Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 170323
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
923 PM MDT SAT AUG 16 2014

.UPDATE...RED FLAG WARNING FOR CENTRAL AND SOUTHERN WYOMING.

&&

SHORT TERM...TONIGHT THROUGH SUNDAY

AN AREA OF LOW PRESSURE WILL HELP TO FLATTEN THE RIDGING OVER THE
FORECAST AREA THIS EVENING...BRINGING SOME ZONAL FLOW. THIS FLOW
PATTER WILL GENERALLY REMAIN DRY...THOUGH A FEW SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE DURING THE EARLY EVENING
HOURS...MAINLY ACROSS EXTREME NORTHERN WYOMING.

THE AREA OF LOW PRESSURE HELPING TO FLATTEN THE RIDGE WILL MOVE
FURTHER EAST THROUGH SUNDAY...ALLOWING SOME RETURN OF NORTHWEST FLOW
TO THE FORECAST AREA. THIS FLOW WILL PERMIT A BIT MORE MOISTURE TO
RETURN TO THE AREA...WITH A FEW SHOWERS AND THUNDERSTORMS
POSSIBLE...MAINLY OVER THE CENTRAL MOUNTAINS. SLIGHTLY COOLER
TEMPERATURES EXPECTED ON SUNDAY...THOUGH NOT MUCH VARIANCE FROM
THOSE TEMPERATURES EXPERIENCED TODAY.

GUSTY WIND WILL REMAIN THROUGH THE EARLY EVENING HOURS...ESPECIALLY
ACROSS SOUTHERN WYOMING. LIGHT WIND EXPECTED THROUGH THE OVERNIGHT
HOURS...WITH A RETURN OF GUSTY WIND POSSIBLE BY EARLY SUNDAY
AFTERNOON.

LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

HIGH PRESSURE RIDGE ALOFT WILL EXTEND NORTH FROM FOUR CORNERS HIGH
SUNDAY NIGHT WITH LIMITED MOISTURE IN WESTERLY FLOW INTO THE WESTERN
MOUNTAINS. MONDAY THE RIDGE ALOFT BEGINS TO SHIFT EAST WITH A SLIGHT
INCREASE IN SUBTROPICAL MONSOON MOISTURE ADVECTING NORTH INTO
WESTERN WYOMING AS A PACIFIC LOW PRESSURE TROUGH MOVES INLAND INTO
THE PACIFIC NORTHWEST.  THERE WILL BE INCREASED SHOWER AND
THUNDERSTORM ACTIVITY MAINLY IN THE WESTERN MOUNTAINS IN THE
AFTERNOON AND EVENING. TUESDAY THE PACIFIC TROUGH WILL DEEPEN AND
SHIFT EAST PROVIDING A BETTER SHEAR ENVIRONMENT ALONG WITH COLD AIR
ADVECTION ALOFT HELPING TO DESTABILIZE THE AIR MASS IN THE AFTERNOON
FOR A CONTINUATION OF INCREASED CONVECTION.  OVERALL TEMPERATURES
WILL COOL. THE PACIFIC TROUGH WILL CONTINUE TO DEEPEN AND SHIFT EAST
INTO THE NORTHERN ROCKIES WITH INCREASED SOUTHWEST FLOW ALOFT ON
WEDNESDAY. WITH A CONTINUATION OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS MOST NUMEROUS IN THE NORTHWEST. AS THE PACIFIC TROUGH
MOVES WAST ACROSS MONTANA AND WYOMING...COLDER AIR WILL CONTINUE TO
COOL TEMPERATURES WITH CONVECTION MAINLY OVER THE NORTHWEST
MOUNTAINS.  AS THE PACIFIC TROUGH MOVES EAST INTO THE NORTHERN
PLAINS...A HIGH PRESSURE RIDGE WILL SURGE NORTH FROM THE DESERT
SOUTHWEST WITH A RETURN OF THE SUBTROPICAL MONSOON MOISTURE FRIDAY
AND SATURDAY WITH INCREASED SHOWERS AND THUNDERSTORMS WITH SLIGHT
WARMING WITH SOUTH SOUTHWEST FLOW ALOFT.  MODELS START OUT IN FAIR
AGREEMENT THEN START TO DIFFER IN THE STRENGTH AND POSITION OF THE
PACIFIC TROUGH.  PREFER THE MORE PROGRESSIVE GFS OVER THE MORE
CLOSED LOW SCENARIO WITH THE ECMWF AT THIS TIME.

AVIATION.../00Z ISSUANCE/

WIDESPREAD VFR CONDITIONS EXPECTED ACROSS THE FORECAST AREA
THROUGH 18Z. A FEW SHOWERS OR THUNDERSTORMS MAY BE PRESENT ACROSS
THE FAR NORTHERN REACHES OF THE FORECAST AREA THROUGH
02Z...INFLUENCING TURBULENCE OVER ANY IMPACTED FLIGHT PATHS. A
SLIGHT SURGE OF MOISTURE ANTICIPATED AFTER 18Z SUNDAY...WHICH WILL
INCREASE CLOUD COVER ACROSS MUCH OF THE AREA. A FEW SHOWERS WILL BE
POSSIBLE...MAINLY OVER THE CENTRAL MOUNTAINS. ADDITIONALLY...A FEW
OTHER LOCATIONS WILL SEE SOME INCREASED WIND AFTER 18Z...MAINLY
ACROSS THE SOUTH AND EAST.

FIRE WEATHER...

RED FLAG CONDITIONS FOR ZONES 279...280...283...289...AND 300 AS
FIRE WEATHER CONCERNS INCREASE ONCE AGAIN WITH DRY WESTERLY FLOW
ACROSS THE REGION. THESE WEST WINDS WILL GUST 25 TO 30 MPH IN THE
AFTERNOON AND MINIMUM RH VALUES WILL DROP INTO THE LOWER TEENS TO
UPPER SINGLE DIGITS WHILE HIGH TEMPS AT THE LOWER ELEVATIONS WILL
RISE INTO THE MIDDLE 80S TO NEAR 90 IN PLACES. ELSEWHERE...FIRE DANGER
WILL CONTINUE ENHANCED WITH WARM AND DRY CONDITIONS NEARLY EVERYWHERE.
HOWEVER...THE COMBINATION OF BOTH STRONGER WINDS AND LOW RH VALUES
WILL NOT COINCIDE AS THEY DO ACROSS THE CENTRAL AND SOUTHERN
ZONES.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM NOON TO 8 PM MDT SUNDAY
WYZ279-280-283-289-300.

&&

$$

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





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