Small Craft Advisory 637, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
310 PM PST FRI FEB 4 2011

.SYNOPSIS...MOIST...ONSHORE FLOW WILL CONTINUE THROUGH THIS
WEEKEND...RESULTING IN WET AND UNSETTLED CONDITIONS. ANTICIPATE A
STRONGER SYSTEM TO USHER IN A COLDER AIR MASS ON SUNDAY AS WELL AS
CREATE WINDY CONDITIONS ACROSS THE AREA. STRONG...NLY FLOW WILL
BRING DRYING TO THE REGION ON MONDAY BUT THERE WILL STILL BE A
CHANCE OF SHOWERS...ESPECIALLY OVER THE INTERIOR. EXPECT A MODIFIED
ARCTIC FRONT TO MOVE ACROSS THE AREA MONDAY NIGHT...RESULTING IN
WINDY CONDITIONS OVER PARTS OF THE FAR NORTH INTERIOR.

&&

.SHORT TERM...
AN UPPER RIDGE WILL REMAIN CENTERED OFFSHORE. SHORT WAVE TROFS WILL
CONTINUE TO RIDE ACROSS THE TOP OF THIS RIDGE...WITH THE TAIL END OF
THESE SYSTEMS MOVING ACROSS THE CWA AT TIMES. FAIRLY STRONG AND
MOIST W-NW FLOW ALOFT WILL CONTINUE ACROSS THE AREA...RESULTING IN
WET WEATHER THIS WEEKEND. PORTIONS OF THE PUGET SOUND REGION WILL
PRIMARILY BE IN THE RAIN SHADOW...WITH THE BEST CHANCE OF RAIN
OCCURRING WITH FROPAS.

THE SUNDAY SYSTEM WILL LIKELY BE THE MOST VIGOROUS ONE AS IT WILL
USHER IN A MUCH COLDER AIR MASS. THE PRES GRADIENT WILL ALSO TIGHTEN
QUITE A BIT...RESULTING IN WINDY CONDITIONS ACROSS MUCH OF THE CWA
SUNDAY AFTERNOON AND EVENING. WILL NEED TO WATCH THE SUNDAY SYSTEM
AS IT HAS THE POTENTIAL TO PRODUCE SIGNIFICANT SNOWFALL IN THE
MOUNTAINS...NAMELY THE CASCADES.

THE ONSHORE GRADIENT WILL ALSO BECOME QUITE STRONG BEHIND THE FRONT
SUNDAY NIGHT...RESULTING IN THE POTENTIAL FOR GALE FORCE WINDS THRU
THE STRAIT OF JUAN DE FUCA AND POSSIBLY VERY WINDY CONDITIONS OVER
WHIDBEY ISLAND. THE NAM SOLUTION INDICATED THAT A PUGET SOUND
CONVERGENCE ZONE /PSCZ/ WILL DEVELOP SUNDAY NIGHT AND PERSIST THRU
MON. HAVE WENT WITH THIS IDEA. FOR NOW...HAVE INDICATED THE PSCZ
OVER THE TYPICAL LOCATION OR ALONG THE KING/SNOHOMISH COUNTY BORDER.

STRONG NLY FLOW IS ANTICIPATED ON MON. THIS SHOULD LEAD TO SOME
DRYING OF THE AIR MASS. HOWEVER THE STATE WILL STILL BE UNDER
CYCLONIC FLOW ALOFT AND WITH VORT LOBES OR MAXES DROPPING DOWN
ACROSS THE CWA...FELT THAT IT WOULD BE A GOOD IDEA TO KEEP THE RISK
OF SHOWERS GOING.

LOW LEVEL CAA IS EXPECTED MON NIGHT IN RESPONSE TO A MODIFIED ARCTIC
FRONT MOVING S ACROSS THE CWA. THE COLDEST AIR WILL HEAD TOWARD THE
PLAINS STATES...THUS EXPECT THE COLD AIR OVER THE CWA TO BE A BIT
SHALLOW. WRN WHATCOM COUNTY CAN ONCE AGAIN EXPECT GUSTY NLY WINDS OR
FRASER OUTFLOW THAT WILL PREVENT MIN TEMPS FROM DROPPING TOO MUCH...
BUT IT WILL FEEL A LOT COLDER.

