Heavy Snow in Washington, January 7 to 11, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST MON JAN 7 2008

.SYNOPSIS...A VIGOROUS OCCLUDED FRONT WILL SPREAD RAIN AND SNOW
ACROSS THE REGION TONIGHT. UP TO 5 INCHES OF SNOW IS EXPECTED ON THE
HILLS AROUND SOUTHERN HOOD CANAL AND IN THE SOUTHERN OLYMPIC
FOOTHILLS. PRECIPITATION WILL TURN TO RAIN IN THE LOWLANDS AROUND
DAYBREAK ON TUESDAY. SHOWERS WILL DEVELOP TUESDAY NIGHT AS THE UPPER
LEVEL TROUGH TRAILING THE FRONT CROSSES THE AREA. AFTER A LULL
WEDNESDAY ANOTHER FRONTAL SYSTEM WILL AFFECT THE AREA WEDNESDAY
NIGHT THROUGH THURSDAY NIGHT. A THIRD FRONTAL SYSTEM WILL REACH THE
AREA FRIDAY NIGHT AND SATURDAY.

&&

.SHORT TERM...THE CURRENT FORECAST PACKAGE IS IN GOOD SHAPE. BACK
EDGE OF THE OCCLUDED FRONT WAS ALONG 129W AT 04Z...BUT THE BACK EDGE
OF THE HIGH CLOUD SHIELD MARKING THE BETTER PRECIP RATES WAS FURTHER
EAST NEAR 127W...STILL 120 NM W OF THE COAST. WITH THE DRY AIR MASS
OVER THE INTERIOR MOST ALL PRECIP HAS BEEN VIRGA UP UNTIL 345Z WHEN
OLYMPIA AND SHELTON STARTED RAINING. DEWPOINTS ARE STILL NEAR OR
BELOW FREEZING ACROSS MUCH OF THE INTERIOR WITH TEMPS IN THE MID TO
UPPER 30S. WILL HAVE TO WAIT UNTIL HEAVIER PRECIP ARRIVES AND
STRONGER WETBULB COOLING DEVELOPS FOR ANY SNOW TO REACH THE GROUND.

FOR THE GENERAL PUGET SOUND AREA UP TO AN INCH OF SNOW IS STILL
POSSIBLE PROBABLY BETWEEN 09Z-12Z...BUT THEN RAIN AFTER THAT SHOULD
QUICKLY START THE MELTING PROCESS. BEST CHANCE FOR ACCUMULATION IS
OVER THE HOOD CANAL AREA AND WESTERN KITSAP COUNTY...DOWN THROUGH
THE HIGHER HILLS OF THE LOWER CHEHALIS VALLEY NEAR ELMA-MONTESANO.
COULD SEE SEVERAL INCHES THERE...THOUGH THE 5 INCHES MENTIONED IN
CURRENT FORECASTS WOULD BE ON HIGHER HILLS ALONG HOOD CANAL. THE UP
TO 3 INCHES FORECAST FOR THE INLAND PART OF THE COASTAL ZONES...NEAR
THE OLYMPICS ALSO LOOKS OK...AS DOES THE WESTERN STRAIT ZONE W OF
PORT ANGELES. 00Z NAM SOUNDINGS FOR THESE VARIOUS AREAS SUPPORT THE
CURRENT FORECAST...NO FORECAST CHANGES NEEDED AT THIS POINT. A QUICK
CHANGEOVER TO RAIN IS STILL EXPECTED BY EARLY TO MID TUESDAY
MORNING. FROPA COAST WILL BE AROUND 13Z PER THE NAM AND BY 18Z OVER
PUGET SOUND.

POPS REMAIN HIGH POST FRONT SHOWERS...BUT THEY LOOK TO BE ONLY
SCATTERED AT BEST TUESDAY AFTERNOON. BEST CHANCE WILL BE TUESDAY
EVENING WHEN AN UPPER LEVEL TROUGH AXIS MOVES THROUGH. AFTER A BRIEF
RELATIVELY DRY SPELL WEDNESDAY...THE NEXT SYSTEM ARRIVES WEDNESDAY
NIGHT. KAM

