Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221741 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE RIVERTON WY
1141 AM MDT SAT AUG 22 2015

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

RED FLAG WARNINGS CONTINUE FOR PORTIONS OF CENTRAL AND SOUTHERN
WYOMING AS A DRY COLD FRONT CONTINUES TO SAG SOUTH. WINDS HAVE BEEN
GUSTING OVER 50 MPH BEHIND THE FRONT AS IT MOVED THROUGH BUFFALO SO
WILL LET THE CENTRAL AND NORTHERN RED FLAGS DIE A NATURAL DEATH
EARLY THIS MORNING ONCE THINGS SETTLE DOWN BEHIND THE FRONT. RED
FLAG CONDITIONS WILL REDEVELOP ACROSS THE SOUTHWEST THIS AFTERNOON
AS THE FRONT HANGS UP ALONG THE DIVIDE.

THE FRONT COULD BE DRAGGING A SIGNIFICANT SMOKE PLUME FROM THE FIRES
RAGING IN THE PACIFIC NORTHWEST. OBSERVATIONS FROM MONTANA AS THE
FRONT MOVED THROUGH ACTUALLY SHOWED SOME IMPROVEMENT IN VISIBILITY
BUT THOSE AREAS ALSO RECEIVED SOME RAIN WITH THE FRONT SO IT IS HARD
TO TELL EXACTLY HOW MUCH SMOKE WILL MAKE IT INTO WYOMING THIS
MORNING. HOPEFULLY THE MODELS ARE WRONG ABOUT SMOKE CONCENTRATION
AND A LOT OF THAT SMOKE WAS SCRUBBED OUT BY THE RAIN ALONG WITH
THE FRONT TO OUR NORTH. WE ARE NOT EXPECTING MUCH RAIN WITH THE
FRONT IN WYOMING HOWEVER AS MUCH OF THE MOISTURE REMAINS ALOFT.

THE FRONT WILL ALSO BRING SOME INCREASED CLOUD COVER TO AREAS ALONG
AND EAST OF THE DIVIDE THAT WILL LIKELY HOLD TEMPERATURES DOWN
THROUGH THE DAY WITH HIGHS PROJECTED IN THE 60S TO NEAR 70 ACROSS
THE CENTRAL BASINS.

CLEARING AND COOL CONDITIONS WILL FOLLOW TONIGHT WITH MOST LOWS IN
THE LOWER TO MID 40S WITH 30S IN THE WESTERN VALLEYS...SOME DEEPER
AND MORE SHELTERED VALLEYS ACROSS THE WEST COULD DIP INTO THE
UPPER 20S LATE TONIGHT INTO SUNDAY MORNING.

UPPER LEVEL HIGH PRESSURE STRENGTHENS OVER THE CENTRAL ROCKIES ON
SUNDAY. THE AIRMASS WILL ONCE AGAIN BE DRY ON SUNDAY WITH SOME
BREEZY AREAS POSSIBLE ACROSS THE SOUTH AND IN THE MOUNTAINS...BUT
GUSTS ARE EXPECTED TO REMAIN IN THE LOW 20 MPH RANGE.

ON MONDAY...SOME MID LEVEL MOISTURE ROTATES AROUND THE PERIPHERY OF
THE HIGH CENTERED TO OUR SOUTH. THERE WILL ALSO BE A WEAK
DISTURBANCE TRAVELING ALONG WITH THIS MOISTURE SO SOME POPS WERE
ADDED TO THE WESTERN MOUNTAINS FOR MONDAY. LOW LEVEL MOISTURE AND
INSTABILITY LOOK TO BE LIMITED HOWEVER SO NO WIDESPREAD
THUNDERSTORMS ARE EXPECTED BUT ISOLATED DRY THUNDER IS POSSIBLE WITH
STRONG DOWNBURST WINDS POSSIBLE IN THE AFTERNOON...WHICH COULD
GENERATE SOME NEW WILDFIRE ACTIVITY. WE WILL CERTAINLY KEEP AN EYE
ON IT.

.LONG TERM...TUESDAY THROUGH SATURDAY

SYNOPSIS...AN UPPER RIDGE WILL PERSIST ACROSS THE REGION THROUGH THE
PERIOD.  AN UPPER LEVEL DISTURBANCE ROTATING THROUGH THE RIDGE
ACROSS THE AREA WEDNESDAY/WEDNESDAY NIGHT WILL BRING CHANCES OF
SHOWERS AND THUNDERSTORMS TO MAINLY SOUTH AND CENTRAL
AREAS...OTHERWISE LATE DAY THUNDERSTORMS ARE EXPECTED TO BE ISOLATED
AND MAINLY OVER AND NEAR THE MOUNTAINS.

DISCUSSION...MEDIUM RANGE GLOBAL MODELS ARE IN GOOD OVERALL
AGREEMENT THOUGH THE PERIOD WITH AN AMPLIFIED PATTERN CONSISTING OF
AN UPPER TROUGH OFF THE WEST COAST...UPPER RIDGE ACROSS THE ROCKIES
AND UPPER TROUGH ACROSS THE EASTERN U.S. PERSISTING THROUGH THE
EXTENDED PERIOD.  MODELS HAVE ALL TRENDED AWAY FROM ANY SIGNIFICANT
PROGRESSION OF THIS OVERALL PATTERN...AND ARE NOW SHOWING A SLIGHT
RETROGRESSION OF THE TROUGH/RIDGE PATTERN OVER THE EASTERN
PACIFIC...WESTERN U.S. LATE IN THE PERIOD.

