Hail and Damaging Winds in Wyoming, July 4, 2023

Area Forecast Discussion
National Weather Service Cheyenne WY
1142 AM MDT Tue Jul 4 2023

.SHORT TERM...(Today through Wednesday night)
Issued at 312 AM MDT Tue Jul 4 2023

1) A strong cold front will cause widespread showers and
thunderstorms today across much of the forecast area. Some storms
could be severe. Large hail and damaging wind in excess of 60mph are
the main hazards.

2) Foggy conditions are likely across the Summit and areas closest
to the WY/NE/CO border Tuesday night and early Wednesday. Dense Fog
headlines are likely from the I-80 Summit toward Sidney.

3) Much cooler temperatures on Wednesday across southeast WY east
of the Laramie Range will make it seem like it is fall outdoors.
Record daily low maximums, and record cold overnight lows are
possible Wednesday and Wednesday night.

The current weather setup depicts a strong cold front advancing
across Central WY and the northern NE Panhandle. Current
observations support this, which is slightly earlier than modeled by
some of the CAMs. A potent, upper level shortwave is quickly
advancing with a secondary, and stronger cold front across MT. Radar
continues to show converging outflow boundaries and subsequent
rain showers and breezy winds across the cwa as well. This is
likely to continue through the remainder of the overnight hours as
mid level height falls and steep lapse rates in excess of 7
degrees C in the 700-500mb levels are present per SPC
mesoanalysis. Nighttime Microphysics satellite imagery depicts low
clouds behind the advancing cold front to our north, with cloud
debris scattered across the rest of the cwa due to the lingering
rain showers.

As we press forward with the remainder of the short-term forecast,
it will be a busy 24-48 hours to discuss. There is model
disagreement with the timing of the cold front today. The NamNest
has the best handle on the timing of the cold front with regard to
CAMs at this time. The HRRR has the cold front advancing much more
slowly, thus causing our cwa in the central and southernmost zones
to destabilize substantially moreso today because of the WAA
advancing further to the north from our south. Have gone with a
more conservative approach in regard to daytime highs. However,
there is a lot more at play for early July. This will be a dynamic
system as we have not only instability from daytime heating, but
there will be frontogenetic forcing as well. The moisture,
forcing, atmospheric dynamics, and instability will all play their
part today to make it an active weather day. The highest focus of
strong to severe thunderstorms will be confined towards the I-80
corridor from Rawlins to Sidney, and northward to approximately
Wheatland. This is highlighted by the SPC Day 1 Severe wx outlook
where Marginal to Slight Risk exists. DCAPE values between
500-1000 J/kg will be present as well, so we will have to contend
with strong wind gusts and large hail. Timing of the cold front
looks to be through a majority of our cwa between 18-21Z today.
However, there will be a jet max that occurs behind the cold FROPA
after 21Z to approximately 3Z this evening. This post-frontal jet
max is anticipated to bring another round of showers and
thunderstorms to the area. With the 700-850mb WAA layer being
present, with much colder temperatures at 200-500mb thanks to the
approaching shortwave and atmospheric dynamics, we will continue
to have steep lapse rates aloft in the mixed layer of the
atmosphere. CAMs do highlight several UH tracks across our cwa
initially, in the form of potential discrete supercells. Although
the HRRR advertises this the most. We will have to watch whether
the convective initiation transitions from discrete thunderstorms
and supercells to storm mergers, and ultimately a possible bow
echo structure. While it is not expected to have the appearance of
a derecho feature, we could easily see a strong wind event develop
later this afternoon where straightline wind gusts of 60-80mph are
possible. We would be remiss to not include the abundant levels of
moisture modeled across the area during the next 12-24 hours.
PWATs in the 75-99th percentile advertise the threat of very heavy
rainfall occurring with the convection that occurs. As the CAMs
also highlight, there is the threat of multiple storms over the
same area, or "training" storms being a hazard. Thus, we will have
to monitor not only the threat of severe weather, but potentially
isolated threats of flash flooding. Fortunately, the threat of
tornadoes are low with this weather setup, but can not be ruled
out entirely.

