FXUS66 KSEW 041723
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
925 AM PST FRI DEC 4 2009

.SYNOPSIS...COLD WEATHER WILL GRIP WESTERN WASHINGTON THROUGH EARLY 
NEXT WEEK AS MODIFIED ARCTIC AIR MOVES INTO THE REGION FROM WESTERN 
CANADA. TEMPERATURES WILL BE GENERALLY BELOW FREEZING AT NIGHT AND 
DAYTIME HIGHS WILL REACH ONLY THE 30S AND LOWER 40S. A DUSTING OF 
SNOW IS POSSIBLE SATURDAY NIGHT. COOL AND DRY NORTHERLY UPPER LEVEL 
FLOW WILL REMAIN IN PLACE OVER THE AREA THROUGH LATE NEXT WEEK.

&&

.SHORT TERM...ANOTHER COLD AND FROSTY MORNING AROUND WESTERN 
WASHINGTON...WITH CURRENT TEMPERATURES RANGING FROM THE 30S FREEZING 
TO LOWER 20S IN THE NORMALLY COLDER LOCALS. STRATUS AND HAS 
DEVELOPED OVER THE CENTRAL/SOUTH PGT SOUND AND LAKE WASHINGTON OVER 
THE LAST FEW HOURS...AND SHOULD LIFT LATER THIS MORNING. 

COOL NORTHWESTERLY FLOW REMAINS OVER THE AREA WITH AN AMPLIFIED 
UPPER LEVEL RIDGE OUT NEAR 135W THAT EXTENDS NORTHWARD INTO ALASKA. 
UPPER LOW OVER ALBERTA/BC BORDER WILL DROP SOUTH INTO THE INTERIOR 
PAC NW TODAY. MOISTURE IS LIMITED...AS A RESULT JUST SOME LIGHT SNOW 
SHOWERS IN THE NORTHERN CASCADES.  THE RIDGE WILL CONTINUE TO 
AMPLIFY INTO ALASKA ON SATURDAY...AND ANOTHER SHORTWAVE WILL DIG 
SOUTH IN THE NORTHERLY FLOW. THIS ONE WILL DIG FURTHER WEST SATURDAY 
NIGHT...WITH AN UPPER LOW SETTING UP SHOP OFF THE SOUTH/CENTRAL 
OREGON COAST BY SUNDAY. STRONG ARCTIC HIGH PRES WILL SLIDE SOUTH 
FROM THE YUKON DOWN JUST EAST OF THE SPINE OF THE CANADIAN ROCKIES 
PUSHING COLDER AIR OVER THE REGION.  AGAIN MOISTURE PROFILES LOOK 
EXTREMELY DRY...BUT MOS MAINTAINS 20/30 POPS OVER THE AREA SATURDAY 
NIGHT SO CANNOT RULE OUT SOME LIGHT SNOW SHOWERS. WITH NORTHEASTERLY 
OUTFLOW DEVELOPING OUT OF THE FRASER VALLEY...COLD AIR PASSING OVER 
THE EASTERN STRAIT WILL PICK UP SOME MOISTURE AND COMBINED WITH 
UPSLOPING ALONG THE CENTRAL STRAIT COULD PRODUCE MORE LOCALLY 
INTENSE SNOW SHOWERS THERE. WILL LIKELY UP POPS AND QPF SLIGHTLY 
ALONG THE STRAIT. MODEL SOUNDINGS SHOW MORE DRYING ON SUNDAY AS 
COLDER AIR FILTERS INTO THE REGION AS THE LOW PASSES FURTHER SOUTH. 
850 MB TEMPS WILL FALL TO AROUND -14C ON SUNDAY. A CHILLY DAY WILL 
FOLLOW ON SUNDAY WITH HIGHS ONLY IN THE 30S. DAMICO 

.LONG TERM...NEWEST 12Z GFS COMES IN LINE WITH 00Z ECMWF SHOWING THE 
RIDGE PINCHING OFF OVER AK AS A STRONGER SOUTHERN STREAM DEVELOPS 
FOCUSING MOST OF THE ENERGY INTO CALIFORNIA. WILL LIKELY DRY OUT WED 
NIGHT AND THURSDAY WITH THE AFTERNOON PACKAGE AS DRY N-NW FLOW ALOFT
REMAINING OVER THE AREA THROUGH FRIDAY...WITH A VERY SLOW MODERATION 
OF WELL BELOW NORMAL TEMPERATURES. DAMICO

&&

.HYDROLOGY...THERE IS NO THREAT OF RIVER FLOODING IN THE FORECAST 
AREA FOR THE NEXT WEEK. THIS INCLUDES THE GREEN RIVER.

RIVERS WILL GRADUALLY RECEDE THROUGH MIDWEEK AS A RESULT OF BELOW 
NORMAL TEMPERATURES AND BELOW NORMAL PRECIPITATION. MCDONNAL

&&

.AVIATION...UPPER TROF MOVG THRU PACNW WITH NW FLOW ALF OVER WRN WA 
BECMG NLY TNGT. ANOTHER UPPER TROF WILL MOVE SOUTH THRU WA SAT NITE. 
AT THE SFC STRONG HIGH PRES BUILDS OVER B.C. AND ALTA THRU THE 
WEEKEND WITH INCREASING NLY SFC FLOW BECMG MORE NE...WITH FRASER 
OUTFLOW DVLPG BY SAT NITE. AMS HAS SOME LOW LEVEL MOISTURE THIS 
MORNING WITH A HODGE PODGE OF LOW STRATUS...FOG...AND CLEAR 
CONDITIONS...BUT AIR MASS WILL DRY THRU SAT AS DRY NLY FLOW 
INCREASES. 19

KSEA...UPPER TROF HAS INDUCED A WEAK LOW PRES TROF AT THE SFC OVER 
WRN WA WHICH IS GVG LIGHT ONSHORE FLOW AND A LITTLE INFLUX OF 
MOISTURE...OR AT LEAST NO DRYING YET...SO AREAS OF STRATUS AND FOG 
PERSISTING THRU MIDDAY THEN SCATTERED CLOUDS THIS AFTERNOON AND 
EVENING AS DRIER NLY FLOW DVLPS. 

&&

.MARINE...GRADIENTS ARE QUITE LIGHT WITH A WEAK SFC TROF OVER WRN 
WA...RATHER BRISK NW WINDS OFFSHORE AND OFF VANCOUVER ISLAND WITH 
NW30KT AT THE LA PEROUSE BUOY...THE NLY GRADIENT WILL COME UP THIS 
AFTERNOON AND TONIGHT OVR WRN WA SO WILL KEEP ALL THE SMALL CRAFT 
ADVISORIES UP...FOR PUGET SOUND THE NLY FLOW WILL NOT LIKELY 
INCREASE THIS LATE THIS AFTERNOON AND EVENING. NE GALES FROM THE 
FRASER OUTFLOW WILL DEVELOP BY SAT NITE...POSSIBLY AS EARLY AS 
DAYBREAK SAT...IT IS REALLY JUST A MATTER OF WATCHING THE GRADIENTS 
WITH BLI-YWL BEING THE GRADIENT TO WATCH FOR THAT...BUT AS I SAID 
GRADIENTS ARE QUITE LIGHT THIS MORNING AND WONT REALLY RAMP UP TIL 
TNGT. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS...NORTHERN INLAND WATERS...
     EAST ENTRANCE JUAN DE FUCA...ADMIRALTY INLET AND PUGET SOUND
     HOOD CANAL. 
     SMALL CRAFT ADVISORY ROUGH BAR CONDITIONS GRAYS HARBOR BAR. 
  
$$

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