Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 260121
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
721 PM MDT THU SEP 25 2014

.UPDATE...

THE RED FLAG WARNING HAS BEEN ALLOWED TO EXPIRE. RECORD HEAT
OCCURRED ACROSS MUCH OF THE AREA. WORLANDS HIGH OF 94 SET A DAILY
RECORD HIGH...AND WAS THE HOTTEST SO LATE IN THE YEAR.

&&

.PREV DISCUSSION... /ISSUED 328 PM MDT THU SEP 25 2014/

SHORT TERM...TONIGHT THROUGH FRIDAY

HIGH PRESSURE REMAINS OVER THE FORECAST AREA THROUGH FRIDAY
MORNING...LEAVING DRY AND WARMING CONDITIONS. AN APPROACHING AREA OF
LOW PRESSURE WILL PUSH THE AREA OF HIGH PRESSURE EASTWARD FRIDAY
MORNING. THIS WILL BRING INCREASED SOUTH-SOUTHWEST FLOW OVER THE
WESTERN HALF OF THE STATE. A SURGE OF MOISTURE IN THIS FLOW WILL
IMPACT THE WESTERN QUARTER OF THE STATE...POTENTIALLY BRINGING SOME
AFTERNOON SHOWERS AND THUNDERSTORMS. THE MAIN AREAS OF IMPACT FOR
THESE SHOWERS AND THUNDERSTORMS WILL BE THE EXTREME WESTERN
MOUNTAINS AND VALLEYS. TEMPERATURES WILL COOL SLIGHTLY ON FRIDAY
ACROSS MUCH OF THE FORECAST AREA AS THE AREA OF LOW PRESSURE BEGINS
TO INFLUENCE AREA WEATHER.

LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

FRIDAY NIGHT  THE WEST COAST TROUGH WILL CONTINUE MOVING INLAND AND
START TO CUT OFF IN CENTRAL CALIFORNIA WITH THE SOUTH SOUTHWEST FLOW
SPREADING EAST ACROSS WESTERN AND CENTRAL WYOMING.  MOISTURE AND
INSTABILITY WILL INCREASE WITH INCREASING COVERAGE OF SHOWERS ACROSS
THE WEST SPREADING EAST...AND ISOLATED THUNDERSTORMS DEVELOPING IN
THE EVENING HOURS. TEMPERATURES WILL COOL WITH INCREASED CLOUD COVER
AND PRECIPITATION WHILE THE MAIN COLD AIR FROM THE TROUGH REMAINS TO
THE WEST OF THE AREA.

SATURDAY AND SATURDAY NIGHT A THE LOW CUTS OFF OVER THE GREAT
BASIN...THE FLOW ALOFT OVER WESTERN AND CENTRAL WYOMING WILL BECOME
INCREASINGLY DIVERGENT WITH STRONG UPPER LEVEL SUPPORT FOR THE
CONVECTION SPREADING OVER THE AREA.  SHOWERS WILL BECOME SOMEWHAT
WIDESPREAD WITH EMBEDDED AFTERNOON AND EVENING THUNDERSTORMS.  SOME
SNOW CAN BE EXPECTED IN THE WESTERN AND NORTHERN MOUNTAINS. THE COLD
AIR FROM THE TROUGH WILL BEGIN TO MOVE OVER THE AREA WITH
SIGNIFICANT COOLING.  THIS FORECAST COOLER THAN PREVIOUS AND TREND
WILL LIKELY CONTINUE THE NEXT FEW DAYS AS BETTER AGREEMENT OCCURS
BETWEEN THE MODELS.  OVERALL...THE MODELS ARE IN FAIR AGREEMENT
WITH THE LOCATION AND STRENGTH OF THE CUT OFF LOW.

SUNDAY AND SUNDAY NIGHT CUT OFF LOW AROUND ELY NEVADA HEADING
TOWARDS SALT LAKE CITY.  UPPER LEVEL DIVERGENCE CONTINUES TO
INCREASE WITH SIGNIFICANT SUPPORT FOR CONVECTION OVER THE AREA.
SHOWERS WILL REMAIN WIDESPREAD AND UPPER DYNAMICS SHOULD HELP
SUPPORT MID LEVEL DEFORMATION AND DEEPENING MID LEVEL LAPSE RATES
FOR SOME THUNDERSTORM ACTIVITY IN THE AFTERNOON AND EVENING.  COLDER
AIR CONTINUES TO SPREAD OVER THE AREA WITH SNOW IN THE MOUNTAINS.
MODELS REMAIN IN FAIR AGREEMENT WITH THE DETAILS OF THE UPPER LEVEL
LOW.

MONDAY AND MONDAY NIGHT THE UPPER LEVEL LOW BEGINS TO OPEN UP AND
EJECT NORTHEAST ACROSS THE AREA.  MODELS ADVERTISE A DRY SLOT FROM
THE SOUTHWEST INTO CENTRAL WYOMING WHICH WOULD COMPLICATE THE
FORECAST WITH THE LOCATION AND INTENSITY OF PRECIPITATION. TOO FAR
OUT AT THIS TIME TO INDICATE POTENTIAL MINIMA OF PRECIPITATION. AS
THE LOW CONTINUES OPENING UP AND MOVING NORTHEAST IS EXPECTED TO END
UP IN EASTERN MONTANA WITH COLD CYCLONIC WEST FLOW OVER WESTERN AND
CENTRAL WYOMING.  THIS REMOVES THE FAVORABLE AREA OF UPPER
DIVERGENCE AND THE FLOW LOOKS TO BECOME MOISTURE STARVED...WHILE
OROGRAPHIC PRECIPITATION SHOULD DOMINATE THE PRECIPITATION PROCESS
OVER THE WESTERN MOUNTAINS WITH AREAS EAST OF THE DIVIDE BECOMING
LESS FAVORABLE FOR SIGNIFICANT PRECIPITATION.  TEMPERATURES CONTINUE
TO DROP WITH SNOW LIKELY IN THE WESTERN MOUNTAINS.

