Severe Thunderstorm Warning 63, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
153 PM MDT SUN SEP 7 2014

.SHORT TERM...TONIGHT THROUGH MONDAY
A COUPLE OF DAYS LEFT OF SUMMER CONVECTION TO GO THROUGH MONDAY.
PRESENTLY SCATTERED THUNDERSTORMS HAVE GOTTEN AN EARLY START WITH T
STORMS FIRING IN THE LATE MORNING HOURS WHERE THE BEST CAPES HAVE
BEEN PROGGED AND THEY ARE ALREADY DRIFTING EAST ALONG THE OWL CREEK
MTNS. RECEIVED A REPORT OF HALF INCH HAIL AT BROOKS LAKE LODGE AS
EARLY AS 1145 AM. THE STEERING FLOW IS INCREASING FROM THE WEST
NORTHWEST AS THE BROAD TROUGH TO OUR NORTH...WHICH WILL AFFECT OUR
WEATHER DRAMATICALLY LATER THIS WEEK...BEGINS TO SAG SOUTH WHICH IS
HELPING CONVECTIVE CELLS TO ACCELERATE TO THE EAST RESULTING IN LESS
RESIDENCE TIME AND LESS POTENTIAL RAINFALL TO OCCUR OVER A GIVEN
LOCATION. FAVORABLE TOTAL TOTALS WILL ENABLE SHOWERS TO PERSIST PAST
MIDNIGHT IN SOME AREAS TONIGHT. WEAK DISTURBANCES WILL CONTINUE TO
RIDE UP AND OVER THE FLATTENING RIDGE OVER THE ROCKIES THROUGH
MONDAY. WE WILL SEE A REPEAT OF CONVECTION MONDAY AFTERNOON WITH THE
BEST CAPES OUT WEST ONCE AGAIN. WITH THE INCREASING GRADIENT...WEST
WINDS IN THE MTNS AND ALONG THE RKS TO CPR CORRIDOR WILL CONTINUE
THROUGH MONDAY. TEMPS EAST OF THE DIVIDE WILL WARM A FEW DEGREES
MONDAY WITH DOWNSLOPE FLOW AND WILL REMAIN AROUND THE SAME WEST.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY
ACTIVE PERIOD COMING UP WITH MONSOONAL/NORBERT MOISTURE AND EMBEDDED
WEAK WAVES IN THE SW FLOW FOLLOWED BY OUR FIRST SIGNIFICANT COLD
FRONT(S) OF THE UPCOMING COLD SEASON. GFS HAS TRENDED STRONGER
AND FURTHER WEST WITH THE SECOND SHORTWAVE DIVING SE WEDNESDAY
NIGHT AND THURSDAY AND THE NAM OUT TO 84 HOURS IS FURTHER WEST YET
AND VERY SIMILAR TO THE ECMWF. EVOLUTION STILL SIMILAR TO WHAT WE
DISCUSSED YESTERDAY WITH THE FIRST COLD FRONT MOVING INTO THE
NORTH TUESDAY MORNING...POSSIBLY BEFORE 12Z IN THE FAR NORTH. COLD
FRONT LOOKS LIKE IT WILL DROP SOUTH ACROSS THE NORTHERN ZONES
DURING THE MORNING AND INTO NATRONA BY MID TO LATE MORNING. FRONT
LOOKS SHALLOW IN NATRONA DURING THE DAY BUT THEN TUESDAY NIGHT A
STRONGER PUSH SHOULD ALLOW IT TO MAKE IT TO THE CONTINENTAL
DIVIDE. THE FRONT MAY TRY AND ERODE IN THE CENTRAL ZONES SOME
WEDNESDAY IN ADVANCE OF OUR SECOND STRONGER SHORTWAVE AND FRONTAL
SURGE. THIS SYSTEM HAS THE COLDEST AIR WITH IT AND MAY VERY WELL
LOWER THE SNOW LEVELS TO THE LOWER ELEVATIONS OF THE FAR NORTH
WEDNESDAY NIGHT INTO THURSDAY MORNING. THE NRN MOUNTAINS FROM THE
BEARTOOTH PLATEAU OVER TO THE NRN BIGHORNS WILL SEE SNOW
DEVELOPING OVER THE PEAK TUESDAY NIGHT NIGHT AND THEN SNOW LEVELS
LOWERING WEDNESDAY INTO WEDNESDAY NIGHT WITH SIGNIFICANT SNOWFALL
POSSIBLE IN THE BIGHORNS AND BEARTOOTH PASS AREA.

