Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 290551
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1150 PM MDT FRI AUG 28 2015

.SHORT TERM...TONIGHT THROUGH MONDAY

A FEW WEAK SHOWERS CONTINUE TO DEVELOP OVER THE CENTRAL MOUNTAINS
THIS AFTERNOON. ACTIVITY SHOULD BE LIMITED WITH THIS MOISTURE
PUSH...WITH THE MAJORITY OF SHOWERS AND THUNDERSTORMS REMAINING OVER
THE HIGHER ELEVATIONS. HIGH PRESSURE EXPECTED TO REMAIN IN CONTROL
OF AREA WEATHER THROUGH THE OVERNIGHT HOURS. THIS WILL LEAVE LIMITED
CLOUD COVER...DRY CONDITIONS...AND LIGHT WIND. SMOKE WILL REMAIN
OVER THE AREA WHICH IS ANTICIPATED TO CONTINUE AIR QUALITY AND
VISIBILITY ISSUES.

SATURDAY WILL REMAIN UNDER THE CONTINUED INFLUENCE OF THE AREA OF
HIGH PRESSURE. HOWEVER...AN APPROACHING COLD FRONT WILL HELP TO
TIGHTEN THE PRESSURE GRADIENT ACROSS THE AREA TO BRING INCREASED
WIND WITH STRONGER GUSTS. AHEAD OF THE FRONT...WARM AND DRY
CONDITIONS WILL CONTINUE...RAISING FIRE WEATHER CONCERNS. A RED
FLAG WARNING HAS BEEN ISSUED FOR MUCH OF EASTERN WYOMING FOR
SATURDAY.

THE COLD FRONT WILL PUSH THROUGH THE AREA ON SUNDAY...HELPING TO
COOL TEMPERATURES AND INTRODUCE SHOWERS AND THUNDERSTORMS. THE
FRONTAL PASSAGE WILL RESULT IN THE OPPORTUNITY FOR DRY
THUNDERSTORMS ACROSS EASTERN WYOMING...WHICH LED TO A RED FLAG
WARNING RETURNING TO PORTIONS OF EASTERN WYOMING.

A DRIER SOUTHWEST FLOW RETURNS TO THE AREA ON MONDAY. HOWEVER...
ENOUGH WEAK MOISTURE MAY BE AROUND TO RESULT IN SOME WIDELY
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS...MAINLY ACROSS
SOUTHERN WYOMING.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY

MODELS INDICATING ELEVATED TO EXTREME FIRE WEATHER DANGER TO
CONTINUE THROUGH THE LONG TERM. A MID LEVEL LOW WILL SLIDE SOUTHWARD
ACROSS THE WESTERN CANADIAN COAST TUESDAY...THEN PARK ITSELF ACROSS
BRITISH COLUMBIA AND WA THROUGH THE END OF THE WEEK...EXTENDING A
TROUGH ACROSS MUCH OF THE WEST COAST. THIS WILL INCREASE THE
GRADIENT BETWEEN THE LOW AND THE LARGE RIDGE ACROSS THE EASTERN U.S.
THE RESULT FOR THE COWBOY STATE IS INCREASED DRY SOUTHWESTERLY FLOW
BEGINNING TUESDAY AND CONTINUING THROUGH FRIDAY. WIND GUSTS ON
TUESDAY WILL BE ENOUGH FOR AT LEAST ELEVATED FIRE WEATHER
CONDITIONS. WEDNESDAY THROUGH FRIDAY SHOULD SEE GUSTS INCREASE AND
POSSIBLY BE OVER 25 MPH...ESPECIALLY IN THE WIND CORRIDOR FROM ROCK
SPRINGS TO CASPER. WITH FORECASTED MIN RH EXPECTED TO BE IN THE
TEENS...THIS COULD SET UP FOR EXTREME FIRE WEATHER CONDITIONS FROM
MID TO LATE NEXT WEEK.

OVERALL A MAINLY DRY FORECAST FOR THE LONG TERM. ENOUGH INSTABILITY
AND SHEAR WILL LINGER ACROSS THE MOUNTAINS ON TUESDAY FOR ISOLATED
MOUNTAIN STORMS. SHEAR WILL BE ON THE INCREASE STARTING
WEDNESDAY...HOWEVER INSTABILITY IS LACKING...WITH ONLY A FEW
ISOLATED STORMS POSSIBLE. A WEAK AND MAINLY DRY FRONT LOOKS TO PUSH
ACROSS THE REGION WEDNESDAY NIGHT THROUGH THURSDAY...WITH A
LINGERING FRONTAL BOUNDARY STICKING AROUND INTO FRIDAY. WITH DRY AIR
IN PLACE ACROSS MANY OF THE LOWER ELEVATIONS...KEPT THE POPS MAINLY
IN THE MOUNTAINS FOR LATE NEXT WEEK. TEMPS LOOK TO BE AROUND TO
SLIGHTLY ABOVE NORMAL TO START THE LONG TERM. THE WEAK MENTIONED
FRONT LOOKS TO COOL TEMPS A FEW DEGREES...BRINGING THEM TO NEAR
NORMAL TO END THE LONG TERM.


&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS AND MAINLY LIGHT WIND...LESS THAN 12KTS...WILL
PREVAIL OVERNIGHT.   A SOUTHERLY LOW LEVEL FLOW WILL RESULT IN AN
OVERALL CONTINUED DECREASE IN AREAS OF SMOKE THOUGH LCL MVFR
CONDITIONS IN FU MAY STILL BE ENCOUNTERED VCNTY AND EAST OF THE
DIVIDE THROUGH SATURDAY MORNING.

