Severe Thunderstorm Warning 3, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
513 AM MDT WED JUN 16 2010

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
A VIGOROUS SHORTWAVE WITH A CIRCULATION OVER THE PACIFIC NORTHWEST
WILL TRACK TOWARD WYOMING TODAY. A STRONG LINE OF THUNDERSTORMS
ARE EXPECTED TO DEVELOP OUT AHEAD OF THIS FRONT TODAY WITH SMALL
HAIL AND STRONG GUSTY WINDS. THE SHOWERS AND THUNDERSTORMS WILL TRACK
TO EASTERN ZONES LATER THIS EVENING LEAVING BEHIND STRATIFORM
PRECIP ACROSS THE WESTERN HALF OF WYOMING TONIGHT. THIS PRECIP
WILL BE A REFLECTION OF THE STRONG QG FORCING OF -40KM^2/1E16S
ASSOCIATED WITH THE STRONG UPPER LOW FORECAST TO TRACK RIGHT
ACROSS CENTRAL WYOMING TONIGHT. IN ADDITION...A STRONG WESTERLY
GRADIENT WILL OCCUR ALONG AND BEHIND THE NEGATIVELY TILTED TROUGH
AXIS WHICH WILL ENHANCE A MOIST WESTERLY UPSLOPE FLOW WHICH WILL
HELP AMPLIFY PRECIP WEST OF THE DIVIDE. WEST WINDS WILL BE STRONG
ENOUGH TO SPILL MUCH OF THE PRECIP OVER TO THE UPPER EAST SLOPES.
PORTLAND OREGON REPORTED H7 TEMPS OF -10C LAST EVENING SO IT IS
CONCEIVABLE THAT THE GFS IS CORRECT IN DROPPING H7 TEMPS TO -7
ACROSS WESTERN WY BY 12Z THU. THIS WILL RESULT IN 3 TO 6 INCHES OF
SNOWFALL ACROSS THE WESTERN AND NORTHERN MTNS AS WELL AS THE WIND
RIVER MTNS. LATER SHIFTS MAY WANT TO CONSIDER ISSUING A WINTER
WEATHER ADVISORY FOR THESE MOUNTAINS ZONES CONSIDERING THE VOLUME
OF TOURISTS IN THESE AREAS FOR THIS TIME OF YEAR. SNOW LEVELS
COULD EVEN DROP TO BETWEEN 6500 AND 7K EAST OF THE DIVIDE WHERE
LIGHT SNOW IS POSSIBLE. PRECIP SHOULD BE ALL SNOW WEST OF THE
DIVIDE BY 12Z THU.

5 H7 ISOHYPSE ARE PROGGED OVER WY THURSDAY. MOS GUIDANCE IS
INDICATING 39 MPH SUSTAINED WINDS FOR CPR THU. HAVE ELECTED TO
ISSUE A HIGH WIND WATCH FROM EASTERN SWEETWATER COUNTY TO CASPER
FROM 12Z THURSDAY TO 21Z THU. THIS TYPE OF RELATIVELY FAST MOVING
FAST MOVING TIGHTLY WRAPPED SHORTWAVE TYPICALLY PRODUCES THESE
TYPE OF STRONG GRADIENT WINDS.

A QUICK REBOUND IN TEMPS IS EXPECTED FRIDAY WHEN H7 TEMPS CLIMB
BACK TO 13C IN SOUTHERN WY.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
SOUTHWEST FLOW ALOFT TO PREVAIL OVER THE AREA THROUGH THE PERIOD
WITH CHANCES FOR AFTERNOON AND EVENING THUNDERSTORMS MAINLY ALONG
AND NORTH OF A FRONTAL BOUNDARY ACROSS NORTHERN WYOMING.
TEMPERATURES ARE EXPECTED TO BE NEAR OR SLIGHTLY ABOVE SEASONAL
NORMALS THROUGH THE PERIOD.

MEDIUM-RANGE GLOBAL MODELS IN OVERALL GOOD AGREEMENT THIS MORNING
WITH MEAN UPPER TROUGH OVER THE INTERMOUNTAIN WEST...A STRONG RIDGE
OF HIGH PRESSURE OVER THE SOUTHEAST U.S. WITH A SOUTHWEST FLOW ALOFT
OVER WYOMING.  MAIN DIFFERENCE BETWEEN THE GFS AND ECMWF IS IN THE
LATTER PERIODS WITH ECMWF STRENGTHENING AND RETROGRADING UPPER RIDGE
OVER THE SOUTHEAST INTO THE CENTRAL PLAINS BY TUESDAY WHILE GFS MORE
PROGRESSIVE WITH UPSTREAM TROUGH...BRINGING A GOOD CHUNK OF ENERGY
ACROSS THE NORTHERN ROCKIES TUESDAY.  FORECAST HAS LOW CONFIDENCE IN
EITHER OF THESE SOLUTIONS...PREFERRING TO GO WITH A PERSISTENT SW
FLOW ALONG THE LINES OF THE GEFS MEAN.  THIS SOUTHWEST FLOW WILL
FAVORABLE FOR NUMEROUS HARD TO TIME WEAK SHORTWAVES WHICH WILL HAVE
TO BE DEALT WITH 24 HOURS OUT OR SO.  MEAN POSITION OF
QUASI-STATIONARY FRONT THROUGH THE PERIOD ON SOUTH SIDE OF
WYOMING/MONTANA BORDER WITH BEST CHANCES OF THUNDERSTORMS ACROSS THE
NORTHWEST MOUNTAINS AND ALONG AND NORTH OF THIS FRONTAL BOUNDARY.
MEAN H7 TEMPERATURES 12-14C ON SOUTH SIDE OF FRONT WHERE LOWER
ELEVATION HIGH TEMPERATURES WILL RANGE FROM 75 TO 85.  TEMPERATURES
ON NORTH SIDE OF THE FRONT WILL BE 5 TO 10F COOLER ON AVERAGE.
SUMMER BEGINS 528 A.M. ON MONDAY AND IT LOOKS LIKE A SUMMER WEATHER
PATTERN WILL TAKE HOLD THIS WEEKEND AND THROUGHOUT NEXT WEEK.