BUT BEFORE THIS COLD FRONT...WE WILL HAVE A GOOD SHOT OF SHOWERS AND
SOME THUNDERSTORMS ACROSS THE SOUTH MONDAY NIGHT AND TUESDAY WITH
THE AFOREMENTIONED MONSOONAL/NORBERT MOISTURE...UPPER DISTURBANCES
AND UPPER JET SUPPORT. AFTER THAT...ALL THE FOCUS TURNS TO THE NORTH
HALF. AN INCREASING CHANCE OF RAIN IN THE NORTH TUESDAY NIGHT WITH
SNOW CONFINED TO THE HIGHER PEAKS.

ON WEDNESDAY...COLDER AIR FILTERS IN WITH SLOWLY LOWERING SNOW LEVELS
AND A GOOD CHANCE OF RAIN IN THE NORTH AND A CHANCE FURTHER SOUTH.
SNOW LEVELS COULD DROP TO BETWEEN 7 AND 8K FEET BY WED AFTERNOON AND
THEN TO AROUND 5K BY THURSDAY MORNING. SO IDEA OF SNOW ACROSS THE
LOWER ELEVATIONS OF JOHNSON COUNTY STILL LOOKS GOOD. TEMPERATURES
ARE A LITTLE WARMER FURTHER WEST IN THE CODY FOOTHILLS BUT EVEN
THERE WE'LL HAVE TO KEEP A CLOSE WATCH AS H7 TEMPERATURES COULD DROP
TO BETWEEN -5 AND -6C WHICH NORMALLY EQUATES TO A SNOW LEVEL UNDER
6K. SIGNIFICANT SNOW IN THE BIGHORNS AND POSSIBLY THE BEARTOOTH
PLATEAU REGION WILL LIKELY LEAD TO WINTER HIGHLIGHTS OVER THE NEXT
COUPLE DAYS. SNOWFALL OVER A FOOT IN THE NRN BIGHORNS IS CERTAINLY
POSSIBLE IN THIS PATTERN. NEW ECMWF IS A LITTLE COLDER AGAIN AND
SLIGHTLY MORE BULLISH WITH PCPN IN CENTRAL WYO AND COLDER AIR.
ECMWF IS BACK TO POTENTIALLY GIVING THE CENTRAL ZONES A QUICK SHOT
OF RAIN/SNOW OR BRIEF SNOW THURSDAY MORNING. STILL A WAYS OUT TO
PIN DOWN THE EXACT DETAILS BUT IT'LL BE WATCHED VERY CLOSELY.

SHARPLY COLDER TUESDAY INTO WEDNESDAY AND CONTINUED COLD THURSDAY
EAST OF THE DIVIDE. THE SW WILL BE SPARED MOST OF THE COLDER AIR
ALTHOUGH IT WILL BE QUITE CHILLY AT NIGHT BY FRIDAY AND SATURDAY.
THAT WILL BE THE NEXT CONCERN AFTER THIS SYSTEM MOVES AWAY THURSDAY
NIGHT. A CLEARING SKY AND POTENTIALLY LIGHT WINDS WILL RESULT IN
FREEZING TEMPERATURES FOR QUITE A FEW AREAS EAST OF THE DIVIDE.
FRIDAY AND SATURDAY STILL LOOK DRIER WITH GRADUALLY WARMING
TEMPERATURES. WHAT HAPPENS BY SUNDAY IS ANOTHER PROBLEM. LAST
NIGHT THE OP ECMWF HAD A STRONG UPSTREAM RIDGE WITH ANOTHER COLD
BLAST MOVING INTO WYO COUNTRY. THE GFS HAD A WEAKER UPSTREAM RIDGE
AND MORE OF A GLANCING BLOW SHORTWAVE. THE NEW 12Z OP ECMWF IS
SIMILAR TO THE GFS NOW EXCEPT FOR ONE IMPORTANT PIECE. IT TAKES A
LITTLE BIT OF THIS CANADIAN SHORTWAVE ENERGY AND DIVES IT SOUTH
INTO THE OR/NERN CA/NRN NV REGION SUNDAY/SUNDAY NIGHT RESULTING IN
A MOIST SW MONSOONAL TYPE FLOW. WILL LEAN TOWARDS SOME MOISTURE
WITH NEIGHBORS ALREADY GOING WITH POPS TO THE SOUTH. CONFIDENCE
LOW FOR NEXT SUNDAY ATTM.

&&

.AVIATION.../00Z ISSUANCE/
WIDELY SCATTERED SHOWERS AND STORMS WILL OCCUR THROUGH 04Z.
LINGERING SHOWERS WILL OCCUR PAST MIDNIGHT TONIGHT. LOCAL MVFR
CONDITIONS AND ISOLD IFR CONDITIONS MAY OCCUR IN STORMS. WIDELY
SCATTERED SHOWERS AND THUNDERSTORMS WILL REDEVELOP MONDAY
AFTERNOON. WEST SOUTHWEST WINDS OF 15 TO 25 MPH WILL DIMINISH
AFTER SUNSET THIS EVENING FROM KRKS TO KCPR AND THEN REDEVELOP
AGAIN BY 15Z MONDAY.

