Small Craft Advisory 940, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
405 AM PDT FRI MAR 16 2012

.SYNOPSIS...COOL AND WET WEATHER WILL CONTINUE THROUGH THE MIDDLE OF
NEXT WEEK AS A SERIES OF WEATHER SYSTEMS MOVE THROUGH THE AREA. YET
ANOTHER COOL TROUGH WILL SET UP OVER WESTERN WASHINGTON OVER THE
WEEKEND LOWER THE SNOW LEVEL DOWN TO BELOW 1000 FEET.

&&

.SHORT TERM...SATELLITE IMAGERY AND WSR-88D'S SHOW ONE BAND OF
SHOWERS EXITING WESTERN WASHINGTON TO THE NORTH WITH ANOTHER BAND OF
SHOWERS MOVING INTO THE AREA FROM THE SOUTHWEST. WESTPORT PROFILER
SHOWS THE FREEZING LEVEL NEAR 3000 FEET EARLY THIS MORNING WITH ALL
OF THE SHOWERS IN THE FORM OF RAIN IN THE LOWLANDS. COOL UPPER LEVEL
TROUGH ANCHORED OFFSHORE WILL KEEP THE AIR MASS OVER WESTERN
WASHINGTON SLIGHTLY UNSTABLE TODAY SO EVEN AFTER THE ORGANIZED BAND
OF SHOWERS MOVES THROUGH THIS MORNING THE THREAT OF SHOWERS WILL
CONTINUE INTO THE AFTERNOON HOURS.

A SMALL BREAK IN THE ACTION THIS EVENING BEFORE A MORE ORGANIZED
SHORTWAVE GETS KICKED OUT OF THE TROUGH AND MOVES THROUGH WESTERN
WASHINGTON LATE TONIGHT INTO SATURDAY MORNING. BEHIND THE
SHORTWAVE...THE AIR MASS OVER WESTERN WASHINGTON COOLS DOWN WITH THE
1000-850 MB THICKNESS VALUES DROPPING BELOW 1300 METERS SATURDAY
EVENING. THE UPPER LEVEL TROUGH AXIS IS STILL OFFSHORE SATURDAY
EVENING BRINGING ABOUT ANOTHER ROUND OF THE LOW SNOW LEVELS...BELOW
1000 FEET...ALONG WITH SHOWER ACTIVITY FOR THE AREA. THIS SCENARIO
WILL CONTINUE THROUGH SUNDAY WITH THE TROUGH AXIS NOT MOVING EAST OF
THE CASCADES UNTIL SUNDAY NIGHT. ON SUNDAY THE SNOW LEVEL WILL LOWER
DOWN TO 500 FEET OR LESS BUT DAYTIME HIGHS WITH A LITTLE BIT OF
MARCH SUNSHINE WILL STILL GET INTO THE LOWER TO MID 40S. AT THIS
POINT NO SIGNIFICANT SNOW ACCUMULATIONS EXPECTED BUT A HEAVY SHOWER
DURING THE OVERNIGHT HOURS SATURDAY NIGHT COULD DROP AN INCH OR TWO
ON THE HIGHER HILLS. FELTON

.LONG TERM...EXTENDED MODELS IN FAIRLY GOOD AGREEMENT THIS MORNING
WITH A VERY FLAT UPPER LEVEL RIDGE MOVING THROUGH THE AREA ON MONDAY
AND A LOW CHANCE OF SHOWERS. THE RIDGE WILL SHIFT EAST QUICKLY WITH
A WARMER AND WETTER SYSTEM MOVING INTO THE AREA FOR TUESDAY. THE
MODEL SOLUTIONS START TO DIVERGE ON WEDNESDAY WITH THE GFS DROPPING
THE SYSTEM SOUTH INTO OREGON WHILE THE ECMWF BRINGS ANOTHER WET
SYSTEM INTO THE AREA. ANOTHER COOL UPPER LEVEL TROUGH SETTING UP
OFFSHORE ON THURSDAY. LITTLE CHANGE TO THE EXTENDED FORECAST THIS
MORNING. FELTON

&&

.HYDROLOGY...HEAVY RAINS FELL OVER THE SOUTH SLOPES OF THE OLYMPIC
MOUNTAINS THURSDAY DRIVING THE SKOKOMISH RIVER ABOVE FLOOD STAGE.
THE RIVER WILL FALL BELOW FLOOD STAGE THIS MORNING.

