Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 210929
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
329 AM MDT MON APR 21 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

SHORTWAVE RIDGE MOVES IN TODAY...WILL BE ANOTHER MILD TO WARM DAY
WITH MOST AREAS NOT SEEING ALL THAT MUCH WIND. SOME INSTABILITY AND
RESIDUAL MOISTURE POSSIBLE ACROSS THE FAR SOUTHWEST THIS
AFTERNOON...KEPT POPS QUIET FOR THE MOST PART BUT ADDED SOME ISOLD
POPS OVER THE MOUNTAINS. RAIN CHANCES INCREASE TONIGHT AS A LEADING
SHORT WAVE EJECTS FROM THE MAIN TROUGH ALONG THE WEST COAST. KEPT
POPS LARGELY UNTOUCHED OVERNIGHT INTO TUESDAY AS THE TIMING AND
EXTENT OF LOOK TO BE ON TRACK. ANOTHER WARM DAY IN STORE FOR TUES AS
WARM SOUTHWEST FLOW INCREASES AHEAD OF THE MAIN TROUGH. THE BROAD
ASCENT AHEAD OF THE MAIN TROUGH ARRIVES ON TUESDAY...ENHANCING
PRECIP CHANCES ACROSS THE WEST AS THE COLD FRONT NEARS. KEPT
ISOLATED SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON BUT THE MAIN
WEATHER FEATURE EAST OF THE DIVIDE WILL BE THE VERY WARM
TEMPERATURES...STRONG SOUTHERLY WINDS AND LOW RH INCREASING THE
FIRE DANGER WHERE VEGETATION IS RECEPTIVE TO FIRE.

THE COLD FRONT SWEEPS WEST TO EAST ON TUESDAY NIGHT INTO WEDNESDAY.
THE SURFACE LOW IS PRETTY FAR NORTH AND FLOW REMAINS WEST TO
NORTHWESTERLY...WHICH IS MOST FAVORABLE FOR THE HIGHER ELEVATIONS
AND NORTHERN BIGHORN BASIN BUT POPS WERE KEPT BROAD AT THIS TIME
WITH MOST AREAS WITH AT LEAST A SLIGHT CHANCE OF RAIN OR HIGH ELEV
SNOW. WEDNESDAY WILL BE CONSIDERABLY COOLER TO COLDER IN SOME
INSTANCES WITH MOUNTAIN SNOW SHOWERS...DECREASING TO SCATTERED RAIN
OR SNOW SHOWERS IN AND NEAR THE FOOTHILLS AND MORE ISOLATED OUT IN
THE BASINS AND SOUTH.

WIND WILL BE QUITE STRONG ON TUESDAY AND WEDNESDAY IN MANY
AREAS...ESPECIALLY MOUNTAINS AND EAST OF THE DIVIDE. SNOW LEVELS
WILL BE QUITE HIGH ON TUESDAY AND MAINLY ABOVE 10K FEET LOWERING TO
THE VALLEY FLOOR TUESDAY NIGHT AND REMAINING THERE ON WEDNESDAY.
SOME MEASURABLE SNOW IS STILL POSSIBLE TUESDAY NIGHT THROUGH
WEDNESDAY IN THE WRN MOUNTAINS AND BIGHORNS.

.LONG TERM...THURSDAY THROUGH MONDAY

UPPER LOW DRIFTS ESE ACROSS THE NORTHERN PLAINS ON
THURSDAY...ALLOWING BRIEF PHASING OF HIGH AMPLITUDE RIDGE NEAR
110W.  NEXT PACIFIC SYSTEM DIGS INTO THE SW U.S. ON
FRIDAY...UNDERCUTTING THE RIDGE...MOVING INTO THE FOUR CORNERS
REGION ON SATURDAY AND THEN DECELERATING AS IT MOVES INTO THE
SOUTHERN/CENTRAL PLAINS ON SUNDAY AND MONDAY...DIRECTLY UNDER THE RIDGE
OVER THE NORTHERN PLAINS/CENTRAL CANADA.

MEDIUM RANGE GLOBAL MODELS ARE IN GOOD AGREEMENT THIS MORNING
WITH THE OVERALL PROGRESSION OF THIS SYSTEM THROUGH SUNDAY. THE GFS
CONTINUES TO DISPLAY A MORE CLOSED SW LOW WHILE THE EC IS MORE
FRAGMENTED WITH THE ENERGY. THE ECMWF HAS TRENDED TOWARD MORE
AMPLIFICATION WITH THE UPSTREAM FLOW OVER THE EASTERN PACIFIC THUS
SHOWING MORE OF A DIGGING SW LOW SIMILAR TO GFS.

