Severe Thunderstorm Warning 8, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
156 PM MDT SUN MAY 26 2013

.SHORT TERM...TONIGHT THROUGH MEMORIAL DAY

CONVECTION FIRING THIS AFTERNOON OFF THE ABSAROKAS AND BIGHORNS.
CIRRUS SHIELD HAS LIMITED HEATING OVER WESTERN WYOMING...BUT VISIBLE
LOOP SHOWING SOME CONVECTIVE ELEMENTS THROUGH THE BREAKS IN THE
SHIELD. WATER VAPOR IMAGERY SHOWS A JET STREAK ROUNDING THE BASE OF
THE SHORTWAVE TRACKING EAST THROUGH OREGON. THIS 70KT+ JET STREAK
WILL HELP TO ENHANCE CONVECTION LATER THIS AFTERNOON AND EVENING
ACROSS NORTHWEST AND NORTHERN WYOMING. VEERING WIND PROFILES
CERTAINLY INDICATE SUFFICIENT SUPPORT FOR STRONG STORMS ACROSS THE
NORTHERN TIER OF THE FORECAST AREA LATER TODAY AND THIS EVENING.
A SLIGHT RISK OF SEVERE STORMS REMAINS ACROSS PORTIONS OF MAINLY
JOHNSON AND BIG HORN COUNTIES. DEW POINTS ARE MOST FAVORABLE IN
JOHNSON COUNTY WHERE 40S TO LOWER 50S EXIST. SOUTHWEST WIND WILL
GRADUALLY MIX TO THE SURFACE BY 21Z WHICH WILL AID DRYING AND
CAUSE A RETREAT OF THE MOIST AIR TO THE NORTH IN THIS REGION.
THEREFORE...STORMS ARE LIKELY TO BE CONFINED TO THE NORTHERN HALF
OF JOHNSON COUNTY AND THE NORTHERN BIG HORN BASIN. DEEP CONVECTION
SHOULD WANE WITH THE LOSS OF DIURNAL HEATING AND DEPARTURE OF JET
STREAK TO THE NORTHEAST. SHORTWAVE OVER OREGON THEN ENTERS THE
PICTURE AND CLIPS NORTHWEST WYOMING OVERNIGHT. HAVE BOOSTED
PRECIPITATION CHANCES IN THIS REGION THROUGH 12Z/MONDAY. SHORTWAVE
WILL COMPLETE ITS TRACK ACROSS THE NORTHERN FORECAST AREA BY
18Z/MONDAY. EXPECT WESTERLY FLOW BEHIND THIS SHORTWAVE TO SHUNT
THE AXIS OF BEST MOISTURE AND INSTABILITY TO ALONG AND NEAR OUR
EASTERN BORDER. COULD STILL SEE ANOTHER NORTHERLY SURGE OF
LOW-LEVEL MOIST AIR ALONG THE EAST SLOPES OF THE BIGHORNS LATE
TONIGHT. THESE CLOUDS SHOULD DISSIPATE AGAIN BY MID-MORNING BUT
WILL AGAIN LEAVE BEHIND A MORE MOIST BOUNDARY LAYER. THUS...WOULD
NOT BE SURPRISED TO SEE SOME ISOLATED AFTERNOON SHOWERS AND
THUNDERSTORMS ACROSS JOHNSON AND NATRONA COUNTIES ON MONDAY.
OTHERWISE...IT LOOKS LIKE MEMORIAL DAY CONVECTION WILL MAINLY BE
CONFINED TO THE HIGHER TERRAIN OF THE NORTH. TEMPERATURES WILL BE
ABOUT 5 DEGREES COOLER ON MEMORIAL DAY FROM TODAY BUT STILL
SEASONAL FOR LATE MAY. GUSTY SURFACE WEST WIND OF 10-25 MPH WILL
BECOME PREVALENT AT MANY LOCATIONS BETWEEN 17Z-20Z/MONDAY.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

