Severe Thunderstorm Warning 56, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
355 PM MDT Thu Jul 5 2018

.SHORT TERM...(This evening through Friday)
Issued at 130 PM MDT Thu Jul 5 2018

Generally unstable conditions this afternoon and evening will
continue isolated to scattered thunderstorms over western and
central Wyoming. Some stronger storms are possible around the
Bighorn Mountains and over Johnson and Natrona counties, where
surface-based CAPE values are over 1500 J/kg and lifted indices
are less than -4C. During the afternoon hours, the primary threat
from the storms will be gusty outflow wind. As the afternoon
progresses and into the evening hours, brief heavy rain and small
to medium hail will also be a threat. The short term model
guidance is suggesting some heavy precipitation rates along the
eastern foothills of the Bighorn mountains in Johnson county and
northwestern Natrona county. As the convection moves to NE WY this
evening, easterly outflow wind will push back into the Wind River
and southern Big Horn Basins. Possibility for some low- to mid-
level ceilings over Johnson and Natrona counties with this
pattern.

Skies will clear more after sunrise Friday morning with some
partly cloudy conditions in the afternoon, with Friday afternoon
having a very slight chance of thunderstorms over the higher
terrain, and SW Sweetwater county off the Uinta mountains.
Temperatures should warm a few degrees over Thursday with the
700mb temperatures warming by 2-3C. Friday afternoon will also be
a bit breezier too over SW WY.

.LONG TERM...(Friday night through Thursday)
Issued at 130 PM MDT Thu Jul 5 2018

A high pressure ridge with southwest flow aloft over the
area will bring generally dry and hot weather conditions
Friday night and Saturday.  Record to near record high
temperatures are expected on Saturday. Some Pacific moisture
will move up from the great basin on Sunday supporting
isolated showers and thunderstorms mainly over the mountains.
Cloud cover and precipitation will cool temperatures slightly
on Sunday about 5 degrees. The Pacific moisture will continue
to surge north from the great basin with increasing clouds,
showers and thunderstorms on Monday and Tuesday with slight
cooling continuing. Then the moisture will become more limited
with decreasing showers and thunderstorms on Wednesday with mostly
dry conditions on Thursday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday afternoon)
Issued at 355 PM MDT Thu Jul 5 2018

VFR conditions expected throughout the forecast period (next 24
hours), although brief local MVFR possible under and around stronger
thunderstorms this evening.  Isolated to scattered showers and
thunderstorms are expected through this evening over much of the
area. Stronger storms possible over eastern Bighorn Basin, and into
Natrona and Johnson counties could produce gusty outflow over 40+
kts brief heavy rain, and small hail. Storms should move northeast
and be out of the area by 03-04Z/Fri. Scattered mid-level clouds
overnight possible from KCPR-KBYG. Friday to see clearing with
breezy SW flow with very isolated thunderstorms.

&&

.FIRE WEATHER...
Issued AT 130 PM MDT Thu Jul 5 2018

Isolated to scattered showers and thunderstorms will continue
into the evening hours, particularly over central to NE WY. The
stronger storms will likely produce outflows over 40 mph along
with brief heavy rain and some small hail. Lightning from
relatively high-based thunderstorms is also a concern as fuels are
drying out more, and some lower elevations fuel in central WY are
critical. This evening will likely see easterly outflow across
central WY as well, that will possibly push into southern WY.
Expect warmer and drier conditions on Friday with only a very
slight chance of thunderstorms over the higher terrain, with most
lower elevations in the teens for afternoon RH values. Winds will
remain below critical values, with some gusty flow up to 25 mph
across SW WY. Saturday will continue the very warm and dry
conditions, with a weak cool front pushing into northern WY late
in the day.

&&

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

&&

SHORT TERM...McDonald/Bourque
LONG TERM...Baker
AVIATION...McDonald/Bourque
FIRE WEATHER...McDonald/Bourque

Hazardous Weather Outlook
National Weather Service Riverton WY
210 AM MDT Thu Jul 5 2018

WYZ001>020-022>030-060815-
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-
210 AM MDT Thu Jul 5 2018

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight

Isolated afternoon and evening thunderstorms in northern and
central Wyoming.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Friday and Saturday...Highs from the mid 90s to low 100s in the
lower elevations East of the Divide.

Sunday through Wednesday...Isolated thunderstorms, mainly across
the north and west.

.SPOTTER INFORMATION STATEMENT...

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

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Special Weather Statement
National Weather Service Riverton WY
541 PM MDT THU JUL 5 2018

WYZ002-003-005-007-060045-
Owl Creek and Bridger Mountains-Cody Foothills-Southwest Big Horn
Basin-Absaroka Mountains-
541 PM MDT THU JUL 5 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN HOT SPRINGS AND
SOUTHEASTERN PARK COUNTIES UNTIL 645 PM MDT...

At 537 PM MDT, Doppler radar was tracking a strong thunderstorms
across the southern Absaroka mountains generally south of Meeteetse,
and west of Grass Creek. These thunderstorms are moving north at 10
to 20 mph.

Very heavy rainfall, dime size hail and winds in excess of 40 mph
are possible with these storms.

Locations impacted by this storm include Sunshine Reservoir and
Grass Creek, and Meeteetse.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to 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 4369 10883 4402 10934 4431 10889 4398 10849
TIME...MOT...LOC 2337Z 201DEG 19KT 4393 10900

21