Severe Thunderstorm Warning 23, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
625 PM MDT WED JUN 12 2013

.UPDATE...MADE A FEW CHANGES FOR THIS EVENING TO INCLUDE LARGE HAIL
IN THE WEATHER GRIPS AND INCREASE POPS ACROSS NORTHERN WYOMING GIVEN
RADAR TRENDS AND SPOTTER REPORTS.

.SHORT TERM...TONIGHT THROUGH THURSDAY
LARGE SCALE WV IMAGERY SHOWING LARGE SCALE RIDGING ACROSS MUCH OF
THE CONUS TODAY...SANDWICHED BETWEEN TWO LARGE TROUGHS EAST AND
WEST...WITH THE PRIMARY RIDGE AXIS RIGHT THROUGH WYOMING. THE RIDGE
IS QUITE DIRTY HOWEVER WITH SHORTWAVE ENERGY IN THE FORM OF JET
SPEED MAXIMUMS AND INCREASED MID/UPPER LEVEL VORTICITY MOVING
THROUGH THE NORTHWEST...NORTHERN BORDER...AND NORTHEAST PORTIONS OF
WYOMING FROM TIME TO TIME. AS OF 13Z THIS MORNING...ONE OF THOSE
PIECES OF ENERGY WAS OVERRIDING THE NORTHWEST CORNER OF THE
CWA...DRAGGING SHOWERS WITH IT AS IT PASSES.

THIS AFTERNOON...MODERATE INSTABILITY WEST AND NORTHWEST...MUCH OF
THE AMOUNT OF INSTABILITY DICTATED BY THE AMOUNT OF CLEARING AND
SUNSHINE IN ADDITION TO THE AMOUNT OF...OR LACK OF...LOW LEVEL
MOISTURE WE END UP WITH OVER THE WEST AS SOUTHWEST FLOW BEGINS TO
PUSH THROUGH THE WESTERN CWA THIS AFTERNOON. ATTM THE IT LOOKS AS
THOUGH DEW POINTS WILL RANGE FROM THE MIDDLE 30S TO THE LOWER 40S
FOR THE MOST PART WHICH WOULD LIMIT THE STRENGTH OF THE STORMS TO
MOSTLY BELOW SEVERE PARAMETERS...EXCEPT FOR PERHAPS THE FAR NORTHERN
PORTION OF YELLOWSTONE. UPPER LEVEL SUPPORT ALSO LOOKS TO BE LOW
UNTIL LATE THIS AFTERNOON WHEN STRONGER FLOW OVERRIDES THIS REGION
AGAIN. MOSTLY ELEVATED ACTIVITY EXPECTED WEST AND NORTHWEST
THROUGH THIS EVENING. LITTLE IN THE WAY OF CAPPING WILL ALSO LIMIT
SEVERE POTENTIAL A BIT WITH JUST A GRADUAL INCREASE IN INTENSITY
THROUGH THE DAY.

BETTER CHANCES FOR STRONG TO SEVERE STORMS FOR A SHORT PERIOD WILL
OCCUR ALONG AND NORTH OF A COOKE CITY MT TO THERMOPOLIS WY TO PINE
TREE JUNCTION LINE...WITH BEST SEVERE SHEAR AND THERMODYNAMICS
NORTHERN HALF OF THE BIG HORN BASIN AND THE NORTHERN 3/4S OF JOHNSON
COUNTY. EFFECTIVE SHEAR WILL MAX OUT OVER THE NORTHEASTERN CWA AS
THE JET STREAK OVER CENTRAL UT THIS MORNING NOSES OVER THIS AREA BY
LATE AFTERNOON/EVENING. THERE WILL BE SOME STRONG CAPPING EARLY
TODAY...WHICH WILL ALLEVIATE BY EARLY TO MID AFTERNOON...JUST A BIT
AHEAD OF ARRIVAL OF UPPER SUPPORT...SO THE TWO CONDITIONS MAY BE
JUST A BIT MISS-TIMED. WILL DEPEND ON LONGEVITY OF STORMS.  CAPPING
IN NORTHERN BIG HORN BASIN WILL HOLD THROUGH LATE MORNING...SOUTHERN
BIG HORN BASIN THROUGH EARLY AFTERNOON...JOHNSON COUNTY TIL AT LEAST
MID AFTERNOON. HAIL AND WIND WILL BE THE MAIN THREAT TODAY...WITH
VERY SLIGHT CHANCE ALONG LL CONVERGENCE ZONES FOR A WEAK
TORNADO.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
THE PROMINENT CIRCULATION NOW OVER THE PACIFIC NORTHWEST WILL
ACCELERATE TOWARD THE ROCKIES THURSDAY NIGHT. AHEAD OF THIS
APPROACHING WEATHER FEATURE...FAIRLY SIGNIFICANT THUNDERSTORMS
WITH AT LEAST SMALL HAIL AND STRONG GUSTY WINDS WILL LINGER OVER
JOHNSON COUNTY WITH A FEW ADDITIONAL STORMS EXPECTED OVER
NORTHWEST AND NORTH CENTRAL WYOMING WHERE AMPLE CAPE WILL BE LOCATED
THROUGH WELL AFTER MIDNIGHT. BY 12Z FRIDAY...THE NAM 80 HAS -4C H7
TEMPS ACROSS YNP SO ANY LINGERING SHOWERS OVER THAT AREA SHOULD FALL
AS A HETEROCYCLIC PRECIP MIX OF RAIN AND SNOW ABOVE 7500 FEET AND
WITH SNOWFALL ABOVE THAT ELEVATION. FRIDAY SHOULD FEATURE YET ANOTHER
DAY OF THUNDERSTORMS IN NORTHERN WYOMING BUT WITH WEAKER
CAPES...THESE STORMS SHOULD NOT BE AS INTENSE AS THEY COULD
POTENTIALLY BE ON THURSDAY GIVEN THE Q VECTOR FORCING AND RIGHT REAR
QUAD DYNAMICS. THESE STORMS WILL HAVE A PROPENSITY FOR PRODUCING
SMALL HAIL GIVEN THE LOW FREEZING LEVEL. THEN ON SATURDAY EXPECT DRY
WEATHER AS A RIDGE BUILDS INTO THE AREA. THE NEXT TROUGH WILL NOT
GIVE US A THREAT OF THUNDERSTORMS UNTIL TUESDAY AND WEDNESDAY. TEMPS
BEHIND THURSDAYS TROUGH WILL RUN ABOUT 10 DEGREES COOLER THROUGH THE
WEEKEND.