FOR SENSIBLE WEATHER...

THURSDAY AND FRIDAY...SCATTERED RAIN AND SNOW SHOWERS LINGER OVER
THE NORTHERN MOUNTAINS ON THURSDAY WITH SOME WRAPAROUND MOISTURE
POSSIBLY LINGERING OVER THE BIGHORNS IN MOIST NW FLOW BEHIND EXITING
UPPER LOW.  UPPER RIDGE SHIFTS INTO HIGH PLAINS ON FRIDAY RAIN AND
SNOW SHOWERS INCREASING ACROSS THE WEST IN INCREASINGLY MOIST
DIFLUENT SW FLOW.  MILD SOUTHERLY FLOW WILL PREVAIL ACROSS THE SOUTH
AND CENTRAL FRIDAY WITH ISOLATED SHOWERS LATE.

SATURDAY AND SUNDAY...UPPER LOW MOVES INTO THE FOUR CORNERS REGION
ON SATURDAY...MOIST AND UNSTABLE SOUTHERLY FLOW WILL BRING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS THROUGH THE DAY...SHOWERS MORE
NUMEROUS IN THE SW MTS...SNOW LEVELS 8K-10KFT.  SURFACE COLD FRONT
PUSHES SOUTH ACROSS THE AREA SATURDAY NIGHT WITH COOLER AND
UNSETTLED NORTHERLY PREVAILING ON SUNDAY. WE SHOULD SEE MOSTLY
SCATTERED RAIN SHOWERS ACROSS THE BASINS AND VALLEYS...POSSIBLY
MIXED WITH WET SNOW...BUT THE HEAVIEST PRECIPITATION SHOULD BE TO
OUR SOUTH AND EAST.

ON MONDAY...SOME UNCERTAINTY ON HOW FAST UNSETTLED NORTHERLY FLOW
WILL EXIT THE AREA WITH UPPER LOW TRAPPED UNDER RIDGE TO OUR SE...SO
FORECAST KEEPS ISOLATED VALLEY...SCATTERED MTN SHOWERS AROUND AND
TEMPERATURES SLIGHTLY BELOW SEASONAL NORMALS.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS WILL OCCUR TODAY AND TONIGHT.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR CONDITIONS WILL OCCUR TODAY THROUGH 06Z TUESDAY. ISOLATED RAIN
SHOWERS WILL DEVELOP OVER THE FAR WEST MOUNTAINS AFTER 03Z TUESDAY.
ISOLATED RAIN OR SHOWERS WILL OCCUR OVER THE WESTERN WY MOUNTAINS
AFTER 06Z TUESDAY WITH LOCAL MVFR CONDITIONS POSSIBLE.

&&

.FIRE WEATHER...

...HAZARDOUS BURNING CONDITIONS ON TUESDAY AND WEDNESDAY...

DRY AND WARM WITH BREEZY AREAS...MAINLY IN THE MOUNTAINS AND
FOOTHILLS. A WEAK WEATHER DISTURBANCE AHEAD OF A MAJOR WEATHER
SYSTEM WILL MOVE INTO THE NORTHWEST TONIGHT WITH A CHANCE OF
SHOWERS WITH HIGH SNOW LEVELS. SOUTHERLY WINDS WILL BE ON THE
INCREASE TONIGHT AND ESPECIALLY TUESDAY INTO WEDNESDAY. THE
COMBINATION OF STRONG TO VERY STRONG SOUTHERLY WINDS ON TUESDAY
COMBINED WITH WARM TEMPERATURES AND LOW RH`S WILL INCREASE THE FIRE
DANGER. OUT WEST...RAIN SHOWERS WITH BE LIKELY ON TUESDAY WITH THE
SNOW LEVEL NEAR 10K FEET. A STRONG COLD FRONT WILL SWEEP EAST ACROSS
THE AREA TUESDAY NIGHT WITH A BAND OF SHOWERS AND ISOLATED
THUNDERSTORMS. IT WILL CONTINUE VERY WINDY THROUGH WEDNESDAY.
WEDNESDAY WILL ALSO BE CONSIDERABLY COOLER THAN TUESDAY BUT STILL
RATHER DRY EAST OF THE DIVIDE WITH MIN RH`S IN THE TEENS AND 20S.

&&

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

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...ALLEN










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