Severe Thunderstorm Warning 388, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
601 PM MDT Thu Sep 21 2023

.SHORT TERM...(This evening through Friday)
Issued at 345 PM MDT Thu Sep 21 2023

A surface trough draped over the eastern half of the CWA with
elevated instability led to scattered showers and thunderstorms this
morning. Early this afternoon, storms dissipated and pushed
northward out of the CWA. Hi-Res guidance, the HRRR in particular,
develops another round of stronger storms off the high terrain mid
this afternoon and pushes them eastward. The HRRR does have almost
2000 J/kg of SBCAPE making it into parts of the Nebraska panhandle
later this afternoon. This could support an isolated strong storm or
two with hail and gusty winds. Cannot rule out a severe storm later
this afternoon/evening in this setup, especially with a Marginal
Risk for severe weather across most of the panhandle. Other Hi-Res
are less aggressive this afternoon and evening, still showing a
decent capping inversion which will limit convective potential.

Heading into Friday morning, a stationary front and surface low
continues to linger over the Pine Ridge. With some leftover
instability from today's storms also lingering in the vicinity of
the Pine Ridge, another round of morning showers and thunderstorms
looks possible across the northern Nebraska panhandle counties and
Converse and Niobrara Counties in east-central Wyoming. Beyond
this, the afternoon looks relatively dry for most locations based
off of Hi-Res guidance. A few isolated storms, potentially strong
to severe, may pop in the aforementioned areas as instability
increases throughout the afternoon. Again, there is another
Marginal Risk for severe storms across much of the panhandle and
into our northern Wyoming forecast zones. Currently, Chadron is
even in a Slight Risk for severe storms. Will continue to monitor
this for updates, however the best chance for severe storms looks
northeast of the CWA.

Friday night, a strong cold front pushes through the CWA. There
could be some precipitation associated with the FROPA, however the
bigger concern will be high winds across the usual southeast Wyoming
wind prones. The cold front will increase gradients rapidly across
the Laramie Range and westward. 700 mb height gradients also rapidly
steepen, peaking above 70 meters by Saturday morning. Winds aloft
will greatly strengthen Saturday morning over the wind prones, with
60 to 70 kt 750 mb winds. Strong downward omegas should easily mix
these winds down to the surface. As a result, issued a High Wind
Watch for the usual wind prones, Arlington/Elk Mountain, the south
Laramie Range and adjacent foothills, Bordeaux, and even for
central Laramie County including the city of Cheyenne. Winds
should ease Saturday afternoon as gradients ease behind the front
and an upper- level ridge builds behind it.

.LONG TERM...(Friday night through Thursday)
Issued at 300 PM MDT Thu Sep 21 2023

Key Impact Messages:

1) After an initial High Wind and breezy period, winds will decrease
Sunday but elevated to near critical fire weather conditions will
remain.

2) Elevated to near-critical fire weather conditions continue Monday
into Tuesday. A Fire Weather Watch might be needed Sunday into
Tuesday for particular fire weather zones.

3) Overall temperatures will be at to slightly above normal with dry
conditions expected through next Thursday.

Weather Discussion: Late Saturday into Sunday pattern will feature a
tight closed H5 low over South Dakota with NW H5 flow as additional
subsidence kicks in over SE WY and the West NE Panhandle. While
Saturday will be the main wind event period, height gradients Sunday
will be enough to support elevated winds during peak afternoon
mixing for fire weather concerns. A Fire Weather Watch could be
needed Sunday and potentially into Monday and Tuesday. Internal AI
guidance highlights that 20 to 30 mph gusts and minimum humidity
values falling into the teens each afternoon appear likely. How
these components align with the fire weather forecast zones that
have drier 1/10-hour fuels could necessitate Fire Weather Watches.
Winds will become more marginal Monday into Tuesday as an H7-H5
ridge develops over WY. H7 temperatures will slowly warm through
early next week from 5C Saturday upwards to 10C to pushing 12C by
mid-week across the GEFS ensemble quartile spread. This will help
support above normal high and low temperatures but not close to any
records. Likewise, the suppressing ridge will keep precipitation
chances below 5-10% if that high, Sunday to Wednesday per the NBM
ensemble spread. Moreso, precipitation chances don't rise above 20%
through into the beginning of October. Minimum relative humidity
values should increase slightly into mid to late week but still
dropping into the low teens to low 20 percentiles per NBM ensembles.

