276
FXUS65 KCYS 081723
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1123 AM MDT Tue Jul 8 2025

.KEY MESSAGES...

- There is a Marginal Risk (Level 1 of 5) for severe weather
  both today and Wednesday.

- Active pattern will continue as monsoonal moisture moves into
  the region today through Wednesday.

- Much cooler Thursday night and Friday as a strong cold front
  moves south across the high plains.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 234 AM MDT Tue Jul 8 2025

A quiet night tonight across southeast Wyoming and western Nebraska
with only a few high clouds slowly drifting over Kimball and
Cheyenne counties. These clouds should be out of the region in the
next 1 to 2 hours, leading to clear skies everywhere tonight.
Temperatures are fairly mild tonight, despite the clear skies
overhead. Temperatures are sitting in the mid-50s to mid-60s as of
07Z. Winds are mostly calm as well, with only a few locations
boasting winds over 10mph. Overall, a quiet night compared to recent
days.

The upper-level ridge over the southern CONUS will continue to push
northward today with the 500mb high right on its heels. The 500mb
high looks to establish itself over the Four Corners Region,
suggesting an influx of monsoonal moisture into the region over the
next few days as the high rotates over the Four Corners Region. As a
result of this, multiple 500mb vorticity maxima with eject out from
the high and move overhead throughout the afternoon hours. The
vorticity lobes will enable a shortwave through to develop just west
of the CWA and move due eastern overhead this afternoon. However,
under the ridge, the 500mb flow is quite weak once more, with only
around 25 to 30kts overhead. Despite this, the vorticity maxima and
subsequent shortwave at 500mb will active as forcing for synoptic
lift across much of the CWA, especially east of the Laramie Range
into the western Nebraska Panhandle. 700mb flow remains fairly weak
and disorganized today, with winds peaking only around 25kts this
afternoon around 21Z. 700mb WAA will be present throughout the
morning and afternoon hours with 700mb temperatures rising into the
15 to 17C range, resulting in surface temperatures maxing out in the
upper-80s to mid-90s across the CWA this afternoon. The terrain-
induced dryline will be present again today and will move easterly
throughout the early afternoon hours, acting as a secondary form of
lift, though closer to the surface. Westerly 700mb winds and
westerly surface flow west of the Laramie Range will aide in the
dryline becoming more defined and pushing further east, thanks in
part to the subsequent dry downsloping with westerly winds aloft and
near the surface. Dewpoints behind the dryline will tank into the
30s to low-40s, while dewpoints east of the dryline will be in the
50s thanks to the monsoonal moisture slowly advecting into the
region. So, while temperatures will be quite warm today behind the
dryline, drier air and breezy conditions will lead to apparent
temperatures lower than the actual temperatures this afternoon.

0-6km Bulk Shear will max out around 40kts across the southern
Panhandle this afternoon and will be oriented nearly perpendicular
to the advancing terrain-induced dryline. Surface winds will be
nearly parallel to the dryline, favoring storm initiation and
initially discrete nature to the storms that form. Fairly straight
hodographs in forecast soundings from both the HRRR and the RAP
suggest again that storms may be initially discrete, then quickly
grown upscale, should they be able to maintain themselves.
Additionally, storm splitting will be favored, however, this one
again requires storms to maintain themselves rather than be pulsey
in nature. Forecast soundings indicate a wide variety of CAPE
values, with HRRR soundings suggesting less than 1000J to around
1200J and RAP soundings suggesting nearly 2000J. The RAP has, once
again, higher dewpoints than the HRRR. With the dryline moving
eastward and reinforced by dry downsloping winds off the Laramie
Range, the HRRR solution appears more likely, with the lower
dewpoints associated with the downsloping. However, both the RAP and
HRRR soundings suggest an Inverted-V sounding shape with around 1500
to 2000J of DCAPE, favoring strong downburst winds. Given the
relatively weak set up today, storms that form this afternoon will
likely produce strong winds and/or just be gusty showers. If these
storms find a decent pocket of CAPE, it is possible to get some
large hail, assuming storms can maintain themselves long enough.
Forecast soundings suggest enough CAPE in the hail growth zone to
get fairly large hail this afternoon, though it may be isolated in
nature. Surface to 3km SRH values are low, though high enough to
favor rotating updrafts, but the slow to non-existant steering flow
will lead to slower storm motions and a higher potential for cool
outflow air to undercut the storms and ultimately lead to the storms
dissipating. There is enough of a threat for strong winds and some
quarter-sized hail that SPC has included much of the Panhandle in a
Marginal Risk (Level 1 of 5) with hail and strong winds as the
primary hazards. One positive indicator on convection today is that
the cap is much weaker than yesterday and will likely not do much in
the way of preventing convective initiation and development, so the
severe hazards and threats stand.

