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000
FXUS65 KRIW 170526 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1126 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 ABSAROKA 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.

.LONG TERM...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.../06Z ISSUANCE/

SCATTERED SHOWERS WITH OCCNL THUNDER WILL CONTINUE OVER WESTERN
MOUNTAINS BETWEEN KJAC AND KBPI THROUGH THE NIGHT AS ANOTHER WAVE
APPROACHES IN THE SOUTHWEST FLOW...OCCNL MVFR CONDITIONS WITH
WIDESPREAD MOUNTAIN OBSCURATIONS EXPECTED THROUGH THE NIGHT AT
KJAC...KBPI AND KPNA.

ELSEWHERE...ISOLATED SHOWERS AND PERHAPS A STRIKE OR TWO OF
LIGHTNING POSSIBLE THROUGH THE NIGHT AS THIS NEXT WAVE MOVES THROUGH
WITH ACTIVITY DIMINISHING ACROSS CENTRAL AND SOUTHERN TERMINALS
TOWARD MORNING. ISOLATED TO SCATTERED CONVECTION IS EXPECTED TO
RETURN AFTER 18Z TOMORROW AT ALL TERMINALS EXCEPT KCPR AND KRKS
WHERE VERY DRY SOUTHWEST WINDS COULD GUST AS HIGH AS 30 KTS IN THE
AFTERNOON...THE MID LEVEL MOISTURE ACROSS THE BIGHORN AND WIND RIVER
BASINS SHOULD WORK TO OVERCOME THE DRY LOWER LEVELS...BUT ANY STORMS
THAT DO FORM WILL HAVE VERY GUSTY AND ERRATIC OUTFLOWS...ESPECIALLY
FROM 18-00Z.

.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...ALLEN
FIRE WEATHER...BRAUN