Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230509
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1107 PM MDT WED JUL 22 2015

UPDATE...ADDED 06Z AVIATION DISCUSSION

.SHORT TERM...TONIGHT THROUGH THURSDAY (ISSUED AT 314 PM MDT)

A SHORT WAVE ARRIVES IN THE SOUTHWEST FLOW WITH SUPPORT ALOFT FROM
THE RIGHT ENTRANCE REGION OF A JET STREAK IN WESTERN
MONTANA/NORTHERN IDAHO THIS EVENING. BROAD LIFT ASSOCIATED WITH AN
APPROACHING TROUGH AND A BROAD AREA OF QG FORCING WILL ALSO
ENCOURAGE UPWARD MOTION LATE THIS AFTERNOON AND TONIGHT.
ADDITIONALLY THERE WILL BE SOME ABNORMALLY HIGH MOISTURE IN THE AREA
AS TROPICAL MOISTURE STREAMS INTO OUR WESTERN MOUNTAINS...THAT
WILL CONTRIBUTE TO EFFICIENT RAINFALL FROM THE STRONGER STORMS AND
PROVIDE SOME FUEL FOR THUNDERSTORM DEVELOPMENT ON BOTH SIDES OF
THE DIVIDE. GENERALLY WE ARE EXPECTING ANYWHERE FROM ONE QUARTER
TO ONE HALF OF AN INCH ACROSS THE WESTERN MOUNTAINS WITH ANY OF
THE STRONGER STORMS CAPABLE OF PRODUCING AN INCH AND A HALF IN
LESS THAN AN HOUR...WHICH IN THE COMPLEX TERRAIN OF THE WEST COULD
INITIATE FLASH FLOODING...ESPECIALLY AS WE MOVE INTO THURSDAY AND
MORE RAIN FALLS OVER THE SAME AREAS.

EAST OF THE DIVIDE...MOST OF THE MOISTURE WILL REMAIN AT THE MID
LEVELS AND ABOVE SO THE PRIMARY THREAT WILL BE STRONG DOWNBURSTS IN
EXCESS OF 50MPH WITH THE MORE ORGANIZED CELLS. THERE WILL BE SOME
DECENT BULK SHEAR IN THE LOW TO MID LEVELS...SO A FEW OF THE MORE
ORGANIZED STORMS COULD HAVE SOME NICKEL SIZED HAIL OR LARGER.

ON THURSDAY ANOTHER JET STREAK MOVES UP FROM THE SW WITH A POSSIBLE
COUPLET FORMING OVER THE NORTHWEST AND NORTH FOR AIDED
THUNDERSTORM/HEAVY RAIN POTENTIAL. THE NORTHWEST LOOKS LIKE THE MOST
LIKELY AREA FOR STRONGER STORMS AND HEAVY RAIN BUT AREAS A LITTLE
FURTHER SOUTH WILL STILL HAVE TO BE WATCHED AND THUS THE WATCH FROM
THE SALT/WYOMING RANGE/UPPER GREEN UP TO YELLOWSTONE AND THE
ABSAROKAS EXTENDING THROUGH THURSDAY AFTERNOON AND INTO THE EVENING.
THE GRADIENT WILL INCREASE A BIT ON THURSDAY WITH STEADY 20 TO 30
MPH WIND EXPECTED THURSDAY AFTERNOON ALONG THE SOUTHERN WIND
CORRIDOR FROM ROCK SPRINGS TO CASPER. THE MOUNTAINS WILL SEE
INCREASING WIND THE NEXT COUPLE DAYS TOO.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

BEGINNING OF FCST...UPR LV SWRLY FLOW WITH EMBEDDED SW TROF MOVING
NEAR OR OVR NWRN WY W/ MODEST BUT DECREASING MID LVL MOISTURE ACROSS
THE NWRN HALF OF THE STATE. GENERALLY WIDELY SCATTERED STORMS
AROUND...MAINLY OVR THE W/NW AND NRN FA. SOUNDINGS SHOW LONG SKINNY
RELATIVELY LOW CAPE IN THIS AREA WITH LOTS OF SHEAR. STRONG TO
OCCASIONAL BORDERLINE SVR DOWNDRAFTS WITH SMALL HAIL POSSIBLE.
OTHERWISE...GUSTY WINDS ACROSS THE S/SERN ZONES SHOULD BE ON THE
DECREASE...SO BORDERLINE RED FLAG CONDITIONS...IF THEY EXISTED IN
THE AFTERNOON.

