Severe Thunderstorm Warning 69, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
126 PM MDT FRI AUG 7 2009

.SHORT TERM...TONIGHT THROUGH MONDAY
AIRMASS IS DRYING QUICKLY ACROSS THE SERN ZONES WITH SURFACE
DEW POINTS PLUNGING INTO THE 20S ENDING. FARTHER NORTH...THE DEW
POINTS ARE IN THE MID 50S TO AROUND 60 WITH ONLY TEMPS HOLDING
SERIOUS CONVECTION FROM STARTING. LAPS ANALYSIS DOES SHOW THE CAP
THINNING ACROSS THE BASIN WITH NO CAP AROUND CODY OR COWLEY.
SOMEWHAT OF A BALANCING ACT WITH COOLER AIR COMING IN ON NLY FLOW
THROUGH THE EVENING. HOWEVER WITH THE JET STREAK MOVING UP FROM
THE SOUTH AND INTERACTING WITH THIS AREA AROUND 00Z...SEVERE
WEATHER MAY BREAK OUT. UPDATED THE ENTIRE NORTH TO A SEVERE RISK
THIS MORNING AND A POTENTIAL WATCH IS FORTH COMING. EVEN JOHNSON
COUNTY IS FINALLY STARTING TO WARM WITH CAPES UP TO 2000 J/KG
AROUND BYG AND ONLY A SMALL CIN TO ERODE. WIND RIVER BASIN IS ALSO
POTENTIALLY INTERESTING AS COLD FRONT MOVES THROUGH THIS EVENING
AND INTERACTS WITH INCREASING QG FORCING AND UPPER JET SUPPORT.
MOISTURE LEVELS INCREASE RAPIDLY THIS EVENING WITH FROPA BUT TEMPS
ALSO DROP. STRONG DYNAMICS COULD OVERCOME THE COOLER TEMPS. UPPER
LOW CONTINUES TO SLOW AND NOW LOOKS LIKE IT WONT MOVE THROUGH
UNTIL SATURDAY NIGHT INTO SUNDAY MORNING. FURTHER SOUTH TRACK WILL
ALSO ENHANCE PCPN CHANCES ACROSS AREAS NORTH OF TRACK AND HAVE
INCREASED POPS CONSIDERABLY FOR MUCH OF THE AREA FOR SATURDAY AND
SATURDAY NIGHT. COLD CORE IS EXPECTED TO MOVE ACROSS THE SOUTHWEST
SATURDAY EVENING AND INTO THE WINDS...NRN RED DESERT LATE SATURDAY
NIGHT WITH -15C H5 AIR AND NEAR 0C TEMPS AT H7. HAVE INDICATED
SOME ACCUMULATION AS LOW AS 8K FEET IN THE NW MTNS AND 9K FEET IN
THE WINDS. COULD SEE AN INCH OR TWO IN THE IN THE FIRST 1K AND 2
TO 4 INCHES ABOVE THAT. TROUGH MAY LINGER INTO SUNDAY MORNING WITH
SOME SHOWERS IN THE FAR EAST...OTHERWISE IT SHOULD BE A DRIER
PERIODS LATER SUNDAY AND MONDAY WITH WARMING TEMPERATURES.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
MEDIUM RANGE MODELS SHOW WESTERLY FLOW AT THE BEGINNING OF THE
EXTENDED...WITH RIDGING DEVELOPING BY THURSDAY AND FRIDAY. THE MAIN
UPPER JET IS PROJECTED TO BE ACROSS SOUTHERN CANADA DURING THE
EXTENDED.  00Z GFS IS SHOWING MARGINAL MOISTURE...GENERALLY 0.50 OR
LESS OF PRECIPITABLE WATER...AND RELATIVELY STABLE ATMOSPHERE FOR
THE EXTENDED.  THEREFORE...WILL KEEP THE EXTENDED MAINLY DRY WITH
ONLY ISOLATED AFTERNOON/EVENING CONVECTION OVER THE HIGHER TERRAIN.
00Z GFS AND ECMWF SHOW A SHORTWAVE MOVING THROUGH THE AREA
MONDAY...BUT WITH LIMITED MOISTURE WILL KEEP THE LOWER ELEVATIONS
DRY FOR NOW. BY THURSDAY/FRIDAY...MONSOONAL MOISTURE FROM THE FOUR CORNERS
RIDGE COULD BE SURGING NORTHWARD INTO THE AREA. WILL WAIT TO SEE
MORE CONSISTENCY IN THIS SCENARIO...BEFORE PUTTING WIDESPREAD POPS
ACROSS THE AREA. TEMPERATURES ARE EXPECTED TO HAVE A GRADUAL
WARMING TREND TO SLIGHTLY ABOVE AVERAGE TEMPS WEDNESDAY THROUGH
FRIDAY...AS THE RIDGE BEGINS TO BUILD OVER THE AREA.

