Severe Thunderstorm Warning 1, NWS Riverton, WY

018 
WWUS55 KRIW 212112
SVSRIW

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
312 PM MDT THU APR 21 2011

WYC023-212122-
/O.EXP.KRIW.SV.W.0001.000000T0000Z-110421T2115Z/
LINCOLN WY-
312 PM MDT THU APR 21 2011

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHWESTERN LINCOLN COUNTY
WILL EXPIRE AT 315 PM MDT...

THE STORM WHICH PROMPTED THE WARNING HAS WEAKENED AND MOVED OUT OF 
THE WARNED AREA.  HOWEVER GUSTY WINDS TO 45 MPH ARE STILL POSSIBLE 
WITH THIS THUNDERSTORM.

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

LAT...LON 4189 11106 4214 11089 4159 11031 4161 11101
      4167 11106
TIME...MOT...LOC 2112Z 239DEG 33KT 4193 11054

$$

BRANHAM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
156 PM MDT THU APR 21 2011

SHORT TERM...TONIGHT THROUGH SUNDAY
IMPRESSIVE NEGATIVELY TILTED TROUGH APPROACHING THE SOUTHWEST
WITH ISOLATED THUNDERSTORMS ACROSS AREAS WEST OF THE DIVIDE. SOME
OF THESE STORMS WILL MOVE EAST OF THE DIVIDE AS THE TROUGH ENERGY
MOVES A LITTLE FURTHER NORTHEAST. LAPS ANALYSIS SHOWING CAPES AS
HIGH AS 600-800 J/KG IN THE SW AND 200-400 J/KG EAST OF THE
DIVIDE. ENOUGH BUOYANCY AND SPEEDS ALOFT TO PRODUCE A FEW STRONGER
STORMS WITH HAIL AND STRONG WIND GUSTS. SLC WARNED ON THE LINE
MOVING THROUGH NORTHERN UTAH EARLY THIS AFTERNOON. STRONG WINDS
WILL ACCOMPANY THIS SYSTEM THROUGH FRIDAY BUT HIGH WINDS NOT
EXPECTED. HEAVY SNOW SHOWERS AND EMBEDDED CONVECTION WILL PRODUCE
HIGH SNOWFALL RATES IN THE WESTERN MOUNTAINS INTO EARLY THIS
EVENING WITH SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR QUITE
POSSIBLE. QUICK SHOT OF SNOW IN THE BIG HORNS AS THIS SYSTEM MOVES
THROUGH OVERNIGHT AND THEN SOME WRAPAROUND LATER FRIDAY BUT
ADVISORY POTENTIAL LOOKS LOWER THAN YESTERDAY. WILL KEEP SOME LOW
END ADVISORY AMOUNTS IN THERE BETWEEN TONIGHT AND FRIDAY BUT DON'T
SEE THE NEED FOR AN ADVISORY ATTM. IT'S STILL POSSIBLE THE MID
LEVEL CIRCULATION WILL MOVE NEAR THE AREA BUT THE SPEED MAY BE TOO
FAST TO PRODUCE A LONG DURATION MODERATE TO HEAVY SNOW EVENT.
STRONG WINDS BEHIND THIS FRONT TONIGHT INTO FRIDAY MAKING FOR A
CHILLY FRIDAY. NEXT UPPER CIRCULATION WILL MOVE INTO THE NORTHWEST
FRIDAY AFTERNOON FOR ANOTHER ROUND OF CONVECTIVE SNOW SHOWERS BUT
NOT LIKE TODAY. SNOWFALL AMOUNTS WILL BE LIGHTER LATER TONIGHT AND
FRIDAY BUT NEVERTHELESS...I BELIEVE SOME LIGHT SNOW WILL PREVAIL
WITH A BRIEF BREAK LATE TONIGHT AND FRIDAY MORNING. COOL...WEAK
WESTERLY FLOW OVER THE WEEKEND WITH EMBEDDED WEAK DISTURBANCES BUT
LITTLE CHANCE OF PRECIPITATION. ONE WEAK MID LEVEL CIRCULATION
TRIES TO SNEAK UP INTO SWEETWATER COUNTY LATE SATURDAY INTO
SATURDAY INTO SATURDAY EVENING WITH ANOTHER WEAK SYSTEM SUNDAY.
MUCH WEAKER WINDS OVER THE WEEKEND.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY
CHANCES OF VALLEY RAIN AND MOUNTAIN SNOW INCREASE ACROSS THE SOUTH
AND WEST SUNDAY. A COLD FRONT WILL PUSH ACROSS THE AREA SUNDAY
NIGHT FOLLOWED BY COOLER AND UNSETTLED WEATHER THROUGH TUESDAY.
WARMER...DRIER AND BREEZY TO WINDY CONDITIONS EXPECTED ACROSS MOST
OF THE AREA WEDNESDAY. ANOTHER PACIFIC COLD FRONT EXPECTED ACROSS
THE AREA THURSDAY WITH PRECIPITATION INCREASING ACROSS THE WEST
AHEAD OF THE FRONT...WINDY AND COOLER CONDITIONS ACROSS CENTRAL
WYOMING BEHIND THE FRONT THURSDAY.