&&

.FIRE WEATHER...
FIRE DANGER WILL BE ENHANCED ACROSS THE SOUTHEAST TO EASTERN
DISPATCH ZONES FOR THE REST OF THIS AFTERNOON ALONG WITH INSTABILITY
AND SOME STRONGER WINDS ALOFT ARE BROUGHT DOWN TO THE SURFACE. AT
THE MOMENT HOWEVER...BOTH WIND AND MINIMUM RH VALUES LOOK TO
REMAIN JUST ABOVE CRITICAL LEVELS...WITH PERHAPS A FEW ISOLATED
AREAS REACHING THESE VALUES FOR AN HOUR OR TWO. AN ISOLATED
THUNDERSTORM IS ALSO POSSIBLE AGAIN ACROSS THIS REGION.
ELSEWHERE...MIN RH VALUES GENERALLY RANGE FROM 20 TO 30
PERCENT...EVEN WITH GUSTY WEST WINDS. MONDAY...ANOTHER DAY OF
ENHANCED FIRE DANGER AS RH VALUES LOOK TO DROP A BIT FURTHER OVER
THE NORTHERN AND CENTRAL BASINS IN ADDITION TO EASTERN
ZONES...HOWEVER WINDS LOOK TO REMAIN BELOW CRITICAL LEVELS IN
THESE AREAS. WILL MONITOR FOR CHANGES TO THIS SITUATION.

&&

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

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
500 AM MDT SUN SEP 7 2014

WYZ001>020-022>030-081100-
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-
500 AM MDT SUN SEP 7 2014

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO WIDELY SCATTERED MOUNTAIN THUNDERSTORMS ACROSS THE
FORECAST AREA TODAY AND THIS EVENING WILL ALLOW FOR OCCASIONAL
LIGHTNING STRIKES...SMALL HAIL AND GUSTY ERRATIC WINDS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

MONDAY...ISOLATED TO WIDELY SCATTERED AFTERNOON AND
EVENING THUNDERSTORMS...MAINLY ACROSS THE SOUTHERN HALF OF THE
FORECAST AREA. HEAVY RAIN WILL BE POSSIBLE WITH SOME STORMS ACROSS
THE SOUTH.

TUESDAY...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS SOUTH.
ISOLATED SHOWERS AND STORMS CENTRAL AND NORTH. WIDELY
SCATTERED TO SCATTERED SHOWERS AND ISOLATED STORMS TUESDAY NIGHT...
WITH SNOW SHOWERS POSSIBLE ABOVE 8500 FEET IN THE HIGHER REACHES OF
THE NORTHERN MOUNTAINS.

WEDNESDAY AND THURSDAY...A STRONG CANADIAN COLD FRONT WILL BRING THE
POTENTIAL FOR SIGNIFICANT SNOW IN THE NORTHERN BIGHORN RANGE...ALONG
WITH HAZARDOUS WINTER DRIVING CONDITIONS OVER MOUNTAIN PASSES. A FEW
INCHES OF SNOW MAY ACCUMULATE IN THE LOWER ELEVATIONS ACROSS NORTHERN
WYOMING WEDNESDAY NIGHT AND THURSDAY MORNING...MAINLY ALONG AND NORTH
OF INTERSTATE 90 ACROSS JOHNSON COUNTY.

FRIDAY...A WIDESPREAD FREEZE OR FROST POSSIBLE ACROSS THE LOWER
ELEVATIONS OF CENTRAL WYOMING FRIDAY MORNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
100 PM MDT SUN SEP 7 2014

WYZ005>007-071945-
OWL CREEK AND BRIDGER MOUNTAINS WY-SOUTHEAST BIG HORN BASIN
WY-SOUTHWEST BIG HORN BASIN WY-
100 PM MDT SUN SEP 7 2014

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN WASHAKIE AND EASTERN HOT
SPRINGS COUNTIES UNTIL 145 PM MDT...

AT 1257 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
A STRONG THUNDERSTORM NEAR WINCHESTER...OR 14 MILES NORTH OF
THERMOPOLIS...MOVING EAST AT 20 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.

THIS STORM WILL BE NEAR...
RURAL WESTERN WASHAKIE COUNTY THROUGH 145 PM MDT
RURAL CENTRAL HOT SPRINGS COUNTY THROUGH 145 PM MDT
RURAL CENTRAL WASHAKIE COUNTY THROUGH 145 PM MDT
RURAL EASTERN HOT SPRINGS COUNTY THROUGH 145 PM MDT

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

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 4407 10768 4359 10771 4367 10826 4407 10824
TIME...MOT...LOC 1900Z 274DEG 16KT 4384 10814

SKRBAC

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