&&

.AVIATION...
AS A STRONG UPPER LEVEL WEATHER DISTURBANCE TRACKS NORTHEAST THROUGH
A VERY UNSTABLE AIRMASS ACROSS WYOMING AHEAD OF AN APPROACHING LOW
PRESSURE CENTER IN NORTHERN CALIFORNIA... THERE IS THE POTENTIAL FOR
STRONG THUNDERSTORMS TO DEVELOP ACROSS MUCH OF THE AREA THIS
EVENING...ESPECIALLY ACROSS WESTERN...NORTHERN AND SOUTHERN WYOMING.
MANY OF THESE STORMS WILL LIKELY CONTAIN HAIL...LOCALLY HEAVY
RAINFALL AND GUSTY 40 TO 50 MPH WINDS. KRIW AND KLND ARE THE LEAST
LIKELY SITES TO EXPERIENCE THESE CONDITIONS...HOWEVER ALL THE ALL
TAF SITES HAVE THE POTENTIAL TO EXPERIENCE THESE STRONGER STORMS.
THESE STORMS WILL LIKELY PRODUCE WIDELY SCATTERED IFR CONDITIONS AND
SCATTERED MVFR CONDITIONS AS WELL AS MOUNTAIN OBSCURATIONS. THESE
SHOWERS WILL LINGER PAST MIDNIGHT BUT GRADUALLY DECREASE IN
INTENSITY AFTER MIDNIGHT AS THEY SLOWLY EXIT TO THE EAST. AS THE
TROUGH OF LOW PRESSURE ASSOCIATED WITH THE APPROACHING
AFOREMENTIONED LOW PRESSURE CENTER APPROACHES WYOMING...NUMEROUS
SHOWERS AND THUNDERSTORMS WILL OCCUR ACROSS WESTERN AND NORTHERN
WYOMING FRIDAY ALONG WITH ISOLATED TO WIDELY SCATTERED COVERAGE
ELSEWHERE. ANY SHOWER ACTIVITY AFTER MIDNIGHT TONIGHT WILL LIKELY
CREATE ISOLATED IFR CONDITIONS AND WIDELY SCATTERED MVFR CONDITIONS
ALONG WITH SOME MOUNTAIN OBSCURATIONS.

