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000
FXUS65 KRIW 180527 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1127 PM MDT FRI MAY 17 2013

.SHORT TERM...TONIGHT THROUGH SATURDAY
TODAY...MORNING LINGERING SHOWERS OVER THE WRN AND NWRN BORDER
REGIONS THIS MORNING GIVING WAY TO SHOWERS WITH SOME THUNDER RUNNING
DIAGONALLY FROM THE EVANSTON AREA NE TO SHERIDAN. LOOKS A BIT SPLIT
AS FAR AS HIGH TEMPS GO TOO...THE 70 DEG DEMARCATION LINE RUNS FROM
AROUND ROCK SPRINGS WY ON THE SOUTH TO JUST WEST OF LOVELL WYO ON
THE NORTH WITH 50 TO 60 DEG HIGHS PREVALENT ACROSS THE MOUNTAINS.
LOWER MID AND UPPER 70S TO NEAR 80 WILL BE COMMON EAST OF THIS LINE.

SPLIT SHORTWAVE ACTIVITY...ONE EXITING NEAR NWRN TO NRN WY WITH
ANOTHER JUST MOVING INTO THE STATE FROM THE SW. BEST INSTABILITY
SHOWING UP NEAR THE SOUTHERN BIG HORNS AND INTERSECTION WITH THE OWL
CREEK RANGE...BOTH ML AND SFC. LINE BETWEEN THERMOPOLIS AND
EDGERTON...INCLUDING SOME OF HOT SPRINGS...WASHAKIE...AND JOHNSON
COUNTIES... LOOKS TO HAVE THE BEST ABILITY TO PRODUCE SOMEWHAT
STRONGER CONVECTION LATER IN THE DAY AS LL MOISTURE AND CONVERGENCE
WILL BE MAXIMIZED HERE...IN ADDITION TO H85 TO H5 SHEAR OF 35 TO 40
KTS. POSSIBLE MARGINAL SEVERE WITH HALF TO THREE QUARTER INCH HAIL
AND STRONG OUTFLOW WINDS. ADDITIONALLY...BIG HORN COUNTY MAY ALSO
GET OUTFLOW DOMINATED LINE TYPE CONVECTION AS T-STORMS DEVELOPING
OFF THE ABSAROKA MOUNTAINS MOVE THROUGH. AFTERNOON DCAPE VALUES ARE
HOVERING BETWEEN 600 AND 700 J/KG FOR MOST AREAS...WHICH WILL PUT
THE CONVECTIVE ACTIVITY TODAY IN A NARROW MARGINALLY SEVERE
WIND...UP TO 55 MPH...CATEGORY THIS AFTERNOON. ELSEWHERE...PRECIP
MODE WILL BE WEAK TO MODERATELY CONVECTIVE WITH RELATIVELY LOW
INSTABILITIES...BUT THE ELEVATED TERRAIN TOGETHER WITH STRONGER JET
LEVEL WINDS NEAR 80KTS FLOWING OVER THIS PART OF THE CWA WILL BE THE
PREFERRED AREA FOR EARLY INITIATION TODAY.