MEDIUM RANGE GLOBAL MODELS IN GOOD AGREEMENT EARLY IN THE PERIOD
WITH STRONG JET PUSHING ACROSS CENTRAL PACIFIC EARLY THIS MORNING
COMING ONSHORE SATURDAY NIGHT AND DIGGING TROUGH INTO THE GREAT
BASIN BENEATH UPPER RIDGE OVER WESTERN CANADA. ECMWF KEEPS
MOISTURE ASSOCIATED WITH THIS TROUGH SOUTH OF OUR AREA SUNDAY
WHILE GFS/GEM ARE MUCH WETTER ACROSS THE SOUTHWEST HALF OF
WYOMING. FORECAST REFLECTS GFS/GEM HIGHER POP SCENARIO HERE. AS
HAS BEEN THE CASE THROUGH MUCH OF APRIL...THE SOUTHERN PORTION OF
THE THIS TROUGH WILL RACE OUT INTO THE CENTRAL PLAINS MONDAY
MORNING AND LEAVE AN ELONGATED TROUGH STRETCHING BACK NW WITH A
COUPLE OF WEAK UPPER LOWS ORPHANED OFF UNDER WESTERN CANADIAN
RIDGE. THESE REMNANTS EVENTUALLY SLIDE DOWN FRONT SIDE OF
SHARPENING EASTERN PACIFIC RIDGE MONDAY NIGHT AND TUESDAY. UPPER
RIDGE THEN TRANSLATES ACROSS INTERMOUNTAIN REGION/ROCKIES TUESDAY
NIGHT AND WEDNESDAY WITH NEXT PACIFIC TROUGH PUSHING ONTO WEST
COAST BY 00Z THURSDAY AND ACROSS ROCKIES THURSDAY MORNING. GFS
ATTEMPTS TO PROGRESS SUB-TROPICAL HIGH EASTWARD OVER MEXICO AND
THUS KEEPS UPPER LOW FURTHER NORTH ALONG U.S./CANADIAN BORDER WITH
TIGHT GRADIENT IN BETWEEN. THIS SCENARIO WOULD RESULT IN A MUCH
WINDIER SCENARIO ACROSS WYOMING THURSDAY. ECMWF OFFERS MORE OF THE
SAME...DIGGING TROUGH INTO CENTRAL ROCKIES BETWEEN THE TWO
OFFSHORE SUB-TROPICAL HIGHS. ECMWF PERSISTENCE SOLUTION PREFERRED.

AVIATION...
SHOWERS AND THUNDERSTORMS ASSOCIATED WITH AN APPROACHING AREA OF LOW
PRESSURE WILL CONTINUE TO IMPACT THE FORECAST AREA THIS EVENING.
SNOW SHOWERS WILL ESPECIALLY BE PREVALENT OVER THE WESTERN MOUNTAINS
AND VALLEYS...WITH PERIODS OF MVFR TO IFR CONDITIONS ANTICIPATED
OVER KJAC. THUNDERSTORM ACTIVITY WILL CEASE WITH THE LOSS OF
SUNLIGHT THIS EVENING...LEAVING WIDESPREAD SNOW SHOWERS OVERNIGHT.
MOST AIRPORTS WILL SEE THE OPPORTUNITY FOR SHOWER ACTIVITY THROUGH
FRIDAY AFTERNOON...RESULTING IN BRIEF PERIODS OF MVFR CONDITIONS.
WIND WILL INCREASE ACROSS MUCH OF THE AREA AFTER 12Z FRIDAY WITH
WIND OF 15G25KT COMMON. WITH CONTINUED PERIODS OF SHOWER
ACTIVITY...EXPECT MOUNTAINS TO REMAIN OBSCURED.