Tonight will have a late ending timeframe of showers and
thunderstorms, but most of the rainfall should dissipate by 6Z.
Lingering light rains showers can be expected through 12Z or later.
As we transition from the severe weather hazards on Tuesday
afternoon and evening, we will have another topic to worry about:
Dense Fog and much colder temperatures. Surface high pressure over
the northern Plains, very strong CAA, and lingering moisture will
cause significant upslope flow to occur east of the Laramie Range.
700mb temperatures by 12Z Wednesday will range from 0C to 5C east
of the Laramie Range. There will be easterly flow heading upslope
across the NE Panhandle and southeast WY. CAMs are pinging very
low visibilities and pesky clouds to linger potentially all of
Wednesday, with the highest impacts located from the I-80 Summit
towards the southern NE Panhandle of Kimball and Cheyenne County.
It is highly likely we will need Dense Fog headlines issued for
portions of Wednesday should there be locally heavy rainfall and
the upslope flow regime occur on Wednesday. Daytime highs east of
the Laramie Range may not reach 50 degrees in Laramie County from
approximately the I-80 Summit to Pine Bluffs. Have gone with a
conservative approach and kept daytime highs in the 50s for the
I-80 corridor. Overall, it will be a very cool and dreary day for
locations south of the North Platte River Valley toward the state
border. Further to the west of the I-80 summit, there will be WAA
and eventual daytime clearing. Conditions will be much different
as afternoon sunshine is possible for Carbon and western Albany
County. All of this being said, we could easily see several areas
with record low daytime maximums on Wednesday.

Wednesday night will be a tough forecast for overnight lows as
weak flow from surface High Pressure sags south toward the Central
Plains. This will allow subsidence and dry air to creep into the
region. We will have to monitor the cloud cover for the cwa,
because if we clear out early for locations closest to the state
borders of CO, temperatures could easily tank to record lows near
40 degrees or colder. Frost may be possible in the higher terrain
of the Snowy/Sierra Madre Range by early Thursday should we clear
out early. For now, have gone with the cloud cover lingering
overnight through approximately daybreak, which should keep most
areas in the middle to upper 40s by early Thursday morning.

.LONG TERM...(Thursday through Monday)
Issued at 312 AM MDT Tue Jul 4 2023

Medium to Long Range forecast looks on track so minimal changes
were made past Friday. Models still indicate an unsettled weather
pattern with below average temperatures for the bulk of the medium
range forecast period. Quasi-zonal flow with periods of northwest flow
aloft will dominate the weather pattern through the weekend. All
models show a potent (for July) 70 to 90 knot jet near the
Colorado and Wyoming border late this week through the weekend
with locally higher maxima associated with individual shortwave
disturbances moving east embedded in the mean flow. These jet
streaks will likely result in periods of enhanced upper level
difluence over eastern Wyoming and wester Nebraska, which will
likely lead to enhanced convective activity when the timing lines up
with the afternoon and evening hours. Primary concern late this week
will be the potential for severe weather on Thursday. Plentiful 0-
6km shear over 40 knots, high CAPE, and moisture convergence
over/near the Laramie Range are supportive of severe thunderstorms
across southeast Wyoming and western Nebraska...mainly along and
east of the Laramie Range. Agree with SPC's Slight Risk for the area
on Thursday with all modes of severe weather possible, including a
few tornadoes given low LCL's and 0-2 km shear within an area of
enhanced SBCAPE in the boundary layer. This is all in addition to
every model lining up with good upper level dynamic forcing due to a
jet couplet across the area with strong upper level diffluence noted
around 00z Friday. Increased POP slightly on Thursday up to 45
percent, but believe coverage of thunderstorms will be limited to
scattered, at best, with discrete cells until the evening hours.

