Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 250914
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
314 AM MDT THU JUN 25 2015

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

THUNDERSTORMS CONTINUE TO DEVELOP OVER CENTRAL JOHNSON COUNTY THIS
MORNING...WITH THE MOST RECENT DEVELOPMENT SHOWING INDICATIONS OF
LARGE HAIL AND DAMAGING WIND. WEAKER DEVELOPMENT IS BEHIND THIS
STORM...WITH PERIODS OF ACTIVITY REMAINING PRESENT THROUGH THE
OVERNIGHT HOURS.

MODELS CONTINUE TO INDICATE ANOTHER STRONGER SURGE OF INSTABILITY
ACROSS THE EASTERN ZONES ON THURSDAY AFTERNOON...POTENTIALLY
BRINGING STRONG TO SEVERE STORMS ACROSS JOHNSON AND NORTHERN NATRONA
COUNTIES. MODELS SHOW THE BEST OPPORTUNITY FOR DEVELOPMENT BEING
THROUGH THE EARLY EVENING HOURS...THOUGH SOME ROGUE ACTIVITY COULD
PERSIST INTO THE LATE EVENING HOURS AGAIN.

MEANWHILE...AS SHOWERS AND THUNDERSTORMS MOVE THROUGH EASTERN
WYOMING...A RIDGE OF HIGH PRESSURE WILL STRENGTHEN OVER THE
INTERMOUNTAIN WEST. THIS RIDGE WILL MOVE INTO WESTERN WYOMING LATE
THURSDAY EVENING...AND WILL CONTROL AREA WEATHER BY FRIDAY
AFTERNOON. THE RIDGE WILL CONTINUE TO AMPLIFY AS IT PROGRESSES
EASTWARD. SOME EMBEDDED MOISTURE WILL RESULT IN ISOLATED SHOWERS AND
THUNDERSTORMS OVER THE NEXT COUPLE DAYS...MAINLY OVER THE MOUNTAINS.
TEMPERATURES WILL WARM UNDER THE INFLUENCE OF THIS RIDGE...WITH
GENERALLY LIGHT WIND EXPECTED.

.LONG TERM...SUNDAY THROUGH TUESDAY

SYNOPSIS...A HOT UPPER LEVEL HIGH PRESSURE SYSTEM WILL BE
CENTERED OVER THE GREAT BASIN THROUGH TUESDAY...BRINGING VERY WARM
CONDITIONS ACROSS THE AREA WITH A FEW AFTERNOON/EVENING
THUNDERSTORMS POSSIBLE MAINLY ACROSS THE NORTHWEST MOUNTAINS.  AN
UPPER LEVEL DISTURBANCE WILL DIVE INTO THE NORTHERN PLAINS ON
WEDNESDAY PUSHING A WEAK COLD FRONT ACROSS CENTRAL AND EASTERN
WYOMING WITH A FEW THUNDERSTORMS ALONG THE FRONT.

DISCUSSION...MEDIUM-RANGE GUIDANCE IN GOOD OVERALL AGREEMENT WITH
BUILDING HEIGHTS ACROSS THE AREA SUNDAY AS UPPER HIGH EXPANDS ACROSS
THE GREAT BASIN.  THIS WILL BRING VERY WARM CONDITIONS ACROSS THE
AREA SUNDAY AND MONDAY WITH HIGHS NEAR 90 IN THE FAR WEST
VALLEYS...AND IN THE MID TO UPPER 90S ACROSS THE LOWER CENTRAL
BASINS.  SLIGHT INSTABILITY WILL RESULT IN A FEW THUNDERSTORMS
ACROSS THE NW MOUNTAINS AND FAVORED MOUNTAIN/VALLEY BREEZE
BOUNDARIES...MAINLY FROM WASHAKIE NEEDLES ACROSS THE OWL CREEK RANGE
WITH NOCTURNAL CLOUD TOP COOLING POSSIBLY SUSTAINING SOME STORMS
FURTHER OUT FROM THE ELEVATED TERRAIN.  SOME PACIFIC PERTURBATIONS
BEGIN TO ROTATE AROUND NORTH SIDE OF UPPER HIGH ACROSS THE
INTERMOUNTAIN WEST AND NORTHERN ROCKIES TUESDAY AND
WEDNESDAY...SUPPRESSING THE UPPER HIGH.  MODELS ARE ABOUT 24 HOURS
SLOWER WITH A MORE POTENT PACIFIC SYSTEM RIDING OVER THE RIDGE AND
DIVING INTO THE NORTHERN PLAINS ON WEDNESDAY.  THE MAIN IMPACTS WITH
THIS SYSTEM ARE EXPECTED TO REMAIN EAST OF THE AREA...BUT BACKDOOR
COLD FRONT WILL LIKELY BE THE FOCUS FOR CONVECTIVE INITIATION
FURTHER OFF THE MOUNTAINS ACROSS THE CENTRAL AND EAST WEDNESDAY
AFTERNOON AND EVENING.  UPPER RIDGE IS EXPECTED TO REBUILD FURTHER
WEST ON THURSDAY...WITH NW FLOW ACROSS THE AREA.  TEMPERATURES WILL
CONTINUE ON AN OVERALL SLIGHT COOLING TREND WITH A FEW THUNDERSTORMS
ONCE AGAIN MAINLY OVER AND NEAR THE NW AND CENTRAL MTNS.
&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