FIRE WEATHER...
ACTIVE STORM SYSTEM WILL MOVE ACROSS THE AREA THROUGH TONIGHT WITH
ANOTHER WEAKER SYSTEM PASSING ACROSS THE NORTH ON FRIDAY.
THUNDERSTORMS WILL BE POSSIBLE ACROSS THE ENTIRE DISTRICT INTO THE
EVENING. HEAVY SNOW SHOWERS WILL OCCUR OUT WEST WITH SOME LOCALLY
STRONG THUNDERSTORMS POSSIBLE. STRONG WEST WINDS WILL BLOW ACROSS
A LARGE PART OF THE DISTRICT THROUGH TONIGHT AND EVEN IN MANY
AREAS ON FRIDAY. WINDS WILL DECREASE OVER THE WEEKEND WITH A MUCH
DRIER PATTERN FOR MOST OF THE AREA.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 3 AM MDT FRIDAY WYZ001-002-012.

&&

SHORT TERM...SKRBAC
LONG TERM...AEM
AVIATION...BRANHAM
FIRE WEATHER...SKRBAC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
158 PM MDT THU APR 21 2011

WYZ001>020-022>030-221100-
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-
158 PM MDT THU APR 21 2011

...WINTER WEATHER ADVISORIES FROM NOON TODAY UNTIL 3 AM FRIDAY FOR
THE NORTHWEST MOUNTAINS...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

SNOWFALL WILL INCREASE ACROSS THE NORTHWEST MOUNTAINS TODAY AND
BECOME HEAVY AT TIMES THROUGH EARLY FRIDAY MORNING.  STORM
TOTAL SNOWFALL AMOUNTS OF 6 TO 12 INCHES ARE EXPECTED. PLEASE SEE
WINTER WEATHER ADVISORY PRODUCTS FOR MORE INFORMATION.  A COLD
FRONT WILL PUSH ACROSS THE AREA TODAY WITH ISOLATED THUNDERSTORMS
ACCOMPANYING THE FRONT.  THE MAIN HAZARDS WITH THESE STORMS WILL BE
SMALL HAIL...WIND GUSTS OF 40 TO 50 MPH AND DANGEROUS CLOUD TO GROUND
LIGHTNING.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

SNOW WILL INCREASE IN THE BIG HORN MOUNTAINS TONIGHT AND CONTINUE
THROUGH FRIDAY ALONG WITH GUSTY NORTH WIND.  SNOWFALL TOTALS OF
3 TO 7 INCHES ARE EXPECTED OVER AND NORTH OF POWDER RIVER PASS.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY STRONG WIND GUSTS OR HAIL WITH
THUNDERSTORMS TODAY ALONG WITH SNOWFALL AMOUNTS.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
136 PM MDT THU APR 21 2011

WYZ001-012-212015-
TETON AND GROS VENTRE MOUNTAINS WY-YELLOWSTONE NATIONAL PARK WY-
136 PM MDT THU APR 21 2011

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN PARK AND
NORTHWESTERN TETON COUNTIES IN NORTHWEST WYOMING UNTIL 215 PM MDT...

AT 136 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 6 MILES SOUTHWEST OF MYSTIC FALLS...OR 17 MILES
SOUTH OF WEST YELLOWSTONE...MOVING NORTHEAST AT 40 MPH.

WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM ALONG WITH
SMALL HAIL.

THIS STORM WILL BE NEAR...
MYSTIC FALLS...OLD FAITHFUL AND KEPLER CASCADES AROUND 145 PM MDT.
FAIRY FALLS...LOWER BASIN LAKE AND GOOSE LAKE AROUND 150 PM MDT.
FOUNTAIN PAINT POT...GRAND LOOP RD MADISON TO GRANT AND FIREHOLE
CANYON AROUND 155 PM MDT.
MADISON AROUND 200 PM MDT.
GIBBONS FALLS AROUND 205 PM MDT.
GIBBON HILL...GRAND LOOP RD NORRIS TO MADISON AND NORRIS JCT AROUND
210 PM MDT.

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

LAT...LON 4484 11106 4500 11077 4499 11057 4499 11056
      4443 11018 4401 11105
TIME...MOT...LOC 1936Z 227DEG 33KT 4444 11099

BRANHAM