991
FXUS65 KCYS 051106
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
506 AM MDT Sat Jul 5 2025

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) for severe weather today
  with gusty winds and large hail being the primary concerns.

- Elevated to near-critical fire weather conditions expected
  west of the Laramie Range today.

- There is a Slight Risk (Level 2 of 5) for severe weather
  Sunday with all hazards possible.

- Hot temperatures are possible by mid to late next week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 233 AM MDT Sat Jul 5 2025

Mostly cloudy skies across much of southeast Wyoming and western
Nebraska tonight as residual showers and storms slowly drift
eastward across the CWA as of 08Z. However, from a line from Morrill
County northwestward through Niobrara County are seeing mostly clear
skies, sandwiched in between the two cloud masses across the region.
Isolated showers and storms are expected to continue for the next 1
to 3 hours, though accumulation totals look to be fairly minimal.
Clouds slowly move out by the early morning hours, but mostly cloudy
skies look to remain for much of the overnight hours.

Southwesterly flow looks to dominate the region throughout much of
the weekend, with a ridge across the eastern CONUS slowly moving
eastward throughout the day Saturday. Several upper-level shortwaves
attempt to push through, but the stout ridge off to the east keeps
most of these disturbances in southern Canada and the far northern
CONUS, mainly along the Canadian border. The first of these
shortwaves attempts to move towards the region Saturday, with a
strong jet present across eastern Montana and western North Dakota
Saturday afternoon and evening. However, being downstream of this
approaching shortwave will allow for syntopic-scale ascent, which is
present downstream of trough axes. While the trough axis will remain
rather far away from southeast Wyoming and western Nebraska, some
synoptic-scale ascent will still be present and multiple 500mb
vorticity maxima will eject out ahead of the trough and across the
CWA this afternoon. These maxima are further steered by a 500mb high
attempting to set up over the Four Corners Region and introduce
monsoonal moisture into the region. 500mb winds and vorticity lobes
will be funneled between the high near the Four Corners Region and
the broad West Coast trough, just off shore of western California.
Southwesterly flow will, therefore, remain dominant at the 500mb
level and bring in a fetch of Pacific moisture into the
Intermountain West and the CWA. In addition to this, a weak, 500mb
shortwave will traverse across the CWA Saturday afternoon, further
providing syntopic-scale ascent across southeast Wyoming and western
Nebraska. This shortwave will likely be the primary forcing
mechanism for showers and storms expected to develop Saturday
afternoon, along with the 500mb vorticity maxima ejecting out from
the approaching trough. At 700mb, a weak shortwave associated with
the weak 500mb shortwave will move across the region Saturday
afternoon, further increasing ascent and forcing across the region.
However, the 700mb winds will be very weak, maxing out only around
20 to 25kts. Even 500mb winds will be quite weak, leading to weak
steering flow from 700 to 500mb. With broad, 700mb warm air
advection through the afternoon and evening, forcing will be fairly
widespread and, therefore, a bit weaker than cold front driven
events. Near the surface, forecast dewpoints suggest that the
terrain-induced dryline will be fairly pronounced tomorrow as winds
turn westerly west of the Laramie Range and some slight downsloping
pushes that dryline further eastward and makes it more stark. This
dryline will give convection a more potent form of lift, with winds
shifting southeasterly to easterly east of the dryline, resulting in
winds perpendicular to the dryline. This indicates that storms may
initially be discrete, but with weak steering flow aloft storms may
quickly conglomerate into clusters, rather than remaining discrete
and moving off the dryline quickly.

Looking at more convective variables for today`s setup, forecast
HRRR soundings suggest very dry low levels with steep lapse rates
throughout the lowest 3km across the Panhandle behind the terrain-
induced dryline. Further east and a little more out ahead of the
dryline, steep lapse rates still exist in the lowest 3km, according
to HRRR soundings, but dewpoints will be higher, in the mid-50s,
rather than upper-40s and lower behind the dryline. HRRR forecast
soundings suggesting nearly 2000 Joules of SBCAPE across the
Panhandle and around 1500 Joules of MLCAPE. Shear is, as expected
with the weaker flow aloft, weak only around 30kts in the lowest
3km. Similarly, low-level SRH values are nearly non-existant in the
lowest 1km with values in the mid-70s in the lowest 3km. With a
fairly straight hodograph in the lowest 3km, tornadoes do not look
favorable this afternoon. Storm splitting also does not look likely,
given the slow steering flow, limited forcing, and the likely
clustering expected this afternoon. Forecast soundings also suggest
significant CAPE within the hail growth zone and steep lapse rates.
Therefore, large hail looks likely with storms this afternoon,
though the clustering may decrease this chance a little and keep
hail slightly smaller as storm mergers come into play this afternoon
and weak steering flow leads to slow storm motion and limited
separation. Finally, with many soundings suggesting an Inverted-V
shape to the sounding, DCAPE values will be well into the 1200 to
1500 range, leading to the chance from strong downbursts with any
storms that form. West of the dryline, any shower that forms may
produce gusty winds due to the DCAPE values this afternoon.
Therefore, large hail and gusty winds look to be the primary
concerns for this afternoon, with limited to no tornado threat. As a
result, SPC has included all locations east of the Laramie Range in
a Marginal Risk (Level 1 of 5) and a smaller portion from Torrington
north into Niobrara County the eastward across the northern three
quarters of the Panhandle in a Slight Risk (Level 2 of 5) for the
afternoon. Luckily, precipitable water values remain around average,
therefore, the slower storm motions will likely not lead to flooding
across the region.

