Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 311739
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1139 AM MDT FRI OCT 31 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

THE HIGH PRESSURE RIDGE OVERHEAD WILL SLIDE OFF TO THE EAST TODAY
ALLOWING THE STEERING FLOW TO BACK MORE TO THE SOUTHWEST USHERING
IN WARMER AIR WITH MANY LOWER ELEVATIONS EAST OF THE DIVIDE
REACHING HIGH TEMPERATURES IN THE 70S TODAY AND IN THE 60S WEST.
THE EASTERN CWA WILL EKE OUT ANOTHER NICE DAY BEFORE CLOUDS
INCREASE AHEAD OF THE NEXT WEATHER SYSTEM. THE CIRCULATION NOW OFF
THE PACIFIC COAST OUT AT 45N/135W IS DRAWING SUBTROPICAL PACIFIC
MOISTURE NORTH INTO THE PAC NW OUT AHEAD OF IT WITH LIGHTNING
BREAKING OUT OVER OREGON WITHIN THE LAST FEW HOURS. THE ENERGY
FROM THE ASSOCIATED TROUGH WILL SPLIT BY SATURDAY AS IT ENCOUNTERS
THE RIDGE OVER THE CENTRAL UNITED STATES. THE MODELS SEEM MORE
REALISTIC WITH THIS APPROACH THAN PREVIOUS RUNS THAT DID NOT SHOW
AS MUCH OF A SPLIT. BOTH THE EURO AND THE GFS SHOW THIS SPLIT
TAKING PLACE. WE WILL FOCUS OUR ATTENTION ON THE CLOSER NORTHERN
PIECE OF ENERGY. SOUTHWEST BREEZES WILL INCREASE TODAY FROM RKS TO
CPR AHEAD OF THE APPROACHING PACIFIC WEATHER SYSTEM. THE TROUGH
WILL MAKE LANDFALL BY SATURDAY. AS IT DOES...CLOUDS WILL INCREASE
FROM THE WEST AND SHOWERS ALONG WITH EMBEDDED ISOLATED
THUNDERSTORMS WILL BREAK OUT IN WESTERN WY ALONG AND WEST OF THE
DIVIDE WITH SHOWERS INCREASING DURING THE AFTERNOON HOURS
SATURDAY. ON SATURDAY...A NORTHERN STREAM CIRCULATION WILL CLOSE
OFF OVER NEVADA/OREGON. THIS H5 LOW WILL OPEN BUT REMAIN A FOCUSED
AREA OF VORTICITY AS IT TRACKS ACROSS IDAHO AND INTO MONTANA
SATURDAY NIGHT AND INTO SUNDAY. THE H7 LOW WILL TAKE A SIMILAR
TRACK WITH THE SFC LOW TRACKING NORTHEAST ACROSS NW WY EARLY
SATURDAY EVENING. THIS LOW WILL HAVE A FAIRLY WELL DEFINED WARM
AND COLD FRONT AND A RESULTING WELL DEVELOPED COMMA CLOUD. MOST OF
THE MORE WIDESPREAD DYNAMICS WILL COME TOGETHER SATURDAY NIGHT.
LEFT FRONT QUAD DYNAMICS WILL ADD TO THE LIFT SATURDAY NIGHT AS
THE JET SHIFTS TO OUR SOUTH. AS THIS TROUGH NEARS...SOUTHWEST
WINDS WILL CONTINUE TO INCREASE FROM RKS TO CPR SATURDAY. WHEN THE
ASCT COLD FRONT TRAILING FROM THE PACIFIC SURFACE LOW...MANY OTHER
AREAS WILL SEE AN INCREASE IN WIND SPEED AS THE WINDS VEER
SATURDAY EVENING WITH SOME AREAS SEEING AN 8MB 3 HOURLY SFC
PRESSURE RISE. SNOW LEVELS WILL DROP TO THE VALLEY FLOORS SATURDAY
NIGHT OUT WEST. AS THE PACIFIC SYSTEM MOVES NORTHEAST INTO
MONTANA...SHOWERS WILL BECOME MORE PREVALENT IN NORTHERN WY AND
WILL CONTINUE IN WESTERN WY SUNDAY FROM THE LIFT MORE DIRECTLY
ASSOCIATED WITH THE LOW. THE HEAVIEST MOST WIDESPREAD PRECIP
SHOULD REMAIN NORTH OF THE AREA SUNDAY IN MT WHERE THE BEST WRAP
AROUND IS ENTROPIC LIFT WILL BE LOCATED. AS THIS WEATHER SYSTEM
CONTINUES TO PULL AWAY FROM US TO THE NORTHEAST SUNDAY NIGHT THE
SHOWERS WILL DIMINISH. AFTER ALL IS SAID AND DONE...2 TO 4 INCHES
OF SNOWFALL IS EXPECTED IN THE WESTERN VALLEYS BY LATE SUNDAY AND
4 TO 8 INCHES IN THE SURROUNDING MOUNTAINS. ONLY 1 TO 3 INCHES ARE
EXPECTED IN THE BIG HORN MOUNTAINS BY SUNDAY NIGHT. AS FAR AS ANY
POTENTIAL SIGNIFICANT SNOW BANDING GOES EAST OF THE DIVIDE...IT
NOW APPEARS THAT THE POST FRONTAL H7 NORTHWEST FLOW WILL BE TOO
WEAK TO SUPPORT ANY WITH THE MAIN ENERGY TO DRIVE THESE TYPE OF
SNOW SHOWERS TO FAR NORTH,