Pattern confidence decreases slightly into late next week but
overall west to southwest flow appears likely with the approach of a
stronger trough over MT. However, most the the dynamic lifting
remaining farther north with the potential for a surface front nearing
the region per ensemble potential and a few deterministic runs. Next
best chance of precipitation could be next Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 547 PM MDT Thu Sep 21 2023

The terminal forecast over the next 12-24 hours will be an active
scenario for most sites. VCTS and VCSH are expected to slowly move
from southwest to northeast between 0z-6z, with KCDR seeing the
longest window of precipitation into the overnight hours. KLAR and
KRWL will remain VFR overnight, and winds gusts picking up by
tomorrow morning to 25-35 knots. KCYS will see the potential for
VCTS to wind down early this evening, and weak upslope flow will
create low CIGS overnight, ultimately in the form of IFR/LIFR
through approximately 15z Friday.

The NE Panhandle terminals will also be impacted by the low CIGs
this evening and overnight. Flight conditions will transition from
MVFR to IFR/LIFR between 6z-15z, and the potential for reduction
in VIS also will become apparent close to the 12z-15z timeframe
for these terminals. Additionally, once the VCSH and VCTS push
northeast, VRB winds with gusts to less than 12 knots will be
expected.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Thu Sep 21 2023

Fire weather concerns will be minimal Friday and Saturday as a cold
front will bring increase moisture and cooler temperatures. Although
RHs will be above 15 percent, very strong winds will accompany this
front. On Friday, areas west of the Laramie Range could see gusts up
to 35 MPH. Even stronger winds are likely across the southeast
Wyoming winds prones early Saturday morning into Saturday afternoon
with gusts up to 65 MPH possible. Fire weather concerns return
Sunday with minimum RHs falling below 15 percent in much of
southeast Wyoming with wind gusts up to 30 MPH. Fire weather
concerns increase into next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from late Friday night through Saturday
     afternoon for WYZ106-110-116>118.

NE...None.
&&

SHORT TERM...SF
LONG TERM...JSA
AVIATION...BW
FIRE WEATHER...SF

Hazardous Weather Outlook
National Weather Service Cheyenne WY
312 PM MDT Thu Sep 21 2023

NEZ020-054-055-WYZ101-103>105-107>109-111>115-119-222045-
Banner County-Kimball County-Cheyenne County-
Converse County Lower Elevations-North Laramie Range-
Ferris/Seminoe/Shirley Mountains-Shirley Basin-East Platte County-
Goshen County-Central Carbon County-Southwest Carbon County-
Sierra Madre Range-Upper North Platte River Basin-Snowy Range-
Laramie Valley-East Laramie County-
312 PM MDT Thu Sep 21 2023

This hazardous weather outlook is for portions of panhandle
Nebraska...east central Wyoming...south central Wyoming and
southeast Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms possible this afternoon.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Another round of scattered showers and thunderstorms possible
Friday afternoon. A strong cold front Friday night will lead to
breezy conditions across the area on Saturday.

.Spotter information statement...

Spotters are encouraged to report severe weather to the NWS.

WYZ106-110-116>118-222045-
Central Laramie Range and Southwest Platte County-
North Snowy Range Foothills-South Laramie Range-
South Laramie Range Foothills-Central Laramie County-
312 PM MDT Thu Sep 21 2023

This hazardous weather outlook is for portions of south central
Wyoming and southeast Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms possible this afternoon with
breezy conditions.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Another round of scattered showers and thunderstorms possible
Friday afternoon. A strong cold front Friday night will lead to
windy conditions across the southeast Wyoming wind prones early
Saturday morning into Saturday afternoon. Please refer to the High
Wind Watches currently in effect for more details.

.Spotter information statement...

Spotter activation will not be needed.

NEZ002-003-019-021-095-096-WYZ102-222045-
Dawes County-Box Butte County-Scotts Bluff County-Morrill County-
Northern Sioux County-Southern Sioux County-Niobrara County-
312 PM MDT Thu Sep 21 2023

This hazardous weather outlook is for portions of panhandle
Nebraska and east central Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered thunderstorms possible this afternoon. An isolated
strong to severe storm is possible.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Another round of potentially strong to severe storms possible on
Friday. Storms could contain gusty winds and hail. A strong cold
front Friday night will lead to breezy conditions across the area
on Saturday.

.Spotter information statement...

Spotters are encouraged to report severe weather to the NWS.

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