SOUTH TO SOUTHWEST SFC WINDS WILL INCREASE TO 10-20KTS ACROSS MOST
AREAS SATURDAY AFTERNOON.  ISOLD-WDLY SCT -TSRA ARE EXPECTED TO PUSH
INTO FAR WEST WYOMING...VCNTY KJAC-KAFO...BY AROUND 21Z AND SLOWLY
TO A VCNTY KEVW-KPNA-KCOD LINE 3Z-6Z SUNDAY.  A FEW THUNDERSTORMS
WILL LIKELY LINGER INTO SUNDAY MORNING VCNTY AND WEST OF THE DIVIDE
WITH AREAS OF GUSTY S-SW WINDS CONTINUING AHEAD OF AN APPROACHING
COLD FRONT IN MOST AREAS.

&&

.FIRE WEATHER...

...RED FLAG WARNING SATURDAY AND SUNDAY FOR PORTIONS OF SOUTHERN AND
CENTRAL WYOMING...

A CRITICAL FIRE WEATHER PATTERN IS SETTING UP FOR THE WEEKEND AS
SOUTHWEST FLOW AHEAD OF A TROUGH DIGGING OVER THE PACNW WILL DRAW IN
DRY...SWIFT MOVING AND UNSTABLE AIR FROM THE FOUR CORNERS REGION.
THE UNCERTAINTY INVOLVED WITH THE TIMING OF CERTAIN ELEMENTS...LIKE
WHEN THE WINDS WILL KICK IN ON SATURDAY IS STILL A BIT QUESTIONABLE
AS LATEST GUIDANCE BRINGS THE 25 MPH PLUS WIND GUSTS IN A LITTLE
LATER IN THE DAY...PROBABLY CLOSER TO LATE AFTERNOON IN THE MORE
PROTECTED BASINS LIKE THE BIGHORN AND WIND RIVER BASINS. OTHER AREAS
SHOULD START GUSTING OVER 25 MPH A BIT EARLIER...CLOSER TO 1400.
RELATIVE HUMIDITY WILL DIP WELL IN THE THE TEENS WITH SOME SINGLE
DIGIT RHS EXPECTED IN CENTRAL AND EASTERN ZONES. IN ADDITION...IT
WILL BE QUITE WARM DURING THE DAY WITH HIGHS IN THE 90S...WHICH WILL
INCREASE LAPSE RATES AT THE SURFACE WITH A HAINES INDEX OF 6
EXPECTED AS WELL. SO EVEN THOUGH THE WINDS AND MINIMUM RELATIVE
HUMIDITIES MAY NOT SYNC PERFECTLY...THERE WILL BE SEVERAL ELEMENTS
OVERLAPPING TO INCREASE THE FIRE DANGER TO CRITICAL LEVELS.

ON SUNDAY...OVERALL IT WILL BE WINDIER BUT WITH SLIGHTLY HIGHER
RELATIVE HUMIDITY. THE COLD FRONT ASSOCIATED WITH THE TROUGH DIGGING
TO THE WEST ADVANCES...IT WILL LIKELY SETTLE INTO WESTERN...NORTHERN
AND SOUTHERN WYOMING FAIRLY EARLY IN THE DAY...WHICH WOULD END THE
FIRE WEATHER THREAT IN THOSE LOCATIONS AS WELL AS BRING A SLIGHT
CHANCE FOR A WETTING RAIN. HOWEVER...LATEST GUIDANCE SUGGESTS THAT
THE FRONT COULD RETREAT BACK INTO MONTANA...CLEARING THE WAY FOR
MORE STRONG SOUTHWEST FLOW AND LOW HUMIDITY IN THE SOUTHERN BIGHORN
BASIN AND POSSIBLY INTO JOHNSON COUNTY. SO...THESE ZONES COULD BE
ADDED FOR SUNDAY AT A LATER TIME IF THIS GUIDANCE REMAINS
CONSISTENT. IN ADDITION...A SWATH OF MID LEVEL MOISTURE AND
CONTINUED INSTABILITY WILL KICK OF A FEW MIXED WET AND DRY
THUNDERSTORMS...SOME OF WHICH COULD CONTRIBUTE TO NEW FIRE STARTS
WITH THE MOST ACTIVITY EXPECTED ACROSS NORTHERN AND WESTERN
WYOMING...WITH A SECONDARY SWATH POSSIBLE OVER NATRONA AND EASTERN
FREMONT COUNTIES LATE SUNDAY AFTERNOON...THE CHANCE OF A WETTING
RAIN OUT OF THESE STORMS IS NEXT TO ZERO.

A REPEAT OF THESE CONDITIONS WILL BE POSSIBLE ON TUESDAY AND
WEDNESDAY OF NEXT WEEK.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM 11 AM TO 9 PM MDT SATURDAY FOR WYZ275>277-
279-281-282-285-287.

RED FLAG WARNING FROM 11 AM SATURDAY TO 9 PM MDT SUNDAY FOR
WYZ280-283-289-300.

&&

$$

SHORT TERM...BRANHAM/ALLEN
LONG TERM...ANGLIN
AVIATION...AEM
FIRE WEATHER...ALLEN



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