Special Weather Statement, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1120 AM MDT WED JUL 11 2012

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

AN UPPER LEVEL HIGH OVER THE GREAT BASIN WILL BE BROKEN DOWN BY A
SHORT WAVE MOVING ALONG ITS PERIPHERY THIS AFTERNOON. THIS SHORT
WAVE ALONG WITH AMPLE MID LEVEL MOISTURE WILL PROVIDE THE
NECESSARY INGREDIENTS FOR THUNDERSTORM FORMATION AGAIN THIS
AFTERNOON AND EVENING. THERE WILL BE PLENTY OF ADDITIONAL SUPPORT
AS A WEAK...BUT PRESENT 55KT JET NOSES INTO THE NORTHWEST. SHARP
INVERTED V SOUNDINGS ADVERTISE THUNDERSTORM BASES AT 10 TO 15K FT
WITH DAMAGING DOWNBURST WINDS AND FREQUENT LIGHTING AS THE PRIMARY
THREATS. THERE WERE A FEW GUSTS IN EXCESS OF 75MPH OBSERVED WITH
THE STORMS ON TUESDAY...BOUNDARY LAYER CONDITIONS WILL BE SIMILAR
TODAY BUT THE INCREASED SUPPORT ALOFT WILL ENCOURAGE A GREATER
NUMBER OF STORMS TO FORM...SO MORE STRONG 70MPH AND HIGHER GUSTS
ARE EXPECTED WITH SOME OF THE STRONGER STORMS AGAIN TODAY. AN
INCREASE IN PWAT WILL LEAD TO MIXED WET AND DRY STORMS WITH MORE
OF THE WET THUNDERSTORMS EXPECTED OVER THE HIGHER TERRAIN. IN
ADDITION...STORM MOTION WILL BE A BIT FASTER TODAY SO THESE STORMS
WILL NOT SIT IN THE SAME SPOT FOR TOO LONG WHICH WILL PREVENT ANY
ONE SPOT FROM RECEIVING A GOOD SOAKING...ALSO THE INCREASED MID
LEVEL FLOW WILL BRING MORE STORMS OFF THE STORM INITIATION
FACTORY THAT IS THE HIGHER TERRAIN INTO THE FOOTHILLS AND BASINS.
A RED FLAG WARNING FOR DRY THUNDERSTORMS HAS BEEN ISSUED FOR THE
ENTIRE AREA...AS THE ENTIRE REGION IS THREATENED EQUALLY TODAY.

A FEW VORTICITY MAXIMA TRAVELLING WITH THE BACK END OF THE UPPER
LEVEL DISTURBANCE WILL STILL HANG AROUND THROUGH 06Z THU...
COMBINED WITH COOLING AT THE MID LEVELS...ESPECIALLY ACROSS THE
NORTH WILL KEEP A FEW STORMS GOING INTO THE NIGHT.

HEIGHTS REBUILD ON THURSDAY AND WARMING ALOFT WILL STABILIZE THE
ATMOSPHERE...BUT STRONG SURFACE HEATING COULD DESTABILIZE THE
ATMOSPHERE JUST ENOUGH TO CAUSE SOME CU DEVELOPMENT OVER THE
HIGHER ELEVATIONS...PRODUCING A FEW SPRINKLES BUT A FLASH OR TWO
OF LIGHTNING CANNOT BE RULED OUT AS HEIGHTS ARE SLOW TO REBUILD.

