FXUS66 KSEW 120523
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
925 PM PST FRI DEC 11 2009

.SYNOPSIS...CLOUDS WILL INCREASE ACROSS THE AREA THROUGH THE WEEKEND 
AS THE FLOW ALOFT BECOMES MORE WESTERLY. A WEATHER SYSTEM WILL MOVE 
INTO NORTHERN CALIFORNIA THROUGH SATURDAY...WITH SOME MOISTURE 
SPREADING AS FAR NORTH AS THE EXTREME SOUTH PART OF WESTERN 
WASHINGTON. A COLD UPPER TROF WILL SAG SOUTH OVER BRITISH COLUMBIA 
ON SUNDAY...AND IT IS THIS SYSTEM THAT WILL BRING THE BEST CHANCE OF 
SNOW TO WESTERN WASHINGTON SUNDAY AFTERNOON AND NIGHT. MUCH WARMER 
AND WETTER WEATHER WILL ARRIVE STARTING AROUND TUESDAY OF NEXT WEEK.

&&

.SHORT TERM...TEMPERATURES WILL CONTINUE TO MODERATE THROUGH THE 
WEEKEND...THERE ARE ONLY DRIBS AND DRABS OF MOISTURE HOWEVER AND 
PARTLY TO MOSTLY CLOUDY WITH ARND A 20PCT CHANCE OF A SNOW OR MIXED 
RAIN AND SNOW SHOWER IS A REASONABLE FORECAST THRU SAT NITE. SUNDAY 
IS MORE INTERESTING AS THE ARCTIC FRONT MOVES SOUTH THRU B.C. ON 
SUNDAY AND IS IS VERY LIKELY THAT COLD FRASER OUTFLOW WILL BEGIN 
AGAIN SUN AFTERNOON. THE BEST CHANCE OF SNOW WILL BE NORTH OF 
SEATTLE SUN AFTERNOON OR NIGHT AS A PSCZ INTERACTS WITH THE LEADING 
EDGE OF THE COLD AIR FLOWING SOUTH FROM B.C...THE MESOSCALE MODELS 
WILL RECEIVE A GREAT DEAL OF CLOSE SCRUTINY THIS WEEKEND BUT SKAGIT 
AND ISLAND COUNTY PROBABLY HAVE THE BEST CHANCE OF SGFNT SNOWFALL 
SUN AFTERNOON AND NITE...FOLLOWED BY WHATCOM AND SNOHOMISH 
COUNTY...WITH THE REST OF WRN WA AT LOW RISK. 19 

.LONG TERM...A MILDER AND WET PATTERN TUE THROUGH THE END OF NEXT 
WEEK...WITH SIGNIFICANT RAINFALL POSSIBLE OVER THE SW FACING SLOPES 
OF THE OLYMPICS IN PARTICULAR. THE SNOW LEVEL WILL RISE IN 
STEPS...WITH MOUNTAIN SNOW FOR THE FIRST COUPLE OF SYSTEMS BUT A 
GRADUALLY RISING SNOW LEVEL WITH EACH FRONT. THE SYSTEM CURRENTLY 
TIMED FOR THURSDAY NIGHT LOOKS ESPECIALLY WARM WITH THE 850MB TEMP 
RISING TO +6C OVER WRN WA AND THE LAST BIT OF COOL AIR FINALLY 
OVERWHELMED ALONG THE EAST SLOPES OF THE NORTH CASCADES. SKIING 
OUGHT TO BE OKAY FOR THE FIRST PART OF THE WEEK BUT DOES NOT LOOK 
GOOD THU AND FRI. 19

&&

.HYDROLOGY...
FLOODING WILL NOT BE A CONCERN FOR THE WRN WASHINGTON RIVERS THROUGH 
MONDAY. MONDAY...HOWEVER...WILL BE A TRANSITION DAY FROM THE CURRENT 
COLD SPELL TO A MILDER AND WETTER PATTERN.

RISING SNOW LEVELS AND INCREASED MOIST...ONSHORE FLOW TUE THROUGH 
NEXT WEEKEND WILL RESULT IN RISING RIVER LEVELS DURING THIS PERIOD.
AT THIS TIME...IT APPEARED THAT THE RIVERS FLOWING OFF THE OLYMPICS
WILL HAVE THE POTENTIAL TO EXPERIENCE MINOR FLOODING...POSSIBLY AS 
EARLY AS ABOUT THE MIDDLE OF NEXT WEEK. 

NO FLOODING IS EXPECTED ON THE GREEN RIVER. 

&&

.AVIATION...LIGHT WEST TO NORTHWEST FLOW WILL BE MAINTAINED ALOFT 
THROUGH SATURDAY.  A LOW PRESSURE SYSTEM WILL MOVE ONSHORE WELL 
SOUTH OF THE REGION LATE SATURDAY WHILE HIGHER PRESSURE WILL REMAIN 
TO THE NORTH AND EAST.  THIS WILL CONTINUE ALLOWING FOR VERY LIGHT 
WINDS.  A THIN LAYER OF STRATUS ACROSS WHATCOM COUNTY WILL LIKELY 
SLOWLY BUILD SOUTH OVERNIGHT TONIGHT BUT STAY NORTH OF KPAE.  A FEW 
FLURRIES ARE POSSIBLE UNDER IT OVER THE NORTHWEST INTERIOR. 

KSEA...THE ONLY POTENTIAL ISSUE WOULD BE THE LAYER OF STRATUS 
CURRENTLY NEAR KBLI REDEVELOPING FAR ENOUGH SOUTH OVERNIGHT TO 
AFFECT THE TERMINAL. AT THIS POINT IT LOOKS LIKE THE STRATUS WILL 
STAY TO THE NORTH. JUST MID/HIGH LEVEL CLOUDS THROUGH SATURDAY WITH 
A 5000 FOOT SCATTERED LAYER DEVELOPING SATURDAY MORNING. WINDS WILL 
REMAIN LIGHT NORTHEAST.  FELTON

&&

.MARINE...A LOW PRES SYSTEM WILL BYPASS WASHINGTON WELL TO THE SOUTH 
LATE SATURDAY...HAVING A VERY LIMITED AFFECT ON OUR WEATHER.  HIGH 
PRES MOVING SOUTH THROUGH BRITISH COLUMBIA WILL INDUCE SOME 
NORTHEAST FRASER OUTFLOW LATE SUNDAY INTO MONDAY WHICH WILL ALSO 
PICK UP THE WINDS IN PORTIONS OF THE STRAIT OF JUAN DE FUCA. 

AN APPROACHING...MORE TYPICAL PACIFIC FRONT WILL REACH THE WATERS ON 
MONDAY...WITH MODERATELY STRONG SOUTHERLY WINDS.  THE REMAINDER OF 
THE WEEK WILL BECOME ACTIVE ONCE AGAIN AS A SERIES OF FRONTS ARE 
EXPECTED TO MOVE ACROSS THE WATERS FOR PERIODS OF SMALL CRAFT TYPE 
WINDS AND SEAS.  CERNIGLIA

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE. 
PZ...NONE.
   
$$

WWW.WEATHER.GOV/SEATTLE

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.