TUESDAY AND TUESDAY NIGHT FLOW ALOFT TRANSITIONS INTO CYCLONIC WEST
FLOW WITH A DEEP LONG WAVE TROUGH OVER THE AREA FROM ALBERTA AND
SASKATCHEWAN SOUTH INTO THE DESERT SOUTHWEST.  THIS SHOULD KEEP
THINGS ON THE COLD SIDE WITH THE PRECIPITATION REMAINING MAINLY OVER
THE WESTERN MOUNTAINS WITH MOISTURE REMAINING LIMITED.

WEDNESDAY AND WEDNESDAY NIGHT A SHORT WAVE TROUGH FROM THE PACIFIC
NORTHWEST WILL MOVE SOUTHEAST DEEPENING THE LONG WAVE TROUGH OVER
THE REGION AND SHOULD SEE AN ENHANCEMENT TO PRECIPITATION IN THE
WEST WITH UNSETTLED SHOWERY COLD WEATHER EAST OF THE CONTINENTAL
DIVIDE.  MODELS SHOW MORE AND MORE SPREAD IN STRENGTH AND LOCATION
OF FEATURES ASSOCIATED WITH THE MAIN LONG WAVE TROUGH AND THE SHORT
WAVE TROUGH MOVING THROUGH THE FLOW.  NO CLEAR WINNER AT THIS TIME
AND NOTHING APPEARS TO MAKE SIGNIFICANT DIFFERENCES IN THE
FORECAST.  LIKELY TO BE COLDER THAN CURRENTLY FORECAST.

THURSDAY...MODELS BECOME VERY CHAOTIC WITH THE 500 MB HEIGHT FIELDS
SHOWING LITTLE AGREEMENT ON ANY FEATURE OTHER THAN A LARGE DEEP LONG
WAVE LOW PRESSURE TROUGH OVER WESTERN CANADA AND WESTERN US.
POTENTIAL SIGNIFICANT SHORT WAVE TROUGHS SHOWN BUT NO AGREEMENT WITH
THE MODELS ON LOCATION OR STRENGTH OF ANY GIVEN FEATURE.  WILL STAY
COLD AND POSSIBLY SHOWERY WITH THE WESTERN MOUNTAINS MOST LIKELY TO
RECEIVE PRECIPITATION AND AREAS EAST OF THE CONTINENTAL DIVIDE LESS
LIKELY.  MODEL POPS SEEM OVERDONE OVER ALL AFTER MONDAY...AND
ESPECIALLY WEDNESDAY AND THURSDAY.  HAVE GONE ALONG WITH HIGHER POPS
TO CONFORM WITH FORECASTS FROM SURROUNDING OFFICES.

AVIATION.../00Z DISCUSSION/

WIDESPREAD VFR CONDITIONS ANTICIPATED FOR MUCH OF THE DISPATCH AREA.
SOME GUSTY WIND MAY CONTINUE TO IMPACT KRKS AND KCPR THROUGH 03Z
THIS EVENING...BUT ARE EXPECTED TO BE LIGHT OVERNIGHT. AN
APPROACHING AREA OF LOW PRESSURE MAY INITIATE SOME SHOWERS AND
THUNDERSTORMS ACROSS THE WESTERN MOUNTAINS AND VALLEYS AFTER 18Z
FRIDAY. SHOWERS WOULD PRIMARILY IMPACT KJAC...ALONG WITH THE WESTERN
MOUNTAIN AVIATION PASSES. SHOWERS AND LOWERING CLOUDS MAY RESULT IN
SOME PERIODS OF MOUNTAIN OBSCURATION FRIDAY AFTERNOON.

FIRE WEATHER...

HIGH PRESSURE WILL REMAIN OVER THE AREA THIS EVENING AND INTO FRIDAY
MORNING. THIS WILL LEAVE WARM AND DRY CONDITIONS ACROSS THE FORECAST
AREA. GUSTY WIND OVER THE WIND CORRIDOR BETWEEN ROCK SPRINGS AND
CASPER WILL WANE THIS EVENING. AN AREA OF LOW PRESSURE WILL MOVE
TOWARDS WESTERN WYOMING FRIDAY MORNING...SENDING A SURGE OF MOISTURE
ACROSS EXTREME WESTERN WYOMING BY THE AFTERNOON. ISOLATED TO WIDELY
SCATTERED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WITH THIS
SURGE. ADDITIONALLY...SOME GUSTY WIND WILL BE POSSIBLE...MAINLY
ACROSS WESTERN WYOMING AND THE WIND CORRIDOR. THIS SYSTEM WILL
EXPAND THROUGH THE WEEKEND...WITH MANY AREAS SEEING COOLER
TEMPERATURES AND PRECIPITATION BY SATURDAY EVENING...WHICH WILL
LINGER INTO EARLY NEXT WEEK.

&&

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

&&

$$

SHORT TERM...BRANHAM
LONG TERM...C.BAKER
AVIATION...BRANHAM
FIRE WEATHER...BRANHAM




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