OTHER RIVERS IN SOUTHWEST WASHINGTON HAD SHARP INCREASES ON THURSDAY
BUT FOR THE MOST PART THEY CRESTED LAST NIGHT. ONLY THE CHEHALIS
RIVER WILL CONTINUE TO RISE TODAY WITH THE CREST MOVING DOWNSTREAM
LATE TODAY INTO SATURDAY. A FLOOD WARNING FOR THE CHEHALIS AT GRAND
MOUND WILL BE ISSUED IN THE NEXT HALF HOUR WITH THE RIVER CRESTING
SLIGHTLY ABOVE FLOOD STAGE LATER TODAY. A FLOOD WATCH REMAINS IN
EFFECT FOR THE MIDDLE AND LOWER CHEHALIS RIVER THROUGH SATURDAY
AFTERNOON.

THE EXTENDED MODELS ARE STILL SHOWING THE POSSIBILITY OF A FLOOD
PATTERN SETTING UP TUESDAY AND WEDNESDAY OF NEXT WEEK WITH A PERIOD
OF POSSIBLE HEAVY RAIN AND WARMER TEMPERATURES. FELTON

&&

.AVIATION...MODERATE SOUTHWEST FLOW ALOFT WILL CONTINUE TODAY THEN
BECOME SOUTHERLY TONIGHT. MODERATE SOUTHERLY SURFACE GRADIENTS WILL
WEAKEN TODAY. A SURFACE LOW WILL MOVE SOUTHWEST TO NORTHEAST ACROSS
THE AREA ON SATURDAY. AIR MASS IS MOIST AND SLIGHTLY UNSTABLE WITH
SHOWERS. MOUNTAINS OBSCURED.

CEILINGS ARE GENERALLY 2-3K FT IN SHOWERS...3-5K FT OR NO CEILINGS
AWAY FROM SHOWERS. THESE CONDITIONS WILL PERSIST THIS MORNING...WITH
A GENERALLY IMPROVING TREND THIS AFTERNOON.

KSEA...DISCUSSION ABOVE APPLIES. WIND WILL BE SOUTHERLY 7-12 KT
TODAY...THEN BECOME NORTHEAST 5-9 KT TONIGHT. CHB

&&

.MARINE...SMALL CRAFT ADVISORY STRENGTH SOUTHWEST WINDS WILL PERSIST
ON THE COAST THIS MORNING...THEN TAPER. WINDS SHOULD REMAIN BELOW 20
KT TODAY OVER INLAND AREAS. HAZARDOUS SEAS WILL REMAIN ABOVE 10 FEET
TODAY AND TONIGHT ON THE COAST.

A DEEP LOW WILL FORM OFF THE OREGON COAST THIS AFTERNOON...THEN FILL
AS IT MOVES NORTHEAST TONIGHT AND SATURDAY. CURRENT TRACK IN THE
MODELS TAKES THE LOW INTO EASTERN WASHINGTON. WIND OVER WESTERN
WASHINGTON WILL SWITCH FROM NORTHEAST TONIGHT TO SOUTHWEST SATURDAY
AFTERNOON. A STRONGER SYSTEM ARRIVES ABOUT TUESDAY. THIS SYSTEM
SHOULD HAVE GALE FORCE WINDS OVER MOST WATERS. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH FOR LEWIS...THURSTON AND GRAYS HARBOR COUNTIES.
PZ...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.

WWW.WEATHER.GOV/SEATTLE