Severe Thunderstorm Warning 79, NWS Riverton, WY

000 
WWUS55 KRIW 050121
SVSRIW

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
718 PM MDT TUE SEP 4 2007

WYC039-050145-
/O.CON.KRIW.SV.W.0079.000000T0000Z-070905T0145Z/
TETON WY-
718 PM MDT TUE SEP 4 2007

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 745 PM MDT
FOR SOUTHERN TETON COUNTY IN NORTHWEST WYOMING...

AT 715 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A SEVERE THUNDERSTORM CAPABLE OF PRODUCING PENNY SIZE
HAIL...AND DAMAGING WINDS IN EXCESS OF 60 MPH.  THIS STORM WAS
LOCATED NEAR JACKSON...MOVING NORTHEAST AT 40 MPH.

THE SEVERE THUNDERSTORM WILL BE NEAR...
JACKSON PEAK BY 725 PM MDT...
KELLY BY 735 PM MDT...
OVER SHEEP MOUNTAIN BY 735 PM MDT...

IF YOU ARE IN THE PATH OF THIS STORM...PREPARE IMMEDIATELY FOR
DAMAGING WINDS...LARGE HAIL...AND DEADLY CLOUD TO GROUND LIGHTNING.
TAKE COVER IN A STURDY STRUCTURE UNTIL THE STORM PASSES.

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

LAT...LON 4338 11104 4324 11089 4363 11015 4386 11050

$$

000 
WWUS55 KRIW 050143
SVSRIW

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
740 PM MDT TUE SEP 4 2007

WYC039-050150-
/O.EXP.KRIW.SV.W.0079.000000T0000Z-070905T0145Z/
TETON WY-
740 PM MDT TUE SEP 4 2007

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHERN TETON COUNTY IN
NORTHWEST WYOMING EXPIRES AT 745 PM MDT...

THE STORM HAS DECREASED IN INTENSITY AND IS NO LONGER SEVERE. 
THEREFORE...THE WARNING WILL BE ALLOWED TO EXPIRE.  HOWEVER...AN 
URBAN AND SMALL STREAM FLOOD ADVISORY REMAINS IN EFFECT FOR HEAVY 
RAIN THAT OCCURRED WITH THIS STORM. A STORM SPOTTER REPORTED...A 
HALF AN INCH OF RAIN...IN ABOUT TWENTY MINUTES.

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

LAT...LON 4338 11104 4324 11089 4363 11015 4386 11050

$$

MURRELL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
412 PM MDT TUE SEP 4 2007

.SHORT TERM...TONIGHT THROUGH FRIDAY

WATER VAPOR IMAGERY SHOWS THE CLOSED UPPER LOW AND ASSOCIATED H5
TROUGH DIGGING THROUGH SOUTH-CENTRAL OR AT 2045Z WITH NUMEROUS
SHOWERS AND THUNDERSTORMS BREAKING OUT WELL AHEAD OF THE SYSTEM IN
A BROAD AREA OF LARGE-SCALE ASCENT EXTENDING FROM NORTHEASTERN NV
AND ALL OF UT INTO SOUTHEASTERN ID. AREA OF STRONG DIFFLUENCE AT
H3...INCREASING PRECIPITABLE WATER TO NEAR ONE INCH AND LIFTED
INDICES FROM MINUS 1 TO MINUS 2 WILL MOVE INTO FAR WESTERN WY
TONIGHT. WILL INCLUDE MID TO HIGH CHANCE POPS ACROSS THIS AREA
THROUGH 12Z WEDNESDAY...WHILE CARRYING SLIGHT CHANCE POPS ACROSS THE
REMAINDER OF THE CWA WHERE INSTABILITY WILL BE LACKING. A SERIES
OF H5 VORTICITY MAXIMA WILL MOVE ACROSS THE ENTIRE CWA WEDNESDAY
AHEAD OF THE APPROACHING TROUGH MOVING INTO SOUTHERN ID. DIFFLUENCE
ALOFT...STRONGER DYNAMIC FORCING AND RAPIDLY FALLING H5 HEIGHTS COMBINED
WITH INCREASING LOW AND MID LEVEL MOISTURE WILL PROVIDE AN
ENVIRONMENT FAVORABLE FOR STRONG TO SEVERE THUNDERSTORMS WEDNESDAY
AFTERNOON. STEEP MID LEVEL LAPSE RATES WEST OF THE DIVIDE WILL
CREATE THE POTENTIAL FOR LARGE HAIL...AND SEVERE WIND GUSTS WILL
BE POSSIBLE ACROSS THE ENTIRE CWA.

