Severe Thunderstorm Warning 71, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
126 PM MDT FRI AUG 7 2009

.SHORT TERM...TONIGHT THROUGH MONDAY
AIRMASS IS DRYING QUICKLY ACROSS THE SERN ZONES WITH SURFACE
DEW POINTS PLUNGING INTO THE 20S ENDING. FARTHER NORTH...THE DEW
POINTS ARE IN THE MID 50S TO AROUND 60 WITH ONLY TEMPS HOLDING
SERIOUS CONVECTION FROM STARTING. LAPS ANALYSIS DOES SHOW THE CAP
THINNING ACROSS THE BASIN WITH NO CAP AROUND CODY OR COWLEY.
SOMEWHAT OF A BALANCING ACT WITH COOLER AIR COMING IN ON NLY FLOW
THROUGH THE EVENING. HOWEVER WITH THE JET STREAK MOVING UP FROM
THE SOUTH AND INTERACTING WITH THIS AREA AROUND 00Z...SEVERE
WEATHER MAY BREAK OUT. UPDATED THE ENTIRE NORTH TO A SEVERE RISK
THIS MORNING AND A POTENTIAL WATCH IS FORTH COMING. EVEN JOHNSON
COUNTY IS FINALLY STARTING TO WARM WITH CAPES UP TO 2000 J/KG
AROUND BYG AND ONLY A SMALL CIN TO ERODE. WIND RIVER BASIN IS ALSO
POTENTIALLY INTERESTING AS COLD FRONT MOVES THROUGH THIS EVENING
AND INTERACTS WITH INCREASING QG FORCING AND UPPER JET SUPPORT.
MOISTURE LEVELS INCREASE RAPIDLY THIS EVENING WITH FROPA BUT TEMPS
ALSO DROP. STRONG DYNAMICS COULD OVERCOME THE COOLER TEMPS. UPPER
LOW CONTINUES TO SLOW AND NOW LOOKS LIKE IT WONT MOVE THROUGH
UNTIL SATURDAY NIGHT INTO SUNDAY MORNING. FURTHER SOUTH TRACK WILL
ALSO ENHANCE PCPN CHANCES ACROSS AREAS NORTH OF TRACK AND HAVE
INCREASED POPS CONSIDERABLY FOR MUCH OF THE AREA FOR SATURDAY AND
SATURDAY NIGHT. COLD CORE IS EXPECTED TO MOVE ACROSS THE SOUTHWEST
SATURDAY EVENING AND INTO THE WINDS...NRN RED DESERT LATE SATURDAY
NIGHT WITH -15C H5 AIR AND NEAR 0C TEMPS AT H7. HAVE INDICATED
SOME ACCUMULATION AS LOW AS 8K FEET IN THE NW MTNS AND 9K FEET IN
THE WINDS. COULD SEE AN INCH OR TWO IN THE IN THE FIRST 1K AND 2
TO 4 INCHES ABOVE THAT. TROUGH MAY LINGER INTO SUNDAY MORNING WITH
SOME SHOWERS IN THE FAR EAST...OTHERWISE IT SHOULD BE A DRIER
PERIODS LATER SUNDAY AND MONDAY WITH WARMING TEMPERATURES.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
MEDIUM RANGE MODELS SHOW WESTERLY FLOW AT THE BEGINNING OF THE
EXTENDED...WITH RIDGING DEVELOPING BY THURSDAY AND FRIDAY. THE MAIN
UPPER JET IS PROJECTED TO BE ACROSS SOUTHERN CANADA DURING THE
EXTENDED.  00Z GFS IS SHOWING MARGINAL MOISTURE...GENERALLY 0.50 OR
LESS OF PRECIPITABLE WATER...AND RELATIVELY STABLE ATMOSPHERE FOR
THE EXTENDED.  THEREFORE...WILL KEEP THE EXTENDED MAINLY DRY WITH
ONLY ISOLATED AFTERNOON/EVENING CONVECTION OVER THE HIGHER TERRAIN.
00Z GFS AND ECMWF SHOW A SHORTWAVE MOVING THROUGH THE AREA
MONDAY...BUT WITH LIMITED MOISTURE WILL KEEP THE LOWER ELEVATIONS
DRY FOR NOW. BY THURSDAY/FRIDAY...MONSOONAL MOISTURE FROM THE FOUR CORNERS
RIDGE COULD BE SURGING NORTHWARD INTO THE AREA. WILL WAIT TO SEE
MORE CONSISTENCY IN THIS SCENARIO...BEFORE PUTTING WIDESPREAD POPS
ACROSS THE AREA. TEMPERATURES ARE EXPECTED TO HAVE A GRADUAL
WARMING TREND TO SLIGHTLY ABOVE AVERAGE TEMPS WEDNESDAY THROUGH
FRIDAY...AS THE RIDGE BEGINS TO BUILD OVER THE AREA.