.LONG TERM...MONDAY THROUGH FRIDAY

WEAK BUT CHILLY NW FLOW STARTS THE PERIOD AS THE WEEKEND TROUGH
LINGERS OVER THE AREA THROUGH THE DAY BUT WITH MOST OF THE ENERGY
SPLIT BETWEEN A LOW NEAR FAR NRN ND AND ANOTHER OVER THE DESERT SW.
JUST SOME CHILLY AIR LEFT BEHIND WITH MAYBE A LITTLE RESIDUAL
MOISTURE IN THE MTNS AND SE FRINGES TO START THE PERIOD. MONDAY
SHOULD BE THE COLDEST DAY AND MONDAY NIGHT THE COLDEST NIGHT BEFORE
WE BEGIN ANOTHER WARMING TREND THROUGH THURSDAY. UPPER LOW AND COLD
AIR BETWEEN ALASKA AND THE ALEUTIAN CHAIN WORK TOGETHER TO DEVELOP
ANOTHER TROUGH OVER THE ERN PACIFIC EARLY NEXT WEEK THAT PUMPS UP
THE RIDGE OVER THE WEST. HEIGHTS RISE THROUGH AT LEAST WEDNESDAY
NIGHT AND MID LEVEL TEMPERATURES PEAK ON THURSDAY. HIGHS GENERALLY
START OUT MONDAY IN THE 40S WITH MAINLY 30S IN THE MOUNTAINS AND
THEN WARM ON AVERAGE 5 TO 8 DEGREES EACH DAY THROUGH THURSDAY. IF WE
GET ENOUGH MIXING...THURSDAY COULD BE EVEN WARMER WITH BOTH THE GFS
AND ECMWF SHOWING H7 TEMPERATURES BETWEEN +6 TO +10 EAST OF THE
DIVIDE. A SHORTWAVE THEN ROTATES THROUGH THE ERN PACIFIC TROUGH AND
THE RIDGE MAY WEAKEN ENOUGH TO BRING A CHANCE OF RAIN/SNOW ACROSS
THE AREA ON FRIDAY. FOR NOW...MAINLY CONFINING POPS TO THE MTNS OF
THE WEST AND NORTH WITH A SLIGHT CHANCE IN THE LOWER ELEVATIONS OF
THE NORTH. NOT A LOT OF PCPN POTENTIAL THROUGH THE WEEK BUT THERE
MAY BE JUST ENOUGH FLOW AND WEAK DISTURBANCES/MOISTURE IN THE NW
FLOW TO ALLOW SOME VERY LIGHT MTN SHOWERS/SPRINKLES/FLURRIES AT
TIMES IN THE NW MTNS TUESDAY AND WEDNESDAY. AN INCREASE IN WINDS AT
TIMES IN THE MOUNTAINS AND NORMALLY WINDY AREAS WITH EACH PASSING
RIPPLE BUT NOTHING TOO SIGNIFICANT EXPECTED. WE DO GET A LITTLE
BETTER GRADIENT ON THE GFS BY THURSDAY AND IF THIS DOES OCCUR THEN
LIKE MENTIONED ABOVE TEMPERATURES COULD SOAR EAST OF THE DIVIDE TO
RECORD TERRITORY. TOO EARLY YET TO GO THAT WARM BUT JUST SOMETHING
TO WATCH OVER THE NEXT SEVERAL DAYS.

.AVIATION.../18Z ISSUANCE/

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

THE AIRPORTS WILL HAVE PREVAILING VFR CONDITIONS THROUGH 18Z SATURDAY.
SOUTHWEST FLOW ALOFT WILL INCREASE WITH INCREASING MID AND UPPER LEVEL
CLOUDS WITH AREAS OF MVFR CEILINGS AND VISIBILITIES DEVELOPING ALONG
AND EAST OF THE CONTINENTAL DIVIDE ABOVE 9000 FEET WITH MAINLY
SNOW SHOWERS MOVING IN.  OVER AND NEAR THE EAST SLOPES OF THE MOUNTAINS
STRONG DOWNSLOPE WINDS WILL DEVELOP WITH AREAS OF LOW LEVEL WIND SHEAR.

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

THE AIRPORTS WILL HAVE PREVAILING VFR CONDITIONS THROUGH 10Z
SATURDAY. SOUTHWEST FLOW ALOFT WILL INCREASE WITH INCREASING MID
AND UPPER LEVEL CLOUDS WITH AREAS OF MVFR CEILINGS AND VISIBILITIES
DEVELOPING OVER THE WESTERN MOUNTAINS AND VALLEYS 8000 FEET WITH
MAINLY SNOW SHOWERS MOVING IN. OVER THE MOUNTAINS STRONG RIDGE TOP
WINDS WILL DEVELOP WITH AREAS OF LOW LEVEL WIND SHEAR.

.FIRE WEATHER...

A RIDGE OF HIGH PRESSURE IS EXPECTED TO LAST THROUGH SATURDAY
MORNING AND BRING MAINLY DRY WEATHER. A GUSTY SOUTHWESTERLY BREEZE
WILL DEVELOP TODAY FROM THE RED DESERT THROUGH NATRONA AND
JOHNSON COUNTIES. THE NEXT POTENTIAL ROUND OF PRECIPITATION MAY
BE FOUND BEGINNING SATURDAY AFTERNOON AS AN AREA OF LOW PRESSURE
APPROACHES WESTERN WYOMING.

&&

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

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...LIPSON






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