Tornado Warning 15, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1137 AM MDT Fri Jun 29 2018

.SHORT TERM...Today through Sunday night

A cold front is currently making its way through the area. This will
have two effects. One, temperatures will be cooler than yesterday,
an average of around 10 to 20 degrees. In addition, with flow
turning more westerly to northwesterly, it should blow out most of
the haze from the wildfires to the south. The weather will remain
active today though. A trough approaching from the west will bring
enough instability to keep the chance of showers and thunderstorms
in the forecast. These would be most numerous in the afternoon and
evening but one is possible at any time. As for stronger storms, the
Storm Prediction Center has pulled the slight risk east out of the
area. We still have a marginal risk covering much of the area East
of the Divide though. Models are showing decent shear although the
best shear looks to stay east of our area. We also have some decent
jet support courtesy of the right, rear quadrant of a jet streak
this afternoon. As a result can't rule out a rotating storm though
as the SPC has a small possibility of a tornado in Johnson and
eastern Natrona County where cloud bases may be a bit lower. Not
enough confidence to put in the forecast through. At this point,
the main threat from the storms today would be hail. There could
be some severe hail, especially in Johnson County where moisture
is deeper. But for now, we will stick with the small hail and
gusty wind wording. There is "hatched area" just to the east
though for larger hail so this will have to be watched closely.
Although, we can't rule out severe wind gust, this looks to be the
least of the threats.

The chance of storms will linger into Saturday. However, they don't
look as numerous and it could be an earlier show. This is due to the
passage of the trough axis, which is expected by mid afternoon. If
there is any chance of stronger storms, it would may be Natrona
County. The NAM is showing a jet streak possibly enhancing upper
level divergence across the area. The GFS is further east however
and keeps most of the storms over eastern Wyoming. We split the
middle for now. With cooler temperatures and low wet bulb zero
temperatures, the main threat this day would be small hail. This
will be the coolest day of the period as well. The guidance may be a
bit cool since any sunshine only 9 days after the solstice would
raise temperatures more. As a result, we went a couple of degrees
above guidance for most locations.

Ridging will then build across the area for Sunday and bring drier
and warmer weather. The GFS is showing some isolated convection
across the northern mountains. However, as I have stated before,
this model tends to overdo orographic influence on precipitation. As
a result, we kept things dry. A gusty wind may develop in the
afternoon though. And this, combined with lower humidity may lead to
enhanced fire behavior across portions of the area Sunday afternoon.

.LONG TERM...Monday through Friday

Mainly dry Monday and Monday night. Isolated showers and storms
over northwest WY are possible Monday afternoon and evening. More
of the same on Tuesday with the isolated showers and storms
developing over the northwest and Bighorn mountains. Wednesday,
the 4th of July, looks dry for most places with very isolated
mountain showers or storms. Thursday keeps with the mostly dry
weather pattern for most places. The exception is Johnson county
where a chance of thunderstorms Thursday evening through the late
night. Next Friday may see an increase in mid and high level
moisture. This would lead to more thunderstorm activity, mainly
along and east of the continental divide. As for temperatures,
Monday will be seasonably warm, the very warm to hot Tuesday
through Thursday. Next Friday high temps may be a degree or two
cooler in places due to more clouds in the afternoon. Overall,
typical summertime weather pattern to kick off July.

&&

.AVIATION...For the 18Z TAFS through 18Z Saturday afternoon
Issued at 1131 AM MDT Fri Jun 29 2018

Scattered showers and thunderstorms have developed over portions
of the Bighorn Basin already, with a few storms already becoming
severe. This trend will continue through the rest of the
afternoon, with the strong to severe storms possible from the
Bighorn Basin eastward over the Bighorns and Johnson Co.
Additional thunderstorm activity expected across northwestern
portions as well. Most of this activity should be east of the
area by 02z Saturday. A cold front dropping south across central
Wyoming this evening may spread areas of MVFR, local IFR ceilings
into the area, primarily affecting KCOD and KCPR.

&&

.FIRE WEATHER...

