Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 151805
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1205 PM MDT TUE APR 15 2014

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

THE DAY LOOKS TO START QUIET AS HIGH PRESSURE SHOULD CONTROL THE
WEATHER THROUGH THE NIGHT AND INTO THE MORNING. AS A RESULT EXPECT
DRY CONDITIONS ALONG WITH A MIX OF SUNSHINE AND HIGH CLOUDS.
HOWEVER...THIS IS WYOMING IN THE SPRING SO YOU KNOW IT IS NOT GOING
TO LAST VERY LONG. A SYSTEM THAT IS MOVING THROUGH THE PACIFIC
NORTHWEST WILL MOVE TOWARD WESTERN WYOMING AND BEGIN TO SPREAD SOME
SHOWERS INTO WESTERN WYOMING STARTING THIS AFTERNOON. TEMPERATURES
SHOULD WARM UP AHEAD OF THE SYSTEM THOUGH SO MUCH OF THE
PRECIPITATION SHOULD FALL AS RAIN WITH THE EXCEPTION OF THE HIGHER
ELEVATIONS DURING THE DAYLIGHT HOURS. MEANWHILE...EAST OF THE DIVIDE
WE HAVE KEPT THE FORECAST DRY THROUGH AROUND 6 PM. HOWEVER...THE
CONCERN HERE WILL BE WIND AS THE FRONT APPROACHES AND THE PRESSURE
GRADIENT TIGHTENS. THE GFS IS SHOWING SOME 700 MILLIBAR WINDS ABOVE
50 KNOTS IN SPOTS. HOWEVER...THE GFS MOS...WHICH USUALLY OVERDOES
THE WIND IS NOT SHOWING HIGH WIND ANYWHERE. MEANWHILE...THE NAM
WINDS SHOW LESS WIND. SO AT THIS TIME WE FEEL NO WIND HIGHLIGHTS ARE
NEEDED...BUT WE WILL ISSUE AN SPS FOR WIND IN THE USUAL WINDY AREAS.
TEMPERATURES WILL BE MUCH WARMER AS WELL WITH SOUTHWESTERLY
DOWNSLOPING ACROSS THE AREA.

THE PRECIPITATION WILL TRY TO JUMP THE DIVIDE TONIGHT. THE MODELS
ARE FAIRLY SIMILAR IN KEEPING THE PRECIPITATION MAINLY NORTH OF A
LINE FROM THERMOPOLIS TO CASPER SO THE HIGHER POPS WERE KEPT IN THAT
VICINITY. THERE IS A BIG RANGE IN QPF WITH THE GFS THE WETTER MODEL.
AS FOR ANY WINTER WEATHER HIGHLIGHTS...WE FEEL A FEW PLACES MAY
REACH CRITERIA. HOWEVER...THE MOST LIKELY PLACES SHOULD BE THE
MOUNTAINS AND ABOVE PASS LEVEL. SINCE THIS WOULD NOT OCCUR UNTIL
TONIGHT...WE WILL PUNT THAT DECISION TO THE DAY SHIFT.

THE TREND THE DAY SHIFT MENTIONED IN KEEPING THE UNSETTLED WEATHER
FURTHER NORTH CONTINUED WITH THE 00Z RUNS OF THE MODELS AS WELL.
THERE ARE DIFFERENCES IN THE DETAILS THOUGH. THE GFS HAS A GOOD SLUG
OF PRECIPITATION OVER NORTHERN AND EASTERN AREAS WHILE THE NAM IS
DRIER. FOR NOW...WE MADE ONLY MINOR TWEAKS WITH THE UNCERTAINTY. IT
WILL BE COOLER BEHIND THE FRONT BY ABOUT 10 TO 15 DEGREES IN MOST
AREAS HOWEVER. IMPROVING CONDITIONS SHOULD BE PRESENT ON THURSDAY
WITH RIDGING BUILDING INTO THE STATE. WE CONTINUED THE TREND OF
TAPERING POPS FROM WEST TO EAST WITH MAINLY DRY CONDITIONS BY
THURSDAY NIGHT. TEMPERATURES SHOULD REBOUND WITH MORE SUNSHINE AND
RISING THICKNESSES.

.LONG TERM...FRIDAY THROUGH TUESDAY

A FAST MOVING WEATHER SYSTEM CROSSES THE REGION ON FRIDAY AND
FRIDAY NIGHT WITH A CHANCE OF RAIN AND MOUNTAIN SNOW SHOWERS. THE
MODELS DIFFER ON SATURDAY WITH RESPECT TO HOW MUCH MOISTURE WILL
BE LINGERING OVER THE REGION WITH A WEAK WEATHER SYSTEM PASSING
THROUGH IN A WEST FLOW ALOFT. ECMWF IS SHOWING MORE SHOWER
DEVELOPMENT SATURDAY AFTERNOON AND EVENING THAN THE GFS/GEM
MODELS. WILL FORECAST ISOLATED SHOWERS OVER THE MOUNTAINS AND
ACROSS THE SOUTH ZONES FOR SAT PM AND SAT EVE. DRY ELSEWHERE.
SUNDAY THROUGH MONDAY EVENING LOOK DRY. THE GFS IS DIGGING A
LARGE UPPER LOW OVER THE WEST COAST NEXT TUE. THE ECMWF IS SLOWER
WITH THE PROGRESSION OVER THE WEST COAST AND THE GEM MODEL IS
CLOSER TO THE GFS. USUALLY SLOWER IS BETTER WITH DIGGING SYSTEMS
OVER THE WEST COAST. WILL INTRODUCE LOW PRECIP CHANCE OVER THE FAR
WEST FOR LATE MONDAY NIGHT AND TUESDAY IN A SOUTHWEST FLOW ALOFT.
DRY ELSEWHERE NEXT TUE. HIGH TEMPS FRIDAY WILL BE QUITE MILD. A
LITTLE COOLER SATURDAY DUE TO A WEAK COLD FRONT PASSING THROUGH
THE AREA. WARMER SUNDAY THROUGH NEXT TUESDAY WITH HIGHS AT OR
ABOVE NORMAL.