THE UPPER LEVEL HIGH SHIFTS EASTWARD ON FRIDAY...POSSIBLY ALLOWING
ANOTHER WEAK DISTURBANCE INTO THE WEST...ALONG WITH ANOTHER PUSH
OF MOISTURE. IN ADDITION...COOLING ALOFT WILL STEEPEN LAPSE RATES
ACROSS THE AREA...SO MORE THUNDERSTORMS ARE POSSIBLE BUT LOW LEVEL
MOISTURE WILL INCREASE...ESPECIALLY IN THE WEST SO HOPEFULLY MOST
OF THE STORMS WILL BE WET ON FRIDAY.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
SIGNIFICANT MONSOONAL SURGE STILL EXPECTED TO START THE MEDIUM
RANGE PERIOD. THE BIGGER QUESTION IS HOW LONG WILL IT LAST? THE
MODELS ARE STRUGGLING WITH THE ENERGY THAT DIVES SE THROUGH WRN
CANADA AND WHETHER IT WILL BE PROGRESSIVE OR NOT. YESTERDAY IT WAS
MAINLY THE GFS THAT KEPT ENERGY GENERALLY OVER THE PACNW THROUGH
THE PERIOD WHILE THE OTHERS KEPT IT WELL TO THE NORTH IN CANADA.
NOW MOST OF THE OTHER MODELS ARE DIVING ENERGY MUCH FURTHER SOUTH
ALBEIT WITH A MORE PROGRESSIVE SOLUTION. THE GFS WOULD MOST LIKELY
BE MORE FAVORABLE FOR AN EXTENDED PERIOD OF FAVORABLE MONSOONAL
FLOW FOR MOST OF THE MEDIUM RANGE PERIOD WHILE THE OTHERS BRIEFLY
TURN THE FLOW MORE WESTERLY AS AN UPPER LOW PASSES ACROSS FAR SRN
CANADA OR EVEN MONTANA. WILL HIT SATURDAY'S POPS THE HARDEST WITH
EXPECTED PW SURGE WELL OVER AN INCH CWA WIDE WITH AT LEAST
MODERATE CAPES AND SURFACE DEW POINTS AT LEAST IN THE 40S IF NOT
SOME 50S. AS LONG AS WE GET SOME SUNSHINE AND WARM INTO THE 80S
ACROSS THE LOWER ELEVATIONS...SATURDAY COULD BE QUITE ACTIVE WITH
SOME HEAVY RAIN PRODUCERS. WILL KEEP SCATTERED POPS GOING SUNDAY
ACROSS THE MOUNTAINS AND WEST BUT CONFIDENCE THAT WE'LL DRY AT ALL
AFTER ONLY ONE DAY IS LOW. MODEL BLEND SHOWS A SLIGHT DOWNWARD
TREND IN THUNDERSTORM COVERAGE INTO EARLY NEXT WEEK AND WILL LEAN
THAT WAY FOR NOW BUT A LOT WILL DEPEND ON HOW THE WRN CANADA
ENERGY EVOLVES AND HOW PROGRESSIVE IT IS. BOTH THE ECMWF AND GFS
SHOW ANOTHER POTENTIAL SURGE OF MOISTURE AND WWD PUSH OF LOW LEVEL
MOISTURE TUESDAY NIGHT INTO WEDNESDAY AS A NRN PLAINS HIGH
DEVELOPS AND FLOW ALOFT BACKS AGAIN. A WET DAY SATURDAY COULD ALSO
SET THE STAGE FOR MORE STORMS THE NEXT SEVERAL DAYS WITH ADDED
MOISTURE TO EVAPORATE AND KEEP THE BL MOISTURE LEVELS UP. A FULL
FLEDGED MONSOONAL SURGE IS DEFINITELY POISED TO MOVE INTO THE
DESERT SW BY FRIDAY MORNING SETTING THE STAGE FOR THE NWD PUSH TO
START THE PERIOD. I LEAN TOWARDS A COUPLE HIGH POPS DAYS OVER THE
WEEKEND...ESPECIALLY OVER AND NEAR THE MOUNTAINS WITH A POTENTIAL
DOWNSWING IN POPS MONDAY AND TUESDAY BEFORE INCREASING MIDWEEK BUT
A LOT WILL DEPEND ON HOW THE PATTERN EVOLVES IN RESPECT TO OUR
UPPER LOW THAT COULD BE ANYWHERE FROM THE PACNW TO MONTANA EARLY
NEXT WEEK.

&&

.AVIATION.../18Z ISSUANCE/

UPPER LEVEL HIGH PRESSURE WILL REMAIN OVER THE GREAT BASIN TODAY AS
A WEAK UPPER LEVEL DISTURBANCE ROTATES ACROSS THE NORTHERN ROCKIES
DURING MAXIMUM DAYTIME HEATING.  SCATTERED CONVECTION IS ALREADY
OCCURRING OVER NORTHERN AND WESTERN PORTIONS OF THE CWA...MAINLY
NEAR KCOD...KJAC AND KBPI. HIGH-BASED CONVECTION IS STILL EXPECTED
TO MOVE INTO THE CENTRAL BASINS PRIMARILY FROM 21Z-12/01Z.  THE MAIN
HAZARD WITH THESE STORMS WILL BE STRONG ERRATIC OUTFLOW WIND GUSTS
40-50KTS.  STORMS WILL BE MOST NUMEROUS VCNTY AND EAST OF THE DIVIDE
AND MORE ISOLATED VCNTY KJAC-KBPI-KPNA. CONVECTIVE OUTFLOWS WILL
INCREASINGLY DOMINATE THROUGH THE AFTERNOON AND EVENING WITH LIGHT
WINDS EXPECTED AFTER 3Z. LARGELY VFR CONDITIONS ARE EXPECTED FROM
LATE THIS EVENING INTO MOST OF THURSDAY.