MOST OF THE PRECIPITATION WILL END BY MONDAY EVENING AS THE
SHORTWAVE EXITS TO THE EAST AND A SHORT LIVED HIGH PRESSURE RIDGE
MOVES OVER THE AREA. BY TUESDAY...THE VORT MAX THAT IS NOW NOSING
INTO AN AREA OFF THE PACIFIC COAST AT 140W/40N AND THE ASSOCIATED
SHORTWAVE TROUGH WILL FOLLOW CLOSELY BEHIND MONDAY/S SHORTWAVE AND
WILL MAKE LANDFALL MONDAY NIGHT. THIS SHORTWAVE WILL ARRIVE IN
THE INTERMOUNTAIN WEST AS A NEGATIVELY TILTED TROUGH WEDNESDAY. AS
IT DOES...THE STEERING WINDS WILL BACK AND BECOME MORE DIFLUENT OVER
THE AREA TUESDAY. THE END RESULT WILL MAKE FOR A WET DAY TUESDAY
WITH NUMEROUS SHOWERS AND LATE DAY EMBEDDED ISOLATED THUNDERSTORMS
WITH SMALL HAIL AS THE TEMPS TURN COLDER ALOFT. THE HIGHEST POPS
WILL BE IN THE WEST AND BIGHORN MTNS TUESDAY. BY WEDNESDAY
MORNING H7 TEMPS WILL DIP DOWN TO -2C IN THE FAR WEST. THE
ASSOCIATED 700MB CIRCULATION WILL TRACK EAST ACROSS THE NORTHERN
TIER OF WYOMING DURING THE COURSE OF THE DAY WEDNESDAY. THEREFORE
THE LOWEST POPS WOULD BE IN SOUTHERN WY WEDNESDAY WITH THE HIGHEST
QPF IN THE NORTH. SNOW LEVELS SHOULD BE AROUND 8K IN THE FAR WEST
WEDNESDAY MORNING. OVERALL...WEDNESDAY WILL BE A COOL AND
UNSETTLED DAY. ON THURSDAY...H7 TEMPS WILL BOTTOM OUT TO -3C IN
THE FAR WEST WITH SNOWFLAKES LIKELY MAKING IT ALL THE WAY DOWN TO
7000 FEET THERE AND 8000 FEET IN THE WIND RIVER MTNS. THE H5
TROUGH WILL CLOSE OFF RIGHT OVER NORTHERN WY THURSDAY WITH
SCATTERED POPS IN THE SOUTH AND HIGH SCATTERED TO LIKELY IN THE
NORTH. BY LATE THURSDAY THE LOW WILL DEEPEN AND BECOME MORE WELL
DEFINED OVER THE NORTHERN PLAINS WITH WRAP AROUND MOISTURE MAKING
IT INTO WYOMING FOR ANOTHER WET AND COOLISH DAY THURSDAY. ON
FRIDAY AND SATURDAY THE PRECIP WILL SLOWLY RETREAT TO THE NORTH AS
WE LOSE THE WRAP AROUND MOISTURE AS THE LOW OVER THE NORTHERN
PLAINS EXITS THE AREA. HOWEVER...JOHNSON COUNTY WILL STILL BE
UNDERNEATH THE WRAP AROUND ISENTROPIC LIFT ROTATING AROUND THE
PLAINS LOW FOR ADDITIONAL MEASURABLE PRECIP. BY SUNDAY IT WILL BE
WARMER AND MILDER ACROSS THE FORECAST AREA.

