Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 171100
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST WED DEC 17 2014

.SYNOPSIS...A WEAK PACIFIC WEATHER SYSTEM WILL BRING SOME AREAS OF
LIGHT RAIN TO WESTERN WASHINGTON THROUGH WEDNESDAY NIGHT. A STRONGER
PACIFIC FRONTAL SYSTEM IS EXPECTED TO MOVE ASHORE THURSDAY NIGHT
WITH MORE SIGNIFICANT RAIN. ANOTHER WET WEATHER SYSTEM IS FORECAST
FOR THIS WEEKEND WITH HEAVIER RAIN AMOUNTS ALONG THE COAST AND IN
THE MOUNTAINS.

&&

.SHORT TERM...A NEGATIVE TILTED UPPER TROUGH WITH SPLIT FLOW IS JUST
OFF THE COAST EARLY THIS MORNING. THE PRIMARY FLOW ALOFT IS INTO
CALIFORNIA WHERE THE BULK OF THE PRECIP IS HEADED. A WEAKENING
SHORTWAVE WAS PRODUCING LIGHT RAIN ALONG THE COAST AND SOME OF THAT
SHOULD MOVE FURTHER INLAND LATER TODAY. RAIN AMOUNTS LIGHT THOUGH.

THE NEXT SHORTWAVE ON SATELITE IMAGERY WAS MOVING INSIDE 135W AGAIN
WITH THE BULK OF THE ENERGY HEADING TOWARD THE GOLDEN STATE. THE
REMAINING STRETCHED OUT PORTION AT OUR LATITUDE WILL LIKELY SPREAD
SOME ADDITIONAL LIGHT RAIN ONSHORE TONIGHT.

THE NEXT UPSTREAM AND STRONGER SHORTWAVE WAS NEAR 160W EARLY THIS
MORNING. THIS SYSTEM WAS PUMPING UP A SHORTWAVE RIDGE AHEAD OF IT
THAT PROGS AGREE WILL MOVE ONSHORE THURSDAY. THEN THE ASSOCIATED
FRONTAL SYSTEM SHOULD BEGIN TO SPREAD RAIN ONSHORE LATE THURSDAY
WITH THE COLD FRONT MOVING INLAND EARLY FRIDAY. BLUSTERY WINDS FOR
THE COAST AND NORTH INTERIOR WITH THIS SYSTEM. THE SHORTWAVE TROUGH
IS THEN FORECAST TO MOVE ASHORE FOR A BIT COOLER SHOWERY DAY FRIDAY.

FOR THE MOUNTAINS...THE LACK OF SNOW IS A CONCERN. THE WEATHER
SYSTEMS TODAY THROUGH FRIDAY SHOULD PRODUCE AT LEAST SOME SNOWFALL
THERE. EAST TO WEST GRADIENTS ACROSS THE CASCADES SHOULD TEND TO
KEEP THE SNOW LEVELS CLOSE TO THE PASSES UNTIL THE THURSDAY NIGHT
SYSTEM MOVES ONSHORE EARLY FRIDAY. BY THEN...THE FOLLOWING SHORTWAVE
TROUGH WILL BRING SOME COOLER UNSTABLE AIR FOR SNOW SHOWERS. NOT A
WHOLE LOT OF SNOW IN THE NEXT 3 DAYS...BUT BETTER THAN LAST WEEKS
MILD WET WEATHER. BUEHNER

.LONG TERM...LOOKS LIKE A SHORT BREAK IN THE WEATHER FRIDAY NIGHT
BEFORE THE NEXT WETTER SYSTEM ARRIVES OVER THE WEEKEND. THIS SYSTEM
WAS CURRENTLY MOVING ACROSS 150E THIS MORNING WITH A SUPPORTING 200
KT JET. THE PROGS ARE STILL TRENDING A BIT DRIER WITH THIS SYSTEM
GIVEN ITS MORE PROGRESSIVE NATURE. EXPECT RAIN TO INCREASE ON
SATURDAY WITH THE WARM FRONT AND THE COLD FRONT MOVING ONSHORE
SUNDAY NIGHT.

RIDGING ALOFT ALONG THE WEST COAST MEANS THE JET STREAM WILL BE AT
OUR LATITUDE WITH A WESTERLY COMPONENT INTO THE CASCADES AND
SHADOWING OFF THE OLYMPICS THIS WEEKEND. THE COAST AND MOUNTAINS
SHOULD GET THE BULK OF THE PRECIPITATION.

