Severe Thunderstorm Warning 102, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1252 PM MDT Thu Aug 2 2018

.SHORT TERM...This evening through Sunday
Issued at 1223 PM MDT Thu Aug 2 2018

Monsoonal moisture in the sw will aid convection down there
spreading ne into the evening hours. Thermal trough/shortwave noted
on the upper air and satellite analysis this morning is moving into
ern ID and far swrn MT and this will be the focus for storms as it
moves into YNP through the afternoon hours and then spreads across
the north. A little better mid level westerlies and mid level
cooling will create the potential for a few stronger storms. A lot
of the area will have the threat of storms through the evening hours
with a few lingering overnight. Another round of storms is expected
Friday. The next approaching shortwave for Friday may draw another
round of monsoonal moisture nwd while some forcing across the north
with the trough and exiting jet may aid in storms across the far
north. The subtle front from today's wave washes out Friday before
the 'stronger' front drops down Friday night into Saturday hanging
around our central zones on Saturday. South of the boundary over
Sweetwater, Uinta and srn Lincoln County up to the Greens and
Rattlesnakes may have critical fire weather conds. The two critical
fuels zones 277 and 279 will have a fire weather watch for Saturday
from noon to 9 pm. If the front washes out further north, then 280
and even 283 could become critical. On Sunday, the system that is
currently out near 31-32N/142W will move onshore Saturday night and
move across us on Sunday. It could be an active day, especially
along and east of the divide as front remains in place while trough
approaches and dual jet structure develops in the nern zones.

.LONG TERM...Monday night through Thursday
Issued at 1223 PM MDT Thu Aug 2 2018

Pattern transition is forecast to be underway next week, as upper
low from the Gulf of Alaska dives south and cuts off over the
eastern Pacific, pumping up a ridge over the western U.S. Medium-
range models show an overall trend westward with this trough/ridge
pattern. This shift will put Wyoming under the influence of NW flow
aloft rather than under the dome of hot air; so forecast
temperatures, at least east of the Divide, have been trended
slightly cooler. Some adjustments further downward may be necessary
if this trend further westward of the ridge continues. A similar
pattern was responsible for severe weather outbreaks in late July;
however, models are placing mean surface trough and higher CAPES
along and east of Wyoming's eastern border, drier air over west and
central Wyoming. We have slight chances of thunderstorms over the
Bighorn Mountains on Monday; otherwise, dry conditions are expected
to prevail Monday through Thursday.

&&

.AVIATION...For the 00Z TAFS through 00Z Friday afternoon
Issued at 1223 PM MDT Thu Aug 2 2018

Showers and thunderstorms will continue through 06Z. Expect showers
and storms to persist through 06Z Fri in the central and east. VFR
conditions will occur at the terminal sites through the period.
Local MVFR conditions will occur with some of the stronger storms
due to heavy rain which would reduce visibility. Mountains will be
obscured at times. Another round of showers and thunderstorms is
likely tomorrow afternoon.

&&

.FIRE WEATHER...
Issued AT 1223 PM MDT Thu Aug 2 2018

...Fire Weather Watch Saturday from Noon to 9 pm for zones 277 and
279...

Scattered thunderstorms will move east across the area through this
evening. Isolated to widely scattered showers will continue through
the overnight hours, especially over southern portions. Another bout
of widely scattered to scattered thunderstorms will occur Friday
afternoon and evening. A Fire Weather Watch is in effect for fire
zones 277 and 279 from noon to 9 pm Saturday, due to very low RH
values and gusty winds up to 35 mph.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for WYZ277-279.

&&

SHORT TERM...Skrbac
LONG TERM...Hulme
AVIATION...Hulme
FIRE WEATHER...Skrbac

Hazardous Weather Outlook
National Weather Service Riverton WY
147 AM MDT Thu Aug 2 2018

WYZ001>020-022>030-031100-
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-
147 AM MDT Thu Aug 2 2018

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...Today and Tonight.

Scattered afternoon and evening thunderstorms. The main threat
will be gusty outflow winds of 50 to 55 mph possible. Warm
conditions and gusty winds will elevate fire weather conditions
across central and eastern portions this afternoon and early
evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Friday through Sunday...Warm with gusty west wind will elevated
fire weather conditions across southern Wyoming during the
afternoon and early evening. Isolated to scattered afternoon and
evening thunderstorms across mainly northern Wyoming.

.SPOTTER INFORMATION STATEMENT...

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

Special Weather Statement
National Weather Service Riverton WY
247 PM MDT THU AUG 2 2018

WYZ004-022115-
North Big Horn Basin-
247 PM MDT THU AUG 2 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN BIG HORN AND EAST
CENTRAL PARK COUNTIES UNTIL 315 PM MDT...

At 246 PM MDT, Doppler radar was tracking a strong thunderstorm 10
miles south of Garland, or 11 miles southeast of Powell, moving east
at 35 mph.

Wind gusts of 50 to 55 mph will be possible with this storm.

This storm will remain over mainly rural areas of northwestern Big
Horn and east central Park Counties, including the following
locations... Bighorn Canyon National Recreation Area and Powell Golf
Course.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near any lakes or streams, get out of the water and move
indoors or inside a vehicle. Remember, lightning can strike out to
10 miles from the parent thunderstorm. If you can hear thunder, you
are close enough to be struck by lightning. Move to safe shelter
now! Do not be caught on the water in a thunderstorm.

&&

LAT...LON 4494 10821 4491 10817 4455 10807 4454 10866
      4478 10873 4498 10822
TIME...MOT...LOC 2046Z 260DEG 31KT 4464 10858

13

Special Weather Statement
National Weather Service Riverton WY
247 PM MDT THU AUG 2 2018

WYZ017-022115-
Wind River Basin-
247 PM MDT THU AUG 2 2018

...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL FREMONT COUNTY UNTIL
315 PM MDT...

At 247 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles north of Riverton, moving east at 15 mph.

Winds in excess of 30 mph will be possible with this storm.

Locations impacted include...
Riverton, Shoshoni, Kinnear, Ocean Lake, Hidden Valley, Pavillion
Natural Gas Processing Plant, Riverton Country Club, Midvale,
Bonneville, Fremont County Fairgrounds and Riverton Regional Airport.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near Boysen Reservoir, get out of the water and move
indoors or inside a vehicle. Remember, lightning can strike out to
10 miles from the parent thunderstorm. If you can hear thunder, you
are close enough to be struck by lightning. Move to safe shelter
now! Do not be caught on the water in a thunderstorm.

&&

LAT...LON 4314 10875 4342 10849 4324 10792 4291 10827
TIME...MOT...LOC 2047Z 286DEG 11KT 4315 10844

Hulme

Special Weather Statement
National Weather Service Riverton WY
252 PM MDT THU AUG 2 2018

WYZ006-022115-
Southeast Big Horn Basin-
252 PM MDT THU AUG 2 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL WASHAKIE COUNTY
UNTIL 315 PM MDT...

At 252 PM MDT, Doppler radar was tracking a strong thunderstorm over
Worland, moving east at 15 mph.

Winds in excess of 30 mph will be possible with this storm.

Locations impacted include...
Worland, Winchester, Worland Municipal Airport, Wyoming Boys School
and Washakie County Fairgrounds.

LAT...LON 4407 10760 4378 10763 4380 10796 4382 10796
      4382 10819 4414 10804
TIME...MOT...LOC 2052Z 286DEG 11KT 4400 10791

Hulme

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