Avalanche and Heavy Snow in Washington, January 4 to 5, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST FRI JAN 04 2008

.SYNOPSIS...A STRONG WEATHER SYSTEM WILL BRING PERIODS OF
RAIN...WITH SNOW OVER THE MOUNTAINS TODAY THROUGH SATURDAY. THIS
SYSTEM WILL ALSO GENERATE STRONG WINDS ALONG THE COAST AND POSSIBLY
VERY WINDY CONDITIONS INLAND SATURDAY MORNING. AFTER THIS SYSTEM
EXITS THE REGION...A VERY COOL SHOWERY AIR MASS WILL FOLLOW...WITH
SNOW SHOWERS POSSIBLE AT TIMES OVER THE INTERIOR LOWLANDS. AFTER A
BREAK LATE MONDAY...YET ANOTHER FRONTAL SYSTEM WILL SWING THROUGH
THE REGION TUESDAY.

&&

.SHORT TERM...A POWERFUL LOW NEAR 45N 132W CONTINUES TO CHURN CLOSER
TO THE COAST THIS MORNING AS A 200+ KT JET UNDERCUTS IT. SHIP
REPORTS IN THE VICINITY OF THE SURFACE LOW SUGGEST IT IS NEAR 960
MB...POSSIBLY A BIT LOWER. AN OCCLUDED FRONT WELL AHEAD OF THE UPPER
LEVEL LOW ITSELF IS EXPECTED TO REACH THE COAST BY MIDDAY THEN
QUICKLY CONTINUE TO MOVE EASTWARD ACROSS WESTERN WASHINGTON. WINDS
WILL INCREASE ALONG THE COAST TODAY AS THE FRONT MOVES ASHORE...WITH
MESOSCALE MODELS SHOWING 925 MB WINDS APPROACHING 50 KNOTS...SOME OF
WHICH COULD MIX DOWN TO THE SURFACE. HOWEVER...OF GREATER CONCERN IS
WHAT WILL HAPPEN AS THE SURFACE LOW MOVES ASHORE OVER NORTH CENTRAL
VANCOUVER ISLAND THIS EVENING. STRONG PRESSURE RISES ON THE BACK
SIDE OF THE LOW ARE EXPECTED TO CREATE A SECONDARY SURGE OF WIND.
THIS WILL IMPACT THE COAST FIRST...THEN THE INTERIOR OVERNIGHT INTO
SATURDAY MORNING. FOR NOW...WE HAVE A HIGH WIND WATCH IN EFFECT FOR
BOTH THE COAST AS WELL AS THE NORTH INTERIOR AS THEY STAND THE BEST
CHANCE OF HIGH WIND. HOWEVER...QUITE A SURGE COULD MAKE ITS WAY DOWN
THE STRAIT BEHIND THE LOW LATE TONIGHT AND THAT BEARS WATCHING.
QUITE COLD TEMPERATURES ALOFT ACCOMPANY THE UPPER LEVEL TROUGH AS IT
MOVES INTO WESTERN WASHINGTON ON SATURDAY WITH 500MB TEMPS DROPPING
TO -32C TO -36C. I EXPANDED ISOLATED THUNDERSTORM TO THE COAST
TONIGHT...BUT THEY MAY WELL NEED TO BE ADDED TO MUCH OF THE INTERIOR
FOR SATURDAYS FORECAST. BY SUNDAY MODEL 1000-850 MB THICKNESS VALUES
ARE NEAR 1290M WITH AN ABSENCE OF ANY REAL ONSHORE GRADIENT...FOR
VERY LOW SNOW LEVELS. ITS TOUGH TO PINPOINT ANY DETAILS THIS
EARLY...BUT SUFFICE TO SAY MOST SPOTS AWAY FROM THE COAST STAND A
CHANCE OF SEEING A LITTLE SNOW.

.LONG TERM...I DID NOT MAKE ANY CHANGES TO THE EXTENDED FORECAST AS
THE TREND OF ANY ACTIVE PATTERN IS EXPECTED TO CONTINUE. THE GFS
CONTINUES WITH BRINGING ANOTHER POTENT SYSTEM INTO THE REGION EARLY
TUESDAY WITH SEVERAL WEAKER SYSTEMS TO FOLLOW. 27

&&

.AVIATION...CLOSED UPPER LOW WILL SWING NE THROUGH SW BC TODAY
THROUGH THIS EVENING WITH SW FLOW ACROSS WA. RADAR SHOWING RAIN
INCREASING THIS MORNING WITH MOIST SOUTHERLY FLOW AS THE SFC. EXPECT
SHOWERS TO DEVELOP THIS AFTERNOON WITH AND ISOLATED THUNDERSTORM
POSSIBLE ALONG THE COAST. SOUTHERLY WINDS ACROSS THE INTERIOR WILL
INCREASE THIS EVENING AS THE SFC LOW HEADS INTO VANCOUVER ISLAND.
WINDY CONDITIONS EXPECTED ACROSS THE AREA THROUGH SAT AFTERNOON.

.KSEA...SYSTEM OFFSHORE WILL SPREAD RAIN THROUGH THE INTERIOR THIS
MORNING WITH SHOWERS EXPECTED DURING THE AFTERNOON. SOUTHERLY
GRADIENTS WILL INCREASE LATE THIS EVENING AS SFC LOW HEADS NE INTO
VANCOUVER ISLAND. EXPECT SOUTH WINDS TO INCREASE TO 15G25KT BY 03Z.
33

&&

.MARINE...WINDS WILL BE INCREASING ACROSS ALL WATERS TODAY AS DEEP
957 MB SFC LOW NEAR 45N AND 135W HEADS NE. THIS SYSTEM WILL HEAD
INTO VANCOUVER ISLAND THIS EVENING WITH FLOW SWITCHING TO SOUTHWEST
TO WEST...WITH A STRONG WESTERLY SURGE THROUGH THE STRAIT. STRONGEST
WINDS ACROSS PUGET SOUND/HOOD CANAL EXPECTED AFT 03Z THIS EVENING.
SWELLS WILL ALSO BE BUILDING TO OVER 25 FT LATE THIS EVENING. STRONG
SOUTHERLY WINDS WILL PERSIST THROUGH SAT AFTERNOON WITH WINDS EASING
A BIT SAT EVENING AS THE SFC LOW WEAKENS AND HEADS FURTHER N INTO
BC. A WEAKER SYSTEM WILL AFFECT THE REGION ON SUNDAY. 33

.SEW WATCHES/WARNINGS/ADVISORIES...
.GALE WARNING ALL WATERS.
.SMALL CRAFT ADVISORY FOR SEVERE BAR CONDITIONS AT THE GRAYS
HARBOR BAR ENTRANCE.
.HIGH SURF WARNING NORTH AND CENTRAL COAST.
.HIGH WIND WATCH NORTH AND CENTRAL WASHINGTON COAST AND THE NORTH
INTERIOR.
.SNOW ADVISORY OLYMPICS AND NORTHERN AND CENTRAL WASHINGTON CASCADES.

WEATHER.GOV/SEATTLE