TUESDAY WILL LIKELY BE THE WARMEST DAY IN THE UPCOMING WEEK WITH H7
TEMPERATURES 17-18C PUSHING UP FROM THE SOUTH RESULTING IN
TEMPERATURES IN THE LOWER TO MID 90S ACROSS THE CENTRAL BASINS.
SOME MID AND HIGH LEVEL MOISTURE MAY RESULT IN A FEW HIGH-BASED
THUNDERSTORMS BLOSSOMING OVER THE WESTERN MOUNTAINS IN THE
AFTERNOON.

WEDNESDAY AND THURSDAY...GFS AND ECMWF CONTINUE TO CLOSE THE GAP
WITH TIMING ISSUES INVOLVING UPPER LEVEL DISTURBANCE LIFTING NORTH
OUT OF NORTHERN MEXICO ACROSS THE GREAT BASIN...BEFORE TURNING EAST
ACROSS WYOMING MID-WEEK.  CONSENSUS SOLUTION WOULD TRACK THIS SYSTEM
INTO SW WYOMING WEDNESDAY AFTERNOON WITH SYSTEM DECELERATING AS IT
TURNS EAST OVER TOP OF RIDGE ACROSS SOUTH CENTRAL...SE WYOMING
WEDNESDAY NIGHT INTO THURSDAY MORNING. NO SIGNIFICANT CHANGES WERE
MADE TO GOING FORECAST OF SPREADING ISOLATED THUNDERSTORMS INTO
THE SW WEDNESDAY MORNING WITH SHOWERS AND THUNDERSTORMS BECOMING
MORE NUMEROUS ACROSS THE SOUTH WEDNESDAY AFTERNOON/EVENING.
THUNDERSTORM COVERAGE WILL BE MOSTLY ISOLATED ACROSS THE NORTH.
RIDGE AXIS IS FORECAST TO SHIFT WEST OF THE DIVIDE BEHIND THIS
SYSTEM ON THURSDAY WITH NW FLOW OVER THE AREA KEEPING TEMPERATURES
CLOSER TO SEASONAL NORMALS. SLIGHT CHANCES OF THUNDERSTORMS WILL
LINGER OVER THE SOUTH AND WEST ON THURSDAY.

FRIDAY AND SATURDAY...SLIGHTLY ABOVE NORMAL TEMPERATURES ARE
EXPECTED UNDER UPPER LEVEL RIDGE.  FORECAST LEANS AWAY FROM SPECIFIC
RIPPLES IN NW FLOW ADVERTISED BY DETERMINISTIC RUNS AS ENSEMBLE
MEANS DO NOT SHOW THE SAME DEGREE OF RETROGRESSION OF LONGWAVE
PATTERN ACROSS THE WESTERN U.S. AND EASTERN PACIFIC.

&&

.AVIATION.../18Z ISSUANCE/

THE COLD FRONT HAS PUSHED SOUTHWEST TO ABOUT THE CONTINENTAL DIVIDE
AND WILL LIE ALONG THE CONTINENTAL DIVIDE THIS AFTERNOON THROUGH
00Z. MOST TERMINALS EAST OF THE DIVIDE WILL KEEP A NORTHEAST WIND
THAT WILL DECREASE DURING THE DAY...THEN BECOME LIGHT BY SUNSET.
AREAS WEST OF THE DIVIDE WILL SEE A GUSTY WIND AS WELL THROUGH THE
DAY TODAY...DECREASING AROUND SUNSET. THE FRONT WILL PUSH WESTWARD
INTO SOUTHWEST WY INCLUDING KRKS AIRPORT AROUND 03Z AND TO KEMMERER
BY 07Z SUNDAY. AREAS OF SMOKE WILL BE OBSERVED IN SOME LOCATIONS
WITH LOCAL VSBY DOWN TO 5 MILES EARLY THIS AFTERNOON BEFORE
CONDITIONS IMPROVE LATER THIS AFTERNOON AS THE FRONTAL
INVERSION DISSIPATES.

&&

.FIRE WEATHER...

..RED FLAG CONDITIONS EXPECTED ACROSS THE SOUTHWEST TODAY...

A DRY COLD FRONT CONTINUES TO MARCH SOUTH THIS MORNING...IT WILL
BECOME HUNG UP ALONG THE DIVIDE BY LATE MORNING WITH RED FLAG
CONDITIONS EXPECTED TO RETURN ACROSS PORTIONS OF TETON AND RAWLINS
DISPATCH. RELATIVE HUMIDITY WILL BE AROUND 10 PERCENT THIS AFTERNOON
WITH WIND SPEEDS AROUND 20 TO 30 MPH SOUTH OF THE FRONT. ALONG AND
EAST OF THE DIVIDE...IT WILL BE MUCH COOLER WITH MANY AREAS
STRUGGLING TO REACH 70 DEGREES WITH INCREASED CLOUD COVER AND
RELATIVE HUMIDITY. HIGH PRESSURE THEN BUILDS ON SUNDAY WITH LIGHTER
WINDS. A WEAK DISTURBANCE COULD SWING THROUGH ON MONDAY WITH SOME
MID LEVEL MOISTURE AND INSTABILITY POSSIBLY KICKING OFF A FEW DRY
THUNDERSTORMS IN THE WESTERN AND CENTRAL MOUNTAINS MONDAY AFTERNOON.
THIS ACTIVITY IS LOOKING RATHER SPARSE AND WEAK AT THIS TIME BUT IT
WILL BE WATCHED.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR WYZ277-279-414.

RED FLAG WARNING UNTIL 6 AM MDT EARLY THIS MORNING FOR WYZ280-
283-285-287>289-300.

RED FLAG WARNING UNTIL 3 AM MDT EARLY THIS MORNING FOR WYZ275-
276-281-282-415-416.

&&

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...AR/LIPSON
 FIRE WEATHER...ALLEN



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