540
FXUS65 KCYS 061711
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1111 AM MDT Sun Jul 6 2025

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) for severe weather today
  and an Enhanced Risk (Level 3 of 5) for severe weather Monday.
  All modes of severe weather are possible both days: large
  hail, damaging winds, and isolated tornadoes.

- Hot temperatures and drier conditions are expected by mid-
  week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 158 AM MDT Sun Jul 6 2025

Partly cloudy skies are ongoing tonight across much of the region
with an outflow boundary visible on satellite racing southward
across the Panhandle. As this boundary moves south, clouds are
forming along and ahead of the boundary, leading to cloudier skies
across the Panhandle. Temperatures are on the mild side in the upper-
50s to mid-60s across much of the region, with the warmest
temperatures across the Panhandle where cloud cover has increased
ahead of the outflow boundary from South Dakota. Winds behind the
boundary are quite breezy, gusting in the 25 to 30 mph range
tonight. Elsewhere, winds are mostly calm between 5 and 10 mph,
except Rawlins and Douglas where gustier conditions are ongoing
tonight, with gusts around 20 mph. Current radar imagery shows all
returns slowly diminishing as they move eastward, leading to a fairly
quiet night tonight.

Unlike tonight, this afternoon and evening will be quite active as
southeast Wyoming and western Nebraska are expecting severe weather
once again. SPC has placed much of the Panhandle under a Slight Risk
(Level 2 of 5) and much of southeast Wyoming in a Marginal Risk
(Level 1 of 5) for severe weather this afternoon. Southwesterly flow
aloft is ongoing this morning with a wind shift expected later this
morning with upper-level winds turning westerly. The region remains
mostly sandwiched between upper-level trough progressing eastward
along the Canadian border and a broad ridge attempting to remain
overhead near the Four Corners Region. However, with the fairly open
southwesterly flow across much of the southwestern CONUS, several
lobes of 500mb vorticity will advect toward and across the region
later today. One lobe appears to have enough CVA with it that a
potent 500mb shortwave develops and races across the region this
afternoon into the early evening hours. This shortwave will be the
primary forcing mechanism to get convective initiation later today,
as the stout, shortwave digs across the region inducing its own
vorticity lobes as it propagates eastward. Fairly weak 700mb flow
will accompany this shortwave. Unlike yesterday, the 500mb shortwave
this afternoon will induce a strong jet as the shortwave moves
across the higher terrain. While the 500mb flow is still fairly weak
overall, the 30 to 40kt jet is strong enough to increase the
steering flow some, despite the lack of strong winds at 700mb. Broad
WAA will be ongoing throughout the morning and afternoon hours at
700mb, leading to continue ascent throughout much of the day.
Further down at the surface, the terrain-induced dryline will once
again be at play and should be stronger than previous days given the
westerly winds west of the Laramie Range. Additionally, surface
winds turn easterly to east-southeasterly this afternoon across the
Panhandle and far eastern Wyoming, leading to ample mesoscale lift
near the surface. Surface temperatures will be a touch cooler today,
with highs in the low- to mid-80s in southeast Wyoming and mid- to
upper-80s across western Nebraska. Southerly to southeasterly wind
through the morning hours will continue to increase available
moisture, especially across the Panhandle, where dewpoints will
increase to the mid- and upper-50s to near 60 in some locations.

With ample moisture and warm surface temperatures in place this
afternoon, SBCAPE values will surge into the 1500 to 2000J range
across much of the Panhandle, according to forecast HRRR and RAP
soundings. The RAP is a touch more aggressive than the HRRR as far
as CAPE is concerns, though both hires models are generally in the
same ball park. 0-6km Bulk Shear values will be strong than
yesterday, maxing out around 45 to 50kts across the Panhandle this
afternoon. 0-3km SRH values are also much higher than yesterday,
favoring rotating updrafts more, though 0-1km SRH still remains
fairly low, with the highest values maxing out around 50. Despite
this, steep lapse rates are present throughout much of the
atmosphere, especially in the lowest 5km. However, forecast
soundings for locations in the northern Panhandle suggest a more
"loaded gun" like sounding this afternoon, while locations in the
southern Panhandle boast more of an Inverted-V sounding, as is
typical of this region. Therefore, the larger hail threat may remain
across the northern Panhandle, while the best wind threat looks to
be the southern Panhandle at this time. A tornado cannot completely
be ruled out with the low-level turning expected tomorrow, but the
threat appears to be lower than the hail and wind threats. Based on
the Bulk Shear orientation to the terrain-induced dryline and the
slight stronger steering flow, storms may be initially discrete
before conglomerating into more of a line or cluster of storms this
afternoon. Therefore, another active severe weather day is expected
today with potentially a north/south difference in primary severe
hazard concern.

