000
FXUS65 KRIW 181700
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1100 AM MDT TUE JUN 18 2013

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

AN UPPER LEVEL TROUGH OFF THE PACNW COAST FINALLY MAKES SOME
PROGRESS INLAND TODAY...WORKING TO BREAK DOWN THE RIDGE ACROSS THE
CENTRAL ROCKIES. LOW LEVEL UPSLOPE FLOW INCREASES AHEAD OF THIS
SYSTEM...MAINTAINING THE MOISTURE FEED EAST OF THE DIVIDE AND
INCREASING THE EFFECTIVE SHEAR NEEDED TO MAINTAIN AN UPDRAFT. STEEP
MID LEVEL LAPSE RATES AGAIN COMBINE WITH THE FAVORABLE SURFACE FLOW
AND AN UPPER LEVEL DISTURBANCE...THAT MOVES THROUGH CENTRAL WYOMING
FAIRLY EARLY AND THEN OFF TO THE NORTH AND EAST LATER IN THE
AFTERNOON...AS WILL THE FOCUS OF THE ACTIVITY. A FEW OF THESE STORMS
COULD POSSIBLY BECOME SEVERE LATE IN THE AFTERNOON WHERE THE
INGREDIENTS COME TOGETHER MOST FAVORABLY ALONG THE I25 CORRIDOR.

SOUTHWEST FLOW INCREASES AHEAD OF THE PACNW TROUGH AS IT MOVES
FURTHER INLAND. VERY HOT DRY AIR WILL OVERSPREAD THE REGION WITH
FREQUENT GUSTS OVER 25 MPH EXPECTED FOR WEDNESDAY...THERE WILL BE
VERY LITTLE CHANCE OF A THUNDERSTORM IN AIR THIS DRY. VEGETATION
ACROSS EASTERN PORTIONS OF THE CWA IS BEGINNING TO CURE AND BECOME
MORE RECEPTIVE TO FIRE...THEREFORE A FIRE WEATHER WATCH HAS BEEN
ISSUED FOR HOT...DRY...WINDY AND UNSTABLE CONDITIONS ON WEDNESDAY. A
COLD FRONT ASSOCIATED WITH THE UPPER LOW FINALLY MOVES INTO THE WEST
LATE ON WEDNESDAY...COOLING THE AIRMASS AND PROVIDING GOOD RH
RECOVERY IN THE WESTERN MOUNTAINS...RH RECOVERY EAST OF THE DIVIDE
WILL LIKELY BE VERY POOR AHEAD OF THE FRONT AND THE FRONTAL PASSAGE
WILL PRODUCE A SUDDEN WIND SHIFT AND NO PRECIPITATION. IF ANY
SMOLDERING FIRES ARE STARTED BY THE LIGHTNING EXPECTED THIS
AFTERNOON...THEY WILL CERTAINLY SHOW THEMSELVES ON WEDNESDAY.

THE FIRST DAY OF SUMMER WILL ACTUALLY BE A BIT COOLER THAN THE LAST
DAY OF SPRING AS THE COOLER AIR ASSOCIATED WITH THE UPPER LOW MOVES
INTO THE REGION. HOWEVER...DRY SOUTHWEST FLOW WILL MAINTAIN A SUNNY
SKY AND NEAR NORMAL TEMPERATURES IN SPITE OF THE COLD FRONT. GUSTY
SOUTHWEST WINDS COULD AGAIN RAISE FIRE WEATHER CONCERN ACROSS THE
SOUTHEASTERN PORTIONS OF THE CWA...HOWEVER THE EVENT LOOKS TO BE
VERY MARGINAL AS WINDS MEETING CRITERIA WILL BE VERY LOCALIZED.

.LONG TERM...FRIDAY THROUGH TUESDAY

UPPER LOW TO DRIFT SLOWLY EAST ACROSS NORTHERN MONTANA FRIDAY AND
SATURDAY AND LIFT INTO SOUTH CENTRAL CANADA SUNDAY AND MONDAY.  UPPER
HIGH OVER THE SOUTHERN PLAINS WILL RETROGRADE AND PHASE WITH THE
RIDGE OVER THE CANADIAN ROCKIES MONDAY AND TUESDAY PER THE ECMWF.
GFS SHOWS LESS PHASING WITH ENERGY FROM UPPER LOW IN THE NE PACIFIC
PUSHING ACROSS THE NORTHERN ROCKIES...OR MORE OF THE SAME.
HOWEVER...AS WE GET FURTHER INTO SUMMER...THIS FAVORS THE UPPER HIGH
SETTING UP FURTHER WEST AS ADVERTISED BY ECMWF OVER THE LAST SEVERAL
RUNS.

