Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 112030
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
230 PM MDT FRI JUL 11 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO THE EVENING HOURS AS A
SHORT WAVE ROTATES THROUGH FROM SOUTHWEST TO NORTHEAST. THERE WILL
BE A LOT OF MOISTURE ACCOMPANYING THE SHORT WAVE WITH PWAT VALUES AT
TWO STANDARD DEVIATIONS ABOVE THE MEAN PWAT VALUES EXPECTED FOR THIS
TIME OF YEAR. IN ADDITION...STORM MOTION IS AT LESS THAN 10KT ACROSS
THE FORECAST AREA. THE STORMS THAT HAVE POPPED UP SO FAR THIS
AFTERNOON HAVE LARGELY STAYED OVER HIGHER TERRAIN EXCEPT FOR THE
STORMS ACROSS THE SOUTH ALONG A NEARLY STATIONARY FRONT PROVIDING A
SECONDARY FOCUS FOR THUNDERSTORMS. THESE STORMS WILL SPREAD INTO THE
ADJACENT FOOTHILLS AND LOWER ELEVATIONS AS TIME GOES ON THIS
AFTERNOON. WIDESPREAD SHOWERS AND STORMS WILL EVENTUALLY TAPER OFF
TO ISOLATED ACTIVITY BY MIDNIGHT WITH THE FOCUS SHIFTING EAST AND
NORTH LATE AS THE SHORT WAVE MOVES BY. A SECONDARY SHORT WAVE COMING
DOWN IN THE NORTHWEST FLOW TO OUR NORTH AND EAST WILL GRAZE THE
NORTHERN ZONES LATE...POSSIBLY CONTINUING SHOWERS AND STORMS IN THE
PARK INTO THE WEE HOURS.

THIS SAME WAVE WILL AGITATE THE ATMOSPHERE ENOUGH FOR MORE SHOWERS
AND THUNDERSTORMS ON SATURDAY...BUT WE WILL LOSE SOME OF THE FORCING
THAT WE HAD TO WORK WITH TODAY SO ONLY ISOLATED SHOWERS AND
THUNDERSTORMS ARE EXPECTED. ADDITIONALLY...HEIGHTS WILL BE A
LITTLE HIGHER TOMORROW AS THE UPPER HIGH SHIFTS A LITTLE FURTHER
NORTH IN RESPONSE TO THE DIGGING TROUGH WELL TO OUR EAST.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

RESIDUAL SHOWERS AND THUNDERSTORMS ARE LIKELY SATURDAY EVENING OVER
MUCH OF THE AREA...ESPECIALLY THE MOUNTAINS...FROM THE AFTERNOON
CONVECTION.  THE RIDGE AXIS SATURDAY INTO SUNDAY SETS UP TO OUR WEST
FROM THE GRAND CANYON AREA NORTH TO NORTHERN IDAHO.  THE HIGH
STRENGTHENS BRIEFLY ON SUNDAY OVER NEVADA ALLOWING WYOMING TO BE
BETWEEN THE HIGH AND THE STRONG LOW OVER MINNESOTA.  PRECIPITABLE
WATER VALUES WILL REMAIN ABOVE NORMAL WITH LIGHT NORTHEAST
FLOW...ALTHOUGH FORCING WILL BE REDUCED ON SUNDAY FOR ANY CONVECTIVE
ACTIVITY.

THE ANTICIPATED SHORTWAVE TROUGH FROM THE PACIFIC NORTHWEST WILL
MOVE INTO WESTERN MONTANA ON MONDAY...INCREASING CLOUDINESS AND THE
CHANCE OF SHOWERS AND THUNDERSTORMS FROM THE NORTHWEST TO THE
SOUTHEAST DURING THE AFTERNOON AND EVENING HOURS.  BOTH THE GFS AND
ECMWF ARE IN DECENT AGREEMENT TODAY WITH THE MOVEMENT AND TIMING OF
THIS FEATURE...ALTHOUGH ONCE AGAIN THE ECMWF IS QUITE A BIT HEAVIER
AND MORE WIDESPREAD WITH THE PRECIPITATION.  WITH THE MID LEVEL
INSTABILITY FROM THE TROUGH AND THE NEAR SURFACE BOUNDARY ALONG THE
DIVIDE...EXPECT SOME STRONG HEAVY STORMS TUESDAY AFTERNOON.  THE
TROUGH ALSO SERVES TO HELP COOLER AIR FROM CANADA MOVE INTO EASTERN
WYOMING SUCH THAT MAX TEMPERATURES DURING THE MIDDLE OF THE WEEK
WILL BE BELOW NORMAL.  SCATTERED SHOWERS AND THUNDERSTORMS ARE
EXPECTED AGAIN ON WEDNESDAY...YET NOT AS STRONG OR WIDESPREAD AS
TUESDAY.

