Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion...Update
National Weather Service Riverton WY
1152 AM MDT Fri Jul 21 2017

.SHORT TERM...Friday through Sunday night

The weather should be entering into a quieter pattern for the next
few days. A cold front and trough moving through the area that
brought the showers and thunderstorms will continue to sag to the
south and east. There are still some showers and thunderstorms out
there early this morning across Sweetwater County, however, coverage
continues to shrink early this morning. And, this will continue to
be the focus for some isolated showers and thunderstorms today with
some leftover monsoonal moisture hanging around. However, coverage
will be much less than today with rainfall amounts much less as
well. Around the northern two thirds of the state should be dry
today with lowering humidity through the day. Temperatures will be
cooler than yesterday as well, around 5 degrees cooler in most
locations. As for possible, fire danger there will be some gusty
winds around Johnson County. However, the strongest winds and lowest
humidity will probably not line up so no fire weather highlights are
expected. Friday's thunderstorms will end around midnight.

Mainly dry conditions for all areas are then expected for the
weekend. Ridging will be build across the state and monsoonal
moisture will get shunted to the south of the state. The result will
be a sunny to partly cloudy sky. In addition, temperatures will be
on the rise once again with high temperatures again climbing into
the 80s and 90s across most of the lower elevations.

.LONG TERM...Monday through Friday

Overview...Monsoonal moisture will make a gradual return to the area
early next week with Tuesday and Wednesday expected to be the most
active days for thunderstorms across the area.  A drier westerly
flow is expected by Friday.

Discussion...Synoptic pattern at the outset on Monday features upper
low moving across central Canada over the top of upper ridge across
the Rockies.  Most monsoonal moisture will remain suppressed to the
south, but kept the idea of isolated thunderstorms across the west
and north with GFS showing some weak perturbations rotating across
the area, ECMWF is dry.  Monday will be the warmest day of the
period with central basin highs in the 90s, mostly 80s across the
western valleys.  Upper high is expected to shift slightly east into
the southern High Plains on Tuesday and Wednesday, allowing
monsoonal moisture to rotate northward across the area with the best
moisture and instability, thunderstorm coverage, expected around the
periphery of the upper high across western and northern Wyoming.
Another upper low is expected to progress east across western and
central Canada Thursday and Friday that is expected to suppress
monsoonal moisture further south and set up a sharper lee side
surface trough across the northern High Plains.  Most of the area is
expected to be on the dry side of this surface trough by Friday.

&&

.AVIATION...18Z Issuance

Mainly VFR conditions will continue through the forecast period.
A persistent thunderstorm will continue to track east across
Southeast Fremont County and Southern Natrona County through 20z,
but should stay just south of KCPR. Otherwise, some thunderstorms
activity will be rolling off the Uinta Mountains northeast into
Southern Sweetwater County, mainly south of Interstate 80 this
afternoon. mainly clear skies are slated for Saturday.

&&

.FIRE WEATHER...

Expect drier conditions across the area today following the passage
of a cold front. The exception will be across Sweetwater County
where some lingering moisture will bring isolated showers and
thunderstorms, most numerous south of Interstate 80. A gusty wind
will blow across Johnson County at times this morning. However, wind
should decrease this afternoon so critical fire weather is not
expected. Relative humidity will fall to around 15 percent at times
in the lower elevations this afternoon. Wind should remain light to
moderate elsewhere. Mixing and smoke dispersal will range from fair
in some of the basins to excellent in the south.
&&

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

SHORT TERM...Hattings
LONG TERM...Meunier
AVIATION...Troutman/Lipson
FIRE WEATHER...Hattings

Hazardous Weather Outlook
National Weather Service Riverton WY
144 AM MDT Fri Jul 21 2017

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-
144 AM MDT Fri Jul 21 2017

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight

Isolated thunderstorms in Sweetwater County.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Monday...Isolated afternoon and evening thunderstorms.

Tuesday and Wednesday...Isolated to scattered showers and
thunderstorms. Some thunderstorms may produce heavy rain and
localized flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today and tonight.

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Special Weather Statement
National Weather Service Riverton WY
1057 AM MDT FRI JUL 21 2017

WYZ019-211745-
Green Mountains and Rattlesnake Range-
1057 AM MDT FRI JUL 21 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN FREMONT COUNTY UNTIL
1145 AM MDT...

At 1055 AM MDT, Doppler radar was tracking a thunderstorm 8 miles
south of Sweetwater Station, which is 19 miles west of Jeffrey City,
moving east at 25 mph.

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

This strong thunderstorm will be near...
  Ice Slough around 1125 AM MDT.
  Jeffrey City around 1145 AM MDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Occasional 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 4240 10826 4247 10830 4262 10779 4238 10776
TIME...MOT...LOC 1655Z 258DEG 20KT 4243 10822

Lipson

Special Weather Statement
National Weather Service Riverton WY
1136 AM MDT FRI JUL 21 2017

WYZ019-211800-
Green Mountains and Rattlesnake Range-
1136 AM MDT FRI JUL 21 2017

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN FREMONT COUNTY...

At 1135 AM MDT, a strong thunderstorm was located 8 miles southwest
of Sweetwater Station, which is 25 miles west of Jeffrey City, moving
northeast at 35 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Sweetwater Station and Ice Slough.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

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 4250 10777 4227 10866 4242 10876 4244 10868
      4248 10865 4275 10792
TIME...MOT...LOC 1735Z 244DEG 30KT 4249 10834

Bourque

Special Weather Statement
National Weather Service Riverton WY
1204 PM MDT FRI JUL 21 2017

WYZ019-211900-
Green Mountains and Rattlesnake Range-
1204 PM MDT FRI JUL 21 2017

...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN NATRONA AND
SOUTHEASTERN FREMONT COUNTIES...

At 1204 PM MDT, a strong thunderstorm was located near Sweetwater
Station, which is 15 miles west of Jeffrey City, moving east at 25
mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Jeffrey City, Sweetwater Station and Ice Slough.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

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 4233 10835 4249 10842 4282 10746 4254 10736
TIME...MOT...LOC 1804Z 251DEG 23KT 4248 10815

Bourque