Special Weather Statement, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
324 AM MDT FRI JUN 24 2011

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

ANOTHER ROUND OF THUNDERSTORMS...SOME SEVERE...EXPECTED TODAY AS
THE ATMOSPHERE DESTABILIZES AGAIN THIS AFTERNOON. LIFTED INDICIES
ARE FORECAST TO DROP WELL BELOW ZERO OVER THE ENTIRE STATE AS
EARLY AS 15Z. CAPE VALUES COULD RANGE FROM 1000 TO 2000 J/KG WITH
SURFACE HEATING THIS AFTERNOON. DEWPOINTS WILL REMAIN IN THE 40S
AND 50S IN THE SOUTHERLY FLOW AHEAD OF THE TROUGH...AMPLE
AVAILABLE MOISTURE FOR THIS AREA. AND 40 TO 50 KT OF 0-6KM SHEAR
WILL ENCOURAGE AN ENVIRONMENT FAVORABLE FOR SEVERE THUNDERSTORMS.
PRIMARY THREAT WITH THESE STORMS WILL BE STRONG WIND AND
HAIL...BUT THERE IS AN ADDED THREAT OF FLOODING DUE TO THE FACT
THAT SPRING RUNOFF IS PEAKING. MANY RIVERS ARE RUNNING VERY HIGH
AND CLOSE TO BANKFULL.

SATURDAY AND SUNDAY WILL ALSO BE UNSTABLE. THUNDERSTORMS ARE
EXPECTED ON THESE DAYS AS WELL...THOUGH THE STORMS WILL BE LESS
SEVERE AS THE BETTER INSTABILITY SHIFTS EAST.

.LONG TERM...MONDAY THROUGH FRIDAY

MAINLY DRY CONDITIONS EXPECTED MONDAY AND TUESDAY WITH SEASONABLY
COOL WEATHER LINGERING EAST OF THE DIVIDE MONDAY...AND MORE
SUMMER-LIKE TEMPERATURES IN THE 80S TO NEAR 90 ON TAP FOR THE VALLEYS
AND BASINS ON TUESDAY. THE MAIN WEATHER MAKER IN THIS PERIOD WILL
MOVE ACROSS THE AREA WEDNESDAY NIGHT AND THURSDAY WITH ISOLATED TO
SCATTERED THUNDERSTORMS AHEAD OF THIS SYSTEM WEDNESDAY/WEDNESDAY
NIGHT LIFTING INTO NORTHERN WYOMING ON THURSDAY. MAINLY DRY
CONDITIONS AND SEASONABLY COOL CONDITIONS WILL FOLLOW ON FRIDAY.

MEDIUM-RANGE GLOBAL MODELS ARE IN MUCH BETTER AGREEMENT THIS MORNING
THROUGH THURSDAY WITH INCREASING SPREAD LATE IN THE PERIOD.  UPPER
RIDGE BUILDS INTO THE NORTHERN ROCKIES ON MONDAY AS UPPER LOW DROPS
SOUTH ALONG 130W OFF THE NORTHWEST COAST.  LOW BOTTOMS OUT ALONG 40N
BEFORE PUSHING ONSHORE TUESDAY NIGHT.  BOTH GFS AND ECMWF HAVE UPPER
LOW NEAR RENO BY 00Z THURSDAY...HOT UPPER HIGH CENTERED OVER
OKLAHOMA AND DIFLUENT FLOW IN BETWEEN OVER WYOMING.  UPPER LOW THEN
OPENS UP AND LIFTS NE ACROSS THE NORTHERN GREAT BASIN WEDNESDAY
NIGHT AND ACROSS WYOMING ON THURSDAY.  AFTERWARDS...GFS/GEFS MEAN
SHOW BROAD CYCLONIC FLOW OVER THE NORTHERN ROCKIES WITH UPPER HIGH
REMAINING OVER THE CENTRAL PLAINS.  ECMWF ATTEMPTS TO RETROGRADE
HIGH BACK INTO FOUR CORNERS AREA ON FRIDAY.  FORECAST WEIGHTED
TOWARD GFS/PERSISTENCE IN THIS LATTER PERIOD.

&&

.AVIATION...