Friday and Saturday will be similar with a continuation of
showers and thunderstorms each day. Jet energy will remain aloft
as a frontal boundary/convergence boundary sets up along the
Laramie Range. This will result in cool easterly flow along and
east of the Laramie Range with westerly flow across Carbon and
most of Albany Counties. High temperatures will remain below
seasonal averages (around 80 to 88 degrees from west to east) with
highs in the mid 70s to low 80s. Believe a few of the models are
trying to dry out the area too much in this pattern due to the
westerly flow aloft, so increased POP above NBM and consensus
blends. Will have to keep an eye on severe weather both these
afternoons also due to strong 0-6km shear and ample low to
midlevel instability.

As we head into the extended portion of the forecast for late next
weekend into early next week, models are trending a little bit
drier as a developing ridge axis amplifies across the eastern
Great Basin region and slides east, resulting in some dry air
entrainment and gradually increasing temperatures. Will continue
with the general trend of lowering POP and increasing temperatures
back above normal, but will do so cautiously as long range models
recently have typically backed off these trends once they enter day
4 or 5. However, there is better ensemble support for a warmer and
drier pattern arriving for the second week of July. Kept a slight
chance for thunderstorms along and east of the I-25 corridor each
day.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1119 AM MDT Tue Jul 4 2023

Very tricky aviation forecast this afternoon with multiple rounds
of showers and thunderstorms. The ongoing cloud cover is adding
additional uncertainty to the strength of thunderstorms we will
experience across mainly southeast Wyoming, but possibly into the
Nebraska panhandle as well later this afternoon/evening. Following
the showers and thunderstorms, there is high confidence in IFR to
LIFR CIGS with areas of dense FG across southeast Wyoming. There
is less confidence in FG in the Nebraska panhandle, but those TAF
terminals will at least experience IFR CIGS.

&&

.FIRE WEATHER...
Issued at 312 AM MDT Tue Jul 4 2023

Fire weather concerns will remain low as fuels continue to remain
in green up mode. Daily chances for wetting rainfall exist behind
a strong cold front that sweeps across the region later today. Gusty
and erratic winds are anticipated today as strong to severe storms
move through the area. RH recovery will be very good the next couple
of days as well as we remain below normal for temperatures.

&&

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

SHORT TERM...BW
LONG TERM...TJT
AVIATION...LK
FIRE WEATHER...BW

Hazardous Weather Outlook
National Weather Service Cheyenne WY
422 AM MDT Tue Jul 4 2023

NEZ019>021-WYZ103>115-051030-
Scotts Bluff County-Banner County-Morrill County-
North Laramie Range-Ferris/Seminoe/Shirley Mountains-
Shirley Basin-Central Laramie Range and Southwest Platte County-
East Platte County-Goshen County-Central Carbon County-
North Snowy Range Foothills-Southwest Carbon County-
Sierra Madre Range-Upper North Platte River Basin-Snowy Range-
Laramie Valley-
422 AM MDT Tue Jul 4 2023

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

.DAY ONE...TODAY AND TONIGHT

Showers and thunderstorms are expected to develop along and behind
a strong cold front today. Some of the thunderstorms could be
strong to even severe. The primary hazards will be wind gusts in
excess of 60 mph and hail of 1 inch in diameter or larger.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Patchy fog is possible Wednesday morning. Visibility less than one
mile at times is possible.

Record low morning temperatures are possible for Wednesday night
into Thursday morning.

Daily chances for showers and thunderstorms exists for the
remainder of the extended forecast.

.Spotter information statement...

Due to the potential for strong to severe thunderstorms across the
area today, spotters are encouraged to report any hail, wind, or
tornadoes to the National Weather Service.

NEZ002-003-095-096-WYZ101-102-051030-
Dawes County-Box Butte County-Northern Sioux County-
Southern Sioux County-Converse County Lower Elevations-
Niobrara County-
422 AM MDT Tue Jul 4 2023

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

.DAY ONE...TODAY AND TONIGHT

Showers and thunderstorms are expected to develop along and behind
a strong cold front today. An isolated thunderstorm could be
strong to potentially severe.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Record low morning temperatures are possible for Wednesday night
into Thursday morning.

