Severe Thunderstorm Warning 69, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1147 AM MDT TUE SEP 17 2013

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

CONVECTION CONTINUES TO BE ONGOING LATER TONIGHT WITH A STRONG
THUNDERSTORM MOVING TO THE SNAKE PLAIN OF IDAHO. THE CULPRIT FOR
THIS IS A JET STREAK RIDING SOUTHWEST TO NORTHEAST THROUGH SOUTHEAST
IDAHO AND WESTERN WYOMING AND THAT AREA IN THE RIGHT REAR QUAD OF
THE JET. SHOWERS AND EMBEDDED THUNDERSTORMS ARE EXPECTED TO CONTINUE
ACROSS THE WEST FOR MUCH OF THE DAY AS A RESULT. AS FOR STRONGER
STORMS...THERE IS A SEE TEXT AREA JUST TO THE NORTH. HOWEVER...THE
BEST DYNAMICS MAY STAY ACROSS IDAHO AND WESTERN MONTANA.
NEVERTHELESS...THERE COULD BE A FEW STRONGER THUNDERSTORMS TODAY
ACROSS THE WEST WITH GUSTY WINDS AND HAIL THE MAIN THREATS.
MEANWHILE...EAST OF THE DIVIDE IT LOOKS TO BE A WARM DAY...PROBABLY
THE WARMEST DAY OF THE FORECAST PERIOD. WITH A COLD FRONT
APPROACHING FROM THE WEST SOUTHWESTERLY FLOW WILL INCREASE TODAY
WITH A WEST TO SOUTHWESTERLY BREEZE DEVELOPING ACROSS THE REGION
THAT WILL PUSH TEMPERATURES IN MANY OF THE LOWER ELEVATIONS INTO THE
80S. AS FOR CONVECTION...WE HAVE AT LEAST OF A SLIGHT CHANCE
EVERYWHERE WITH THE SHORTWAVE MOVING ACROSS THE AREA. HOWEVER...WITH
DOWN SLOPING FLOW AND THE BEST UPPER LEVEL FORCING WAITING UNTIL
LATER IN THE DAY STORMS WILL LIKELY HOLD OFF UNTIL LATER IN THE
AFTERNOON AND EVENING FOR MOST LOCATIONS. ANY CONVECTION SHOULD
CLEAR THE AREAS EAST OF THE DIVIDE BY MIDNIGHT.
HOWEVER...PRECIPITATION LOOKS TO CONTINUE ACROSS NORTHWESTERN
WYOMING WITH THE APPROACH OF THE COLD FRONT. IN ADDITION...THE
REGION WILL BE IN THE LEFT FRONT QUADRANT OF A 90 TO 95 KNOT JET
THAT WILL ENHANCE UPLIFT. WITH COLDER AIR COMING IN BEHIND THE
FRONT...IT IS POSSIBLE THAT THE HIGHER ELEVATIONS COULD SEE AN INCH
OR TWO OF SNOW TONIGHT. WORKING AGAINST IS MUCH DRIER AIR WILL BE
MOVING IN LATE AT NIGHT THAT COULD SHUT OFF ANY PRECIPITATION.

THE COLD FRONT WILL SWEEP ACROSS THE STATE ON WEDNESDAY. AT THIS
TIME...ANY PRECIPITATION LOOKS TO BE RELATIVELY LIGHT WITH VERY DRY
AIR IN PLACE OVER MUCH OF THE AREA. WE HAVE SOME POPS IN PLACE
ACROSS NORTHWESTERN AND FAR NORTHERN WYOMING WITH THE FAVORABLE JET
DYNAMICS THOUGH. THE BIG EFFECT IS GOING TO BE THE DEVELOPMENT OF
WINDY CONDITIONS ACROSS PORTIONS OF THE AREA WITH THE TIGHTENING OF
THE PRESSURE GRADIENT. THE WINDIEST AREAS WILL LIKELY BE THE FAVORED
AREAS LIKE THE SOUTHWESTERN WIND CORRIDOR FROM THE RED DESERT
THROUGH CASPER. THERE COULD ALSO BE SOME GAP FLOW IN THE FAVORED
AREAS SUCH AS CLARK. 700 MILLIBAR WINDS ARE GENERALLY AROUND 30 TO
40 KNOTS AT THE MAXIMUM SO HIGH WIND WARNING CRITERIA IS NOT
EXPECTED. HOWEVER...WITH DOWNWARD FORCING AND GOOD MIXING IT WILL
DEFINITELY BE A TOUPEE ALERT DAY. THIS WILL MAKE HIGH TEMPERATURES
TRICKY EAST OF THE DIVIDE SINCE COLD ADVECTION WILL BE FIGHTING
STRONG DOWN SLOPING FLOW. FOR NOW WE MADE FEW CHANGES TO HIGH
TEMPERATURES. WIND WILL SUBSIDE WEDNESDAY NIGHT AS HIGH PRESSURE
BUILDS IN FROM THE WEST. WITH THIS HIGH BEING A COOL ONE...COMBINED
WITH A CLEAR SKY AND LIGHT WIND...THERE COULD BE FROST IN MANY AREAS
WEST OF THE DIVIDE AND POSSIBLY A FREEZE IN THE MORE PROTECTED
AREAS.