.LONG TERM...
CONFIDENCE IN THIS PERIOD WAS LOW...ESPECIALLY IN THE DETAILS. IN
GENERAL...THE GFS KEPT THE MEAN UPPER RIDGE AXIS CLOSER TO THE
COAST...THEREBY KEEPING THE AREA DRY THRU MUCH OF THE PERIOD. IN
CONTRAST...THE ECMWF GENERALLY KEPT THE MEAN RIDGE AXIS FARTHER
OFFSHORE...THUS KEEPING THE DOOR OPEN FOR STRONG AND COLD TROFS TO
MOVE SE ACROSS THE CWA. HAVE COMPROMISED BETWEEN THE COLDER...WETTER
ECMWF SOLUTION AND THE DRIER...WARMER GFS SOLUTION FOR THIS PERIOD.

&&

.HYDROLOGY...
MOIST...ONSHORE FLOW WILL CONTINUE ACROSS THE CWA THRU THIS WEEKEND.
PRECIP TOTALS FOR THE 72-HR PERIOD ENDING 1200 UTC SUNDAY ARE
EXPECTED TO MAINLY BE IN THE 1 TO 2.5 INCH RANGE ON THE COAST AND
THE MOUNTAINS WHILE ELSEWHERE...AMOUNTS WILL MAINLY BE IN THE
QUARTER TO THREE QUARTERS RANGE. THERE IS A POSSIBILITY THAT THESE
AMOUNTS MAY BE UNDERESTIMATED. AT ANY RATE...EXPECT SOME RISES ON
AREA RIVERS DURING THIS PERIOD.

ANOTHER 1 TO 3 INCHES OF PRECIP /TOTAL/ IS ANTICIPATED ON THE COAST
AND IN THE MOUNTAINS DURING THE SUN/MON PERIOD...WITH THE HEAVIEST
AMOUNTS FALLING ON THE CASCADES. HOWEVER THE SNOW LEVELS WILL BE
FALLING DURING THIS PERIOD DUE TO COLD AIR ADVECTION...THUS PART OF
THIS PRECIP WILL FALL AS SNOW. BY MON MORNING...THE SNOW LEVELS ARE
ANTICIPATED TO BE NEAR 2K FT.

EXPECT DRY WEATHER THE MIDDLE OF THE NEXT WEEK. THE SNOW LEVELS WILL
REMAIN FAIRLY LOW AND THIS WILL KEEP THE RISK OF ANY RIVER FLOODING
LOW.

BEYOND MON OF NEXT WEEK...HYDROLOGICALLY SIGNIFICANT RAINFALL IS NOT
EXPECTED OUT TO 10 DAYS. THUS FLOODING ON AREA RIVERS...INCLUDING
THE GREEN...IS NOT ANTICIPATED TO BE A CONCERN.

&&

.AVIATION...AN UPPER RIDGE WILL BUILD OVER THE EASTERN PACIFIC
TONIGHT AND SATURDAY WITH NORTHWEST FLOW ALOFT OVER WESTERN
WASHINGTON. A WARM FRONT WILL MOVE THROUGH THE UPPER RIDGE AND INTO
WESTERN WASHINGTON SATURDAY. AIR MOIST AND STABLE.

KSEA...S/SW WIND 8-12 KNOTS WILL EASE TO 4-8 KNOTS TONIGHT AND
SATURDAY. SCHNEIDER

&&

.MARINE...WINDS EASING MOST AREAS TONIGHT IN THE WAKE A COLD FRONT
WHICH MOVED ONSHORE FRIDAY. THERE WILL BE SOME RESIDUAL 10-12 FOOT
SWELL OVER THE COASTAL WATERS TONIGHT AND SATURDAY BEHIND THE FRONT.

A WARM FRONT WILL BRING INCREASING WINDS THIS WEEKEND WITH SMALL
CRAFT CONDITIONS MOST WATERS AGAIN BY SUNDAY. OFFSHORE FLOW WILL
DEVELOP EARLY NEXT WEEK AS HIGH PRESSURE BUILDS INTO SOUTHERN
BRITISH COLUMBIA. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ALL WATERS.

     A SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS
     REMAINS IN EFFECT TL 6 AM SATURDAY.

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