Severe Thunderstorm Warning 47, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
221 PM MDT Thu Jun 21 2018

.SHORT TERM...(This evening through Sunday)
Issued at 202 PM MDT Thu Jun 21 2018

Potent shortwave trough moving from northern ID and western MT
into southern MT and northern WY this afternoon. Thunderstorms
have already kicked off by 130pm, and are expected to continue
across the northern 2/3 of the forecast area into the evening
hours. Likely that some of the storms will be strong with very
gusty outflow wind, small to moderate hail, and brief heavy rain.
Dry windy west flow will move in behind the storms/wave across
southern WY. Wrap-around moisture in northwest flow will keep
showers going overnight across northwest WY. As the low moves into
SE MT Friday, showers with isolated thunderstorms should cover the
area east of the divide with some possible moderate to heavy rain
in northeast upslope areas. Brief ridging early Saturday before
another shortwave trough moves through about the same area on
Saturday. More widespread showers and thunderstorms are expected
Saturday afternoon and evening. The NAM is showing the 500mb low
moving right over western WY Saturday evening, so possibility for
heavy rain likely. As the low moves into SE WY on Sunday,
precipitation will decrease across western WY, but cool air will
remain.

.LONG TERM...(Sunday night through Thursday)
Issued at 202 PM MDT Thu Jun 21 2018

On Sunday evening, the GFS is still tracking the closed low east
across Southern Wyoming, more like the Canadian. The Euro and the
SREF still track the low east, farther north, across central
Wyoming. So will keep the idea of the bulk of the precip over areas
east of the divide. The precip intensity will be dissipating by then
along with shrinking areal coverage as the area of strong QG forcing
shifts off to the east. There will still likely be pockets of
heavier rainfall from thunderstorms in the vcnty of Casper near the
track of the slow moving asct h7 circulation. In fact, the GFS
indicates a six hour window of 2 inches of rainfall in Natrona
County ending 12Z Monday, but this amount will likely occur, if it
does, Sunday evening.

Monday is shaping up to be drier and precip free underneath the
northerly confluent flow on the backside of the exiting trough.
Temperatures will be warmer by 10 to 15 degrees as a flat ridge
builds east into the area.

Then on Tuesday, high temperatures will level off in the far west
but will climb another ten degrees or so east of the divide. Dry
weather will continue.

On Wednesday, a weak shortwave will track east across the Northern
Rockies and send a weak dry front across Northern Wyoming. All this
front will do is veer the winds around to the northeast with an
isolated shower or thunderstorm possible in the far north. Thursday
will feature high temperatures a few degrees cooler behind this
front.

Then the GFS brings the next well defined shortwave east across the
Western United States and then close to Western Wyoming by Friday,
thus keeping us in this active progressive weather pattern. The Euro
keeps this shortwave well west of Wyoming by Friday. This next
weather feature will increase the chances of late day convection
Thursday and Friday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 202 PM MDT Thu Jun 21 2018

A quick round of isolated showers and thunderstorms are expected
mainly north of a KJAC-KRIW-KCPR line between 20Z this afternoon
through and 02Z Friday. The most confidence is across the far
northwest and north-central areas. The convection is expected to
rapidly shift away during the early evening. Then after 09Z, some
light shower activity could push into far northwest Wyoming. These
showers will transition to scattered thunderstorms in the west after
18Z Friday before moving east across the rest of the northern half
of Wyoming.

.FIRE WEATHER...
Issued AT 202 PM MDT Thu Jun 21 2018

Scattered showers and thunderstorms this afternoon and evening
across the northern 2/3 of the area due to a low pressure system
moving through southern MT and northern WY. Some of the storms
could be strong with very gusty outflow wind, moderate size hail,
and brief heavy rain. The southern part of the state will see
breezy to windy drier west wind. Wrap-around moisture will
continue showers into NW WY overnight, then across northern WY
Friday morning. The northwest cooler wetter flow will bring
showers east of the divide Friday afternoon. Some clearing Friday
night and Saturday morning. Another low pressure system on
Saturday will bring showers and thunderstorms back Saturday into
Sunday.

&&

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

&&

SHORT TERM...McDonald
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...McDonald

Hazardous Weather Outlook
National Weather Service Riverton WY
214 AM MDT Thu Jun 21 2018

WYZ001>020-022>030-221100-
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-
214 AM MDT Thu Jun 21 2018

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight

Isolated to scattered thunderstorms in the mountains and over
northern and eastern portions this afternoon into the evening.
Some storms could be strong to severe with large hail and damaging
winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Friday and Saturday...An increasing chance of showers and
thunderstorms, especially northern and central areas.

Saturday Night through Sunday night...Scattered to numerous
showers and thunderstorms with potential areas of heavy rain
along and east of the continental divide.

.SPOTTER INFORMATION STATEMENT...

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

Special Weather Statement
National Weather Service Riverton WY
336 PM MDT THU JUN 21 2018

WYZ005>007-212215-
Owl Creek and Bridger Mountains-Southeast Big Horn Basin-Southwest
Big Horn Basin-
336 PM MDT THU JUN 21 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL HOT SPRINGS AND
NORTHWESTERN WASHAKIE COUNTIES UNTIL 415 PM MDT...

At 334 PM MDT, the public reported a strong thunderstorm 10 miles
north of Legend Rock State Petroglyph Site, or 17 miles southeast of
Meeteetse, moving east at 40 mph. A funnel cloud was reported with
this storm around 330 PM MDT.

One-half inch diameter hail, wind gusts of 40 to 50 mph, and
dangerous lightning be possible with this storm.

This storm will remain over mainly rural areas of north central Hot
Springs and northwestern Washakie Counties, including the following
locations... Badlands Overlook and Grass Creek.

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 4382 10806 4381 10884 4382 10882 4384 10882
      4384 10886 4386 10885 4385 10888 4386 10891
      4389 10887 4391 10888 4391 10890 4393 10886
      4395 10889 4394 10890 4399 10892 4399 10879
      4403 10879 4408 10856 4417 10824 4417 10811
TIME...MOT...LOC 2134Z 253DEG 34KT 4394 10868

CNJ

Special Weather Statement
National Weather Service Riverton WY
336 PM MDT THU JUN 21 2018

WYZ004>006-212215-
North Big Horn Basin-Southeast Big Horn Basin-Southwest Big Horn
Basin-
336 PM MDT THU JUN 21 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL HOT SPRINGS...SOUTH
CENTRAL BIG HORN AND NORTHWESTERN WASHAKIE COUNTIES UNTIL 415 PM
MDT...

At 334 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles northwest of Winchester, or 15 miles west of Worland, moving
northeast at 40 mph.

A funnel cloud in the vicinity of Gooseberry Road or Highway 431 west
of Worland was observed with this particular storm. Half inch hail
and winds in excess of 40 mph will be possible with this storm.

This strong thunderstorm will be near...
  Wyoming Boys School around 350 PM MDT.
  Worland Municipal Airport around 355 PM MDT.
  Worland around 400 PM MDT.

Other locations impacted by this storm include Badlands Overlook and
Washakie County Fairgrounds.

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.

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 4381 10832 4399 10863 4432 10773 4399 10752
TIME...MOT...LOC 2134Z 239DEG 34KT 4396 10826

Lipson

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RIVERTON WY
337 PM MDT THU JUN 21 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0330 PM     FUNNEL CLOUD     20 NW THERMOPOLIS       43.85N 108.50W
06/21/2018                   HOT SPRINGS        WY   TRAINED SPOTTER

&&

NMYERS

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