HIGH PRESSURE WILL CONTROL THE WEATHER ON THURSDAY AND BRING A DRY
AND SETTLED DAY. IT WILL BE COOL WITH TEMPERATURES AVERAGING 5 TO 10
DEGREES COOLER THAN NORMAL FOR MOST LOCATIONS. A JET STREAK MOVING
OVER THE AREA COULD BRING A FEW MID TO HIGH LEVEL CLOUDS BUT NO
PRECIPITATION IS EXPECTED.

.LONG TERM...FRIDAY THROUGH TUESDAY

FRIDAY WILL BE DRY WITH THE UPPER RIDGE AXIS PASSING THROUGH THE
AREA. SW FLOW ALOFT FRIDAY NIGHT THROUGH SATURDAY AHEAD OF THE NEXT
WEATHER SYSTEM. IT NOW APPEARS THE FAR WEST WILL STAY DRY THROUGH
00Z SUNDAY SO WENT WITH DRY FORECAST ALL AREAS. BREEZY TO LOCALLY
WINDY SATURDAY AFTERNOON/EVENING. THE WEATHER SYSTEM MOVES INTO THE
WEST SATURDAY NIGHT AND ACROSS THE REGION ON SUNDAY. GFS AND ECMWF
MODELS STILL DIFFER ON STRENGTH OF THE SYSTEM AND THE SPEED AT WHICH
IT MOVES THROUGH SUNDAY/SUNDAY NIGHT. HAVE KEPT THE FORECAST GOING
WITH CHANCE OF SHOWERS AND STORMS. MONDAY LOOKS DRY AS THE SYSTEM
DEPARTS. BOTH THE GFS AND ECMWF MODELS HINT AT SOME PRECIP IN NW WY
NEXT TUESDAY AFTERNOON SO WILL PUT LOW PRECIP CHANCE IN FORECAST.
TEMPS WILL BE MILD TO WARM FRIDAY AND SATURDAY...THEN COLDER FOR
SUNDAY...SOME SLIGHT WARMING NEXT MONDAY AND TUESDAY.

.AVIATION.../18Z ISSUANCE/

A TROUGH PUSHING ACROSS THE PACIFIC NORTHWEST TODAY...AND THEN
ACROSS THE NORTHERN INTER MOUNTAIN WEST TONIGHT WILL RESULT IN
INCLEMENT WEATHER ESPECIALLY ACROSS THE WEST AND NORTHWEST. ONGOING
SHOWER ACTIVITY IS EXPECTED THIS MORNING NORTHWEST OF A KBPI-KCOD
LINE...WITH KJAC MOST LIKELY TO BE IMPACTED. THERE COULD ALSO BE
CONVECTION IS EXPECTED TO INTENSIFY AND SPREAD EAST OF THE
DIVIDE. HOWEVER COVERAGE EAST OF THE DIVIDE WILL BE LESS. SOME
THUNDERSTORMS COULD BE QUITE STRONG DUE TO THE ANTICIPATED
INSTABILITY AND LIFT ASSOCIATED WITH THE APPROACHING TROUGH.
SHOWERS AND THUNDERSTORMS WILL OBSCURE THE HIGHER MOUNTAINS ALONG
AND WEST OF THE CONTINENTAL DIVIDE.  CONVECTION WILL LINGER WELL
INTO THE NIGHT...MAINLY NORTHWEST OF A KBPI-KDUB- KWRL LINE.
ALSO...WINDY SOUTHWEST WINDS ARE EXPECTED TO INCREASE ACROSS MUCH
OF THE REGION WITH AREAS OF LOW LEVEL WIND SHEAR. THE ASSOCIATED
COLD FRONT WITH THIS SYSTEM IS EXPECTED TO PUSH INTO WESTERN
WYOMING AFTER 06Z WEDNESDAY. IFR/MVFR CONDITIONS WILL OCCUR NEAR
CONVECTION AND IN FOG WITH MOUNTAIN OBSCURATIONS AT TIMES.