FRIDAY THROUGH THE WEEKEND...TEMPERATURES WILL BE COOLER...CLOSE TO
NORMAL ACROSS NORTHERN WYOMING BEHIND A COLD FRONT THAT WILL BECOME
QUASI-STATIONARY.  SOME MOISTURE AND INSTABILITY WILL LIE TO THE
NORTH OF THE FRONT FOR MAINLY ISOLATED LATE DAY THUNDERSTORMS.
DRIER AND WARMER CONDITIONS WILL PREVAIL ACROSS THE CENTRAL AND
SOUTH AFTERNOON W-SW BREEZES KICKING UP IN THE AFTERNOON.

A WARMING TREND IS EXPECTED MONDAY AND TUESDAY WITH HIGHS IN THE
LOWER CENTRAL BASINS PUSHING PAST 90F ON TUESDAY AFTERNOON.
MOISTURE AND SLIGHT INSTABILITY WILL REMAIN ACROSS THE NORTH...AND
POSSIBLY FURTHER SOUTH DOWN THE INTERSTATE 25 CORRIDOR WHERE A FEW
LATE DAY THUNDERSTORMS WILL BLOSSOM IN THE AFTERNOON/EVENING.

&&

.AVIATION.../18Z ISSUANCE/

WEATHER STORY THIS AFTERNOON AND EARLY EVENING WILL BE SCATTERED
STRONG THUNDERSTORMS FROM EASTERN BIG HORN COUNTY INTO JOHNSON
COUNTY. NATRONA COUNTY WILL ALSO HAVE A FEW STRONG STORMS WITH HIGH
CLOUD TOPS. ADDITIONALLY...GUSTY WIND AND HEAVY RAIN WITH THESE
STORMS COULD RESULT IN BRIEF IFR CONDITIONS. AGAIN...THIS ACTIVITY
SHOULD BE EAST OF A WORLAND-THERMOPOLIS-RIVERTON LINE THIS AFTERNOON.

OTHERWISE...VFR CONDITIONS WILL OCCUR TODAY THROUGH TONIGHT. A FEW
LINGERING SHOWERS OR THUNDERSTORMS ARE POSSIBLE UNTIL MID EVENING...
THEN THE SKY WILL CLEAR OVER WEST CENTRAL WYOMING TONIGHT.

&&

.FIRE WEATHER...

..FIRE WEATHER WATCH FOR CASPER DISPATCH ON WEDNESDAY...

IT WILL BE QUITE UNSTABLE THIS AFTERNOON AND EVENING AS AN UPPER
LEVEL DISTURBANCE MOVES THROUGH...INCREASING THE LAL WHERE AN
ADEQUATE MOISTURE SUPPLY EXISTS...ALONG AND EAST OF THE
DIVIDE...WHILE AREAS ACROSS THE SOUTH AND WEST WILL BE TOO DRY FOR
STORMS BUT WILL ALSO BE UNSTABLE...RESULTING IN A HAINES INDEX OF 6
FOR THE DAY. AN UPPER LOW APPROACHES FROM THE WEST ON
WEDNESDAY...INCREASING SOUTHWEST FLOW AHEAD OF IT...RAISING CONCERN
FOR AREAS WITH CRITICAL FUELS. A FIRE WEATHER WATCH HAS BEEN ISSUED
FOR THE CASPER DISPATCH ZONES. THESE CONDITIONS WILL ALSO BE PRESENT
ACROSS RAWLINS AND CODY DISPATCH WHERE FUELS ARE A LITTLE LESS
CRITICAL...NO WATCH FOR THESE AREAS BUT THE WIDESPREAD
HOT...DRY...WINDY AND UNSTABLE CONDITIONS WILL STILL RAISE SOME
CONCERN. IN ADDITION...A DRY COLD FRONT WILL APPROACH THE WEST LATE
WEDNESDAY...IT WILL MOVE EAST THROUGH EARLY THURSDAY. CONTINUED DRY
AND BREEZY CONDITIONS EXPECTED ON THURSDAY...BUT MORE MARGINAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
EVENING WYZ280-281-285-300.

&&

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...KPL
FIRE WEATHER...ALLEN