstorms mainly along and east of I-25
  into the Nebraska Panhandle Wednesday afternoon with large
  hail and strong winds.

- Active weather pattern will continue through the weekend with
  daily chances for showers and thunderstorms.

- Summertime temperatures will be on the horizon next week.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 131 PM MDT Wed May 29 2024

Latest radar loop was showing the cluster of showers and
thunderstorms continuing to develop along and east of the I-25
corridor. The storms so far have been producing small hail and
some gusty winds over 50mph. This cluster of showers and storms
should continue their trend with moving east-northeast at 20 to
30 mph through the remainder of the afternoon. The one
interesting thing we have noticed this afternoon is that
dewpoints have been dropping into the 40s across much of the
Nebraska panhandle this afternoon which is quite a bit lower
than what some of the hi resolution models have been projecting
this afternoon. Meanwhile, the effective shear is closer to
30kts. These factors may limit the large hail potential this
afternoon to sizes mainly to quarter to half dollar with the
bigger threat becoming strong winds of 50 to 60 mph. The bulk of
these storms should move out the forecast area by 8pm or so, but
cannot rule out a few showers or an isolated storm or two
developing behind this cluster during the evening and overnight in
response to the shortwave moving through Wyoming.

Thursday afternoon should be a much quieter day with regards to
convection. We are looking at much drier air, but still cannot
rule out a few isolated thunderstorms developing along the
higher terrain. However, things may become more active over the
Nebraska panhandle Thursday evening into Thursday night as the
isentropic lift and low level jet kicks in and surges good
moisture advection into that region.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 131 PM MDT Wed May 29 2024

The pattern of mild to warm temperatures and near daily chances for
thunderstorms will continue through the weekend, but a warming and
drying trend is expected for the first part of next week.

On Friday, a broad trough will be located to our north, and another
piece of 500-mb vorticity will rotate through the area. As a result,
Friday looks like the coolest day of the forecast period across the
area with a sharp north to south gradient in 700-mb temperatures
across the area from about 2 to 3C near US20 to 6 to 8C along I-80.
Meanwhile, a surface high sliding down the east side of the Rockies
Thursday night will push the dryline back west against the Laramie
range and return low-level southerly to southeasterly flow over much
of the High Plains. With some subtle added lift from the passing
vorticity maximum, look for another round of thunderstorms to
develop. While storms may just be isolated to widely scattered, they
may have a slightly greater potential to become strong to severe on
the Wyoming side. Veering wind profiles and more low-level moisture
will be present. Forecast soundings show higher instability and
sufficient wind shear over southeast Wyoming. However, a potent
inversion around 700-mb will be stronger further north and east,
which will limit the severe potential in the northern/eastern
portions of the forecast area.

The upper level trough quickly skirts to the east into the weekend,
with a more quasi-zonal flow pattern setting up after this. The axis
of a subtle ridge moves through the area on Saturday with another
weak vort-max on its leading edge. Expect temperatures to climb back
above normal as 700-mb temperatures return to around +10C. The
dryline position is expected to be a little further east on Saturday
compared to Friday, but its too early to say exactly where this will
set up. While the vort-max aloft should help kick off scattered
showers and thunderstorms, this will mainly be a virga and wind
threat west of the dryline. However, once these storms reach a more
moisture rich environment with southerly low-level flow, strong to
severe convection could be on the table once again. There is still
uncertainty regarding whether this will occur in our forecast area
or to the east. Sunday looks similar, just a touch warmer and a
touch drier as the ensemble mean dryline position edges further to
the east. Thunderstorm activity should be a little bit more limited
with drier air working into the area, but we`ll have to watch the
exact dryline position as areas to the east of this will once again
have a greater strong to severe storm potential. Right now, it looks
like this area will be to our north/east, but it`s very close. Low
level westerly downslope winds should support enhanced warming over
the high plains, with highs expected in the mid 80s. Some of our
hotter spots (Torrington/Scottsbluff, etc.) will also have a chance
at the first 90F day of the year. Probabilities for a high over 90F
are around 60% for Scottsbluff, 50% for Chadron, and 40% for Sidney
at this time.

While 700-mb temperatures may drop briefly behind a weak shortwave
Sunday night into early Monday, they should rebound quickly.
Ensemble mean values over KCYS climb tack to +15C by 00z Monday.
Look at another warm to hot day. Temperatures aloft, around 500-mb,
will warm faster than the low levels as the more potent upper-level
ridge tries to work in across the area. The warmth aloft will limit
instability and thunderstorm potential on Monday, and possibly into
Tuesday as well. Almost all ensemble members keep most of the area
dry on Monday, and most continue this through Tuesday and Wednesday.
There is good consensus around another upper level shortwave pushing
across the northern Rockies in the Tuesday/Wednesday timeframe, but
the chance for precipitation with this is fairly low. However, this
introduces some uncertainty in temperatures, with a more southerly
track leading to a stronger shot of cool air, and a more northerly
track leading to the hot temperatures continuing.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1140 PM MDT Wed May 29 2024

While the main thunderstorm threat has moved out, some scattered
shower activity along and ahead of a cold front currently
crossing the area is ongoing. A few showers with the potential
for gusty winds will be pushing near to KCDR, KBFF, and KAIA
over the next 2-3 hours before winds turn more northwesterly
behind. A few rumbles of thunder can`t be ruled out.

An initial round of low clouds may graze the northern panhandle
Thursday morning with MVFR CIGs favored at KCDR and KAIA, and
could extend to KBFF and KSNY. This should clear by mid morning
with clearing skies later in the day. A reinforcing cold front
will arrive late afternoon or early evening, bringing a quick
round of gusty north to northeast winds across the High Plains
towards the end of the TAF period. Shower/storm activity is
expected to be fairly minimal Thursday, but a round of nocturnal
thunderstorms is expected to develop late Thursday evening.

&&

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

&&

$$

SHORT TERM...REC
LONG TERM...GCC
AVIATION...MN