Small Craft Advisory 772, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT MON JUL 18 2011

.SYNOPSIS...A WEAKENING UPPER LOW OFF THE N CALIFORNIA COAST WILL
MOVE INTO OREGON ON TUESDAY. LOW LEVEL ONSHORE FLOW WILL INCREASE
TUESDAY LEADING TO COOL AND CLOUDY CONDITIONS FOR WESTERN WASHINGTON
WEDNESDAY. A STRONGER UPPER LEVEL TROUGH WILL BRING WIDESPREAD
SHOWERS TO THE REGION WEDNESDAY NIGHT AND THURSDAY. HIGH PRESSURE
WILL BUILD FOR WARMING INTO THE WEEKEND.

&&

.SHORT TERM...AN UPPER LOW OFF THE CALIFORNIA COAST CONTINUES TO
DIRECT A FEW SHOWERS ALONG...AND MOSTLY EAST OF THE CASCADE CREST
THIS EVENING. THE MAJORITY OF THE CWA IS ENJOYING A PLEASANT EVENING
WITH TEMPERATURES AROUND 70 AWAY FROM LARGE BODIES OF WATER AND
MOSTLY CLEAR SKIES.

THE UPPER LOW WILL DRIFT NE INTO WESTERN OREGON BY TUESDAY MORNING
AND THEN QUICKLY KICK EASTWARD DURING THE DAY TUESDAY. AGAIN...BEST
AREA OF INSTABILITY WILL BE LOCATED TO SOUTH AND EAST OF OUR AREA.
ONSHORE GRADIENTS WILL INCREASE RAPIDLY TOMORROW AFTERNOON AS HIGHER
SURFACE PRES BUILDS ALONG THE COAST AND LOWER PRES BUILDS INLAND.
DIFFICULT FORECAST FOR THE AMOUNT OF SUN OVER THE INTERIOR LOWLANDS
TOMORROW. MARINE LAYER SHOULD LIFT SOMEWHAT BY LATE MORNING/EARLY
AFTERNOON BUT WITH INCREASING ONSHORE FLOW...IT WILL BE DIFFICULT TO
SCATTER OUT FOR VERY LONG. THE COAST SHOULD REMAIN CLOUDY ALL DAY.
NAM12/WRFGFS 4KM DEPICT AN AREA OF  CONVERGENCE AND SQUEEZES A FEW
DROPS AROUND THE USUAL AREAS OF CENTRAL/NORTH PGT SOUND TOMORROW
AFTERNOON. THE MARINE LAYER SHOULD DEEPEN OVERNIGHT
TUESDAY...LEADING TO POCKETS OF DRIZZLE WED MORNING. MODERATE
ONSHORE FLOW AND LONGWAVE TROUGHING WILL CONTINUE DRIPS AND DRABS IN
THE MOUNTAINS AND CLOUDS AND COOLER THAN NORMAL HIGHS ON WEDNESDAY.
ANOTHER JULY UPPER LOW WILL DROP DOWN FROM THE NORTHWEST THURSDAY
MORNING...PASSING TO THE EAST IN THE AFTERNOON. THIS WILL PRODUCE
MORE WIDESPREAD SHOWERS AND CONTINUED COOL TEMPS. DAMICO

.LONG TERM...FROM PREVIOUS DISCUSSION...AN UPPER TROF OVER WA THU
DEPARTS WITH A WEAK UPPER RIDGE QUICKLY BUILDING INTO THE AREA FRI.
OVER THE WEEKEND UPPER HEIGHTS CONTINUE TO TREND UP FOR A FEW DAYS
OF AVERAGE TEMPS AND SUNSHINE...THIS IS WHAT THE GFS AND ECMWF SHOW.
IF THE CANADIAN MODEL IS CORRECT UPPER HEIGHTS WILL BE LOWER AND
NIGHT AND MORNING CLOUDS WOULD PROBABLY PERSIST WITH TEMPS A NOTCH
LOWER THAN FCST.

&&

.AVIATION...AN UPPER TROF ALONG THE W COAST WILL MOVE INLAND
OVERNIGHT. SLY FLOW ALOFT WILL BECOME LIGHT AND VARIABLE OVERNIGHT.
CONTINUED LOW LEVEL ONSHORE FLOW. MEANWHILE...THE AIR MASS WILL
REMAIN UNSTABLE E AND WELL S OF THE FORECAST AREA THRU TONIGHT.

THERE WERE AREAS OF LIFR CIGS IN THE CASCADES AT THIS TIME...AND
THESE CONDITIONS ARE EXPECTED TO PERSIST OVERNIGHT. ANTICIPATE
STRATUS /CIGS NEAR 015/ TO DEVELOP OVER THE COAST AFTER 0900
UTC.

KSEA...VFR CONDITIONS ARE EXPECTED TO PERSIST OVERNIGHT. THE
LATEST MODEL GUIDANCE...IN PARTICULAR THE NAM...INDICATED THE
POSSIBILITY OF CIGS NEAR 2K FT TUE MORNING.

&&

.MARINE...
HIGH PRES OVER THE NE PAC AND LOWER PRES E OF THE CASCADES WILL
KEEP THE FLOW ONSHORE THROUGH WED. THERE IS THE POTENTIAL FOR GALE
FORCE WESTERLIES OVER THE CENTRAL STRAIT OF JUAN DE FUCA AND THE
FAR W PORTION OF THE EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA
ON TUE DUE TO TIGHTENING OF THE ONSHORE PRES GRADIENT. EXPECT A
COLD FRONT TO MOVE ACROSS THE AREA ON THU.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT TIL NOON TUESDAY FOR THE
     CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

     GALE WATCH IN EFFECT FROM TUESDAY AFTERNOON THROUGH LATE
     TUESDAY NIGHT FOR THE CENTRAL AND EASTERN STRAIT OF JUAN DE
     FUCA.

&&

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