Severe Thunderstorm Warning 61, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
344 PM MDT SUN AUG 19 2007

.SHORT TERM...TONIGHT THROUGH WEDNESDAY
THE WEATHER WILL ONCE AGAIN BE VERY ACTIVE FOR THE REMAINDER OF
THE AFTERNOON THROUGH LATE EVENING. WATER VAPOR IMAGERY SHOWS
NEGATIVELY TILTED TROUGH SWINGING THROUGH PACIFIC NORTHWEST AND
IDAHO CURRENTLY. THIS FEATURE WILL QUICKLY PUSH NORTHEAST...INTO
SOUTHERN CANADA AND WESTERN MONTANA BY MIDNIGHT...WITH THE ASSOCIATED
PACIFIC COLD FRONT QUICKLY MOVING THROUGH THE AREA FROM WEST TO
EAST...FROM 6 PM TO MIDNIGHT TONIGHT. WINDY CONDITION ARE EXPECTED
AHEAD AND BEHIND THE FRONT...SHIFTING FROM GENERALLY SOUTHWEST TO
WEST/NORTHWEST. DYNAMICS WITH THIS SYSTEM SHOULD KEEP THE THREAT OF
SEVERE GOING UNTIL THE CONVECTION EXITS THE AREA...WITH THE BEST
CHANCE OF SEVERE ACROSS THE WESTERN AND NORTHERN SECTIONS OF THE
FORECAST AREA. AFTER MIDNIGHT...ALL OF THE CONVECTION SHOULD BE
EAST OF THE AREA...WITH DECREASING CLOUDINESS.

WILL KEEP RED FLAG WARNING GOING...AS RH AS FINALLY DIPPED INTO
THE 15 TO 20 PERCENT RANGE WITH DECENT WINDS...EXCEPT ACROSS THE
UPPER GREEN BASIN.  CLOUD COVER AND SOME PRECIPITATION WILL
CONTINUE TO HAMPER RH FALLING TO CRITICAL LEVELS...BUT ARE CLOSE
ENOUGH TO KEEP IT GOING. WILL HAVE ANOTHER RED FLAG WARNING FOR
MONDAY AFTERNOON AND EVENING FOR THE SAME AREAS PLUS ZONE 280
INCLUDING MUCH OF NATRONA COUNTY. BETTER SHOT MONDAY AFTERNOON
GETTING BELOW THE 15 PERCENT RH CRITICAL THRESHOLDS.

MONDAY IS EXPECTED TO BE MAINLY DRY...BUT A WEAK DISTURBANCE IN
THE ZONAL FLOW IS EXPECTED TO AFFECT NORTHERN PARTS OF THE AREA LATE
MONDAY AFTERNOON INTO MONDAY NIGHT. WILL ONLY HAVE SLIGHT CHANCES
UP ACROSS THE NORTH...BUT KEEP THEM IN FOR ENTIRE NIGHT...FOR THIS
DISTURBANCE. ATMOSPHERE IS STABLE...SO WILL MENTION ONLY SHOWERS.

A RIGHT EXIT REGION OF A STRONG 120KT 250MB JET WILL PUSH ACROSS
THE AREA MONDAY NIGHT...WHICH COULD HELP PRODUCE A MOUNTAIN
WAVE ACTIVITY ACROSS THE NORTH...AND LATER SHIFTS WILL NEED TO
MONITOR THIS FOR HIGH WIND POTENTIAL.