High temperatures today will be cooler than yesterday with minimum
relative humidities above critical levels. However, winds will be
gusty again across southern and central Wyoming. Behind the cold
front, winds will be north to northwest and some thunderstorms
will develop in the afternoon. A few showers could linger into
Saturday with thunderstorms redeveloping in the afternoon. Mixing
and smoke dispersal will range from good in the north to excellent
in the south.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...LaVoie
FIRE WEATHER...Hattings/Bourque

Hazardous Weather Outlook
National Weather Service Riverton WY
230 AM MDT Fri Jun 29 2018

WYZ001>020-022>030-301100-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Big Horn Basin-Southwest Big Horn Basin-
Southeast Big Horn Basin-Owl Creek and Bridger Mountains-
Bighorn Mountains West-Bighorn Mountains Southeast-
Northeast Johnson County-Southeast Johnson County-
Teton and Gros Ventre Mountains-Jackson Hole-
Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
230 AM MDT Fri Jun 29 2018

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight

Isolated to scattered mainly afternoon and evening thunderstorms.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Saturday...Isolated to scattered thunderstorms.

Sunday through Wednesday...Elevated fire conditions in the
central and south. Isolated thunderstorms Monday and Tuesday
in the north and northwest.

.SPOTTER INFORMATION STATEMENT...

Spotters are urged to report hail and wind gusts past 45 mph.
Thank you.

Special Weather Statement
National Weather Service Riverton WY
1039 AM MDT FRI JUN 29 2018

WYZ003-004-006-291715-
North Big Horn Basin-Southeast Big Horn Basin-Cody Foothills-
1039 AM MDT FRI JUN 29 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BIG HORN...
NORTHWESTERN WASHAKIE AND EAST CENTRAL PARK COUNTIES UNTIL 1115 AM
MDT...

At 1038 AM MDT, Doppler radar was tracking a strong thunderstorm 14
miles east of Meeteetse, moving northeast at 15 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

This storm will remain over mainly rural areas of southwestern Big
Horn...northwestern Washakie and east central Park Counties,
including the following locations... Burlington.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4417 10817 4408 10854 4408 10862 4422 10872
      4446 10842
TIME...MOT...LOC 1638Z 243DEG 12KT 4418 10858

TL

Special Weather Statement
National Weather Service Riverton WY
1110 AM MDT FRI JUN 29 2018

WYZ003>006-291745-
North Big Horn Basin-Southeast Big Horn Basin-Cody
Foothills-Southwest Big Horn Basin-
1110 AM MDT FRI JUN 29 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN HOT SPRINGS...
SOUTHWESTERN BIG HORN AND NORTHWESTERN WASHAKIE COUNTIES UNTIL 1145
AM MDT...

At 1110 AM MDT, Doppler radar was tracking a strong thunderstorm 15
miles east of Meeteetse, moving northeast at 15 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

This storm will remain over mainly rural areas of northern Hot
Springs...southwestern Big Horn and northwestern Washakie Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4401 10855 4415 10871 4436 10845 4415 10821
TIME...MOT...LOC 1710Z 229DEG 13KT 4413 10856

TL

Special Weather Statement
National Weather Service Riverton WY
1133 AM MDT FRI JUN 29 2018

WYZ004-291815-
North Big Horn Basin-
1133 AM MDT FRI JUN 29 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BIG HORN COUNTY
UNTIL 1215 PM MDT...

At 1131 AM MDT, Doppler radar was tracking a strong thunderstorm 7
miles south of Otto, or 10 miles southwest of Basin, moving northeast
at 20 mph.

One-quarter inch to three-quarter inch diameter hail, brief heavy
rain, wind gusts of 35 to 50 mph, and dangerous lightning will all
be possible with this storm.

This strong thunderstorm will be near...
  Basin around 1205 PM MDT.
  Greybull around 1215 PM MDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Seek a safe shelter inside a building or vehicle.

&&

LAT...LON 4418 10825 4433 10838 4452 10806 4434 10780
TIME...MOT...LOC 1731Z 237DEG 18KT 4430 10823

Jones

Special Weather Statement
National Weather Service Riverton WY
1146 AM MDT FRI JUN 29 2018

WYZ004>006-291830-
North Big Horn Basin-Southeast Big Horn Basin-Southwest Big Horn
Basin-
1146 AM MDT FRI JUN 29 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BIG HORN AND
NORTHWESTERN WASHAKIE COUNTIES UNTIL 1230 PM MDT...

At 1145 AM MDT, Doppler radar was tracking a strong thunderstorm 20
miles east of Meeteetse, moving northeast at 15 to 20 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

This storm will remain over mainly rural areas of southwestern Big
Horn and northwestern Washakie Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm 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 4407 10811 4401 10855 4408 10858 4408 10856
      4409 10855 4417 10855 4416 10859 4435 10834
TIME...MOT...LOC 1745Z 242DEG 14KT 4411 10846

CNJ