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000
FXUS65 KRIW 162208
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
408 PM MDT THU MAY 16 2013

.SHORT TERM...TONIGHT THROUGH FRIDAY

WV IMAGERY SHOWING AMPLIFYING TROF NEAR THE EPAC COASTAL REGION. AS
TROF CONTINUES TO AMPLIFY THERE WILL BE SEVERAL CHANCES FOR SHORT
WAVE/JET STREAK ENHANCEMENT AHEAD OF THE SLOW MOVING TROF TO MAKE
THEIR WAY INTO AT LEAST THE WRN TO NWRN PORTION OF OUR CWA. MORNING
CONVECTION...ASSOCIATED WITH ONE OF THESE UPPER SPEED MAXES...MOVED
IN FROM SERN ID AFFECTING THE AFTON AREA...AND ALL AFTER THEY WERE
MILDLY ROCKED BY A 3.6 EARTHQUAKE LAST NIGHT. ANOTHER ONE OF THESE
VORT MAXES HAS BEGUN TO INFLUENCE OUR FORECAST AREA THIS AFTERNOON
WITH STRONG HIGH BASED THUNDERSTORMS THAT DEVELOPED IN THE LEE OF
THE WIND RIVER MOUNTAINS AND BLEW THROUGH LANDER AND RIVERTON
BETWEEN 0100 AND 0130 PM.  LATER THIS EVENING AND
TONIGHT...ESPECIALLY THE NWRN QUAD INCLUDING THE TETON AND
YELLOWSTONE REGIONS...EXPECT SHOWERS TO CONTINUE THROUGH THE NIGHT.
OVERALL INSTABILITY IS IS FAIRLY LOW WITH MIXED LAYER CAPE AOBL 100
J/KG MOST PLACES EXCEPT HIGHER TERRAIN OF BIG HORNS...AND TO A
LESSER EXTENT ALONG THE WIND RIVER...OWL CREEK...GREEN
MOUNTAIN...AND ABSOROKA RANGES WHERE ML CAPE IS RIDING BETWEEN 100
AND 200...TO AROUND 500 J/KG BIG HORNS. EVEN THOUGH SFC DPTS ARE A
BIT HIGHER TODAY AND STRETCH FURTHER WEST THAN YESTERDAY... PWS ARE
ONLY A FEW HUNDREDTHS HIGHER THAN YESTERDAY...SO MODE OF CONVECTION
WILL BE SIMILAR...RELATIVELY DRY...OUTFLOW DOMINATED...OCCASIONAL
BRIEF SMALL HAIL AND BRIEF HEAVY RAIN. BEST CHANCE FOR SCATTERED
THUNDERSTORMS WILL OCCUR ALONG AND NEAR THESE ELEVATED POINTS AND IN
THE ADJACENT VALLEY/BASINS. MAX TEMPS TODAY WILL BE CLOSE TO
YESTERDAY`S HIGHS...SO NO REAL CHANGES HERE.

FIRST SVR WARNING AND STATEMENT THIS AFTERNOON WITH 60MPH GUSTS HERE AT THE
STATION.

FRIDAY...LOOKS A BIT SPLIT AS FAR AS HIGH TEMPS GO...FEW DEGREES
WARMER OVER THE EASTERN HALF OF THE CWA...SOMEWHAT COOLER WEST AND
NORTHWEST. SHORTWAVE MOVING QUICKLY THROUGH BOTTOM OF DEVELOPING
TROF NEAR CNTRL CA THAT WILL BEGIN TO AFFECT OUR WRN AND NWRN CWA
LATE THIS AFTERNOON WILL BE FOLLOWED CLOSELY BY ANOTHER WHICH WILL
KEEP CHANCES OF SHOWERS AND THUNDER GOING OVERNIGHT TONIGHT AND
THROUGH THE MORNING HOURS...ALL BEFORE YET ANOTHER DISTURBANCE MOVES
OVER WRN WY AS TROF BEGINS TO DEFORM AND BECOME NEGATIVELY TILTED.
AGAIN...THIS WILL KEEP MOST OF THE ACTION OVER THE WRN AND NWRN CWA.
ALSO...DYNAMICS ASSOCIATED WITH THESE DISTURBANCES LOOK TO BE MORE
VIGOROUS IN PROVIDING UPWARD VERTICAL AND IMPROVED SHEAR VALUES
WOULD ALSO KEEP STORMS GOING LONGER. STORM MOTION WILL TEND TOWARDS
A MORE SSW TO NNE TRACK. WRN MOUNTAINS...ESPECIALLY WEST OF A LYMAN
TO LOVELL LINE...LOOKS TO MAKE OUT BEST...WITH A SECONDARY WIDELY
SCATTERED ARE ACROSS THE BIGHORNS.

.FRIDAY NIGHT THROUGH THURSDAY...