The severe threat continues for Monday afternoon, where SPC has
placed a sliver of the Panhandle in an Enhanced Risk (Level 3 of 5),
the remaining Panhandle in a Slight Risk (Level 2 of 5), and
southeast Wyoming in a Marginal Risk (Level 1 of 5) for severe
weather. Portions of the Enhanced Risk include a 5% tornado threat,
with the remaining Panhandle in the 2% tornado threat. So, let`s get
into it. Westerly flow aloft will be present throughout the day
Monday as the region remains sandwiched between a trough across the
northern CONUS and the expanding across much of the southern CONUS.
Multiple 500mb vorticity lobes will eject out towards and across the
region once more, resulting in a surging of the upper-level heights
northward and a stout, shortwave trough once again at 500mb,
resulting in a quick hitting jet streak across portions of the CWA.
500mb winds will be a bit stronger Monday with a weak jet developing
across the terrain at 45 to 50kts. This shortwave and subsequent jet
streak will enable showers and storms to get going once again Monday
afternoon, due to the concentrated lift across the CWA. The 700mb
flow remains messy at best, with a subtle shortwave pushing towards
the region Monday afternoon. Very warm 700mb temperatures will be
present once again, however, it may act to increase the cap across
the region Monday due to the warming above the surface, especially
since WAA is not really present Monday. Southerly to southeasterly
flow will be present again early Monday morning through the early
afternoon hours, ushering in plenty of moisture as dewpoints remain
in the 50s to near 60s throughout the day Monday across the
Panhandle. The terrain-induced dryline will surge eastward late
Monday morning into the early afternoon hours. This dryline will
collide with easterly surface winds, resulting in fairly potent
convective initiation, assuming the cap breaks and the warm 700mb
temperatures do not hinder this process.

Surface temperatures Monday will increase into the mid-80s to low-
90s across the Panhandle as dewpoints increase into the upper-50s to
low-60s across the same area. As a result, SBCAPE will increase
towards the 2000J mark and beyond, especially across the Panhandle,
with MLCAPE not fair behind in the 1800J range. Bulk shear values
will once again be in the 45 to 50kt range Monday afternoon.
Forecast HRRR soundings once again show a stout CAPE profile Monday
across the Panhandle, with more of a "loaded gun" shape, rather than
the Invertd-V commonly seen across the high plains. Low-level
turning is fairly good once again, though surface to 1km SRH values
remain fairly low. However, surface to 3km SRH values will be well
into the 100s, supporting rotating updraft once again on Monday.
With the stronger surging of the terrain-induced dryline on Monday,
initially discrete supercells do look possible, assuming the cap can
be broken. However, with fairly weak steering flow still, these
storms will likely conglomerate into clusters and/or a line once
again. Large hail, strong winds, and tornados all look possible
Monday afternoon, but some uncertainty remains with the strength of
the cape. Future forecast packages will look closer into the severe
threat Monday, though it does look to be the best severe weather
chance in the upcoming days.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 358 PM MDT Sat Jul 5 2025

The upcoming work week will be bookended by stormy weather patterns,
while dry and hot weather will dominate the middle part of the week.

Picking up on Monday, a compact upper level ridge will remain parked
over the Four Corners states, allowing for a parade of shortwave
troughs to continue to move over the top of it. The dryline is
expected to remain parked more or less over the Laramie Range once
again on Monday. Moist southerly low-level flow will be present in
the morning, but the low-level wind and pressure patterns will be
fairly complicated moving into the afternoon hours. Guidance depicts
a weak surface low trying to develop near Laramie county, while a
high to the north may push northeast winds into our northern/eastern
counties. The result will likely be numerous trigger points for
scattered afternoon thunderstorms across the High Plains. In
addition, plentiful moisture and steep lapse rates will likely put
ample instability in place. Modest overrunning and vorticity
advection aloft will provide some forcing. While all of this points
towards strong to severe thunderstorms, the main piece working
against this will be the possible presence of a significant cap.
Models show fairly substantial CIN in place, particularly over the
Nebraska panhandle. This will be the main failure mode to watch for
in the coming days, but if we manage to see storms break through the
cap, there will be the potential for strong to severe thunderstorms
with all hazards possible.

The upper level ridge will amplify heading into Tuesday, bringing
much drier air into most of Wyoming. This will decrease storm
probabilities for Tuesday and Wednesday at least, but a few high
based showers and thunderstorms can`t be ruled out. Attention
midweek will shift to hot temperatures as 700-mb temperatures push
towards +16C to +19C across the area, peaking on Wednesday. Highs
will be some 5-10F above average for Tuesday through Thursday.
Wednesday will be the hottest day, with widespread 90s, and a good
chance at 100F in the typical low elevation hotter spots such as
Torrington, Scottsbluff, and Chadron. Thursday will be a transition
day as a shortwave trough nudges the ridge down to the south. Expect
plentiful moisture to return to the middle to upper atmosphere, but
the low levels will remain fairly dry. This points to possible
scattered thunderstorms with a dry microburst potential before a
surface cold front plows through the area late Thursday or early
Friday. Expect much cooler temperatures on Friday with an increase
in possible shower and thunderstorm coverage.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1111 AM MDT Sun Jul 6 2025

Main aviation concern will be strong to severe thunderstorms in
southeast Wyoming and the Nebraska panhandle this afternoon and
evening. Storms could contain damaging winds and large hail. Heavy
rain could also be possible leading to reduced visibility at times.
Low CIGs could also be possible in storms. Storms will dissipate
this evening, leading to calmer conditions. Cannot rule out patchy
low CIGs developing in the Nebraska panhandle early Monday
morning.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...MN
AVIATION...SF