Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 032218
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT TUE MAY 3 2016

.SYNOPSIS...A TROUGH OFF THE PACIFIC NORTHWEST COAST WILL MAINTAIN
COOLER ONSHORE FLOW AND SOMEWHAT UNSETTLED CONDITIONS OVER THE AREA
THROUGH THURSDAY. HIGH PRESSURE WILL BUILD OVER THE REGION FRIDAY
AND SATURDAY WITH WARMER TEMPERATURES. AN UPPER TROUGH WILL BRUSH
WESTERN WASHINGTON SUNDAY WITH A RETURN TO COOLER ONSHORE FLOW INTO
MONDAY. DRY AND WARMER WEATHER IS POSSIBLE TUESDAY.

&&

.SHORT TERM...SATELLITE AND RADAR INDICATE SHOWERS ARE MOSTLY
LIMITED TO THE CASCADES AND TOWARD THE COAST THIS AFTERNOON WITH
THIN MID/HIGH CLOUDS ACROSS THE REST OF THE AREA. LIGHTNING
DETECTION INDICATES A COUPLE STRIKES ALONG THE CASCADE CREST THIS
PAST HOUR. THE AIR MASS REMAINS WEAKLY UNSTABLE ALOFT BUT THE BEST
SURFACE BASED INSTABILITY BASED OFF MODEL LI`S IS OVER THE CASCADES.
WILL KEEP THE CHANCE OF THUNDERSTORMS IN THE FORECAST THROUGH THIS
EVENING FOR THE HIGHER CASCADES. OTHERWISE...THE MAIN FRONTAL BAND
WILL GRADUALLY EDGE INTO WRN WA WITH AN EMBEDDED SHORT WAVE LIFTING
ACROSS THE AREA. THIS WILL BRING A BETTER CHANCE OF MEASURABLE RAIN
TO THE LOWLANDS BUT STEADY OR WIDESPREAD RAIN IS NOT EXPECTED.

THE FRONTAL BAND REMAINS STALLED ACROSS WRN WA WEDNESDAY AS THE FLOW
ALOFT TURNS MORE SWLY. THIS WILL KEEP THUNDERSTORMS CONFINED EAST OF
THE CASCADE CREST. WITH THE MAIN MOISTURE BAND OVER THE AREA IT WILL
STAY MOSTLY CLOUDY WITH SPOTTY SHOWERS ACROSS THE AREA. A STRONGER
ONSHORE PUSH MAY ALSO RESULT IN AREAS OF MORNING STRATUS WITH COOLER
HIGH TEMPERATURES...CLOSER TO AVERAGE IN THE LOW 60S.

MODELS ARE A BIT FASTER SHIFTING THE UPPER TROUGH AXIS THROUGH THE
AREA ON THURSDAY. BUT THERE IS STILL SOME TIMING UNCERTAINTY WITH A
CHANCE OF SHOWERS UNTIL THE AXIS SHIFTS EWD. AREAS WEST OF PUGET
SOUND WILL STAY MOSTLY DRY WITH PARTIAL SUNSHINE. EXPECT MORE CLOUDS
AND CHANCE OF LINGERING SHOWERS EAST OF PUGET SOUND.

WRN WA SHOULD GENERALLY CLEAR OUT THURSDAY NIGHT AS LOW LEVEL
NORTHERLY FLOW DEVELOPS UNDER A BUILDING UPPER HIGH. MODELS STILL
SHOW A SKINNY RIDGE NOSING NE OVER THE REGION FRIDAY WITH 500 MB
HEIGHTS OVER 5700M. HIGH TEMPERATURES SHOULD WARM BACK ABOVE AVERAGE
WITH LOW 70S AROUND THE INTERIOR LOWLANDS...ROUGHLY 10 DEGREES ABOVE
AVERAGE FOR THIS TIME OF YEAR.

.LONG TERM...UPPER LEVEL HIGH PRESSURE WILL PERSISIT OVER THE PAC NW
THROUGH SATURDAY. IT SHOULD REMAIN DRY WITH LIGHT WLY ONSHORE
GRADIENTS DURING THE AFTERNOON. THIS WILL INHIBIT HIGH TEMPERATURES
ALONG THE COAST BUT IT SHOULD BE A FEW DEGREES WARMER OVER THE
INTERIOR.

THE GFS/ECMWF/CANADIAN ARE IN BETTER AGREEMENT TODAY IN SHOWING A
TROUGH CROSSING B.C. AND BRUSHING WRN WA ON SUNDAY. THIS SYSTEM
SHOULD INDUCE STRONGER ONSHORE FLOW AND DEEPEN THE MARINE LAYER.
HIGHS SHOULD DROP BACK DOWN INTO THE LOW 60S IN THIS PATTERN WITH
AREAS OF MORNING CLOUDS AND ONLY PARTIAL AFTERNOON SUN. THE 12Z
GFS/ECMWF BOTH SHOW SOME SPOTTY LIGHT QPF MOST LIKELY FALLING AS
SOME DRIZZLE FROM THE MARINE LAYER. THIS IS DIFFERENT THAN PREVIOUS
DRY MODEL RUNS AND ANY DRIZZLE COULD VERY WELL NOT EVEN MEASURE.
HAVE LEFT OUT ANY MENTION OF PRECIPITATION FOR NOW.

COOL ONSHORE FLOW MAY CONTINUE INTO MONDAY BUT THERE SHOULD BE A BIT
MORE AFTERNOON SUNSHINE AS THE TROUGH MOVES EAST. THE GFS/ECMWF
BOTH BUILD A RIDGE TUESDAY GIVING DRY AND WARMER WEATHER. MERCER

&&

.AVIATION...THERE IS SOUTHERLY FLOW ALOFT WITH MID LEVEL MOISTURE
AND SCATTERED SHOWERS AND TSTMS...MAINLY OVER THE CASCADES. CLOUDS
WILL INCREASE OVERNIGHT AS THE SHOWERS OVER THE CASCADES INCREASE
AND LOW LEVEL ONSHORE FLOW ALSO FORCES MORE MOISTURE INTO WRN WA.


KSEA...CLOUDS WILL INCREASE OVERNIGHT AS ONSHORE FLOW FORCES SOME
MORE MOISTURE INTO WRN WA. SHOWERS WILL ALSO INCREASE OVER THE
CASCADES AND THERE IS A CHANCE THAT THEY WILL ALSO DEVELOP OVER THE
LOWLANDS.

&&

.MARINE...ONSHORE FLOW IS INCREASING AND A GALE WARNING IS IN EFFECT
FOR THE CENTRAL AND EASTERN STRAIT OF OF JUAN DE FUCA. NORTHWEST
FLOW BETWEEN A SURFACE HIGH PRESSURE AREA OFFSHORE AND LOWER
PRESSURE INLAND WILL PERSIST WED THRU SUN. OVER THE WEEKEND THE LOW
PRESSURE INLAND WILL BECOME THERMAL LOW PRESSURE AND THAT MIGHT
CREEP INTO WRN WA...BUT THE PATTERN OF NW WINDS SHOULD
CONTINUE...ESPECIALLY FOR THE COAST.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING IN EFFECT CENTRAL AND EASTERN STRAIT OF JUAN DE
     FUCA.

  SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING
     WATERS...EXCEPT THE PUGET SOUND/HOOD CANAL.

&&

$$

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