THE GFS PROGRESSION OF THE UPPER LOW IS SLOWER THAN THE NAM/ECMWF
THURSDAY...AND WILL FAVOR THE NAM/ECMWF SOLUTION GIVEN THE STRONG
ZONAL H5 FLOW IN THE PAC NW BEHIND THE TROUGH. STILL THE LEFT
FRONT QUAD OF A 60-70 KT H25 JET MAX WILL MOVE ACROSS WY JUST TO
THE WEST OF THE TROUGH AXIS...AND THIS FORCING AND MOISTURE
ALREADY IN PLACE WILL FAVOR AT LEAST ISOLATED SHOWERS AND
THUNDERSTORMS THROUGH THURSDAY AFTERNOON WITH ACTIVITY DIMINISHING
FROM WEST TO EAST. NORTHWEST FLOW ALOFT FRIDAY WITH AN UPSTREAM
TROUGH IN NORTHWESTERN MT SHOULD PRODUCE ISOLATED SHOWERS ACTIVITY
ACROSS THE NORTHERN TIER OF WY. COLD FRONT WILL MOVE ACROSS WY
WEDNESDAY...AND HIGHS THURSDAY ARE EXPECTED TO BE SLIGHTLY BELOW
NORMAL. H7 TEMPERATURES WILL RISES 1-2 C FRIDAY...BUT WITH
NORTHWEST FLOW ALOFT...HIGHS WILL ONLY RECOVER TO NEAR NORMAL.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

ACTIVE N TO NW FLOW IS EXPECTED THROUGH AT LEAST THE WEEKEND AND
PERHAPS LONGER. SERIES OF WEATHER DISTURBANCES SHOULD KEEP AT
LEAST THE NORTH UNSETTLED AND MUCH COOLER WITH A CHANCE OF
SHOWERS AND EVEN SOME HIGHER ELEVATION SNOW. DECENT COLD FRONT
DROPPING DOWN FROM THE NORTH SATURDAY WILL LIKELY DROP TEMPERATURES
INTO THE 60S AND LOWER 70S BEHIND IT AND PERHAPS LOWER IF LOW
CLOUDS AND RAIN DEVELOP. HAVE ADDED OR INCREASED POPS OVER THE
WEEKEND AND WILL CONTINUE THAT TREND TONIGHT IF THIS PATTERN
CONTINUES TO HOLD TONIGHT. GFS INDICATES ANOTHER SYSTEM ON TUESDAY
THAT THE ECMWF HOLDS WELL TO OUR NE. WILL PUT IN SOME SLIGHT
CHANCES ACROSS THE N TO MATCH WITH OUR NEIGHBOR BUT WILL HAVE TO
SEE HOW THIS LOOKS AGAIN TONIGHT. EITHER WAY...THE RECENT BOUT OF 80S
AND 90S WILL BE REPLACED BY MAINLY 60S AND 70S WITH 50S AND 60S IN
THE HIGH COUNTRY. THE FAR NORTH WILL BE THE COOLEST WITH SNOW
POSSIBLE ABOVE 8000 TO 9000 FEET BASED ON CURRENT TRENDS.

&&

.AVIATION...

WINDS AT THE SURFACE AND ALOFT WILL BEGIN TO INCREASE ACROSS CENTRAL
AND WESTERN WYOMING WEDNESDAY INTO THURSDAY AS LOW PRESSURE MOVES
ACROSS THE REGION. THE CHANCES FOR THUNDERSTORMS ARE ALSO GREATER ON
WEDNESDAY AS MOISTURE INCREASES ALONG A COLD FRONT ASSOCIATED WITH
THE LOW PRESSURE.

THE RESULT WILL BE SCATTERED THUNDERSTORMS WEDNESDAY AFTERNOON AND
EVENING WITH HEAVY RAINFALL AND GUSTY WINDS. HAIL IS ALSO A POSSIBILITY
OVER THE HIGHER ELEVATIONS OF WESTERN WYOMING. THESE STORMS WILL LIKELY
CREATE OCCASIONAL IFR CONDITIONS. OTHERWISE...VFR CONDITIONS PREVAIL
THROUGH THURSDAY.

&&

.FIRE WEATHER...

UPPER LEVEL LOW PRESSURE WILL MOVE FROM SOUTHERN OREGON INTO
NORTHERN NEVADA TONIGHT. MOISTURE FROM THIS SYSTEM WILL INCREASE
FROM WEST TO EAST ACROSS WYOMING TONIGHT. EXPECT SOME SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS OVER THE WEST TONIGHT...WITH
ISOLATED ACTIVITY ELSEWHERE. INCREASED CLOUD COVER AND ADDITIONAL
MOISTURE WILL CONTINUE TO MOVE OVER THE AREA AS THE SYSTEM MOVES
FURTHER EAST WEDNESDAY AND WEDNESDAY NIGHT...BRINGING MUCH COOLER
TEMPERATURES...HIGHER RELATIVE HUMIDITIES AND HIGHER CHANCES FOR
WETTING RAINS. A FEW THUNDERSTORMS THURSDAY WILL BE CAPABLE OF
PRODUCING STRONG TO POSSIBLY SEVERE WIND GUSTS. THE SYSTEM WILL
CONTINUE TO MOVE EAST TO WESTERN SOUTH DAKOTA BY THURSDAY
EVENING...WITH MOST SHOWER ACTIVITY MOVING TO THE EAST OF THE
REGION BY THURSDAY AFTERNOON.