THE LEAD SHORTWAVE THAT WILL EJECT OFF THE MAIN TROUGH THAT IS
CURRENTLY DIGGING JUST OFF THE PACIFIC COAST WILL DRIVE A COLD FRONT
SOUTH ACROSS THE CWA FRIDAY NIGHT. NORTH WINDS WILL PICK UP SOMEWHAT
WITH THIS FRONT EAST OF THE DIVIDE ALONG AND BEHIND THE FRONT WITH 3
HOURLY 5MB SURFACE PRESSURE RISES. H7 TEMPS WILL DROP TO -1C IN
WESTERN WYOMING BY 12Z SATURDAY AND TO 6C OVER EASTERN NATRONA
COUNTY. THUS WE WILL SEE A DOWNWARD SLIDE IN TEMPERATURES THROUGH
SUNDAY. MOST OF THE SHOWERS AND THUNDERSTORMS ASSOCIATED WITH
THIS SHORTWAVE WILL BE OVER WESTERN AND NORTHWESTERN WYOMING FRIDAY
NIGHT. AS THE MAIN TROUGH ITSELF APPROACHES THE CWA...PRECIP WILL
SPILL OVER THE DIVIDE WITH ALONG WITH LIKELY POPS IN THE WEST. BY
SUNDAY HIGHS WILL ONLY BE IN THE 60S AT THE LOWER ELEVATIONS EAST OF
THE DIVIDE WITH 50S WEST. THE BROAD MAIN TROUGH AXIS SHOULD BE
OVERHEAD BY SUNDAY. THEN BY SUNDAY NIGHT AND MONDAY...COOL AIR WILL
ADVECT AROUND THE BACKSIDE OF THE CLOSING LOW OVER THE PLAINS THAT
WILL BE ORGANIZING AND DEEPENING. THE COLD AIR AND MOISTURE WRAPPING
AROUND THE BACKSIDE OF THIS STRENGTHENING LOW MAY BE ENOUGH TO
PRODUCE UP TO 6 INCHES OF SNOWFALL IN THE BIG HORN MOUNTAINS SUNDAY
NIGHT INTO MONDAY...4 INCHES IN THE ABSAROKAS AND 3 INCHES IN THE
WIND RIVER MOUNTAINS. SNOW ACCUMULATION LEVELS SHOULD BE AT AROUND
8K. MONDAY WILL BE THE SECOND OF TWO COOL WET DAYS IN A ROW. THEN A
SHORT LIVED RIDGE OF HIGH PRESSURE WILL ALLOW TEMPS TO WARM TO THE
60S AND 70S TUESDAY BEFORE THE NEXT DEEPENING TROUGH INCREASES A
WARMING SOUTHWEST FLOW FOR THE REST OF THE WEEK. THE PRECIP FROM
THIS NEXT TROUGH WILL MAINLY AFFECT THE WESTERN CWA TOWARD THE END
OF NEXT WEEK IN THE FORM OF CONVECTION. HIGHS SHOULD RECOVER TO THE
70S AND 80S BY WEDNESDAY.


&&

.AVIATION.../00Z ISSUANCE/

ISOLATED THUNDER OVER WESTERN MOUNTAINS BETWEEN KJAC AND KBPI THIS
MORNING ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE. ISOLATED TO
SCATTERED CONVECTION IS EXPECTED THIS AFTERNOON INTO THE EVENING.
OUTFLOW DOMINATED STORMS THIS AFTERNOON IN THE LEE OF THE WIND
RIVERS. THE BEST CONCENTRATION SHOULD BE ACROSS THE NORTHWEST...BUT
ALL TAF SITES EXCEPT WILL HAVE THE POSSIBILITY OF THUNDERSTORM
ACTIVITY THIS AFTERNOON. MOST OF THIS ACTIVITY WILL WANE AN HOUR OR
TWO AFTER SUNSET...EXCEPT ACROSS THE WEST AND NORTHWEST. KJAC WILL
HOWEVER HAVE CONVECTION AROUND THROUGH THE ENTIRE NIGHT WITH DECENT
UPPER LEVEL SUPPORT. VFR CONDITIONS ARE EXPECTED AT MOST TAF
SITES...EXCEPT FOR BRIEF PERIODS OF MVFR/IFR CONDITIONS ASSOCIATED
WITH ANY SHOWER/THUNDERSTORM ACTIVITY.  KJAC COULD BE AFFECTED AFTER
03Z FRIDAY WHERE A SIGNIFICANT MVFR AREA COULD DEVELOP AS MORE
STRATIFORM TYPE OF CLOUDS AND PRECIP DEVELOPS.  WILL KEEP VFR
CONDITIONS FOR NOW AND JUST MONITOR AS CIGS COULD BECOME MVFR OR
EVEN IFR FOR A FEW HOURS AROUND SUNRISE. ALSO TOMORROW...KCPR AND
KRKS COULD GUST AS HIGH AS 30 KTS IN THE AFTERNOON WITHOUT THUNDER
AROUND.


&&

.FIRE WEATHER...

SHOWERS AND THUNDERSTORMS CONTINUE TODAY AS A FEW UPPER LEVEL
DISTURBANCES MOVE THROUGH THE REGION.  THESE STORMS WILL PRESENT AT
TIMES...BRIEF STRONG ERRATIC WINDS...SMALL HAIL AND OCCASIONAL
LIGHTNING. AMBIENT WINDS WILL BECOME QUITE GUSTY IN THE AFTERNOON
HOURS THE NEXT FEW DAYS...ESPECIALLY ON FRIDAY AND SATURDAY AND OVER
SWEETWATER AND NATRONA COUNTIES AND THE HIGHER ELEVATIONS OF THE
WIND RIVERS.  AFTERNOON SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR
THE NEXT COUPLE OF DAYS BEFORE A MUCH STRONGER TROUGH OF LOW
PRESSURE MOVES ACROSS THE FORECAST AREA ON SATURDAY...BRINGING
COOLER TEMPERATURES AND A MUCH BETTER CHANCE TO SHOWERS AND THUNDERSTORMS.

&&

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

$$

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