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000
FXUS65 KRIW 080642
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SAT DEC 7 2013

.SHORT TERM...TONIGHT THROUGH SUNDAY

COLD AIR WILL REMAIN TRAPPED IN THE VALLEYS AND BASINS TONIGHT AND
SUNDAY.  A WEAK UPPER LEVEL LOW PRESSURE TROUGH WITH LIMITED
MOISTURE WILL PASS ACROSS WESTERN AND CENTRAL WYOMING TONIGHT AND
SUNDAY OVERRUNNING THE COLD AIR.  OROGRAPHIC LIFT AND WEAK
ISENTROPIC LIFT WILL ACCOMPANY THE TROUGH PRODUCING LAYERED
STRATUS CLOUDS AND LOW DENSITY LIGHT SNOWFALL ACROSS THE WEST.
SNOW ACCUMULATIONS OF 4 TO 6 INCHES CAN BE EXPECTED IN THE
MOUNTAINS WITH AN INCH OR TWO IN THE VALLEYS. CLOUDS AND LIGHT
SNOW WILL DECREASE BY LATE MORNING SUNDAY WITH PARTIAL CLEARING
THROUGH THE AFTERNOON. CLOUD COVER OVERNIGHT WILL HELP KEEP LOWS
UP SLIGHTLY FROM LAST NIGHT IN THE SOUTH AND WEST. AS THE
UPPER TROUGH PASSES COOLING WILL OCCUR KEEPING TEMPERATURES WELL
BELOW NORMAL.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

NOT TOO MANY CHANGES TO THE LONG RANGE AS CONTINUITY LOOKED PRETTY
DARN GOOD. THE FIRST ALBERTA CLIPPER SLASH COLD FRONT WILL CONTINUE
TO DROP SOUTHWARD ACROSS THE AREA SUNDAY EVENING AND BRING SOME
LIGHT SNOW. THE OPERATIVE WORD IS LIGHT AS THIS SYSTEM IS VERY
MOISTURE STARVED WITH IT`S ORIGINS FROM THE CANADIAN PRAIRIES. IT
WILL ALSO BRING A REINFORCING SHOT OF COLD AIR TO THE AREA AND KEEP
TEMPERATURES RATHER LOW. ANOTHER ONE WILL MOVE ACROSS THE AREA ON
MONDAY. BUT ONCE AGAIN...IT HAS VERY LITTLE MOISTURE TO WORK WITH.
ALSO...THE BEST UPPER LEVEL SUPPORT WILL GO BY TO THE EAST SO AGAIN
ANY SNOWFALL WILL BE LIGHT AND ACCUMULATIONS WILL BE MINOR. THIS
SYSTEM WILL INCREASE THE WIND ACROSS THE SOUTHWESTERN WIND CORRIDOR
AND AS A RESULT TEMPERATURES WILL MODERATE A BIT FOR THE WARMEST
HIGHS...A RELATIVE TERM...SINCE LAST MONDAY FOR THESE AREAS. LOWS WILL
STILL BE WELL BELOW NORMAL HOWEVER.

BY TUESDAY THE LAST SHORTWAVE ASSOCIATED WITH THE NORTHWEST FLOW
WILL MOVE DROP INTO NORTHWESTERN WYOMING. THIS ONE MAY MAY HAVE A
BIT MORE MOISTURE TO WORK WITH BUT AGAIN...ANY ACCUMULATIONS WILL BE
MINOR AND PROBABLY CONFINED TO THE MOUNTAINS ONCE AGAIN. WITH THE
SHORTWAVE PASSAGE GUSTY WINDS WILL ONCE AGAIN BLOW ACROSS THE
SOUTHWESTERN WIND CORRIDOR AND WARM TEMPERATURES A BIT MORE.
MEANWHILE...ACROSS THE BASINS THE INVERSIONS SHOULD BE HARD TO BREAK
SO WE KEPT THE TEMPERATURES COLD...COLDER THAN GUIDANCE. RIDGING
WILL THEN BUILD ACROSS THE AREA FOR WEDNESDAY INTO WEDNESDAY NIGHT
AND BRING MAINLY QUIET WEATHER. AS TO THE END OF THE WEEK...THE
MODELS DO SHOW SOME SYSTEMS GOING INTO WESTERN WYOMING AS FLOW
BECOMES MORE WESTERLY. THIS WOULD FAVOR SOME SNOW OVER THE WESTERN
MOUNTAINS. HOWEVER...THE MODELS ARE CONTINUING TO DIFFER AS TO THE
DETAILS SO AT THIS POINT...WE MADE FEW CHANGES TO CONTINUITY. SO WE
WENT WITH SLIGHT TO CHANCE POPS ACROSS THE WEST WITH THE LOWER
ELEVATIONS MAINLY DRY. WITH THE FLOW TURNING MORE WESTERLY
TEMPERATURES SHOULD MODERATE BUT AT THIS POINT WE KEPT TEMPERATURES
BELOW GUIDANCE WITH THE THINKING THAT IF IT GETS WARMER...MOST
PEOPLE WILL BE HAPPY.

&&

.AVIATION.../06Z ISSUANCE/

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

CONDITIONS WILL CONTINUE TO GRADUALLY IMPROVE NW-SE OVERNIGHT AS AN
UPPER LOW OVER THE GREAT BASIN MOVES INTO THE FOUR CORNERS REGION.
AREAS OF MVFR CIGS WITH -SN AND LOCAL IFR FG ALONG WITH FQT MTN
OBSCURATIONS WILL PERSIST THROUGH 14Z WITH THESE CONDITIONS BECOMING
LOCALIZED THROUGH THE REST OF THE MORNING.  AN UPPER LEVEL
DISTURBANCE WILL MOVE SOUTH ACROSS THE AREA SUNDAY
EVENING...SPREADING WIDESPREAD MVFR/LOCAL IFR CIGS AND VSBYS IN -SN
NORTH TO SOUTH ACROSS THE AREA 00Z-06Z MONDAY FOLLOWED BY CLEARING
WITH PATCHY FOG 06Z-12Z MONDAY.

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

AN UPPER LOW PRESSURE SYSTEM WILL MOVE ACROSS THE FOUR CORNERS
REGION TONIGHT AND OUT INTO THE CENTRAL PLAINS ON SUNDAY.  AREAS OF
MVFR CIGS AND VSBY IN -SN WILL PERSIST VCNTY AND SOUTH OF A
KRKS-KCPR LINE THROUGH 12Z WITH THESE CONDITIONS IMPROVING THROUGH
THE REST OF THE MORNING.  LOCAL MVFR/IFR CONDITIONS IN -SN/FG WILL
BE ENCOUNTERED ELSEWHERE THROUGH SUNDAY MORNING.  VFR CONDITIONS
WILL PREVAIL SUNDAY AFTERNOON.  ANOTHER DISTURBANCE WILL BRING
PREVAILING MVFR CIGS AND VSBYS SOUTH ACROSS THE REGION SUNDAY
EVENING...FOLLOWED BY IMPROVING CONDITIONS FROM NORTH TO SOUTH AFTER
MIDNIGHT.

&&

.FIRE WEATHER...

VERY COLD WEATHER WITH LIGHT ACCUMULATING SNOW IN THE MOUNTAINS
WITH FLURRIES AND FOG IN THE LOWER ELEVATIONS WILL PERSIST TONIGHT
THROUGH SUNDAY.  MIXING HEIGHTS WILL BE VERY LOW WITH POOR SMOKE
DISPERSAL.  RELATIVE HUMIDITY WILL BE ELEVATED WELL ABOVE NORMAL.

&&

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

$$

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