Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 210514
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1112 PM MDT WED AUG 20 2014

.SHORT TERM...TONIGHT THROUGH THURSDAY (ISSUED AT 208 PM MDT)

AN UPPER LEVEL LOW PRESSURE TROUGH OVER THE NORTHERN ROCKIES
EXTENDING SOUTH INTO THE NORTHERN GREAT BASIN WILL PARTIALLY MOVE
EAST ACROSS MONTANA AND WYOMING WITH REFORMATION OCCURRING TO THE
WEST THROUGH THURSDAY. SUFFICIENT MOISTURE...SHEAR AND INSTABILITY
WILL ACCOMPANY THE TROUGH AS IT MOVES EAST FOR SCATTERED SHOWERS
WITH ISOLATED THUNDERSTORMS WITH STRONG WIND GUSTS. TEMPERATURES
WILL CONTINUE A GRADUAL COOLING TREND.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

SHOWERS AND STORMS CONTINUE INTO THURSDAY EVENING AS THE TROUGH
CONTINUES TO TREK EAST...SENDING OUT SHORT WAVES AS IT APPROACHES.
BY FRIDAY MORNING...THE MAIN TROUGH WILL CLOSE OFF OVER WASHINGTON
AND TRACK TO IDAHO BY FRIDAY NIGHT. THERE WILL BE PLENTY OF UPPER
LEVEL DYNAMICS WITH THE APPROACHING JET AND BROAD LIFT AHEAD OF
THE TROUGH TO ENHANCE SHOWER AND THUNDERSTORM COVERAGE...SO POPS
WERE BUMPED UP A BIT FOR FRIDAY...KEEPING WITH THE TREND FROM THE
PREVIOUS SHIFT.

ON SATURDAY...THE MAIN TROUGH MOVES INTO THE REGION...SENDING A
SIGNIFICANT COLD FRONT THROUGH THE FORECAST AREA WITH A GOOD CHANCE
OF SHOWERS AND SOME THUNDERSTORMS ALONG WITH SOME SNOW TO THE
HIGHER MOUNTAINS. THE MODELS HAVE YET TO AGREE ON EXACTLY HOW COLD
IT WILL BE BUT THE LATEST THINKING IS THAT SNOW LEVELS COULD DROP
TO 9KFT LATE SATURDAY NIGHT.

THE FLOW FLATTENS ON SUNDAY...TURNING DRIER AND MORE STABLE
HOWEVER ANOTHER TROUGH WILL BE APPROACHING THE REGION...WHICH
COULD BEGIN TO AFFECT THE FAR NORTHWEST BY THE EVENING...OTHERWISE
FLOW WILL SLOWLY TURN BACK TO THE SOUTHWEST. THERE COULD BE
ANOTHER ROUND OF SHOWERS...THUNDERSTORMS AND PERHAPS EVEN SOME
MORE HIGH ELEVATION SNOW MONDAY NIGHT INTO TUESDAY WITH MODELS
TRYING TO BUILD A RIDGE IN THEREAFTER...WHERE THE RIDGE IS
CENTERED REMAINS UNCERTAIN BUT THERE IS AGREEMENT IN A WARM UP BY
MID WEEK.

&&

.AVIATION.../06Z ISSUANCE/

AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL CONTINUE TO LIFT
NORTHEAST ACROSS THE NW HALF OF WYOMING INTO S CEN MT BY MIDDAY
THURSDAY.  THIS SYSTEM WILL CONTINUE TO BRING SCT SHRA/ISOLD TSRA
MAINLY VCNTY AND NW OF A KEMM-KDUB-KBYG LINE.  ACTIVITY WILL BE MORE
ISOLD SOUTH OF THIS LINE.  LCL IFR/LIFR FG AND CIGS MAY DEVELOP IN
THE WESTERN VALLEYS THROUGH 15Z...MAINLY VCNTY KJAC-KAFO.  ISOLD-SCT
TSRA WILL BLOSSOM IN THE SAME GENERAL AREA ACROSS THE WEST AND NORTH
THURSDAY AFTERNOON.   THE ATMOSPHERE WILL QUICKLY STABILIZE FROM
0Z-3Z FRIDAY WITH MOST SHOWER AND THUNDERSTORM ACTIVITY MOVING NE
INTO MONTANA AND THE NORTHERN PLAINS.  LCL IFR/LIFR FOG MAY
RE-DEVELOP IN THE FAR WEST VALLEYS AFTER 06Z FRIDAY.

&&

.FIRE WEATHER...

AN UPPER LEVEL LOW PRESSURE TROUGH OVER THE NORTHERN ROCKIES
EXTENDING SOUTH INTO THE NORTHERN GREAT BASIN WILL PARTIALLY MOVE
EAST ACROSS MONTANA AND WYOMING WITH REFORMATION OCCURRING TO THE
WEST THROUGH THURSDAY. SUFFICIENT MOISTURE...SHEAR AND INSTABILITY
WILL ACCOMPANY THE TROUGH AS IT MOVES EAST FOR SCATTERED SHOWERS WITH
ISOLATED THUNDERSTORMS WITH STRONG WIND GUSTS.  TEMPERATURES WILL
CONTINUE A GRADUAL COOLING TREND WITH INCREASING RELATIVE HUMIDITY.
THERE WILL BE SUFFICIENT MOISTURE AVAILABLE TO KEEP MIXING HEIGHTS
SUPPRESSED...ESPECIALLY OVER THE WEST.

&&

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

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER









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