Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 251930
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
130 PM MDT SAT JUL 25 2015

.SHORT TERM...TONIGHT THROUGH SUNDAY

WV IMAGERY SHOWING CONTINUING LOW AMPLITUDE TROF RIDGE TROF PATTERN
ACROSS THE CONUS WITH CNTRL HIGH LOCATED OVR TX/NM. MINOR
DISTURBANCE CURRENTLY MAKING ITS WAY ACROSS NRN WY WITH ANOTHER
SMALL DISTURBANCE IN SCNTRL ID HEADED THIS WAY. SFC HAS WEAK HIGH P
WRN FA...WEAK P E INTO THE CNTRL PLAINS. WEAK SFC BOUNDARY FROM NERN
WY TO SCNTRL WY.

AS FOR THE LAST COUPLE OF DAYS...NEAR RED FLAG CONDITIONS WILL EXIST
ACROSS FIRE WX ZONES 280...281 AND 300...NATRONA COUNTY AND SRN
JOHNSON COUNTY BOTH TODAY AND SUNDAY. MIN RH VALUES WILL LIKELY DROP
AND HOVER IN THE MID/LOWER TEENS...WITH WINDS GUSTING FROM 15 TO
NEAR 25 MPH RANGE AT TIMES.

THIS AFTERNOON AND TONIGHT...RIDGING...DRYING AND MORE ROBUST
CAPPING WILL BE IN CONTROL ACROSS MOST OF THE FA WITH ONLY ISOLATED
SHOWERS OR THUNDER POSSIBLE OVR A FEW OF THE HIGHER PEAKS IN THE
NW/NRN ZONES INCLUDING THE BIGHORN MOUNTAINS. SHOWERS AND STORMS
SHOULD DIE OFF QUICKLY EARLY THIS EVENING.

SUNDAY...SAME STORY DIFFERENT DAY BEING LOCATED ON THE BACKSIDE OF
UPR LVL RIDGE. A LITTLE WARMER THAN SATURDAY...BUT DRY AND CAPPED
FOR MOST OF THE FA EXCEPT THE FAR NW WHERE ANOTHER WEAK DISTURBANCE
LIFTING OUT AHEAD OF THE MAIN WCST TROF WILL COMBINE WITH WEAK
MOISTURE AND OROGRAPHIC LIFTING TO GIVE ISOLATED CHCS FOR SHRA/TSRA.
GUSTY WINDS AND VERY BRIEF HEAVY RAIN WILL BE THE MAIN THREATS.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SOUTHWEST FLOW WILL DOMINATE THE WEATHER ACROSS WESTERN AND CENTRAL
WYOMING THROUGH TUESDAY AHEAD OF AN UNSEASONMABLY STRONG PACIFIC
LOW PRESSURE TROUGH THAT WILL BE MOVING INTO THE PACIFIC NORTHWEST.
MOISTURE WILL BE LIMITED TO THE NORTHWEST AND FAR NORTH WHERE
SCATTERED MOUNTAIN SHOWERS AND ISOLATED THUNDERSTORMS WILL BE A
THREAT EACH AFTERNOON AND EVENING WITH A FEW SHOWERS LINGERING OVER
THE HIGHER MOUNTAINS THROUGH THE NIGHT AND INTO THE MORNING HOURS.
TEMPERATURES WILL WARM WITH WINDY CONDITIONS INCREASING ACROSS THE
SOUTH...CENTRAL AND EAST...AND ALONG AND NEAR THE EAST SLOPES OF THE
MOUNTAINS.  THE STRONG WINDS AND DEEP MIXING WILL BRING VERY DRY AIR
TO THE SURFACE WITH RELATIVE HUMIDITY DROPPING BELOW 15 PERCENT OVER
A LARGE AREA ON MONDAY.  THE PACIFIC TROUGH WILL MOVE ACROSS
SOUTHERN CANADA AND MONTANA CLIPPING NORTHERN WYOMING MONDAY NIGHT
DRIVING A COLD FRONT SOUTH MONDAY NIGHT AND TUESDAY.  THE COLD FRONT
WILL BRING COOLER TEMPERATURES AND HIGHER HUMIDITY WITH WINDS
SHIFTING TO THE NORTHEAST.  THE SOUTH WILL REMAIN WINDY ON TUESDAY
WITH LOW RELATIVE HUMIDITY BEFORE THE COLD FRONT PUSHES SOUTH
THROUGH THE AREA.  COOLER AND DRY WEATHER WILL THEN BE IN PLACE
WEDNESDAY...WITH A GRADUAL WARMING TREND THROUGH FRIDAY WITH DRY
CONDITIONS PREVAILING.  WINDS MAY PICK UP ON FRIDAY AND VERY LOW
RELATIVE HUMIDITY IN THE AFTERNOON.  FRIDAY NIGHT AND SATURDAY...
THE HIGH PRESSURE RIDGE WILL PICK UP SUBTROPICAL MOISTURE ADVECTING
IT NORTH AND THE EAST INTO WESTERN AND SOUTHERN WYOMING BRINGING
AN INCREASED CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS IN THE
WESTERN MOUNTAINS AND THE SOUTHWEST.