.LONG TERM...PREVIOUS VERSION FROM THE 230 PM AFD...ADDITIONAL
WARMER AND WEAKER SYSTEMS ARE TIMED THRU HERE BY WED NIGHT AND AGAIN
FRI NIGHT SATURDAY. THE GFS HAS BEEN MOVING THE LONG WAVE RIDGE TO
THE WEST COAST AND SO I TOOK THE EDGE OFF THE SATURDAY SYSTEM BY
CALLING IT LIGHT RAIN OR DRIZZLE IN THE ZONES. SUNDAY AND MONDAY
WILL PROBABLY BE DRY UNDER A RIDGE. MM

&&

.AVIATION...MID AND HIGH LEVEL MOISTURE HAS OVERSPREAD THE AREA. THE
LOW LEVELS REMAIN QUIT DRY BUT WILL MOISTEN UP OVER THE NEXT COUPLE
HOURS AS PRECIP BEGINS (PIC5). SO FAR...ALL PRECIP HAS BEEN IN THE
FROM OF RAIN FROM THE COAST TO THE SW INTERIOR. ELSEWHERE...PRECIP
WILL PROBABLY BEGIN AS RAIN OR A RAIN/SNOW MIX BY 06Z.  IF STEADY
PRECIP CONTINUES...SOME LOCATIONS OVER THE INTERIOR MAY CHANGE OVER
TO SNOW MAINLY BETWEEN 08-12Z. ACCUMULATIONS WILL BE LESS THAN 1
INCH...WITH MOST AREAS SEEING NO ACCUMULATION AS TEMPERATURES ARE
MARGINAL. THE FRONT WILL MOVE THROUGH BY 14Z. DTM

.KSEA...PRECIP WILL LIKELY BEGIN AS LIGHT RAIN OR MIX AROUND 06Z. IF
PRECIP REMAINS STEADY...THERE MAY BE A CHANGE OVER TO WET SNOW FOR A
FEW HOURS FROM 08-12Z.  MAX ACCUMULATION ONE HALF INCH...MAINLY ON
THE GRASS. SURFACE TEMPS ARE TOO MARGINAL TO SUPPORT MUCH STICKING
SNOW. PRECIP SHOULD BECOME MORE SHOWERY AFTER 14Z. S/SE WIND 3-6
KT...BECOMING S 4-8 KT AFT 14Z. DTM

.MARINE...A WARM FRONT MOVING ACROSS WESTERN WA (PIC6)WILL PRODUCE
STRONG SE/ELY GRADIENTS OVER THE WATERS TONIGHT AND SLY ON TUE.
GALES ARE ALREADY OCCURING OVER THE COASTAL WATERS AND W ENTRANCE.
WINDS WILL BE MARGINAL FOR GALES OVER THE INTERIOR WATERS BUT MAY
BRIEFLY HIT TONIGHT. SMALL CRAFT CONDITIONS STILL EXPECTED FOR PUGET
SOUND. DTM

&&

.AVALANCHE...PREVIOUS VERSION FROM THE 230 PM AFD...AN AVALANCHE
WARNING HAS BEEN ISSUED FOR TUESDAY. STRONG WINDS, HEAVY SNOW AND A
SLIGHT WARMING TREND SHOULD BUILD NEW DENSER SURFACE SNOW LAYERS ON
LEE SLOPES. THIS SHOULD CAUSE A HIGH AVALANCHE DANGER TO DEVELOP AT
HIGHER ELEVATIONS IN THE OLYMPICS AND CASCADES TUESDAY MORNING.
PLEASE SEE WWW.NWAC.US FOR DETAILS. FERBER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
  1. HEAVY SNOW WARNING TONIGHT THROUGH TUESDAY NIGHT FOR THE
OLYMPICS AND CASCADES.
  2. HEAVY SNOW WARNING FOR THE HOOD CANAL AREA AND THE LOWER
CHEHALIS VALLEY AREA ZONES.
  3. SNOW ADVISORY FOR SOUTHWEST INTERIOR...NORTH AND CENTRAL
COAST...AND WESTERN STRAIT OF JUAN DE FUCA ZONES.
  4. GALE WARNING FOR THE COAST...ENTRANCES TO THE STRAIT...
     ADMIRALTY INLET...AND NORTHERN INLAND WATERS.
  5. SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL TONIGHT.
  6. SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH TO SEVERE BAR
CONDITIONS.
  7. AVALANCHE WARNING FOR TUESDAY.

WEATHER.GOV