FRIDAY...UPR RIDGING BEGINNING WITH DECREASING MOISTURE THROUGHOUT
THE ATMOSPHERE...AND ISOLATED TO WIDELY SCATTERED STORMS OVR ROUGHLY
THE SAME AREA AS ON THURSDAY...JUST LESS OF THEM. AGAIN...LOW CAPE
AND HIGH SHEAR WITH GUSTY STRONG...ISOLATED SVR...WINDS POSSIBLE.

SATURDAY...DRY ACROSS MOST OF THE SRN CWA...ISOLATED TO WIDELY
SCATTERED STORMS W AND N...MAINLY MOUNTAINS. LOW CAPE AND DECREASING
SHEAR...WITH STRONGER STORMS SHOWING WITHIN THE FIRST HR OR SO OF
CI. GUSTY WINDS AGAIN THE MAIN THREAT.

SUNDAY THRU THE END OF THE FCST...MAINLY DRY FCST WITH A FEW
ISOLATED...MAINLY OROGRAPHICALLY DRIVEN...STORMS ACROSS THE NW AND N
FA. UPR LVL SW FLOW REMAIN UNTIL MON NIGHT ONWARD WHEN A STRONG UPR
TROF PASSES ACROSS THE NRN CONUS...FLATTENING THE FLOW AND PUSHING A
FRONT THRU THE REGION...DROPPING HIGH TEMPS TO JUST BELOW SEASONAL
THRU THE END OF THE FCST.

&&

.AVIATION.../06Z ISSUANCE/

AN UPPER LEVEL DISTURBANCE AND AN ASSOCIATED LINE OF SHOWERS AND
ISOLATED THUNDERSTORMS WILL CONTINUE TO LIFT ACROSS THE NORTHERN
THIRD OF WYOMING OVERNIGHT WITH MOST OF THIS ACTIVITY VCNTY AND WEST
OF A KCOD-KJAC LINE THROUGH 09Z BEFORE MOVING NORTH OF THE WYOMING
BORDER.  EXPECT LOCAL MVFR CONDITIONS AND OCNL MTN OBSCURATIONS
ACROSS THE NORTHWEST.  PARTIAL CLEARING BEHIND THIS SYSTEM WILL
LIKELY BRING PATCHY FOG AND PARTIAL TERRAIN OBSCURATIONS ACROSS THE
WESTERN VALLEYS THROUGH 15Z.

ON THURSDAY...SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP
VCNTY AND NORTH OF A KAFO-KBYG LINE IN THE AFTERNOON WITH A DRY
WESTERLY FLOW PREVAILING SOUTH OF THIS LINE.  THUNDERSTORMS WILL BE
MOST NUMEROUS AGAIN ACROSS THE NW OR VCNTY AND WEST OF A KCOD-KJAC
LINE WHERE BRIEF MVFR CONDITIONS AND HIGHER MTN OBSCURATIONS WILL
OCCUR IN THE AFTERNOON AND EVENING.  SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ARE LIKELY TO LINGER WEST OF THE DIVIDE OVERNIGHT
THURSDAY.

&&

.FIRE WEATHER...

AFTERNOON SHOWERS AND THUNDERSTORMS WILL REMAIN IN THE FORECAST FOR
TONIGHT AND TOMORROW. MAIN THREAT WITH THE STORMS EAST OF THE DIVIDE
WILL BE LIGHTNING AND STRONG WIND WHILE THE PRIMARY THREATS ACROSS
THE WEST WILL BE HEAVY RAIN AND HAIL.

A GUSTY 15 TO 30 MPH ACROSS THE WIND CORRIDOR BETWEEN ROCK SPRINGS
AND CASPER AS WELL AS OVER THE MOUNTAINS. THE GOOD NEWS IS THAT THE
RELATIVE HUMIDITY WILL BE MARGINAL IN AREAS WITH CRITICAL FUELS BUT
WITH WIND THAT STRONG AND PERSISTENT...THERE COULD BE SOME LOCAL
ISSUES SHOULD A FIRE START AND GET INTO CERTAIN FINER FUELS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH THURSDAY EVENING FOR WYZ001-002-012-
013-023>026.

&&

$$

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



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