Small Craft Advisory 785, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT SAT JUL 30 2011

.SYNOPSIS...TODAY WILL BE SUNNY WITH TEMPERATURES CLIMBING A FEW
DEGREES ABOVE NORMAL. A WEAK FRONT WILL MOVE THROUGH WESTERN
WASHINGTON SUNDAY FOR MOSTLY CLOUDY COOLER WEATHER AND A CHANCE OF
SHOWERS. A PATTERN OF WEAK ONSHORE FLOW WILL PREVAIL NEXT WEEK FOR
AFTERNOON SUNSHINE...PATCHY NIGHT AND MORNING CLOUDS...AND NEAR
NORMAL TEMPERATURES.

&&

.SHORT TERM...WESTERLY FLOW ALOFT OVER THE PACIFIC NORTHWEST IS
BACKING GRADUALLY TO SOUTHWESTERLY AHEAD OF AN UPPER TROUGH CENTERED
JUST OFF SOUTHEAST ALASKA. LIGHT NORTHERLY ONSHORE FLOW PREVAILS AT
THE SURFACE. A LARGE FIELD OF MARINE STRATUS REMAINS OVER THE
COASTAL WATERS EARLY THIS MORNING. THERE WAS ALSO AN AREA OF STRATUS
ALONG THE NORTH COAST...AND AT 2 AM PATCHY STRATUS WAS BEGINNING TO
FORM FROM THE SOUTH PUGET SOUND THROUGH THE SOUTHWEST INTERIOR.

THE UPPER LOW WILL MOVE SLOWLY SOUTHEAST TODAY TO A POSITION NEAR
HAIDA GWAII -- RECENTLY KNOWN AS THE QUEEN CHARLOTTES -- LATE THIS
AFTERNOON. A WEAK FRONT AHEAD OF THE UPPER LOW WILL EXTEND ACROSS
NORTH VANCOUVER ISLAND AND THE NORTHWEST CORNER OF THE WASHINGTON
OFFSHORE WATERS. THE AIR MASS OVER WESTERN WASHINGTON WILL WARM
SEVERAL DEGREES OVER FRIDAY...AND HIGH TEMPERATURES WILL GENERALLY
BE A FEW DEGREES WARMER AS WELL...BEFORE LOW LEVEL FLOW TURNS MORE
STRONGLY ONSHORE LATE IN THE DAY.

THE SYSTEM UPSTREAM WILL CONTINUE TO MOVE SOUTHEASTWARD TONIGHT...
WITH THE FRONT REACHING THE NORTH COAST LATE TONIGHT AND THE UPPER
TROUGH REACHING 130W. THIS COULD BRING SOME LIGHT SHOWERS TO THE
COAST AND NORTH PART OF WESTERN WASHINGTON OVERNIGHT. IN ADDITION
LOW LEVEL ONSHORE FLOW SHOULD PUSH THE MARINE LAYER INLAND
OVERNIGHT.

THE FRONT WILL MOVE ACROSS WESTERN WASHINGTON SUNDAY...WITH THE
UPPER TROUGH MOVING INLAND IN THE AFTERNOON. THE COMBINATION OF THE
WEAK FRONTAL SYSTEM AND ONSHORE FLOW WILL KEEP THE FORECAST AREA
MOSTLY CLOUDY AND COOLER. IN ADDITION THE MODELS AGREE THAT MOST OF
WESTERN WASHINGTON WILL GET SOME LIGHT SHOWERS. THE GFS AND UW
WRF-GFS SHOW THE PRECIPITATION FAIRLY WIDESPREAD...WHILE THE NAM12
AND UW MM5-NAM INDICATE THAT MOST OF IT WILL FALL IN A WEAK PUGET
SOUND CONVERGENCE ZONE.