WRN CONUS TROF BECOMING MORE NEGATIVELY TILTED TODAY THROUGH
TOMORROW. AS IT DOES...WE WILL LOSE MUCH OF THE UPPER LEVEL
SUPPORT/FLOW...SHIFTING OVER FAR EASTERN CWA. ALSO...CLOUD COVER AND
COOL MOIST CONDITIONS OVER WESTERN 3/4RDS OF FA WILL KEEP OVERALL
INSTABILITY ON THE LOW SIDE COMPARED WITH TODAY. JOHNSON COUNTY
HOWEVER WILL ONCE AGAIN HAVE THE BEST SHOT AT PRODUCING STRONGER
THUNDER SATURDAY. OTHERWISE...EXPECT SCATTERED SHOWERS AND ISOLATED
THUNDER OVER MOST AREAS...WITH LESS PRCIP AND AREAL COVERAGE OVER
THE SOUTH CENTRAL AND SOUTHWEST CWA.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY
THE MAIN DIGGING NEGATIVELY TILTED TROUGH SHOULD BE OVER OUR CWA BY
SATURDAY NIGHT BEFORE CLOSING OFF BY 18Z SUNDAY. ON SATURDAY NIGHT
MOST OF THE PRECIP WILL BE CONFINED TO CENTRAL AND NORTHERN WYOMING.
THEN AS THE LOW CLOSES OFF OVER THE EASTERN HALF OF
WYOMING...MOISTURE AND COLD AIR WILL WRAP AROUND THE CLOSED LOW
SPREADING PRECIP INTO SOUTHERN WYOMING. THE COOLING TREND WILL
CONTINUE ON SUNDAY. H7 TEMPS WILL COOL DOWN TO BETWEEN -3 AND -4C IN
NW WYOMING BY SUNDAY WITH SNOW LEVELS GETTING DOWN TO 6500 FEET
THERE. ELSEWHERE...SNOW LEVELS SHOULD BE AROUND 8K. ON SUNDAY NIGHT
CYCLOGENESIS WILL TAKE PLACE AT H7 AND ABOVE OVER SOUTH DAKOTA WHICH
WILL DEEPEN THE NORTHERLY UPSLOPE FLOW EAST OF THE DIVIDE. THE
UPSLOPE COMPONENT WILL LOWER THE SNOW LEVEL DOWN TO 7500 FEET DUE TO
ADIABATIC COOLING ALONG THE EAST SLOPE OF THE WIND RIVER...ABSAROKA
AND BIG HORN MOUNTAINS SUNDAY NIGHT. CONVERSELY...SNOW LEVELS SHOULD
BE UP AS HIGH AS 9K ALONG THE WEST SLOPE OF THE WIND RIVER MTNS
SUNDAY NIGHT DUE TO DOWNSLOPE FLOW THERE. THESE SNOW LEVELS SHOULD
PERSIST THROUGH MONDAY WITH THE PRECIP BECOMING MORE STRATIFORM EAST
OF THE DIVIDE AS THE UPSLOPE DEEPENS. THE MOST SNOWFALL SHOULD FALL
ALONG THE EAST SLOPE OF THE WIND RIVER MTNS WHERE THE ORIENTATION OF
THE MOUNTAIN RANGE WILL BE BETTER SUITED TO FORCING THE NORTHERLY
FLOW INTO AN UPSLOPE COMPONENT WHERE AT LEAST 4 TO 5 INCHES OF SNOW
IS EXPECTED SUNDAY NIGHT INTO MONDAY. THE BIG HORN AND ABSAROKA MTNS
SHOULD SEE 2 TO 3 INCHES. ON MONDAY NIGHT THE PRECIP SHOULD START TO
WIND DOWN. ON TUESDAY A SHORT LIVED RIDGE OF HIGH PRESSURE WILL
PROVIDE A PRECIP FREE DAY AND SLIGHTLY MILDER TEMPS. THEN BY
WEDNESDAY A STRONG CLOSED LOW MIGRATING DOWN ALONG THE CANADIAN
PACIFIC COAST WILL SET UP SHOP OVER THE PACIFIC NORTHWEST. THE FIRST
SHORTWAVE THAT THIS CIRCULATION WILL EJECT TOWARD THE NORTHEAST WILL
PROVIDE A SHOT OF THUNDERSTORMS TO NW WYOMING FOR WEDNESDAY. A
SURFACE BASED SOUTHEAST FLOW PROVIDING AMPLE LOW LEVEL MOISTURE
COMBINING WITH INSTABILITY WILL RESULT IN THUNDERSTORM DEVELOPMENT
IN JOHNSON COUNTY AND THE BIG HORN MTNS AS WELL WEDNESDAY. THE NEXT
SUCH EJECTED SHORTWAVE WILL PROVIDE ANOTHER SHOT OF T STORMS FOR NW
WYOMING NEXT FRIDAY WITH SOUTHEAST SURFACE WINDS FEEDING LOW LEVEL
MOISTURE INTO JOHNSON COUNTY AND THE BIG HORN MOUNTAINS FOR
THUNDERSTORMS THERE AS WELL. THE SOUTHWEST STEERING FLOW OUT AHEAD
OF THIS CLOSED LOW IN THE PACIFIC NW WILL PROVIDE A WARMING TREND
FOR THE CWA THROUGH NEXT WEEK. THE EURO AND THE GFS BOTH SUPPORT
THIS TREND.

.AVIATION.../06Z ISSUANCE/
SHOWERS CONTINUE ACROSS THE WEST TERMINAL AREA AS ANOTHER WAVE MOVES
OVERHEAD IN SOUTHWEST FLOW...KJAC KBPI AND KPNA WILL CONTINUE TO
BE IN AND OUT OF MVFR TO IFR CONDITIONS THROUGH THE MORNING WITH
WIDESPREAD MOUNTAIN OBSCURATIONS ONGOING. MVFR TO IFR CONDITIONS
ARE ALSO POSSIBLE ACROSS THE BIGHORN BASIN AND AT KBYG THROUGH THE
MORNING HOURS AS FOG BEGINS TO FORM IN LOCATIONS WHERE HEAVY RAIN
FELL WITH THE STORMS ON FRIDAY AFTERNOON.

SHOWERS AND SOME STORMS WILL INCREASE IN COVERAGE ACROSS THE
ENTIRE FORECAST AREA AFTER 18Z...SO WILL KEEP VCTS AND VCSH IN
FORECAST FOR ALL TERMINALS. THE HIGHEST BASED STORMS WILL BE VCNTY
KCPR BETWEEN 20Z SAT AND 02Z SUN...THE THREAT FOR DOWNBURST WINDS
WILL BE GREATEST AT THIS TIME.

.FIRE WEATHER...
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS CONTINUE TODAY AS ANOTHER
COUPLE UPPER LEVEL DISTURBANCES MOVE THROUGH THE REGION...ESPECIALLY
ACROSS THE WESTERN HALF OF THE CWA. THESE STORMS WILL PRESENT AT
TIMES...BRIEF STRONG ERRATIC WINDS...SMALL HAIL AND OCCASIONAL TO
FREQUENT LIGHTNING. AMBIENT WINDS WILL ALSO BECOME STRONG AND QUITE
GUSTY THIS AFTERNOON...ESPECIALLY ACROSS SWEETWATER AND NATRONA
COUNTIES...EAST OF A LINE FROM ROCK SPRINGS TO MUDDY GAP AND ON TO
CASPER. AFTERNOON SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR
SATURDAY AND SUNDAY...HOWEVER COOLER HIGH TEMPERATURES...MORE
MOISTURE IN THE AREA AND EXITING INSTABILITY - LESS CHANCES FOR
LIGHTNING SATURDAY AND SUNDAY - WILL LIMIT FIRE DANGERS THIS
WEEKEND AND INTO THE BEGINNING OF NEXT WEEK.

&&

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

$$

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