&&

.AVIATION.../00Z ISSUANCE/

CONVECTION ONGOING ACROSS THE NORTHERN-THIRD OF THE FORECAST AREA
THIS AFTERNOON. SHOWERS AND THUNDERSTORMS...SOME TO BE STRONG TO
MARGINALLY SEVERE...WILL CONTINUE UNTIL AROUND SUNSET. SMALL HAIL
AND GUSTY OUTFLOW WIND TO AROUND 40KTS ARE THE LIKELY HAZARDS IN
ASSOCIATION WITH THE STRONGER STORMS. SHOWERS ARE LIKELY TO LINGER
UNTIL AROUND MIDNIGHT BEFORE DISSIPATING. THE EXCEPTION WILL BE THE
NORTHWEST CORNER OF WYOMING WHICH WILL BE IMPACTED BY A PASSING
SHORTWAVE OVERNIGHT. SCATTERED SHOWERS AND ISOLATED WEAK
THUNDERSTORMS ARE POSSIBLE MUCH OF THE NIGHT IN AND AROUND
YELLOWSTONE NATIONAL PARK. VFR CONDITIONS WILL BE FOUND AT ALL
TERMINALS THROUGH THE FORECAST PERIOD. HOWEVER...COULD STILL SEE A
RETURN OF LOW CLOUDS IN MOIST BOUNDARY LAYER EAST OF THE BIGHORNS
AFTER MIDNIGHT. CEILINGS BELOW 3K FEET AND OBSCURATIONS OF THE
FOOTHILLS WOULD AGAIN POSE A PROBLEM IN THIS REGION AROUND KBYG.
THE SOUTH HALF OF THE REGION WILL CONTINUE TO BE FED BY DRY
SOUTHWEST FLOW THROUGH THIS EVENING LIMITING EVEN THE DEVELOPMENT
OF CUMULUS CLOUDS. GUSTY SOUTHWEST WIND OF GENERALLY 12-25KTS WILL
DECREASE EARLY THIS EVENING. WEST WINDS WILL KICK-UP AT THE
SOUTHERN AND CENTRAL TERMINALS BETWEEN 17Z-20Z/MON AND CONTINUE
THROUGH THE AFTERNOON. OVERALL...MEMORIAL DAY AFTERNOON IS SHAPING
UP TO BE AT LEAST A LITTLE QUIETER. BEST INSTABILITY WILL BE OVER
JOHNSON AND NATRONA COUNTIES AND POINTS EAST. THEREFORE...HAVE
TRENDED TOWARD VCSH FOR KCPR WITH THIS ISSUANCE.

&&

.FIRE WEATHER...

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS NORTHERN
WYOMING INTO THE EVENING HOURS BEFORE DISSIPATING. THE EXCEPTION
WILL BE ZONE 140 AND NEARBY PORTIONS OF ZONES 415 AND 286 WHICH WILL
BE CLIPPED BY A PASSING DISTURBANCE OVERNIGHT. THIS WEAK SYSTEM WILL
ALLOW FOR SHOWERS AND ISOLATED THUNDERSTORMS TO PREVAIL ACROSS THESE
AREAS OVERNIGHT. DRIER WESTERLY FLOW GRADUALLY SPREADS EAST ACROSS
THE STATE ON MEMORIAL DAY. THIS WILL LEAVE THE CASPER DISPATCH AREA
AND THE HIGHER ELEVATIONS OF THE NORTH WITH THE BEST CHANCE FOR
AFTERNOON SHOWERS AND THUNDERSTORMS. GUSTY WEST WIND WILL INCREASE
TO 12-25MPH IN MANY ZONES BETWEEN 1100L AND 1400L ON MEMORIAL DAY.
MONDAY NIGHT LOOKS DRY AHEAD OF THE NEXT ROUND OF MOISTURE POISED
TO AFFECT WESTERN WYOMING ON TUESDAY. SHOWERS AND STORMS WILL BE
WIDESPREAD TUESDAY AFTERNOON ALONG AND WEST OF THE CONTINENTAL
DIVIDE. A TROUGH OF LOW PRESSURE THEN LOOKS TO SET-UP SHOP ACROSS
THE NORTHERN AND CENTRAL ROCKIES FOR MOST OF THE REMAINDER OF THE
WORK WEEK. TEMPERATURES WILL BE BELOW NORMAL AND EACH DAY WILL
BRING A CHANCE OF PRECIPITATION INCLUDING LIGHT SNOW ABOVE 9000 FT
AT NIGHT LATER IN THE WEEK.

&&

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

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

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
539 PM MDT SUN MAY 26 2013

WYZ004-008-270030-
BIGHORN MOUNTAINS WEST WY-NORTH BIG HORN BASIN WY-
539 PM MDT SUN MAY 26 2013

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN BIG HORN COUNTY IN NORTH
CENTRAL WYOMING UNTIL 630 PM MDT...

AT 537 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 8 MILES NORTH OF MEDICINE LODGE ARCHAEOLOGICAL
SITE...OR 23 MILES EAST OF BASIN...MOVING NORTHEAST AT 35 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER IS EXPECTED WITH THIS STORM...
ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING.

THIS STORM WILL BE NEAR...
RURAL EASTERN BIG HORN COUNTY THROUGH 630 PM MDT

THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS... FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO POSSIBLE. 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 4461 10745 4433 10738 4429 10760 4444 10775
      4463 10747
TIME...MOT...LOC 2338Z 235DEG 30KT 4442 10757

LIPSON