&&

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

SHORT TERM...SMITH
LONG TERM...SKRBAC
AVIATION...KPL
FIRE WEATHER...SMITH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
412 PM MDT TUE SEP 4 2007

WYZ001>020-022>030-051100-
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-
412 PM MDT TUE SEP 4 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL MOVE INTO WESTERN WYOMING
TONIGHT...WHILE ISOLATED SHOWERS AND THUNDERSTORMS WILL OCCUR
ELSEWHERE ACROSS THE STATE. A FEW STRONGER THUNDERSTORMS WEST OF
THE DIVIDE COULD PRODUCE HEAVY RAINFALL AND GUSTY WINDS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A COLD FRONTAL PASSAGE WEDNESDAY AND A STRONG UPPER LOW APPROACHING
FROM THE WEST WILL BRING SCATTERED SHOWERS AND THUNDERSTORMS TO THE
ENTIRE AREA. STRONGER THUNDERSTORMS WILL POSE A THREAT OF
SEVERE WIND GUSTS ACROSS THE ENTIRE AREA WEDNESDAY AFTERNOON AND
EVENING...WITH LARGE HAIL ALSO POSSIBLE WEST OF THE DIVIDE. HEAVY
RAIN FROM THUNDERSTORMS COULD ALSO RESULT IN LOCALIZED FLASH FLOODING
WEDNESDAY AFTERNOON AND EVENING.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT THUNDERSTORM WIND GUSTS OVER 40 MPH
ACROSS THE WEST AND SOUTH THIS AFTERNOON AND EVENING. THANK YOU.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
519 PM MDT TUE SEP 4 2007

WYZ023-024-027-050030-
SALT RIVER AND WYOMING RANGES-SOUTH LINCOLN COUNTY-STAR VALLEY-
519 PM MDT TUE SEP 4 2007

EXPECT SCATTERED SHOWERS AND THUNDERSTORMS ACROSS NORTHERN UTAH AND
SOUTHEAST IDAHO...TO MOVE NORTHEAST INTO LINCOLN COUNTY...
INCLUDING STAR VALLEY...BETWEEN 545 PM AND 645 PM.  SOME OF
THESE THUNDERSTORMS COULD BE STRONG...PRODUCING GUSTY WINDS NEAR 50
MPH...SMALL HAIL...CONTINUOUS LIGHTNING...AND BRIEF HEAVY RAINFALL.
ISOLATED RAINFALL AMOUNTS NEAR A HALF AN INCH WILL BE POSSIBLE...
WHICH COULD CAUSE MINOR FLOODING IN LOW LYING AND POOR DRAINAGE
AREAS.

21

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
606 PM MDT TUE SEP 4 2007

WYZ023-024-027-050050-
SALT RIVER AND WYOMING RANGES-SOUTH LINCOLN COUNTY-STAR VALLEY-
606 PM MDT TUE SEP 4 2007

SCATTERED SHOWERS AND THUNDERSTORMS ACROSS NORTHERN UTAH AND
SOUTHEAST IDAHO...WILL CONTINUE TO MOVE NORTHEAST INTO LINCOLN
COUNTY. THROUGH 630 PM...THE STRONGEST STORMS WILL AFFECT AREAS
BETWEEN COKEVILLE AND SAGE JUNCTION IN SOUTHERN LINCOLN COUNTY.
ANOTHER THUNDERSTORM COULD AFFECT THE SOUTHERN PARTS OF STAR VALLEY
BETWEEN 620 AND 700 PM.  SOME OF THESE THUNDERSTORMS COULD BE
STRONG...PRODUCING GUSTY WINDS NEAR 50 MPH...SMALL HAIL...CONTINUOUS
LIGHTNING...AND BRIEF HEAVY RAINFALL. ISOLATED RAINFALL AMOUNTS NEAR
A HALF AN INCH WILL BE POSSIBLE...WHICH COULD CAUSE MINOR FLOODING IN
LOW LYING AND POOR DRAINAGE AREAS.

21

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
628 PM MDT TUE SEP 4 2007

WYZ012-013-023-050105-
JACKSON HOLE-STAR VALLEY-TETON AND GROS VENTRE MOUNTAINS-
628 PM MDT TUE SEP 4 2007

THROUGH 700 PM...A STRONG THUNDERSTORM IS EXPECTED TO MOVE OUT OF
IDAHO...AND AFFECT NORTHERN STAR VALLEY...AND SOUTHERN JACKSON
HOLE...AFFECTING AREAS FROM ALPINE TO HOBACK JUNCTION...INCLUDING
TRAVELLERS ALONG HIGHWAY 26...89.  THIS THUNDERSTORM IS CAPABLE OF
PRODUCING GUSTY WINDS NEAR 50 MPH...SMALL HAIL...CONTINUOUS
LIGHTNING...AND HEAVY RAINFALL. ISOLATED RAINFALL AMOUNTS NEAR
A HALF AN INCH WILL BE POSSIBLE...WHICH COULD CAUSE MINOR FLOODING IN
LOW LYING AND POOR DRAINAGE AREAS.

21