Heavy Snow in Washington, January 14 to 15, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
933 AM PST MON JAN 14 2008

.SYNOPSIS...A STRONG COLD FRONT WILL MOVE ACROSS THE AREA TODAY FOR
GUSTY WINDS AND RAIN. THE RAIN WILL TAPER OFF TO SHOWERS THIS
AFTERNOON BEHIND THE FRONT. THIS COLD FRONT WILL ALSO USHER IN A
MUCH COOLER AIR MASS. THUS EXPECT ANY LINGERING RAIN SHOWERS
ACROSS THE LOWLANDS TONIGHT TO CHANGE OVER TO SNOW. DRY AND COOL
WEATHER WILL OCCUR OVER MUCH OF THE AREA ON TUESDAY. EXPECT DRY
WEATHER TO PERSIST THROUGH THE END OF THE WEEK UNDER STRONG HIGH
PRESSURE ALOFT.

&&

.SHORT TERM...
A STRONG...NE TO SW ORIENTED...CDFNT WAS JUST OFF THE COAST AT
THIS TIME. WINDS HAVE INCREASED ACROSS PORTIONS OF THE CWA AHEAD
OF THIS FRONT...ESPECIALLY ACROSS THE N INTERIOR...COAST...AND THE
WRN STRAIT. IN FACT...SPEEDS WERE IN THE ADVISORY CRITERIA RANGE
THIS MORNING ACROSS THE N INTERIOR AND WRN STRAIT...PROMPTING THE
ISSUANCE OF A WIND ADVISORY. THE FRONT WILL MOVE ONTO THE COAST
THIS MORNING AND THEN QUICKLY SWEEP ACROSS THE REMAINDER OF THE
CWA BY MIDAFTERNOON.

AS STATED IN PREVIOUS DISCUSSIONS...A COLDER AIR MASS WILL INVADE
THE REGION BEHIND THE CDFNT...RESULTING IN PLUMMETING FREEZING
LEVELS. BY LATE THIS AFTERNOON...FREEZING LEVELS WILL BE NEAR 1500
FEET ON THE COAST TO NEAR 3500 FEET OVER THE CASCADES. WOULD NOT BE
SURPRISED IF THE RAIN SHOWERS ON THE NORTH COAST AND THE W STRAIT
CHANGE OVER TO SNOW OR A RAIN/SNOW MIX NEAR THE 500 FOOT LEVEL. BY
LATE THIS EVENING...THE SNOW LEVEL WILL BE NEAR SEA LEVEL. AT THIS
TIME...SNOW ACCUMULATIONS ACROSS THE LOWLANDS WILL BE NEGLIBLE...
ALTHOUGH ELEVEATIONS AT AND ABOVE 500 FEET COULD RECEIVE AN INCH.

WILL NEED TO MONITOR PRECIP TRENDS TODAY BECAUSE THERE IS THE
POSSIBILITY THAT THE CASCADES COULD RECEIVE SNOWFALL AMOUNTS IN
THE ADVISORY RANGE BY TUE.

AN AMPLIFYING UPPER RIDGE WILL BRING DRY...NLY FLOW ALOFT TO THE
AREA ON TUE. THERE SHOULD BE ENOUGH INSTABILITY TO WARRANT A
CHANCE OF...ALBEIT LOW...SNOW SHOWERS TO THE MOUNTAINS. DRY
WEATHER WILL PREVAIL ON WED.

.LONG TERM FROM THE PREV DISCUSSION...THE UPPER LEVEL RIDGE OFF THE
WA COAST WILL DOMINATE ACROSS THE AREA THROUGH MUCH OF THE
EXTENDED FORECAST...KEEPING WESTERN WA DRY. THE RIDGE MAY BEGIN TO
BREAK DOWN BY SAT AS AN UPPER LEVEL TROUGH ROUNDS SE THROUGH CENTRAL
BC. FORECAST ALREADY COVERS THIS SO NO NEED FOR ANY TWEAKS. ENJOY
THE BREAK. 33

&&

.AVIATION...A STRONG COLD FRONT EXTENDING SW FROM CENTRAL VANCOUVER
ISLAND EARLY THIS MORNING WILL SWEEP ONSHORE LATE THIS MORNING AND
THROUGH THE INTERIOR EARLY THIS AFTERNOON. ONSHORE FLOW WILL FOLLOW
THE FRONT. A 2-4 HOUR BAND OF STEADY RAINFALL WILL ACCOMPANY THE
FRONT AND WILL BE FOLLOWED BY SHOWERS...MAINLY TIED TO THE
TERRAIN...AND CONVERGENCE ZONES OVER THE CENTRAL AND NORTHERN PUGET
SOUND AREAS. COLD AIR MOVES IN TONIGHT AND A LITTLE SNOW IS POSSIBLE
IN THE NORTH KING/SOUTH SNOHOMISH COUNTY AREA...BUT THE CHANCES OF
ACCUMULATIONS OF AN INCH OR MORE AT ANY OF THE TERMINALS IS LESS
THAN 30 PERCENT. SURFACE WINDS AND WINDS ALOFT WILL BE THE MAIN
FACTOR WITH THIS INCOMING FRONTAL SYSTEM. AHEAD OF THE FRONT MANY
TERMINALS WILL SEE S/SE WINDS 18G28KT AND WINDS AT 040 WILL RISE TO
SW45KT. WIND WILL SHIFT TO SW20G30KT BEHIND THE FRONT EXCEPT AT
KHQM...AND AROUND THE STRAIT OF JUAN DE FUCA...WHERE THEY WILL COME
AROUND TO 29025G35KT. WIND WILL DIMINISH AFTER 05Z. CHB

&&

.MARINE...GALES VERIFYING NICELY ON THE COAST AND EXPECT THE GALE SE
WINDS TO SPREAD INLAND PRESENTLY. FRONT PASSED BUOY 206 OFF THE
SOUTH VANCOUVER ISLAND COAST AT 13Z AND WILL PROBABLY REACH TATOOSH
ISLAND BY 18Z OR SO. THAT RATE BRINGS IT TO PUGET SOUND 21Z OR SO.
OBSERVATIONS IN THE WESTERLY FLOW BEHIND THE FRONT HAVE SO FAR NOT
YIELDED ANY GALE FORCE WINDS AND HAVE DOWNPLAYED THAT ASPECT IN THE
FORECAST. SHOULD STILL GET GOOD WESTERLY GALES IN THE STRAIT BUT
PERHAPS NOWHERE ELSE. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY IN EFFECT UNTIL 9 PM PST THIS EVENING FOR THE
     ADMIRALTY INLET AREA-SAN JUAN COUNTY-WESTERN SKAGIT COUNTY-
     WESTERN STRAIT OF JUAN DE FUCA-WESTERN WHATCOM COUNTY.

     WIND ADVISORY FROM NOON TODAY UNTIL 9 PM PST THIS EVENING FOR
     THE EASTERN STRAIT OF JUAN DE FUCA.

PZ...GALE WARNING ALL WATERS EXCEPT THE PUGET SOUND/HOOD CANAL.

     SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PUGET
     SOUND AND HOOD CANAL.

     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS.

WEATHER.GOV