&&

.FIRE WEATHER...

A RED FLAG WARNING CONTINUES FOR DRY THUNDERSTORMS ACROSS THE STATE.
SCATTERED TO WIDELY SCATTERED THUNDERSTORMS...MOST OF WHICH WILL BE
DRY WILL BE FOUND ACROSS WESTERN AND CENTRAL WYOMING THROUGH THE
NIGHT. THUNDERSTORMS ABOVE 8500 FEET WILL BE MIXED WET AND DRY WITH
RAINFALL OF UP TO ONE HALF OF AN INCH POSSIBLE. WITH THE THREAT OF
DRY LIGHTNING... CRITICALLY DRY FUELS... LOW HUMIDITY...AND SOME
GUSTY WIND...A RED FLAG WARNING IS IN EFFECT FOR THE AREA. PLEASE
VIEW OUR FIRE WEATHER PRODUCTS FOR ADDITIONAL INFORMATION. THE RIDGE
OF HIGH PRESSURE WILL CONTINUE TO LEAVE WARM TEMPERATURES...AND LOW
DAYTIME HUMIDITY ACROSS THE AREA THOUGH MUCH OF THE WEEK. MONSOONAL
MOISTURE WILL RETURN TO THE AREA BY THE WEEKEND...PROVIDING SOME
RELIEF FOR THE AREA.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL MIDNIGHT MDT TONIGHT
WYZ140-275>283-285>289-300-414>416.

&&

SHORT TERM...ALLEN
LONG TERM...SKRBAC
AVIATION...HATTINGS
FIRE WEATHER...ALLEN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
500 AM MDT WED JUL 11 2012

WYZ001>020-022>030-121200-
ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST-
BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS-
EAST SWEETWATER COUNTY-FLAMING GORGE-
GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS-
NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN-
NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS-
ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES-
SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN-
SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY-
TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN-
UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN-
WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST-
YELLOWSTONE NATIONAL PARK-
500 AM MDT WED JUL 11 2012

...RED FLAG WARNING IN EFFECT FOR DRY LIGHTNING AND LOW HUMIDITY
THROUGH MIDNIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO WIDELY SCATTERED THUNDERSTORMS OVER THE MOUNTAINS...
MOVING INTO THE FOOTHILLS IN THE LATE AFTERNOON TO EARLY EVENING
HOURS. SOME THUNDERSTORMS COULD PRODUCE DAMAGING WIND GUSTS IN
EXCESS OF 60 MPH WITH FREQUENT LIGHTNING AND VERY LITTLE RAIN.
STRONG THUNDERSTORM WIND GUSTS COULD COME SUDDENLY...PLEASE SECURE
LOOSE OBJECTS THAT MAY BE BLOWN AROUND BY THE WIND BEFORE THE
STORMS HIT...AND USE CAUTION WHEN TRAVELLING WITH LIGHT TRAILERS OR
IN HIGH PROFILE VEHICLES THIS AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THURSDAY...A SLIGHT CHANCE OF THUNDERSTORMS OVER THE MOUNTAINS WITH
GUSTY WINDS.

FRIDAY...A SLIGHT CHANCE OF THUNDERSTORMS ACROSS THE REGION.

SATURDAY AND SUNDAY...AN INCREASED CHANCE OF THUNDERSTORMS ACROSS
THE AREA AS MONSOONAL MOISTURE SURGES NORTHWARD.

MONDAY...A CHANCE OF MOUNTAIN THUNDERSTORMS CONTINUES WITH ISOLATED
THUNDERSTORMS ELSEWHERE.

TUESDAY...A CHANCE OF MOUNTAIN THUNDERSTORMS WITH ISOLATED LOWER
ELEVATIONS THUNDERSTORMS...MAINLY ACROSS THE NORTH.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT WIND DAMAGE AND ANY WIND GUSTS IN
EXCESS OF 50 MPH. THANK YOU.

TEAM RIVERTON

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