&&

.AVIATION.../00Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH THE
FORECAST PERIOD. ISOLATED SHOWERS AND STORMS WILL DEVELOP OVER THE
NORTHWEST MOUNTAINS UNTIL 02Z. SHOWERS AND STORMS WILL ALSO DEVELOP
OVER THE BIGHORN MOUNTAINS THROUGH 01Z. ONE OR TWO STORMS COULD
PRODUCE WIND GUSTS TO 40 KNOTS AND BRIEF HEAVY RAIN. LOCAL MVFR
CONDITIONS COULD OCCUR IN STORMS WITH HEAVY RAIN. THE REST OF THE
REGION SHOULD NOT SEE ANY THUNDERSTORMS. OTHERWISE...SMALL CHANCES
FOR AN ISOLATED SHOWER OR STORM WILL OCCUR AFTER 16Z OVER
NORTHWESTERN WYOMING.

&&

.FIRE WEATHER...

FUELS ARE CRITICAL ACROSS MOST OF NATRONA AND JOHNSON COUNTIES. NEAR
RED FLAG CONDITIONS AGAIN TODAY AND SUNDAY ACROSS ZONES
280...SOUTHERN 281 AND 300...NATRONA COUNTY AND SOUTHERN JOHNSON
COUNTY...AS BOTH WINDS AND MINIMUM RH VALUES GET CLOSE TO EXTREME
LEVELS. HOWEVER...AT THE MOMENT IT APPEARS THAT DANGEROUS RH AND/OR
WIND SPEED LEVELS...WHILE APPROACHED...WILL EITHER NOT BE MET OR
WILL BE TOO SHORT-LIVED BOTH TODAY AND SUNDAY. ELSEWHERE...FIRE
DANGER WILL BE ENHANCED AS USUAL AS A WARM AND RELATIVELY DRY
ATMOSPHERE CONTINUES AND WINDS BECOME GUSTY AT TIMES OUT OF THE
SOUTHWEST TO WEST...OR NEAR ISOLATED THUNDERSTORMS ACROSS THE
NORTHWEST AND NORTH. A SMALL POTENTIAL FOR FIRE STARTS WILL EXIST
DUE TO LIGHTNING STRIKES ACROSS THOSE AREAS WHERE THUNDERSTORMS
EXIST. MONDAY...HOWEVER...WILL BE A CRITICAL FIRE WEATHER DAY ACROSS
ALL OF NATRONA AND AT LEAST SOUTHERN JOHNSON COUNTY AS MINIMUM RH
VALUES DROP INTO THE LOWER TEENS...POSSIBLY SINGLE DIGITS...AND
WINDS GUST OUT OF THE SOUTHWEST 35 TO 40 MPH.

&&

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

$$

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



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