THE TROUGH WILL MOVE QUICKLY EAST OF THE CASCADES SUNDAY NIGHT...AND
WE WILL HAVE JUST WEAK NORTHWEST LOW LEVEL FLOW. ASIDE FROM SPOTTY
EVENING SHOWERS OVER THE CASCADES...THE FORECAST AREA SHOULD BE DRY
WITH PARTLY CLOUDY SKIES. MONDAY WILL BRING A RETURN TO A PATTERN
SIMILAR TO TODAY -- FAIRLY WEAK ZONAL FLOW ALOFT...LIGHT ONSHORE LOW
LEVEL FLOW...AND MOSTLY SUNNY SKIES WITH TEMPERATURES NEAR OR
SLIGHTLY ABOVE NORMAL.   MCDONNAL

.LONG TERM...MODELS BASICALLY AGREE THAT A PATTERN OF WEAK ZONAL
FLOW ALOFT AND ONSHORE LOW LEVEL FLOW WILL CONTINUE THROUGH THE
EXTENDED PERIOD TUESDAY THROUGH FRIDAY. IN GENERAL THIS WILL
TRANSLATE TO MOSTLY SUNNY DAYS...PATCHY NIGHT AND MORNING LOW
CLOUDS...AND NEAR NORMAL TEMPERATURES. A WEAK UPPER TROUGH WILL
ARRIVE TUESDAY NIGHT OR WEDNESDAY...WHICH IS SHOWN AS A SOMEWHAT
STRONGER FEATURE BY THE EUROPEAN MODEL. HOWEVER IT WILL PROBABLY NOT
AMOUNT TO MORE THAN A DRIZZLE OR LIGHT SHOWER PRODUCER AT THE COAST
AND IN THE OLYMPIC MOUNTAINS.   MCDONNAL

&&

.AVIATION...SOUTHWESTERLY FLOW ALOFT TODAY WITH A SHORTWAVE MOVING
INTO WESTERN WASHINGTON SUNDAY MORNING. SATELLITE IMAGERY SHOWS
LITTLE IN THE WAY OF LOW CLOUDS AND FOG EXCEPT NEAR THE WEST
ENTRANCE TO THE STRAIT AND ALONG THE NORTH COAST. KUIL-KBLI GRADIENT
STILL ABOVE A MILLIBAR BUT THE REMAINDER OF THE GRADIENTS ARE FLAT.
SANDPOINT PROFILER SHOWS NORTH NORTHEASTERLY WINDS ALOFT IN THE
LOWER LEVELS UP TO 2500 FEET. GIVEN THESE VARIABLES WILL CONFINE
MOST OF THE LOW STRATUS IN THE MORNING TO THE KHQM AND KCLM TAFS.
TEMPERATURE DEW POINTS OVER THE SOUTHWEST INTERIOR ARE 1 OR ZERO AT
10Z SO WILL STAY WITH THE FOG SCENARIO AT KOLM. FOR MOST OF THE
REMAINDER OF THE AREA JUST SOME HIGH CLOUDS FLOATING. LOW LEVEL
MOISTURE INCREASING AFTER MIDNIGHT TONIGHT WITH THE WEAK SHORTWAVE
MOVING INTO THE AREA ON SUNDAY MORNING. EXPECT MVFR CEILINGS TO
DEVELOP SUNDAY MORNING.

KSEA...WILL PUT A LOW SCATTERED LAYER AT THE TERMINAL FOR A COUPLE
OF HOURS THIS MORNING OTHERWISE JUST SOME HIGH CLOUDS. NORTHERLY
WINDS 5-10 KNOTS SWITCHING TO SOUTHWESTERLY THIS EVENING. FELTON

&&

.MARINE...ONSHORE FLOW WILL REMAIN THE DOMINANT FEATURE THROUGH
EARLY NEXT WEEK...BETWEEN THE SURFACE HIGH OVER THE THE NORTHEAST
PACIFIC AND A SURFACE TROUGH OVER EASTERN WASHINGTON. ONSHORE
GRADIENTS WILL PICK UP TONIGHT AHEAD OF A SHORTWAVE MOVING INTO THE
AREA SUNDAY MORNING. GALES ARE LIKELY IN THE CENTRAL AND EASTERN
STRAIT BOTH THIS EVENING AHEAD OF THE SHORTWAVE AND AGAIN SUNDAY
LATE AFTERNOON INTO THE EVENING HOURS BEHIND THE SHORTWAVE.

FOR THE FIRST PART OF NEXT WEEK A TYPICAL SUMMER PATTERN LOOKS TO BE
SETTING UP WITH DIURNALLY DRIVEN WINDS LEADING TO POSSIBLE SMALL
CRAFT ADVISORY IN THE CENTRAL AND EASTERN STRAIT IN THE EVENING
HOURS. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL AND EAST STRAIT.

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