&&

.AVIATION.../18Z ISSUANCE/

A STRONG COLD FRONT WILL BLAST SOUTHEAST ACROSS THE AREA LATE THIS
AFTERNOON INTO EARLY THIS EVENING WITH STRONG WEST TO NORTHWEST
WINDS. SCATTERED CONVECTION WILL ACCOMPANY THE FRONT. THE BEST
CHANCE WILL BE ALONG AND NORTH OF A LINE FROM KJAC-KDUB-
KCPR...BETWEEN 21Z TODAY AND 06Z WEDNESDAY WITH A LATER START AND END
TIME OVER THE EAST. BRIEF MVFR/IFR CONDITIONS WILL BE POSSIBLE IN
THE LOWER ELEVATIONS WITH CONVECTION. INSTABILITY IS VERY
WEAK...SO VERY ISOLATED TO NO LIGHTNING STRIKES ARE EXPECTED.
NORTHWEST AND NORTHERN MOUNTAINS ARE EXPECTED TO BECOME OBSCURED
IN THE AFTERNOON WITH SNOW SHOWERS LIKELY AND REMAIN OBSCURED MUCH OF
THE TIME INTO THIS EVENING.

WINDY WEST WINDS WILL INCREASE FROM KRKS TO KCPR INTO THE EARLY
EVENING HOURS AND OF THE COLD FRONT. MANY AREAS WILL BECOME OR
REMAIN WINDY INTO THE EARLY EVENING. ANOTHER VERY WINDY AREA WILL
AFFECT FREMONT COUNTY INCLUDING KDUB...KLND AND KRKS WITH STRONG
TO VERY STRONG WEST TO NORTHWEST WINDS THROUGH 03Z. THE UPPER
GREEN RIVER BASIN WILL ALSO BE QUITE WINDY WITH A CHANCE OF
SHOWERS AS THE COLD FRONT MOVES THROUGH INCLUDING KBPI AND KPNA.
BREEZY SOUTHERLY WINDS ARE EXPECTED THIS AFTERNOON/EVENING AT
KJAC WITH RAIN SHOWERS DEVELOPING AND CHANGING OVER THE SNOW
BRIEFLY BEFORE ENDING AROUND 03Z WEDNESDAY. A CANADIAN COLD FRONT IS
EXPECTED TO PUSH SOUTH...EAST OF THE DIVIDE THIS EVENING CHANGING
WINDS FROM SOUTHWEST OR WEST...TO THE NORTH. THERE COULD BE A
PERIOD OF MVFR CEILINGS NOT ASSOCIATED WITH CONVECTION FOR A FEW
HOURS AFTER FRONTAL PASSAGE...MAINLY OVER JOHNSON AND NATRONA
COUNTIES. HOWEVER CONFIDENCE IS NOT HIGH ENOUGH TO PREVAIL MVFR
CONDITIONS AT THIS TIME. IMPROVING CONDITIONS IN THE LOWER
ELEVATIONS ARE EXPECTED AFTER 06Z WEDNESDAY AS THE DISTURBANCE
PULLS AWAY AND THE BOUNDARY LAYER TRENDS DRIER AS THE FLOW BACKS
TO THE WEST.

&&

.FIRE WEATHER...

IT WILL WARM UP AND DRY TODAY EAST IF THE DIVIDE WITH THE DRIEST AIR
BEING IN THE SOUTHWEST WHERE AFTERNOON RH`S MAY DIP INTO THE TEENS
ALONG WITH STRONG WEST WINDS. WEST TO NORTHWEST WINDS WILL ALSO
INCREASE TONIGHT IN THE MOUNTAINS...CODY FOOTHILLS AND DUBOIS DOWN
TO CROWHEART. AN APPROACHING COLD FRONT WILL MOVE INTO THE NORTHWEST
CORNER LATER TOMORROW AFTERNOON AND ACROSS CENTRAL WYOMING TOMORROW
EVENING. GUSTY TO STRONG WEST TO SOUTHWEST WINDS WILL OCCUR AHEAD OF
THIS SYSTEM SHIFTING TO THE NORTH OR NORTHWEST BEHIND IT. A PERIOD
OF RAIN OR SNOW SHOWERS IS EXPECTED WITH THE FRONT...ESPECIALLY
ACROSS THE WEST AND NORTH HALF. EXPECT COOLER AND MORE UNSETTLED
WEATHER FOR WEDNESDAY AFTER THE COLD FRONT PASSAGE.
&&

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

&&

$$

UPDATE...SKRBAC
SHORT TERM...HATTINGS
LONG TERM...AR
AVIATION...WM
FIRE WEATHER...HATTINGS








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