&&

.AVIATION.../00Z ISSUANCE/ SOUTHWEST FLOW AT 15 TO 25KT ACROSS THE
SOUTH AND SOUTHWESTERN PORTION OF THE FORECAST AREA TODAY SOUTH OF
A JACKSON TO CASPER LINE... WITH MORE SHOWERS AND THUNDERSTORMS
MOVING THROUGH THE NORTH AND WEST TERMINAL AREAS. CHANCES WILL
EXIST FOR -GS AND STRONG WIND GUSTS VCNTY KCOD KWRL...AS WELL AS
MVFR CONDITIONS IN RA AT TIMES. HIGHER BASED THUNDERSTORMS IN
CENTRAL WYOMING WILL BE ABLE TO PRODUCE VERY STRONG OUTFLOW
WINDS...HOWEVER IT WILL LIKELY BE TOO DRY FOR STORMS AGAIN VCNTY
KRKS AND KCPR. VCTS HAVE BEEN ALSO BEEN KEPT OUT OF THE KRIW AND
KLND TAFS SINCE THE BEST CHANCES FOR THUNDER WILL OCCUR NORTH AND
WEST OF THIS REGION...HOWEVER EFFECT FROM DISTANCE THUNDERSTORMS
TO THE NORTH AND WEST MAY BE FELT AT TIMES IN THE FORM OF ERRATIC
GUSTY WINDS. LATER...SHOWERS AND STORMS WILL EXIT THE AREA AFTER
06Z EXCEPT FOR PERHAPS THE CODY AND JACKSON AREAS WHICH COULD HAVE
SHOWERS CLOSE BY THROUGH THE EARLY MORNING HOURS...SO MAY EXTEND
VCSH FOR 0Z ISSUANCE.

&&

.FIRE WEATHER...
SEVERAL UPPER LEVEL DISTURBANCES WILL SWING UP THROUGH THE REGION
TODAY...TONIGHT...AND TOMORROW...WITH THE POSSIBILITY OF PRODUCING
SOME STRONGER STORMS ACROSS THE NORTHERN QUARTER OF WYOMING. THESE
STORMS MAY ALSO PRODUCE WIND THAT IS STRONG AND ERRATIC WITH HAIL
CHANCES IN ADDITION TO PERIODS OF HEAVY RAINFALL AND FREQUENT
LIGHTNING. AREAS OF SOUTHERN WYOMING WILL AGAIN HAVE A WARM AND
GENERALLY DRY DAY WITH GUSTY WEST TO SOUTHWESTERLY WINDS...WITH
HUMIDITY AGAIN DIPPING INTO THE LOWER TEENS AND SINGLE DIGITS THIS
AFTERNOON. TEMPERATURES WILL REMAIN WARM THURSDAY...BUT COOL
SOMEWHAT FRIDAY BEHIND A COLD FRONT.

&&

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

UPDATE...HATTINGS
SHORT TERM...BRAUN
LONG TERM...LIPSON
AVIATION...BRAUN
FIRE WEATHER...BRAUN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
400 AM MDT WED JUN 12 2013

WYZ001>020-022>030-131200-
ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST-
BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS-
EAST SWEETWATER COUNTY-FLAMING GORGE-
GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS-
NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN-
NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS-
ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES-
SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN-
SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY-
TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN-
UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN-
WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST-
YELLOWSTONE NATIONAL PARK-
400 AM MDT WED JUN 12 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS THE NORTH THIS
AFTERNOON AND EVENING. THE MOST LIKELY AREA WILL BE ALONG AND
NORTHWEST OF A LINE...FROM JACKSON TO CODY...INCLUDING YELLOWSTONE
NATIONAL PARK. THE REST OF THE BIG HORN BASIN AND JOHNSON COUNTY
COULD ALSO SEE SOME STRONG TO POTENTIALLY SEVERE STORMS. LARGE HAIL
AND DAMAGING WINDS ARE POSSIBLE IN THE STRONGER STORMS. ALSO STORMS
COULD PRODUCE BRIEF TORRENTIAL RAINFALL...WITH THE POTENTIAL OF
LOCALIZED FLASH FLOODING OR MUD SLIDES.

ELSEWHERE...THE PRIMARY HAZARD FROM THUNDERSTORMS WILL BE VERY GUSTY
WINDS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THURSDAY...ISOLATED THUNDERSTORMS POSSIBLE ACROSS NORTHERN AND
EASTERN PORTIONS OF THE COUNTY WARNING AREA.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT THUNDERSTORM WIND GUSTS OVER 40
MPH...ANY HAIL...FLOODING...OR ANY DAMAGE. THANK YOU.

TEAM RIVERTON

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