ZONAL FLOW CONTINUES TUESDAY AND WEDNESDAY. TUESDAY IS EXPECTED TO
BE DRY...BUT ANOTHER DISTURBANCE IS EXPECTED IN THE ZONAL FLOW
WHICH COULD GIVE THE AREA A SLIGHT CHANCE OF CONVECTION.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
A BROAD CYCLONIC FLOW WILL FOLLOW TUESDAYS SHORTWAVE ON WEDNESDAY
AND THURSDAY WITH SOME EMBEDDED WEAK UPPER LEVEL DISTURBANCES.
MOISTURE WILL REMAIN LIMITED SO SHOWER AND THUNDERSTORM ACTIVITY
WILL REMAIN ISOLATED AT BEST. TEMPERATURES WILL REMAIN NEAR
SEASONABLE LEVELS MID-WEEK WITH HIGHS MAINLY IN THE MID 70S TO MID
80S ACROSS THE LOWER ELEVATIONS. MEDIUM RANGE MODELS AGREE ON
BUILDING AN UPPER RIDGE INTO THE AREA FRIDAY AND THROUGH NEXT
WEEKEND WITH EVEN THE MOISTURE-BULLISH GFS (BEYOND 120H) GENERALLY
KEEPING PWAT VALUES 0.50 OF AN INCH OR LESS. FORECAST KEEPS FRIDAY
DRY AND BRINGS IN SLIGHT CHANCE POPS INTO THE SOUTHWEST OVER THE
WEEKEND WITH A GRADUAL WARMING TREND...HIGH TEMPERATURES IN THE
80S TO NEAR 90.

&&

.AVIATION...
STRONG TO SEVERE THUNDERSTORMS...WITH VERY GUSTY WINDS NEAR 60
MPH AND LARGE HAIL WILL BE POSSIBLE FOR THE REMAINDER OF THE
AFTERNOON AND THIS EVENING ACROSS ALL TAF SITES. THE ACTIVITY WILL
END FROM WEST TO EAST DURING THE EVENING...AS A STRONG COLD FRONT
MOVES THROUGH. KJAC...KBPI...KPNA SHOULD SEE AN END TO THE
THUNDERSTORMS BETWEEN 00Z AND 02Z...WITH AN END ACROSS
KCOD...KRIW...KLND AND KRKS BETWEEN 01Z AND 03Z. KCPR SHOULD SEE
IT END BY AROUND 05Z. EXPECT IFR CONDITIONS NEAR
THUNDERSTORMS...WITH VFR ELSEWHERE. AFTER MIDNIGHT...EXPECT
IMPROVING CONDITIONS WITH VFR EXPECTED...BUT STRONG WEST TO WEST
NORTHWEST WILL CONTINUE.

&&

.FIRE WEATHER...
A POTENT TROUGH...AND ASSOCIATED COLD FRONT WILL QUICKLY MOVE
THROUGH THE AREA FROM WEST TO EAST THIS EVENING. THE STRONG TO
SEVERE THUNDERSTORMS WILL END QUICKLY FROM WEST TO EAST THIS
EVENING...AS THE COLD FRONT AND ASSOCIATED TROUGH PUSHES THROUGH
THE REGION. THIS ACTIVITY IS EXPECTED PUSH OUT OF THE AREA BY
MIDNIGHT. BEHIND THE COLD FRONT...EXPECT WINDY WEST TO NORTHWEST
WINDS...AND MUCH DRIER AIR. AHEAD OF THIS FRONT...VERY WINDY
SOUTHWEST WINDS WERE OCCURRING...WITH NEAR CRITICAL RH VALUES
ACROSS THE SOUTHERN LOW ELEVATION FIRE DISTRICTS. SO WILL KEEP
CURRENT RED FLAG WARNING GOING THROUGH 9 PM. MONDAY IS EXPECTED
TO BE WINDY...WITH RH REACHING CRITICAL VALUES ACROSS THE SOUTHERN
FIRE DISTRICTS...SO HAVE ISSUED A RED FLAG WARNING FOR MONDAY
AFTERNOON AND EVENING FOR THE SAME FIRE DISTRICTS INCLUDING IN
TODAYS RED FLAG WARNING WITH THE ADDITION OF FIRE DISTRICT ZONE
280. MONDAY IS EXPECTED TO BE DRY...EXCEPT FOR PERHAPS FOR AN
ISOLATED SHOWER LATE MONDAY AFTERNOON INTO THE OVERNIGHT HOURS
ACROSS THE NORTH. WINDY CONDITIONS ARE EXPECTED TO CONTINUE ON
TUESDAY...BUT WITH NO PRECIPITATION EXPECTED.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING FOR WYZ277>279-283-
288-289.