Daily chances for showers and thunderstorms exists for the
remainder of the extended forecast.

.Spotter information statement...

Due to the potential for strong to severe thunderstorms across the
area today, spotters are encouraged to report any hail, wind, or
tornadoes to the National Weather Service.

NEZ054-055-WYZ116>119-051030-
Kimball County-Cheyenne County-South Laramie Range-
South Laramie Range Foothills-Central Laramie County-
East Laramie County-
422 AM MDT Tue Jul 4 2023

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

.DAY ONE...TODAY AND TONIGHT

A strong cold front will move south across the area today. The
potential for strong to severe thunderstorms exists this
afternoon and evening. The primary hazards will be wind gusts in
excess of 60 mph and hail of 1 inch in diameter or larger.

Lingering moisture, rain showers, and easterly winds from an
approaching surface high pressure will cause dense fog to occur
along the Interstate 80 corridor from the I-80 Summit to
potentially eastern Cheyenne County. The primary hazards will be
visibilities less than one mile at times in the patchy, dense fog
that occurs.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Patchy, dense fog is anticipated on Wednesday. Visibility less
than one mile is possible through the afternoon hours.

Record low morning temperatures are possible for Wednesday night
into Thursday morning.

Daily chances for showers and thunderstorms exists for the
remainder of the extended forecast.

.Spotter information statement...

Due to the potential for strong to severe thunderstorms across the
area today, spotters are encouraged to report any hail, wind, or
tornadoes to the National Weather Service.

BW

Special Weather Statement
National Weather Service Cheyenne WY
118 PM MDT Tue Jul 4 2023

WYZ108-116>119-042000-
South Laramie Range WY-Goshen County WY-Central Laramie County WY-
South Laramie Range Foothills WY-East Laramie County WY-
118 PM MDT Tue Jul 4 2023

...Strong thunderstorms will impact portions of southeastern Albany,
southwestern Goshen and western Laramie Counties through 200 PM
MDT...

At 118 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from Horse Creek to near Crystal Lake Campground to
Virginia Dale. Movement was east at 35 mph.

HAZARD...Wind gusts of 50 to 55 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Cheyenne, South Greeley, Vedauwoo, Federal, Crystal Lake Reservoir,
Pumpkin Vine, Crystal Lake Campground, Vedauwoo Campground, Buford,
North Crow Campground, Granite Springs Reservoir, Ranchettes, Granite
Springs Campground, Warren AFB, Frontier Park, Whitaker, North
Cheyenne, Horse Creek, Warren Af Base and Fox Farm-College.

This includes the following highways...
 Interstate 25 in Wyoming between mile markers 1 and 41.
 Interstate 80 in Wyoming between mile markers 329 and 377.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4116 10541 4151 10533 4163 10452 4119 10450
      4100 10465 4100 10552
TIME...MOT...LOC 1918Z 262DEG 40KT 4143 10518 4114 10517 4093 10533

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...55 MPH

Kubelka

Special Weather Statement
National Weather Service Cheyenne WY
158 PM MDT Tue Jul 4 2023

WYZ117>119-042030-
Central Laramie County WY-South Laramie Range Foothills WY-
East Laramie County WY-
158 PM MDT Tue Jul 4 2023

...Strong thunderstorms will impact portions of southeastern Laramie
County through 230 PM MDT...

At 157 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 11 miles east of Whitaker to 6 miles east of
South Greeley to near Carr. Movement was east at 40 mph.

HAZARD...Wind gusts of 50 to 55 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Cheyenne, Pine Bluffs, Burns, Albin, South Greeley, Hillsdale,
Ranchettes, North Cheyenne, Gun Barrel, Carpenter, Fox Farm-College
and South Greeley High.

This includes Interstate 80 in Wyoming between mile markers 362 and
402.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4100 10488 4109 10482 4142 10479 4149 10406
      4100 10406
TIME...MOT...LOC 1957Z 270DEG 49KT 4139 10464 4109 10468 4087 10485

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...55 MPH

Kubelka