MVFR CEILINGS ARE EXPECTED TO IMPACT PORTIONS OF JOHNSON AND NATRONA
COUNTIES...INCLUDING KCPR THROUGH ABOUT 16-18Z THURSDAY.
OTHERWISE...VFR CONDITIONS ARE EXPECTED AT AREA TERMINALS...EXCEPT
FOR BRIEF MVFR/IFR CONDITIONS IN CONVECTION.

A DISTINCT SHORTWAVE IN THE WESTERLY FLOW MOVING INTO SOUTHERN
MONTANA/NORTHERN WYOMING EARLY THIS MORNING IS EXPECTED TO PUSH INTO
THE NORTHERN PLAINS BY EARLY THIS AFTERNOON. THIS DISTURBANCE SHOULD
RESULT IN ISOLATED TO LOCALIZED SCATTERED SHOWERS WITH A FEW
THUNDERSTORMS THIS MORNING...WITH THE BEST CHANCE OF CONVECTION OVER
JOHNSON COUNTY. THE MAIN ACTIVITY IS EXPECTED TO PUSH EAST OF THE
FORECAST AREA BETWEEN 18Z AND 21Z...BUT THERE WILL BE ENOUGH
MOISTURE AND INSTABILITY FOR ISOLATED CONVECTION THROUGH ABOUT 02Z
FRIDAY...ESPECIALLY OVER THE FAR EAST INCLUDING JOHNSON AND NATRONA
COUNTIES.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MAINLY DRY IS EXPECTED WITH A BREEZY WEST TO NORTHWEST WINDS IN
THE AFTERNOON AND EVENING. WINDS MORE SOUTH TO SOUTHWEST IN JACKSON
HOLE. THERE WILL BE AN OUTSIDE CHANCE FOR AN ISOLATED SHRA/TSRA
ALONG THE HIGHER TERRAIN ALONG THE DIVIDE...AND NEAR THE WYOMING AND
UTAH/COLORADO BORDERS FOR ACTIVITY COMING OFF THE UINTA MTS. ANY
ROUTES GOING INTO EASTERN WYOMING WILL HAVE A SHOT OF SOME
CONVECTION THROUGH EARLY EVENING.

&&

.FIRE WEATHER...

SHOWERS AND THUNDERSTORMS WILL CONTINUE TO IMPACT EASTERN WYOMING
TODAY...ESPECIALLY OVER JOHNSON AND NATRONA COUNTIES. SOME STORMS
MAY BECOME STRONG TO SEVERE...WITH DAMAGING WIND AND LARGE HAIL.
SHOWERS WILL WEAKEN OVERNIGHT AS AN AREA OF HIGH PRESSURE GAINS
INFLUENCE. AS THIS HIGH PRESSURE STRENGTHENS...EXPECT WARMING
TEMPERATURES...LOWERED DAYTIME HUMIDITY...AND GENERALLY LIGHT WIND.
FIRE BEHAVIOR IS EXPECTED TO REMAIN LOW...THOUGH LIGHTNING AND GUSTY
AND ERRATIC WIND ASSOCIATED WITH THUNDERSTORMS COULD BRING PERIODS
OF MORE ACTIVE FIRE BEHAVIOR.

&&

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

$$

SHORT TERM...BRANHAM
LONG TERM...AEM
AVIATION...WM
FIRE WEATHER...BRANHAM



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