RED FLAG WARNING FROM 1 PM TO 8 PM MDT MONDAY FOR WYZ277>280-283-
289.

&&

SHORT TERM...WM
LONG TERM...AEM
AVIATION...WM
FIRE WEATHER...WM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
135 PM MDT SUN AUG 19 2007

WYZ001>020-022>030-201300-
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-
135 PM MDT SUN AUG 19 2007

...RED FLAG WARNING IN EFFECT SUNDAY 2 PM THROUGH 9 PM FOR
PORTIONS OF CENTRAL AND SOUTHERN WYOMING...

...SEVERE THUNDERSTORM WATCH 617 IS IN EFFECT UNTIL 8 PM FOR MUCH OF
WESTERN AND CENTRAL WYOMING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...THIS AFTERNOON AND TONIGHT

STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AND
TONIGHT...MAINLY BETWEEN 3 PM AND 9 PM.  THE MOST LIKELY AREAS TO
HAVE SEVERE THUNDERSTORMS WILL BE ACROSS WESTERN AND NORTHERN
WYOMING.  THE MAIN HAZARDS WILL BE LARGE HAIL AND DAMAGING WINDS.
THE ONLY AREAS NOT INCLUDED IN SEVERE THUNDERSTORM WATCH 617 ARE
NATRONA AND JOHNSON COUNTIES.

SOUTHWEST WIND WILL CONTINUE TO INCREASE THIS MORNING AND BECOME
STRONG LATER THIS AFTERNOON...AHEAD OF AN APPROACHING STORM SYSTEM.
THIS SOUTHWEST WIND WILL BEGIN TO USHER IN DRIER AIR INTO THE
REGION. THESE STRONG WINDS COMBINED WITH LOW HUMIDITIES WILL CREATE
RED FLAG CONDITIONS IN PORTIONS OF CENTRAL AND SOUTHERN WYOMING THIS
AFTERNOON AND EVENING. A STRONG COLD FRONT WILL MOVE ACROSS WEST
AND CENTRAL WYOMING THIS EVENING.  WEST WIND AT 20 TO 30 MPH WITH
GUSTS TO 40 MPH WILL ACCOMPANY THE FRONT.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS...PLEASE REPORT ANY WIND GUSTS OVER 40 MPH AND HAIL SIZES
THIS AFTERNOON AND TONIGHT.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
410 PM MDT SUN AUG 19 2007

WYZ001>003-192300-
ABSAROKA MOUNTAINS-CODY FOOTHILLS-YELLOWSTONE NATIONAL PARK-
410 PM MDT SUN AUG 19 2007

A FEW STRONG THUNDERSTORMS WILL MOVE OUT OF THE EAST PART OF
YELLOWSTONE NATIONAL PARK AND INTO THE NORTH ABSAROKA MOUNTAINS
THROUGH 500 PM. THE STORMS WILL BE MOVING TOWARD SUNLIGHT BASIN AND
CRANDALL CREEK AND SHOULD ARRIVE BETWEEN 430 PM AND 5 PM.
THE STORM WILL BE CAPABLE OF PRODUCING WIND GUSTS TO 45 MPH...BRIEF
HEAVY RAIN AND HAIL TO ONE HALF INCH IN DIAMETER.

IF YOU HAVE OUTDOOR ACTIVITIES PLANNED THIS AFTERNOON AND THIS
EVENING...BE SURE TO HAVE A SAFE SHELTER TO MOVE TO IMMEDIATELY...
SHOULD THE STORMS APPROACH YOUR LOCATION. FREQUENT LIGHTNING WILL
OCCUR IN ASSOCIATION WITH SOME STORMS...SO BE SURE TO MOVE INSIDE AND
AWAY FROM OPEN AREAS AND WATER. ALSO...TAKE ALONG A NOAA WEATHER
RADIO RECEIVER WHICH CAN PROVIDE UP-TO-THE MINUTE INFORMATION ON
THUNDERSTORM DEVELOPMENT AND POSSIBLE WARNINGS.

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