&&

.AVIATION...
AS A STRONG UPPER LEVEL WEATHER DISTURBANCE TRACKS NORTHEAST THROUGH
A VERY UNSTABLE AIRMASS ACROSS WYOMING AHEAD OF AN APPROACHING LOW
PRESSURE CENTER IN NORTHERN CALIFORNIA... THERE IS THE POTENTIAL FOR
STRONG THUNDERSTORMS TO DEVELOP ACROSS MUCH OF THE AREA THIS
EVENING...ESPECIALLY ACROSS WESTERN...NORTHERN AND SOUTHERN WYOMING.
MANY OF THESE STORMS WILL LIKELY CONTAIN HAIL...LOCALLY HEAVY
RAINFALL AND GUSTY 40 TO 50 MPH WINDS. KRIW AND KLND ARE THE LEAST
LIKELY SITES TO EXPERIENCE THESE CONDITIONS...HOWEVER ALL THE ALL
TAF SITES HAVE THE POTENTIAL TO EXPERIENCE THESE STRONGER STORMS.
THESE STORMS WILL LIKELY PRODUCE WIDELY SCATTERED IFR CONDITIONS AND
SCATTERED MVFR CONDITIONS AS WELL AS MOUNTAIN OBSCURATIONS. THESE
SHOWERS WILL LINGER PAST MIDNIGHT BUT GRADUALLY DECREASE IN
INTENSITY AFTER MIDNIGHT AS THEY SLOWLY EXIT TO THE EAST. AS THE
TROUGH OF LOW PRESSURE ASSOCIATED WITH THE APPROACHING
AFOREMENTIONED LOW PRESSURE CENTER APPROACHES WYOMING...NUMEROUS
SHOWERS AND THUNDERSTORMS WILL OCCUR ACROSS WESTERN AND NORTHERN
WYOMING FRIDAY ALONG WITH ISOLATED TO WIDELY SCATTERED COVERAGE
ELSEWHERE. ANY SHOWER ACTIVITY AFTER MIDNIGHT TONIGHT WILL LIKELY
CREATE ISOLATED IFR CONDITIONS AND WIDELY SCATTERED MVFR CONDITIONS
ALONG WITH SOME MOUNTAIN OBSCURATIONS.

&&

.FIRE WEATHER...
AN UNSEASONABLY STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL SPIN
AROUND IDAHO THROUGH SATURDAY MORNING BEFORE GRADUALLY MOVING INTO
SOUTHWEST WYOMING THIS AFTERNOON AND ACROSS CENTRAL WYOMING
SATURDAY NIGHT. A DRY SOUTHWEST WIND ACROSS THE SOUTHEASTERN ZONES
WILL MEET A COLD FRONT MOVING SOUTH FROM THE BIG HORN BASIN AND
JOHNSON COUNTY THIS EVENING FOR ANOTHER ROUND OF SHOWERS AND
THUNDERSTORMS. ANOTHER FRONT WILL ALSO MOVE FROM WESTERN WYOMING
INTO CENTRAL WYOMING THIS EVENING WITH NUMEROUS MOUNTAIN SHOWERS
AND SOME THUNDERSTORMS. A FEW STORMS COULD BE SEVERE ACROSS THE
NORTH END OF THE DISTRICT THROUGH THIS EVENING. MUCH COOLER AIR
WILL BE USHERED IN TONIGHT AND SATURDAY WITH THE SNOW LEVEL
LOWERING TO 8000 FEET IN NORTHWEST MOUNTAINS AND 9000 FEET IN THE
WIND RIVER MOUNTAINS. SOME ACCUMULATION IS EXPECTED...ESPECIALLY
ABOVE 9000 TO 10000 FEET. SHOWERS AND SOME THUNDERSTORMS WILL BE
QUITE NUMEROUS ACROSS MUCH OF THE AREA SATURDAY INTO SATURDAY NIGHT.
THE FAR SOUTH WILL LIKELY SEE THE LEAST AMOUNT OF SHOWERS. SUNDAY AND
MONDAY WILL SEE A WARMING TREND WITH LITTLE OR NO CHANCE OF
PRECIPITATION.

&&

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

&&

SHORT TERM...SKRBAC
LONG TERM...WM
AVIATION...LIPSON
FIRE WEATHER...SKRBAC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
652 PM MDT FRI AUG 7 2009

WYZ001>020-022>030-081200-
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-
652 PM MDT FRI AUG 7 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED ACROSS WESTERN AND
CENTRAL WYOMING THIS EVENING AND OVERNIGHT. SOME THUNDERSTORMS MAY BE
STRONG IN NORTHERN WYOMING...WITH GUSTY WIND TO 45 MPH...SMALL HAIL
AND BRIEF HEAVY RAIN.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

AN UNSTABLE AIRMASS OVER THE REGION SATURDAY WILL ALLOW FOR A
CONTINUED CHANCE OF SHOWERS AND THUNDERSTORMS. COOLER AND DRIER AIR
WILL FOLLOW SUNDAY. SNOW IS ALSO EXPECTED OVER THE NORTHWEST
MOUNTAINS FRIDAY NIGHT AND SATURDAY WITH THE SNOW LEVEL BETWEEN 8500
AND 9500 FEET. SEVERAL INCHES OF SNOW IS EXPECTED ABOVE 9000 TO 10000
FEET.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO REPORT HAIL AND WIND GUSTS IN EXCESS OF 40 MPH
FROM THUNDERSTORMS. THANK YOU.

TEAM RIVERTON

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