While severe weather will be the concern east of the Laramie Range,
warm temperatures and dry conditions will be present west of the
Laramie Range. Portions of Carbon County will likely be gusting
around 25 mph in the afternoon with relative humidity values
dropping into the 10-15% range. Therefore, elevated to near-critical
fire weather conditions will be present west of the Laramie Range.
Confidence is low that Red Flag conditions will continue for three
consecutive hours, therefore, a Red Flag Warning was not issued for
Carbon County. Additionally, fuels are mostly green at this time in
Carbon County, with the exception of the Arlington area and far
southeast Carbon County. Temperatures will rise into the mid-80s to
low-90s across the CWA, favoring instability to the east and
increasing fire weather concerns to the west. It will be an active
day across the CWA.

Southwesterly flow aloft will continue throughout the day Sunday.
However, upper-level winds turn more westerly Sunday night into
Monday morning as the upper-level ridge finally pushes east off the
East Coast and the shortwaves across southern Canada and the
northern CONUS flatten out the upper-level flow. However, the 500mb
high near the Four Corners Region will continue to spin and advect
multiple vorticity lobes into and across the region Sunday afternoon
leading to synoptic-scale lift across much of the CWA once again.
another 700mb shortwave will push across the region, leading to
additional ascent across the CWA, but 700mb flow remains weak once
more. Similar to today, the terrain-induced dryline will be present
once more, though likely stronger given the westerly wind shift.
1000 to 1500 J of MLCAPE will once again be present east of the
dryline so severe weather looks likely once more. SPC has included
much of Panhandle in a Slight Risk (Level 2 of 5) for Sunday with
the remaining portions of the CWA in a Marginal Risk (Level 1 of 5)
for severe weather Sunday.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 300 PM MDT Fri Jul 4 2025

An active start to the long term is expected as a few shortwaves
move north of the CWA. The first shortwave will graze the northern
part of the forecast area on Sunday. This shortwave will provide
needed lift and some of the moisture to produce thunderstorms across
the area. Model soundings show a decent environment for strong to
severe storms to develop in the Nebraska panhandle. Soundings show
about 1800 J/kg of MUCAPE with around 35 kts of effective shear.
DCAPE values are also high with values around 1500 J/kg. This will
lead to primarily a wind and hail threat in storms that develop.
Severe chances look even more favorable on Monday. Model soundings
in the Nebraska panhandle show up to 2500 J/kg of MUCAPE with 35 to
40 kts of shear. This will support a large hail threat. DCAPE values
are similar to Sunday, so damaging winds will still be a
possibility. MLCAPE is also rather high, at about 1600 J/kg with SFC-
3km SRH at about 100 m^2/s^2. This could support an isolated tornado
threat Monday afternoon as a secondary shortwave passes north of the
CWA.

The 500 mb high over the Four Corners region will strengthen mid-
week, also strengthening the ridge over the Rockies. As a result, a
fast warm up is expected. High temperatures will make a return to
the 90s for most locations by Tuesday, with even hotter temperatures
expected Wednesday as 700 mb temperatures climb to +20C!
Precipitation chances during this time will also be minimal as
desert air and subsidence under the ridge keep conditions dry.
Slightly cooler temperatures and better precipitation chances return
to the area on Thursday as a shortwave moves across the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 504 AM MDT Sat Jul 5 2025

Skies are slowly clearing this morning as showers moves out of
the region. Expecting calm winds this morning with winds
increasing towards 18Z. Isolated to scattered showers and storms
are expected across southeast Wyoming and western Nebraska.
Included PROB30 groups for most terminals. Confidence in
specific terminals being impacted by storms is low at this
time, but the chance exists for all terminals east of the
Laramie Range. Winds increase this afternoon and evening with
skies becoming cloudy.

&&

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

&&

$$

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