&&

.AVIATION...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED OVER THE
WEST THIS MORNING.  THE SHOWERS AND THUNDERSTORMS WILL BECOME MORE
NUMEROUS THIS AFTERNOON AND EVENING AFFECTING THE WEST AND NORTH.
THE SHOWERS AND THUNDERSTORMS WILL BE MORE SCATTERED TO ISOLATED
OVER THE CENTRAL AND SOUTH.  VERY GUSTY WINDS TO 45KTS...FREQUENT
LIGHTNING...SMALL HAIL AND HEAVY RAINFALL IS POSSIBLE WITH THE
STRONGER STORMS.  OTHERWISE...SOUTHWEST WINDS WILL BE ON THE
INCREASE MOST AREAS BY LATE MORNING/EARLY AFTERNOON.

&&

.FIRE WEATHER...
A LINE OF STRONG THUNDERSTORMS WITH SMALL HAIL AND GUSTY WINDS
WILL DEVELOP OUT AHEAD OF A STRONG COLD FRONT TODAY. THIS FRONT
WILL PRODUCE RAIN SHOWERS TONIGHT WITH RAIN TURNING TO SNOW IN
THE MOUNTAINS WHERE SEVERAL INCHES OF SNOW ARE EXPECTED IN THE
CENTRAL... NORTHERN AND WESTERN MOUNTAINS BY THURSDAY MORNING. IN
ADDITION... STRONG WEST WINDS ARE EXPECTED ACROSS THE MOUNTAINS
AND ACROSS SOUTHERN WYOMING THURSDAY BEHIND THE COLD FRONT THURSDAY.
TEMPERATURES WILL WARM UP FRIDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON
WYZ019-020-030.

FLOOD WATCH THROUGH SATURDAY AFTERNOON WYZ017-018.

FLOOD WATCH THROUGH THURSDAY AFTERNOON WYZ028.

&&

SHORT TERM...LIPSON
LONG TERM...AEM
AVIATION...TWB
FIRE WEATHER...LIPSON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
148 PM MDT WED JUN 16 2010

WYZ001>020-022>030-171200-
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-
148 PM MDT WED JUN 16 2010

...FLOOD WARNING THROUGH WEDNESDAY AFTERNOON FOR THE BLACKS FORK
RIVER FROM GRANGER TO LITTLE AMERICA IN WESTERN SWEETWATER COUNTY...

...FLOOD WATCH THROUGH FRIDAY AFTERNOON FOR THE LITTLE POPO
AGIE RIVER...THE MIDDLE FORK POPO AGIE RIVER...AND ALL FORKS OF
THE LITTLE WIND RIVER...

...HIGH WIND WARNING FOR SOUTHERN WYOMING FOR THURSDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

MINOR FLOODING IS EXPECTED TO CONTINUE ALONG THE BLACKS FORK RIVER
BETWEEN GRANGER AND LITTLE AMERICA THROUGH TODAY.

OTHERWISE...THE MAJORITY OF STREAMS AND RIVERS WILL REMAIN FAIRLY
HIGH AND SWIFT ACROSS THE AREA AS SEASONAL SNOWMELT CONTINUES.

STRONG THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING ACROSS
WESTERN AND CENTRAL WYOMING. THESE THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING STRONG WIND GUSTS...SMALL HAIL...BRIEF HEAVY RAIN AND
FREQUENT LIGHTNING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

WARMER TEMPERATURES AND GUSTY WINDS TODAY WILL LEAD TO
ANOTHER ROUND OF SIGNIFICANT MELTING OF THE NEW SNOWFALL IN THE WIND
RIVER MOUNTAINS. THIS WILL LEAD TO RISES IN AREA RIVERS AND CREEKS...
WHICH MAY LEAD TO MORE FLOODING THURSDAY. STAY TUNED FOR UPDATES ON
THIS SITUATION.

RAIN IS EXPECTED TO TURN TO SNOW AFTER MIDNIGHT TONIGHT IN THE
WESTERN MOUNTAINS INCLUDING THE WEST SLOPE AND UPPER EAST
SLOPE OF THE WIND RIVER MOUNTAINS. 3 TO 6 INCHES OF SNOWFALL
COULD FALL IN THESE MOUNTAINS BY EARLY THURSDAY MORNING
AFFECTING TRAVEL ACROSS THE MAJOR PASSES.

ADDITIONALLY...STRONG SOUTHWESTERLY WIND IS EXPECTED TO DEVELOP
ACROSS THE WIND CORRIDOR OF EASTERN SWEETWATER THROUGH NATRONA
COUNTIES THURSDAY MORNING. THIS STRONG WIND WILL CONTINUE THROUGH
EARLY THURSDAY EVENING...WITH FAVORED LOCATIONS SEEING WIND OF 40 MPH
GUSTING TO 60 MPH.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY STREAMS OR RIVERS RISING
RAPIDLY...NEAR BANKFULL OR WHERE FLOODING IS OCCURRING. SPOTTERS
ARE ALSO ENCOURAGED TO REPORT ANY HAIL OR STRONG WINDS IN
THUNDERSTORMS TODAY. SPOTTERS ARE ALSO ENCOURAGED TO REPORT ANY
SNOWFALL AMOUNTS. THANK YOU.

TEAM RIVERTON

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