National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KRIW 072120
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
220 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.../00Z ISSUANCE/

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

AIRPORTS WILL HAVE PERIODS OF MVFR TO IFR CEILINGS AND VISIBILITIES
REDUCED IN LIGHT SNOW AND FOG THROUGH 12Z WITH GRADUALLY IMPROVING
CONDITIONS FROM 12Z - 18Z. MOIST WEST FLOW ALOFT WILL OVERRUN COLD
ARCTIC AIR IN THE LOWER ELEVATIONS WITH OROGRAPHIC AND WEAK
ISENTROPIC LIFT PRODUCING WIDESPREAD LAYERED STRATUS CLOUD LAYERS
AND LIGHT SNOW. IFR CEILINGS AND LIGHT SNOWFALL AND FOG WILL
PRODUCE WIDESPREAD MOUNTAIN OBSCURATIONS. AFTER 18Z VFR CONDITIONS
WILL BECOME MORE PREVAILING...HOWEVER SHALLOW STRATUS CLOUDS MAY
STILL LINGER OVER THE MOUNTAINS WHILE CLEARING OCCURS ABOVE THE
STRATUS.

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

AIRPORTS WILL HAVE PERIODS OF MVFR TO IFR CEILINGS AND VISIBILITIES
REDUCED IN LIGHT SNOW AND FOG THROUGH 12Z WITH GRADUALLY IMPROVING
CONDITIONS FROM 12Z - 18Z. MOIST WEST FLOW ALOFT WILL OVERRUN COLD
ARCTIC AIR IN THE LOWER ELEVATIONS WITH OROGRAPHIC AND WEAK
ISENTROPIC LIFT PRODUCING WIDESPREAD LAYERED STRATUS CLOUD LAYERS
AND LIGHT SNOW. IFR CEILINGS AND LIGHT SNOWFALL AND FOG WILL
PRODUCE WIDESPREAD MOUNTAIN OBSCURATIONS. AFTER 18Z VFR CONDITIONS
WILL BECOME MORE PREVAILING...HOWEVER SHALLOW STRATUS CLOUDS MAY
STILL LINGER OVER THE MOUNTAINS WHILE CLEARING OCCURS ABOVE THE
STRATUS.

&&

.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...C.BAKER
FIRE WEATHER...C.BAKER