Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 312142
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
242 PM MST SAT JAN 31 2015

.SHORT TERM...TONIGHT THROUGH SUNDAY

LOW CLOUDS AND FOG TOOK UNTIL EARLY AFTERNOON TO LIFT IN THE CENTRAL
VALLEYS AS WELL AS IN THE STAR VALLEY. OTHERWISE A MOSTLY SUNNY DAY
WITH MILD TEMPS FOR THE MOST PART. A COLD FRONT HAS ENTERED NORTHERN
WY AS OF 19Z. PRECIP IS BREAKING OUT IN SOUTHERN MONTANA AS A
WEATHER SYSTEM DIVES SOUTHEAST THROUGH MONTANA AND HEADS TOWARD WY
FOR THE TONIGHT PERIOD. THIS SYSTEM WILL MAINLY IMPACT THE AREAS
EAST OF THE CONTINENTAL DIVIDE TONIGHT INTO EARLY SUNDAY WITH SOME
SNOW AND WIND AND COLDER TEMPS. THE BEST CHANCE OF SNOW WILL BE FROM
THE BIGHORN MOUNTAINS SOUTH TO CASPER MOUNTAIN...INCLUDING BUFFALO
TO CASPER. HAVE WENT HIGHER WITH THE CHANCE OF SNOW WITH
ACCUMULATIONS AROUND AN INCH IN PLACES. THE BIG HORN BASIN SHOULD
SEE SOME LIGHT SNOW TONIGHT...ENDING BY SUNDAY MORNING. THE WIND
RIVER BASIN SHOULD SEE SOME LIGHT SNOW AT TIMES LATE THIS EVENING TO
AROUND SUNRISE SUNDAY. LESS THAN AN INCH IS EXPECTED FOR THE MOST
PARTS IN THE THOSE BASINS. OUT WEST NOT MUCH EXPECTED ASIDE FROM
SOME MOUNTAIN SNOW SHOWERS OVER THE NORTHWEST MOUNTAINS AND WIND
RIVER MOUNTAINS. WILL HAVE TO DEAL WITH THE FOG AND LOW CLOUDS IN
THE STAR VALLEY AGAIN TONIGHT INTO SUNDAY MORNING. COLDER LOWS EAST
OF THE DIVIDE AS THE BRUNT OF THE COLD AIR WILL REMAIN EAST OF THE
DIVIDE TONIGHT AND SUNDAY. CLOUDS WILL BE ON THE DECREASE SUNDAY
EAST OF THE DIVIDE AS THE SYSTEM DEPARTS. SOME HIGH CLOUDS WILL
FILTER IN SUNDAY PM IN THE NORTHWEST FLOW ALOFT. OUT WEST...SUNDAY
WILL BE DRY FOR MOST OF THE DAY. INCREASING CLOUDS SUNDAY AFTERNOON
WITH SCATTERED LIGHT SNOW FOR THE NORTHWEST WY MOUNTAINS AS MOISTURE
INCREASES IN THE NW FLOW ALOFT. IT SHOULD STAY DRY IN THE WESTERN
VALLEYS THROUGH 00Z MONDAY. HIGHS ON SUNDAY WILL BE 5 TO 10 DEGREES
COLDER THAN SATURDAY EAST OF THE DIVIDE AND SLIGHTLY COLDER WEST OF
THE DIVIDE.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

THROUGH THE FIRST PORTION OF THE LONG TERM FORECAST...MAINLY THROUGH
TUESDAY...REMAINS OF AN OLD SHOW ON PBS MANY YEARS AGO. THE SHOW IS
UPSTAIRS DOWNSTAIRS. EXPECT...THIS IS THE WEATHER VERSION CALLED
UPSLOPE DOWNSLOPE. IN AREAS WEST OF THE DIVIDE...THEY WILL BE IN THE
UPSLOPE PORTION OF THE FORECAST. THE FIRST SHORTWAVE APPROACHES FROM
THE WEST FOR SUNDAY NIGHT WITH THE FIRST SHOT OF POTENTIAL
ACCUMULATING SNOW. THE NEXT WAVE THEN ARRIVES SOMETIME ON MONDAY.
THE MODELS DO HAVE A FEW TIMING DIFFERENCES WITH THE NAM HAVING A
BIT OF A BREAK ON MONDAY AND THE GFS KEEPING THE PRECIPITATION GOING
THROUGH MUCH OF THE DAY. AT THIS POINT...CONTINUITY LOOKED
REASONABLE SO WE MADE FEW CHANGES. MEANWHILE...EAST OF THE DIVIDE IS
ON THE DOWNSLOPE SIDE. THIS MEANS MAINLY DRY CONDITIONS FOR MOST
LOCATIONS EXPECT FOR THE BIGHORN RANGE AND POSSIBLY THE NORTHERN BIG
HORN BASIN WHERE SOME JET ENERGY COULD BRING SOME LIGHT
PRECIPITATION. WITH THE DOWNSLOPING FLOW...EXPECT TEMPERATURES TO BE
NEAR TO ABOVE NORMAL FOR MOST LOCATIONS. THERE MAY BE THE POTENTIAL
FOR SOME HIGH WINDS...ESPECIALLY MONDAY NIGHT WITH A COUPLE OF
MODELS SHOWING 700 MILLIBAR WINDS AT OR OVER 50 KNOTS...ESPECIALLY
NEAR THE FAVORED AREAS LIKE NEAR CLARK AND PORTIONS OF NATRONA
COUNTY.