Upper-level ridging remains in place for Wednesday, along with the
500mb high over the Four Corners Region continually advecting in
monsoonal moisture. Similar to today, 500mb vorticity maxima will
eject out from the high and move overhead, leading to the
development of a 500mb shortwave and increased synoptic lift across
the region. 700mb flow will be a touch strong, but remain from the
westerly direction leading to a strong surface, terrain-incuded
dryline in the afternoon. Stronger 0-6km Bulk Shear is possible
Wednesday with the overall stronger winds aloft. CAPE will be lower
though, with models suggesting only around 500 to 1000J. Therefore,
storms look likely again Wednesday and the shear will be stronger,
but CAPE will be lacking. The dryline should be enough forcing to
get a few isolated storms going and these storms will be capable of
producing strong winds and large hail. There is a Marginal Risk
again for portions of the CWA on Wednesday. It will also be warmer,
with afternoon high temperatures in the low-90s to low-100s area-
wide.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 234 AM MDT Tue Jul 8 2025

Main forecast concern in the medium to long range is a
relatively strong cold front diving south out of Canada Thursday
night and Friday, resulting in cooler temperatures, showers and
thunderstorms, and possibly some fog across the eastern plains
and/or the I-80 Summit. Thursday will be pleasant with near
average temperatures for this time of the year ahead of the
front with a better chance for showers and thunderstorms in the
afternoon and evening hours. Models show the some potential for
nocturnal thunderstorms Thursday night as the front gradually
moves south across the region with MUCAPE around 500 to 800
j/kg around midnight. Not very confident with how far south
these storms will develop into early Friday morning, so kept POP
between 15 to 25 percent well north of I-80 for now. As we head
into Friday, all models show 700mb temperatures lowering below
5c with little recovery during the day as upslope north to
northeast winds continue through the day. Kept temperatures a
few degrees above guidance mainly due to the high July sun
angle, but expect highs to be nearly 10 degrees below normal for
this time of the year. Models disagree with precipitation
chances as the GFS wants to keep low clouds in through most of
the day while the ECMWF and Canadian show showers and weak
convection most of the day. Ensemble guidance favor the ECMWF
and Canadian solution so kept POP between 30 to 50 percent for
most of eastern Wyoming and western nebraska.

For next weekend, a gradual warming trend is expected as the
upper level high across the desert southwest builds northward
and intensifies. Thunderstorm activity is forecast to become
more isolated as 700mb climb above 15c. Highs in the upper 80s
to mid 90s will return for much of the forecast area by Sunday
and next Monday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1117 AM MDT Tue Jul 8 2025

A ridge looks to start building across the Intermountain West.
Winds will be relatively light and switch to a more southerly
direction tomorrow. Looking at model soundings they all show a
pretty stout dry layer at the surface. SO TS was kept from
previous Prob30 as virga seems to be the most likely scenario.
Most of the model guidance has the thunderstorms in the southern
portion of the Panhandle and KAIA as well. However, there is
still a slight chance KCYS and KBFF may have a shower produce
near them.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 10 PM MDT Wednesday for WYZ420>423-425-
     427.
NE...None.

&&

$$

SHORT TERM...AM
LONG TERM...TJT
AVIATION...MM