&&

.FIRE WEATHER...
AN UNSEASONABLY STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL SPIN
AROUND IDAHO THROUGH SATURDAY MORNING BEFORE GRADUALLY MOVING INTO
SOUTHWEST WYOMING THIS AFTERNOON AND ACROSS CENTRAL WYOMING
SATURDAY NIGHT. A DRY SOUTHWEST WIND ACROSS THE SOUTHEASTERN ZONES
WILL MEET A COLD FRONT MOVING SOUTH FROM THE BIG HORN BASIN AND
JOHNSON COUNTY THIS EVENING FOR ANOTHER ROUND OF SHOWERS AND
THUNDERSTORMS. ANOTHER FRONT WILL ALSO MOVE FROM WESTERN WYOMING
INTO CENTRAL WYOMING THIS EVENING WITH NUMEROUS MOUNTAIN SHOWERS
AND SOME THUNDERSTORMS. A FEW STORMS COULD BE SEVERE ACROSS THE
NORTH END OF THE DISTRICT THROUGH THIS EVENING. MUCH COOLER AIR
WILL BE USHERED IN TONIGHT AND SATURDAY WITH THE SNOW LEVEL
LOWERING TO 8000 FEET IN NORTHWEST MOUNTAINS AND 9000 FEET IN THE
WIND RIVER MOUNTAINS. SOME ACCUMULATION IS EXPECTED...ESPECIALLY
ABOVE 9000 TO 10000 FEET. SHOWERS AND SOME THUNDERSTORMS WILL BE
QUITE NUMEROUS ACROSS MUCH OF THE AREA SATURDAY INTO SATURDAY NIGHT.
THE FAR SOUTH WILL LIKELY SEE THE LEAST AMOUNT OF SHOWERS. SUNDAY AND
MONDAY WILL SEE A WARMING TREND WITH LITTLE OR NO CHANCE OF
PRECIPITATION.

&&

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

&&

SHORT TERM...SKRBAC
LONG TERM...WM
AVIATION...LIPSON
FIRE WEATHER...SKRBAC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
652 PM MDT FRI AUG 7 2009

WYZ001>020-022>030-081200-
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-
652 PM MDT FRI AUG 7 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED ACROSS WESTERN AND
CENTRAL WYOMING THIS EVENING AND OVERNIGHT. SOME THUNDERSTORMS MAY BE
STRONG IN NORTHERN WYOMING...WITH GUSTY WIND TO 45 MPH...SMALL HAIL
AND BRIEF HEAVY RAIN.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

AN UNSTABLE AIRMASS OVER THE REGION SATURDAY WILL ALLOW FOR A
CONTINUED CHANCE OF SHOWERS AND THUNDERSTORMS. COOLER AND DRIER AIR
WILL FOLLOW SUNDAY. SNOW IS ALSO EXPECTED OVER THE NORTHWEST
MOUNTAINS FRIDAY NIGHT AND SATURDAY WITH THE SNOW LEVEL BETWEEN 8500
AND 9500 FEET. SEVERAL INCHES OF SNOW IS EXPECTED ABOVE 9000 TO 10000
FEET.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO REPORT HAIL AND WIND GUSTS IN EXCESS OF 40 MPH
FROM THUNDERSTORMS. THANK YOU.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
427 PM MDT FRI AUG 7 2009

WYZ010-011-072315-
NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY-
427 PM MDT FRI AUG 7 2009

...SIGNIFICANT WEATHER ADVISORY FOR JOHNSON COUNTY UNTIL 515 PM
MDT...

AT 425 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR I90 EXIT 73...OR 16 MILES EAST OF BUFFALO...
MOVING NORTHEAST AT 20 MPH.

PENNY SIZE HAIL...HEAVY RAIN AND WIND GUST AROUND 40 MPH ARE
LIKELY WITH THIS STORM.

RESIDENTS IN NORTHEASTERN JOHNSON COUNTY...INCLUDING THE LOCATIONS OF
I90 EXIT 66 TO EXIT 77...SHOULD MONITOR THE WEATHER SITUATION
CLOSELY.

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

LAT...LON 4455 10638 4455 10602 4415 10629 4426 10658
TIME...MOT...LOC 2225Z 221DEG 17KT 4427 10641

AR

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RIVERTON WY
555 PM MDT FRI AUG 07 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0444 PM     HAIL             4 SE BURLINGTON         44.41N 108.37W
08/07/2009  M1.00 INCH       BIG HORN           WY   TRAINED SPOTTER

0451 PM     HAIL             2 NW OTTO               44.42N 108.30W
08/07/2009  M1.25 INCH       BIG HORN           WY   TRAINED SPOTTER

0510 PM     HAIL             GREYBULL                44.49N 108.06W
08/07/2009  M2.00 INCH       BIG HORN           WY   TRAINED SPOTTER

            HAIL LASTED 5 MINUTES. MOST OF THE HAIL WAS ONE TO TWO
            INCHES IN DIAMETER.