THE GFS AND ECMWF DIVERGE WITH THE FORECAST FROM WEDNESDAY EVENING
ONWARD...WITH THE GFS DIGGING A TROUGH INTO THE PAC NW GIVING WY
MOIST SW FLOW AND POTENTIALLY STRONGER SW SURFACE FLOW AND DRIER
SURFACE CONDITIONS.  THE ECMWF INSTEAD KEEPS THE ENERGY IN SOUTHERN
ALBERTA.  HAVE TRENDED THE FORECAST TOWARD THE GFS SOLUTION FOR
NOW...WITH INCREASING SW WIND AND TEMPERATURES FOR THE END OF THE
WEEK...AS WELL AS INCREASED CHANCE OF PRECIPITATION IN THE WESTERN
MOUNTAINS.

&&

.AVIATION.../00Z ISSUANCE/

SCTD-NMRS -SHRA TO TSRA FROM A KKYC TO JUST N OF DUB AND THEN FROM
CPR TO RKS...EXPECT OCCNL MVFR CONDITIONS IN +RA AND FREQUENT
LIGHTNING THROUGH 02Z. ISOLD TO WIDELY SCT ACTIVITY ELSEWHERE WITH
MAINLY VFR CIGS AND VSBY. THE FOCUS OF THE STORMS WILL SHIFT EAST
AFTER 02Z WITH SOME -SHRA AND -TSRA POSSIBLE THROUGH 08Z AT MOST
TERMINALS...AND UNTIL 10Z AT CPR AND BYG AS THE RESPONSIBLE UPPER
LEVEL DISTURBANCE EXITS. ANOTHER WAVE WILL DROP SOUTH OUT OF MONTANA
LATE...WHICH COULD GET SOME LATE NIGHT -SHRA GOING VCNTY P60 AND MAY
GET SOME -SHRA AND -TSRA GOING EARLY VCNTY COD. ISOLD -SHRA AND
-TSRA WILL RETURN AFTER 17Z SAT POSSIBLE AT ALL TERMINALS BUT MORE
LIKELY NORTH AND EAST FURTHER AWAY FROM THE UPPER LEVEL HIGH.

&&

.FIRE WEATHER...

ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WITH A GOOD CHANCE
OF A WETTING RAIN WILL CONTINUE ACROSS THE FORECAST AREA INTO THE
EARLY EVENING HOURS. MORE SHOWERS AND WET STORMS WILL BE POSSIBLE ON
SATURDAY BUT THERE WILL BE LESS COVERAGE OVERALL. EVEN LESS COVERAGE
IS EXPECTED ON SUNDAY. WE SHIFT TO A NORTHWEST FLOW PATTERN BY
MONDAY WITH A COLD FRONT POSSIBLY DROPPING SOUTHWEST INTO THE DIVIDE
DURING THE DAY...AND BEYOND OVERNIGHT. THIS COULD BE THE FOCUS OF
ANOTHER ROUND OF WET SHOWERS AND THUNDERSTORMS. ANOTHER WAVE OF
SHOWERS AND STORMS IS POSSIBLE EACH AFTERNOON WITH THE HIGHEST
CHANCE OF WETTING RAIN ON TUESDAY...WITH TEMPERATURES AT OR BELOW
NORMAL...ESPECIALLY EAST OF THE DIVIDE WHILE IT REMAINS ON THE
WARMER AND DRIER SIDE WEST.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE TONIGHT
WYZ007>011-014>020-022>030.

&&

$$

SHORT TERM...ALLEN
LONG TERM...MCDONALD
AVIATION...ALLEN
FIRE WEATHER...ALLEN






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