VFR CONDITIONS TO PREVAIL THROUGH THE FORECAST PERIOD WITH THE
EXCEPTION OF LOCALIZED MVFR WITH CONVECTION. BEST CHANCE FOR STRONG
TO SEVERE THUNDERSTORMS STILL APPEARS TO BE OVER JOHNSON AND NATRONA
COUNTIES THIS AFTERNOON AND EARLY EVENING. IN THIS REGION...SURFACE
DEW POINTS OF 50-55F IN E-NE SURFACE FLOW WILL PROVIDE FAVORABLE
SHEAR ENVIRONMENT. BETTER CHANCE FOR ROTATING STORMS AND LARGER HAIL
IN THIS ENVIRONMENT THAN THURSDAY. KCPR WILL BE MOST SUSCEPTIBLE TO
THESE STORMS. TO THE WEST...FUNNELED W-SW FLOW ALOFT WILL CONTINUE
TO BRING MID-LEVEL MOISTURE ACROSS THE REGION. THUS...STILL EXPECT
ISOLATED CONVECTION PRIOR TO 18Z WITH SCATTERED CONVECTION AFTER
THAT TIME. DRIER AIR FILTERS IN BETWEEN 23Z/FRI-02Z/SAT...SO
CONVECTION SHOULD DWINDLE QUICKLY FROM WEST-TO-EAST BY MID-EVENING.
WESTERLY SURFACE WINDS IN THE RANGE OF 15-25KTS WILL IMPACT
KPNA...KBPI...AND KRKS TERMINALS THIS AFTERNOON. SHOWER AND
THUNDERSTORM COVERAGE WILL BE LESS WIDESPREAD AND INTENSE SATURDAY.

&&

.HYDROLOGY...

THE WIND RIVER FROM DUBOIS TO RIVERTON CONTINUES TO RISE TO NEAR
FLOOD STAGE. A FLOOD WARNING HAS BEEN ISSUED. THE GREEN RIVER FROM
WARREN BRIDGE TO FONTENELLE CONTINUES TO RISE AND IS EXPECTED TO
BE NEAR FLOOD STAGE BY TUESDAY. THE FORKS OF THE SHOSHONE CONTINUE
TO RISE AS WELL. SMALL CREEKS AND HEADWATER STREAMS THAT ARE
ALREADY FLOWING AT MODERATE TO HIGH LEVELS ARE EXPECTED TO RUN
ABOVE BANKFULL THROUGH SUNDAY.

WARMER MOUNTAIN TEMPERATURES TODAY WILL INCREASE SNOWMELT BELOW
10000 FEET. RUN OFF HAS BEEN BETWEEN 1.5 AND 2 INCHES FROM THIS
SNOW PACK AND IS EXPECTED TO CONTINUE AROUND THIS RATE. SCATTERED
THUNDERSTORMS ARE EXPECTED MAINLY ACROSS NORTHERN AND EASTERN WYOMING
THIS AFTERNOON HOWEVER THESE STORMS WILL MOVE FAIRLY QUICKLY. COOLER
TEMPERATURES WILL PREVAIL ACROSS NORTHERN WYOMING TODAY WHILE
TEMPERATURES WILL REMAIN WARM ACROSS THE SOUTH. THE BEST POTENTIAL
FOR SIGNIFICANT RAIN PRODUCING THUNDERSTORMS WILL BE ACROSS
NATRONA AND JOHNSON COUNTIES THIS AFTERNOON AND EVENING. SHOWER
AND THUNDERSTORM ACTIVITY IS EXPECTED TO BE MORE ISOLATED OVER THE
WEEKEND WITH NEAR OR SLIGHTLY BELOW NORMAL TEMPERATURES ACROSS THE
NORTHERN BASINS AND NEAR OR ABOVE NORMAL TEMPERATURES ACROSS THE
SOUTH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH THROUGH LATE SATURDAY NIGHT WYZ016-017.

&&

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...CNJ
HYDROLOGY...ALLEN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
1138 AM MDT FRI JUN 24 2011

WYZ001>020-022>030-251102-
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-
1138 AM MDT FRI JUN 24 2011

...FLOOD WATCH FOR AREAS OF NORTHERN WYOMING TONIGHT THROUGH SUNDAY
NIGHT...

...FLOOD WARNING FOR THE WIND RIVER FROM DUBOIS TO RIVERTON...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS THE BIG HORN
BASIN...JOHNSON AND NATRONA COUNTIES WITH LARGE HAIL AND DAMAGING
WIND THE PRIMARY HAZARDS.  LESS INTENSE STORMS ARE POSSIBLE
ELSEWHERE...HOWEVER A FEW OF THESE STORMS COULD BE VERY STRONG WITH
WIND GUSTS IN EXCESS OF 45 MPH...FREQUENT CLOUD TO GROUND
LIGHTNING...SMALL HAIL AND HEAVY DOWNPOURS.

EXCESSIVE SNOWMELT DUE TO WARM TEMPERATURES WILL CAUSE A RISE IN
RIVER LEVEL ON THE WIND RIVER FROM DUBOIS THROUGH RIVERTON.
FLOODING IS LIKELY IN LOW LYING AREAS ADJACENT TO THE WIND RIVER.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY...