0517 PM     HAIL             GREYBULL                44.49N 108.06W
08/07/2009  E2.00 INCH       BIG HORN           WY   TRAINED SPOTTER

            HAIL SIZE WAS ESTIMATED TO BE AT LEAST TWO INCHES IN
            DIAMETER WHEN IT LANDED ON AND DENTED THE HOOD OF A
            TAVELING VEHICLE. MOST OF THE HAIL WAS HALF DOLLAR SIZE.

0517 PM     HAIL             1 E GREYBULL            44.49N 108.04W
08/07/2009  M1.25 INCH       BIG HORN           WY   TRAINED SPOTTER

0524 PM     TSTM WND GST     GREYBULL                44.49N 108.06W
08/07/2009  M59 MPH          BIG HORN           WY   ASOS

&&

DLIPSON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
749 PM MDT FRI AUG 7 2009

WYZ002>004-080300-
ABSAROKA MOUNTAINS-CODY FOOTHILLS-NORTH BIG HORN BASIN-
749 PM MDT FRI AUG 7 2009

EXPECT SHOWERS AND A FEW THUNDERSTORMS TO MOVE THROUGH PARK AND BIG
HORN COUNTY THROUGH 900 PM. THE STORMS WILL BE CAPABLE OF PRODUCING
PEA TO MARBLE SIZE HAIL...BRIEF HEAVY RAIN AND WIND GUSTS TO 30 MPH.
THE STORMS WILL BE MOVING FROM SOUTH TO NORTH ACROSS THE AREA AT 30
MPH.

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

AR

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1009 PM MDT FRI AUG 7 2009

WYZ009>011-080445-
BIGHORN MOUNTAINS SOUTHEAST-NORTHEAST JOHNSON COUNTY-SOUTHEAST
JOHNSON COUNTY-
1009 PM MDT FRI AUG 7 2009

...SIGNIFICANT WEATHER ADVISORY FOR JOHNSON COUNTY UNTIL 1045 PM
MDT...

AT 1006 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 21 MILES SOUTH OF
BUFFALO TO BARNUM...INCLUDING MAYOWORTH...OR AREAS JUST WEST OF
INTERSTATE 25...MOVING NORTHEAST AT 10 MPH.

PENNY SIZE HAIL...AND WINDS AROUND 50 MPH ARE POSSIBLE WITH THESE
STORMS. RAINFALL AMOUNTS OF THREE-QUARTERS OF AN INCH TO ONE INCH...
AND DANGEROUS CLOUD-TO-GROUND LIGHTNING ARE POSSIBLE WITH THESE
STORMS. THIS HEAVY RAIN IN A SHORT AMOUNT OF TIME COULD CAUSE RAPID
RISES OF SMALL STREAMS AND NORMALLY DRY WASHES.

RESIDENTS IN CENTRAL JOHNSON COUNTY...INCLUDING THE LOCATIONS OF
STATE HWY 196...MAYOWORTH...SHOULD MONITOR THE WEATHER SITUATION
CLOSELY. LISTEN FOR POSSIBLE WARNINGS AND BE PREPARED TO TAKE
APPROPRIATE ACTION SHOULD SEVERE WEATHER THREATEN.

THIS INCLUDES INTERSTATE 25 IN WYOMING BETWEEN MILE MARKERS 247 AND
286.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

MOVE INDOORS IMMEDIATELY AS THIS STORM APPROACHES YOUR LOCATION. THIS
IS A POTENTIALLY DANGEROUS STORM. IF YOU ARE IN ITS PATH...YOU SHOULD
BE PREPARED FOR GUSTY WINDS...HAIL...AND DEADLY CLOUD TO GROUND
LIGHTNING. IF A STURDY STRUCTURE IS NOT AVAILABLE...SEEK SHELTER IN A
VEHICLE WITH THE WINDOWS UP.

&&

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

LAT...LON 4420 10645 4361 10659 4353 10707 4414 10688
TIME...MOT...LOC 0407Z 255DEG 11KT 4404 10674 4364 10691