THE NEXT DECENT CHANCE FOR PRECIPITATION ACROSS THE AREA WOULD BE
TUESDAY NIGHT INTO WEDNESDAY. BOTH THE GFS AND EUROPEAN SHOW SOME
PRECIPITATION GETTING KICKED ACROSS THE DIVIDE AS A COLD FRONT AND
ASSOCIATED SHORT WAVE DROPS SOUTHWARD OUT OF CANADA AND INTO WYOMING
WITH MAYBE SOME LIGHT UPSLOPE EAST OF THE DIVIDE. AT THIS
POINT...THIS DOES NOT LOOK LIKE A BIG EVENT BUT THERE WILL BE THE
POTENTIAL FOR SOME PRECIPITATION EVERYWHERE. THERE ARE SOME
DIFFERENCES IN THE MODELS TIMING THE SYSTEMS WITH THE GFS MOVING
PRECIPITATION OUT FASTER THAN THE GFS AT THIS POINT.

BOTH THE GFS AND EUROPEAN NOW BUILD RIDGING ACROSS THE AREA FOR LATE
NEXT WEEK WITH MAINLY DRY CONDITIONS DOMINATING FOR THURSDAY AND
EVEN INTO FRIDAY. WE STILL HAVE SOME LIGHT POPS ACROSS THE WEST BUT
FUTURE SHIFTS MAY WANT TO REMOVE IT. WITH THE RIDGING...THE PATTERN
OF ABOVE NORMAL TEMPERATURES WILL CONTINUE WITH SOME 50S POSSIBLE BY
FRIDAY IN WARMER AREAS EAST OF THE DIVIDE. THEN BOTH MODELS SHOW THE
NEXT SYSTEM MOVING IN FOR NEXT WEEKEND.

&&

.AVIATION.../00Z ISSUANCE/

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

CLOUDS WILL LOWER OVER NORTHERN WY WITH AREAS OF LIGHT SNOW
DEVELOPING AROUND 00Z THROUGH 09Z BEFORE IT ENDS AND CONDITIONS
IMPROVE BY 12Z. EXPECT MVFR TO IFR CONDITIONS THROUGH 15Z WITH VFR
CONDITIONS AFTER 15Z SUNDAY. FOR THE CENTRAL AREA FROM KCPR TO
KLND THE LOWER CLOUDS AND AREAS OF LIGHT SNOW WILL OCCUR AROUND
03Z AND CONTINUE THROUGH 12Z. EXPECT MVFR TO IFR CONDITIONS
THROUGH 15Z...THEN CONDITIONS WILL IMPROVE AFTER 15Z WITH VFR
CONDITIONS PREVAILING BY 18Z SUNDAY.

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

SOME FOG AND LOW CLOUDS WILL OCCUR IN THE STAR VALLEY TONIGHT INTO
SUNDAY MORNING WITH IFR CONDITIONS UNTIL 17Z. A COLD FRONT MAY PUSH
LOWER MVFR/IFR CIGS INTO VCNTY KRKS AFTER 07Z TONIGHT. ISOLATED
SNOW SHOWERS ARE EXPECTED OVER THE NORTHWEST MOUNTAINS AND OVER
THE WIND RIVER MOUNTAINS TONIGHT UNTIL 12Z SUNDAY. LOCAL MVFR
CONDITIONS WILL OCCUR IN THESE MOUNTAINS. VFR CONDITIONS WILL
PREVAIL SUNDAY AT THE TERMINAL SITES. SOME LIGHT SNOW FORMS OVER
THE NORTHWEST MOUNTAINS AFTER 20Z SUNDAY WITH SOME MVFR CONDITIONS
DEVELOPING BY 00Z MONDAY IN NW WY.

&&

.FIRE WEATHER...

A WEATHER SYSTEM WILL BRING SOME LIGHT SNOW EAST OF THE DIVIDE
TONIGHT AND SUNDAY MORNING. THEN MOSTLY DRY SUNDAY AFTERNOON
THROUGH MONDAY EAST OF THE DIVIDE. WEST OF THE DIVIDE WILL BE DRY
TONIGHT AND SUNDAY MORNING. LIGHT SNOW DEVELOPS OVER THE NORTHWEST
MOUNTAINS SUNDAY AFTERNOON. PERIODS OF SNOW FOR THE WESTERN
MOUNTAINS AND FAR WEST VALLEYS SUNDAY NIGHT THROUGH MONDAY NIGHT.

&&

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

&&

$$

SHORT TERM...AR
LONG TERM...HATTINGS
AVIATION...AR
FIRE WEATHER...AR





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