SATURDAY AND SUNDAY...ISOLATED TO SCATTERED THUNDERSTORMS ACROSS
NORTHERN WYOMING.

WEDNESDAY AFTERNOON AND EVENING...ISOLATED TO SCATTERED
THUNDERSTORMS OVER MOST OF WEST AND CENTRAL WYOMING.

THURSDAY...ISOLATED THUNDERSTORMS ACROSS NORTHERN WYOMING.

CREEKS AND RIVERS WILL CONTINUE TO RUN HIGH AND SWIFT AS RECORD
MOUNTAIN SNOWPACK BEGINS TO MELT MORE RAPIDLY WITH THE EXPECTED
WARM-UP INTO THE WEEKEND. SOME LOCATIONS COULD DEVELOP OR CONTINUE TO
EXPERIENCE MINOR FLOODING.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE WEATHER AND FLOODING.
THANK YOU.

TEAM RIVERTON

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1058 AM MDT FRI JUN 24 2011

WYZ014-015-017>019-241745-
GREEN MOUNTAINS AND RATTLESNAKE RANGE WY-LANDER FOOTHILLS WY-WIND
RIVER BASIN WY-WIND RIVER MOUNTAINS EAST WY-WIND RIVER MOUNTAINS WEST
WY-
1058 AM MDT FRI JUN 24 2011

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN FREMONT COUNTY
UNTIL 1145 AM MDT...

AT 1048 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
A STRONG THUNDERSTORM 14 MILES EAST OF SOUTH PASS CITY...OR 30 MILES
SOUTH OF LANDER...MOVING EAST AT 50 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN.

THIS STORM WILL BE NEAR...
SWEETWATER STATION AND STATE HWY 135 MILE MARKER 30 AROUND 1115 AM
MDT.
ICE SLOUGH AND U.S. HWY 287 MILE MARKER 30 AROUND 1125 AM MDT.

BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A
FLOODED ROADWAY.

REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN
RIVERTON AT 1-800-211-1448.

LAT...LON 4319 10771 4261 10737 4225 10854 4253 10881
TIME...MOT...LOC 1657Z 251DEG 41KT 4245 10841

BERC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1102 AM MDT FRI JUN 24 2011

WYZ001>003-012-241745-
ABSAROKA MOUNTAINS WY-CODY FOOTHILLS WY-TETON AND GROS VENTRE
MOUNTAINS WY-YELLOWSTONE NATIONAL PARK WY-
1102 AM MDT FRI JUN 24 2011

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL PARK AND EASTERN TETON
COUNTIES IN NORTHWEST WYOMING UNTIL 1145 AM MDT...

AT 1059 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
A STRONG THUNDERSTORM NEAR EAGLE CREEK MEADOWS...OR 24 MILES
SOUTHEAST OF LAKE YELLOWSTONE...MOVING NORTHEAST AT 65 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN.

THIS STORM WILL BE NEAR...
HWY 14/16/20 MILE MARKER 20 AROUND 1115 AM MDT.
WAPITI AROUND 1125 AM MDT.
STATE HWY 296 MILE MARKER 40 AROUND 1135 AM MDT.

BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A
FLOODED ROADWAY.

REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN
RIVERTON AT 1-800-211-1448.

LAT...LON 4436 11043 4485 10964 4481 10925 4453 10914
      4394 11026 4409 11044 4422 11039
TIME...MOT...LOC 1702Z 242DEG 57KT 4439 10992

BERC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1149 AM MDT FRI JUN 24 2011

WYZ017-019-020-241830-
GREEN MOUNTAINS AND RATTLESNAKE RANGE WY-NATRONA COUNTY LOWER
ELEVATIONS WY-WIND RIVER BASIN WY-
1149 AM MDT FRI JUN 24 2011

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN NATRONA AND
SOUTHEASTERN FREMONT COUNTIES UNTIL 1230 PM MDT...

AT 1145 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
A STRONG THUNDERSTORM NEAR JEFFREY CITY...MOVING EAST AT 40 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN.

THIS STORM WILL BE NEAR...
U.S. HWY 287 MILE MARKER 20 AROUND 1155 AM MDT.
U.S. HWY 287 MILE MARKER 10 AROUND 1205 PM MDT.
SPLIT ROCK AROUND 1210 PM MDT.

BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A
FLOODED ROADWAY.

REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN
RIVERTON AT 1-800-211-1448.

LAT...LON 4291 10728 4253 10707 4239 10793 4260 10809
TIME...MOT...LOC 1749Z 255DEG 35KT 4250 10785

BERC