ANOTHER SHORT BREAK MONDAY BEFORE THE NEXT NOT AS WET SYSTEM ARRIVES
TUESDAY. THE PROGS CONTINUE TO SUGGEST A KONA LOW DEVELOPING BUT
THEY ARE INCONSISTENT IN ITS POSITION. THE FURTHER WEST USUALLY
RESULTS IN BUILDING AN UPPER RIDGE NEAR 150W OR 160W AND PRODUCING
NORTHERLY FLOW ALOFT INTO THE PACIFIC NW FOR A MUCH COOLER FLOW
PATTERN. FURTHER EAST WITH THE PATTERN AND THE PACIFIC NW GETS A
MILDER NORTHERLY FLOW ALOFT. STAY TUNED HERE. BUEHNER

&&

.HYDROLOGY...RIVER FLOODING IS NOT EXPECTED THROUGH SATURDAY. MOIST
WESTERLY FLOW WILL DEVELOP SATURDAY NIGHT AND CONTINUE THROUGH
SUNDAY NIGHT...WITH HEAVY MOUNTAIN RAIN AMOUNTS POSSIBLE.
GUIDANCE IS NOW SHOWING A BIT LIGHTER AMOUNTS GIVEN THE MORE
PROGRESSIVE NATURE OF THIS SYSTEM. PRIMARY CONCERN FOR ANY RIVER
RISING ABOVE FLOOD STAGE IS THE SKOKOMISH BUT ALSO NEED TO KEEP AN
EYE ON OTHER CASCADE FLOOD PRONE STREAMS. BUEHNER

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL GIVE LIGHT SOUTHWEST FLOW
ALOFT OVER WESTERN WASHINGTON TODAY. LOW LEVEL OFFSHORE FLOW WILL
EASE AS A SURFACE TROUGH MOVES ONSHORE AND RIDGING EAST OF THE
CASCADES WEAKENS. THE AIR MASS WILL REMAIN MOIST AND STABLE WITH
AREAS OF VERY LIGHT PRECIPITATION MOVING THROUGH AT TIMES.

STRATUS OVER THE SOUTHWEST INTERIOR OVERNIGHT IS ERODING AS HIGHER
LEVEL MOISTURE ASSOCIATED WITH INCOMING TROUGH INCREASES. A FEW
POCKETS OF SURFACE VSBYS 3-5SM COULD PERSIST AROUND KOLM THROUGH
15Z. MAINLY VFR CEILINGS EXPECTED THIS MORNING...BUT MODELS INDICATE
THE LOW LEVELS WILL MOISTEN UP LATER TODAY WITH SOME HIGHER END MVFR
CEILINGS POSSIBLE MIDDAY INTO THE EVENING AS LIGHT PRECIP ASSOCIATED
WITH TROUGH MOVES INLAND.

KSEA...VFR CEILINGS EXPECTED THROUGH LATE MORNING...BUT MAY SEE SOME
TEMPO BKN-OVC030 WITH LIGHT RAIN 18Z-00Z. MVFR CEILINGS MAY STICK
AROUND TONIGHT WITH LIGHT SURFACE GRADIENTS AND MOIST AIR MASS IN
PLACE. EAST-SOUTHEAST WIND 5 TO 10 KNOTS...BECOMING LIGHT SOUTHERLY
TONIGHT.

&&

.MARINE...OFFSHORE GRADIENTS CONTINUE TO RELAX WITH A WEAK SURFACE
TROUGH APPROACHING THE COASTAL WATERS. SMALL CRAFT ADVISORIES
CONTINUE FOR THE OUTER COASTAL WATERS WHERE SEAS REMAIN NEAR 10
FEET. FOR THE REMAINDER OF THE WATERS...A PERIOD OF QUIET WEATHER IS
FORECAST TODAY WITH A WEAK SURFACE TROUGH OVER THE REGION. A BETTER
ORGANIZED AND STRONGER FRONT WILL APPROACH THE WATERS LATE THURSDAY.
A GALE WATCH FOR THE COASTAL WATERS MIDDAY THURSDAY THROUGH THURSDAY
NIGHT REMAINS IN EFFECT FOR THIS. ANOTHER FRONT ON SATURDAY COULD
PRODUCES GALES OVER THE NORTHERN INLAND WATERS...ENTRANCES TO THE
STRAIT OF JUAN DE FUCA...AND COASTAL WATERS. LONG PERIOD SWELL IN
EXCESS OF 20 FEET COULD REACH THE COAST ON FRIDAY. 27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY TODAY FOR HAZARDOUS SEAS OUTER COASTAL
     WATERS.
     SMALL CRAFT ADVISORY TODAY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH THURSDAY MORNING THROUGH LATE THURSDAY NIGHT FOR THE
     COASTAL WATERS.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML







USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.