Small Craft Advisory 1093, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PDT THU OCT 4 2012

.SYNOPSIS...STRONG HIGH PRESSURE OVER THE NORTHEAST PACIFIC AND
BRITISH COLUMBIA WILL MAINTAIN DRY NORTHERLY FLOW. THIS PATTERN WILL
LAST INTO NEXT WEEK. EXPECT SUNSHINE EACH DAY WITH HIGHS NEAR OR
SLIGHTLY ABOVE NORMAL.

&&

.SHORT TERM...DRY NORTHERLY FLOW ALOFT WILL CONTINUE TODAY WITH AN
UPPER TROUGH OVER THE MIDDLE PART OF THE COUNTRY AND AN UPPER RIDGE
CENTERED NEAR 140W. THE FLOW ALOFT WILL TURN NORTHEASTERLY FRIDAY
AND SATURDAY AS THE UPPER TROUGH OVER THE MIDDLE PART OF THE COUNTRY
SHIFTS EAST AND THE PACIFIC RIDGE BUILDS EAST INTO BRITISH COLUMBIA.
FLOW AT THE LOWER LEVELS WILL REMAIN NORTH/NORTHEAST THROUGH
SATURDAY. ALL OF THIS ADDS UP TO CONTINUED DRY AND SUNNY DAYS. HIGHS
WILL REMAIN NEAR TO SLIGHTLY ABOVE NORMAL EACH DAY. CLEAR SKIES AND
DRY LOW LEVELS WILL PRODUCE SOMEWHAT CHILLY MORNING LOWS...
ESPECIALLY IN THE SHELTERED VALLEYS. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...THE BLOCK OVER THE NE PAC WILL
PROLONG THE DRY SPELL ACROSS WESTERN WA THROUGH THE MIDDLE OF NEXT
WEEK. THE FLOW WILL TURN WEAKLY ONSHORE BY TUES SO MAY SEE AN
INCREASE IN COASTAL STRATUS. THE ECMWF AND GFS BOTH SHOW THE PATTERN
BREAKING DOWN TOWARD THE END OF THE WEEK AS THE CLOSED LOW IN THE
REX BLOCK IS FINALLY EJECTED EASTWARD. THE RIDGE WILL FLATTEN OVER
THE PAC NW WITH THE FLOW ALOFT BECOMING MORE WESTERLY...LEADING TO
AN INCREASE IN CLOUD COVERAGE. A PAC SYSTEM WILL BRING A SHOT OF
RAIN TO B.C. WHICH MAY CLIP WESTERN WA THURSDAY OR FRIDAY. EXACT
DETAILS ARE STILL UNCLEAR SO NO MAJOR CHANGES TO THE FORECAST JUST
YET. 33

&&

.AVIATION...A STRONG UPPER RIDGE OFFSHORE WILL CONTINUE PROVIDING
THE REGION WITH STRONG NLY FLOW ALOFT...ALTHOUGH THE FLOW WILL
WEAKEN WITH TIME THRU TONIGHT. CONTINUED LOW LEVEL OFFSHORE FLOW.
THE AIR MASS WILL REMAIN DRY AND STABLE.

KSEA...NLY WINDS OF 10-15 KT WITH OCCASIONAL GUSTS NEAR 20 KT WILL
PERSIST DURING THE DAY TODAY. EXPECT THE WINDS TO GRADUALLY DIMINISH
OVERNIGHT.

&&

.MARINE...STRONG HIGH PRES OVER BRITISH COLUMBIA COMBINED WITH LOWER
PRES ALONG THE WASHINGTON COAST WILL RESULT IN PERSISTENT OFFSHORE
FLOW THROUGH SATURDAY. THE HIGH OVER BRITISH COLUMBIA WILL WEAKEN
DURING THIS WEEKEND.

&&

.FIRE WEATHER...FUEL DRYNESS LEVELS ARE CURRENTLY ABOUT A STANDARD
DEVIATION DRIER THAN NORMAL VALUES TYPICALLY SEEN IN AUGUST...WHICH
IS HISTORICALLY THE DRIEST TIME OF YEAR. IN OTHER WORDS...FUEL
DRYNESS LEVELS ARE NEAR RECORDS FOR THIS TIME OF YEAR.
WEATHERWISE...A THERMAL PRESSURE TROUGH NEAR THE COAST AND COOL HIGH
PRESSURE EAST OF THE CASCADES WILL LEAD TO AN INCREASE IN EAST WIND
TODAY AND FRIDAY THROUGH THE CASCADE GAPS...INTO THE FOOTHILLS AND
EAST-WIND PRONE PORTIONS OF THE OLYMPIC PENINSULA. THIS EAST WIND
PATTERN WILL PERSIST THROUGH SUNDAY MORNING. IN ADDITION...
TIME-HEIGHT SECTIONS SHOW EXTREMELY DRY AIR GETTING DOWN LOW IN THE
ATMOSPHERE TONIGHT...SO LOOKING AT SOME VERY POOR NIGHTTIME HUMIDITY
RECOVERY. WITH ALL THIS SAID...RED FLAG WARNINGS ARE NOW IN EFFECT
FOR ZONES WHERE CRITICAL COMBINATIONS OF WIND AND LOW HUMIDITY ARE
FORECAST. EAST WIND WILL DIE OFF ON SUNDAY AFTERNOON...BUT LOW
HUMIDITY WITH LOW-LEVEL SUBSIDENCE INVERSIONS WILL THEN PREVAIL
EARLY NEXT WEEK.
HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...RED FLAG WARNING FOR MUCH OF THE SOUTH PART OF THE CWA.
PZ...NONE.

&&

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