.FIRE WEATHER...

SOUTHWEST FLOW WILL CONTINUE THROUGH TODAY. A SERIES OF WEAK LOW
PRESSURE TROUGHS IN THE FLOW WILL BRING ENHANCED INSTABILITY THROUGH
THE AFTERNOON WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS.
TEMPERATURES WILL WARM WITH DECREASING RELATIVE HUMIDITY. WINDS WILL
BECOME WINDY AND GUSTY INCREASING TUESDAY AFTERNOON. A COLD FRONT
WILL MOVE ACROSS THE AREA ON WEDNESDAY WITH COOLER TEMPERATURES AND
A GUSTY WIND.

&&

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

SHORT TERM...HATTINGS
LONG TERM...AR
AVIATION...C.BAKER
FIRE WEATHER...HATTINGS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
400 AM MDT TUE SEP 17 2013

WYZ001>020-022>030-181200-
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-
400 AM MDT TUE SEP 17 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL OCCUR MAINLY THIS AFTERNOON AND EVENING
WITH THE MOST NUMEROUS AND STRONGEST STORMS IN THE WESTERN
MOUNTAINS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ISOLATED THUNDERSTORMS WILL BE POSSIBLE OVER THE NORTH HALF OF THE
AREA WEDNESDAY.

ISOLATED THUNDERSTORMS ARE POSSIBLE ON SUNDAY WHEN A NEW WEATHER
SYSTEM MOVES INTO THE ROCKY MOUNTAIN REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY RAPIDLY RISING CREEKS OR
STREAMS...AS WELL AS ANY FLOODING...INCLUDING MUDSLIDES. THANK
YOU.

TEAM RIVERTON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1216 PM MDT TUE SEP 17 2013

WYZ023-024-027-172000-
SALT RIVER AND WYOMING RANGES-SOUTH LINCOLN COUNTY-STAR VALLEY-
1216 PM MDT TUE SEP 17 2013

ISOLATED THUNDERSTORMS CONTINUE TO DEVELOP IN EASTER IDAHO THIS
AFTERNOON...MOVING NORTHEAST INTO WESTERN WYOMING AT AROUND 40 MPH
THROUGH 2 PM. THE STORMS WILL PRODUCE WIND GUSTS FROM 35 TO 40 MPH...
SMALL HAIL...AND FREQUENT LIGHTNING AT TIMES. THE WIND GUSTS MAY BE
WELL AWAY FROM THE STORMS THEMSELVES DURING THIS ACTIVITY. STAY
INDOORS OR SEEK SHELTER INDOORS WHEN THREATENING WEATHER APPROACHES.

JFB

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1234 PM MDT TUE SEP 17 2013

WYZ024-027-171930-
SALT RIVER AND WYOMING RANGES WY-SOUTH LINCOLN COUNTY WY-
1234 PM MDT TUE SEP 17 2013

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN LINCOLN COUNTY UNTIL 130
PM MDT...

AT 1230 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
A STRONG THUNDERSTORM 7 MILES NORTHWEST OF WOODRUFF...OR 27 MILES
NORTHWEST OF EVANSTON...MOVING NORTHEAST AT 35 MPH.

HAIL UP TO THREE-EIGHTS INCH IN DIAMETER AND WIND GUSTS UP TO 45 MPH
ARE EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.

THIS STORM WILL BE NEAR...
U.S. HWY 30/89 MILE MARKER 30 AND SAGE JUNCTION AROUND 110 PM MDT.
U.S. HWY 30 MILE MARKER 40 AROUND 120 PM MDT.
FOSSIL BUTTE NATIONAL MONUMENT AROUND 125 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
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 4205 11105 4231 11084 4169 11019 4157 11077
      4158 11105
TIME...MOT...LOC 1833Z 232DEG 29KT 4160 11124

BRAUN

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