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 151730
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PST MON DEC 15 2014

.SYNOPSIS...WEAK DISTURBANCES IN THE SOUTHERLY FLOW ALOFT WILL
BRING A THREAT OF LIGHT PRECIPITATION TO THE AREA AT TIMES THROUGH
TUESDAY. OTHERWISE LOOK FOR OFFSHORE FLOW TO PERSIST. A WEAK LOW
PRESSURE SYSTEM WILL MOVE ACROSS THE REGION ON WEDNESDAY FOR A
BETTER THREAT OF PRECIPITATION.

&&

.SHORT TERM...
PRECIP ASSOCIATED WITH A WEAK UPPER LEVEL DISTURBANCE MOVING
ACROSS THE CWA THIS MORNING HAS BEEN LIGHT AND SPOTTY. EXPECT THE
BEST CHANCE OF MEASURABLE RAIN /ALBEIT LIGHT/ TO BE OVER THE COAST
AND FAR SOUTHERN PART OF THE CWA,

A MEAN UPPER LEVEL TROF WILL REMAIN OFFSHORE THROUGH TUE. THE
UPPER FLOW PATTERN WILL REMAIN SPLIT...THEREFORE EXPECT THE BULK
OF THE UPWARD FORCING AND DEEP LAYER MOISTURE TO BE AIMED AT CA.
SOUTHERLY FLOW ALOFT WILL PREVAIL OVER WESTERN WA DURING THIS
PERIOD. WEAK SHORT WAVE TROFS MOVING ACROSS ACROSS THE AREA WILL
RESULT IN A THREAT OF PRECIP AT TIMES. THE BEST CHANCE WILL BE
OVER THE COAST. OTHERWISE LOOK FOR LOW LEVEL EASTERLY OR OFFSHORE
FLOW TO PERSIST.

THE OFFSHORE TROF WILL HEAD EAST ON WED...MOVING ACROSS THE CWA
DURING THE AFTERNOON/EVENING TIME FRAME. THE ASSOCIATED COLD OR
OCCLUDED FRONT WILL MOVE ACROSS THE AREA DURING THE LATE MORNING/
EARLY AFTERNOON PERIOD. THE BEST CHANCE OF PRECIP WILL BE ON THIS
DAY.

.LONG TERM FROM THE PREV DISCUSSION...
EXTENDED MODELS IN GOOD AGREEMENT WITH THE FLOW ALOFT BECOMING
MORE CONSOLIDATED ON THURSDAY WITH A WEAK UPPER LEVEL RIDGE MOVING
THROUGH THE AREA. THE CONSOLIDATED FLOW ALOFT WILL ALLOW THE NEXT
SYSTEM TO REMAIN FAIRLY INTACT AS IT MOVES INTO WESTERN WASHINGTON
THURSDAY NIGHT AND FRIDAY. CURRENT FORECAST HAS LIKELY POPS AND
WILL STAY WITH THAT IDEA FOR THE MORNING PACKAGE. FLOW ALOFT
REMAINS CONSOLIDATED INTO THE WEEKEND WITH BOTH THE GFS AND THE
ECMWF SHOWING A POSSIBLE ATMOSPHERIC RIVER SCENARIO SETTING UP.
THE 00Z RUN MAKES MULTIPLE RUNS IN A ROW FOR THIS SOLUTION ON
SUNDAY ALTHOUGH THE HEAVIER RAIN IN THE SOLUTIONS HAS BEEN UP OVER
VANCOUVER ISLAND. WILL STAY WITH THE LIKELY POPS FOR SUNDAY IN THE
MORNING PACKAGE. FELTON

&&

.HYDROLOGY...
RIVER FLOODING IS NOT EXPECTED DURING THE NEXT 7 DAYS.

&&

.AVIATION...AN UPPER LEVEL RIDGE WELL TO THE EAST OF THE AREA
COMBINED WITH A TROUGH OVER THE OFFSHORE WATERS IS GIVING SOUTHERLY
FLOW ALOFT. AT THE SURFACE...HIGH PRES IS OVER EASTERN WA WITH LOWER
PRES OFFSHORE. THE AIR MASS IS STABLE WITH MAINLY MID AND UPPER
LEVEL MOISTURE OVER W WA AND IS MAINLY DRY AT LOWER LEVELS.

CURRENT CONDITIONS WILL CONTINUE TODAY. DESPITE WIDESPREAD CLOUD
COVER AND SOME OCCASIONAL LIGHT RA...EXPECT GOOD VFR CONDITIONS WITH
DRY LOWER LEVELS. CEILINGS WILL LOWER FROM THE WEST TONIGHT AS THE
WEAKENING UPPER LEVEL TROUGH OVER THE OFFSHORE WATERS MOVES INTO THE
AREA. LOW LEVEL OFFSHORE FLOW WILL TEND TO KEEP CEILINGS AND
VISIBILITIES TONIGHT VFR WITH MUCH OF THE PRECIPITATION MOVING IN
FROM THE WEST EVAPORATING AS IT FALLS THROUGH A LOWER DRIER LAYER IN
THE PRESENCE OF LOW LEVEL OFFSHORE FLOW. ALBRECHT

KSEA...VFR WITH INCREASING HIGH AND MID LEVEL CLOUDS ABOVE 7K FEET.
EAST WIND 8-13 KNOTS. ALBRECHT

&&

.MARINE...MODERATELY STRONG OFFSHORE FLOW TODAY WILL GRADUALLY EASE
TONIGHT INTO TUESDAY AS A TROUGH OF LOW PRESSURE OFFSHORE MOVES INTO
THE WATERS AND WEAKENS. SMALL CRAFT ADVISORY CONDITIONS WILL
CONTINUE OVER THE COASTAL WATERS...THROUGH THE STRAIT OF JUAN DE
FUCA AND OVER THE NORTHERN INLAND WATERS --MAINLY SOUTH OF THE SAN
JUAN ISLANDS. SMALL CRAFT ADVISORY CONDITIONS WILL EASE FROM THE
EAST TONIGHT AND WILL LIKELY BE LIMITED TO THE COASTAL WATERS ON
TUESDAY.

A COLD FRONT WILL APPROACH THE WATERS LATER THU AND THU NIGHT AND
MOVE THROUGH THE REGION ON FRI. GALE FORCE WINDS ARE POSSIBLE WITH
THIS FRONT...MAINLY OVER THE COASTAL WATERS. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS...
     STRAIT OF JUAN DE FUCA AND NORTHERN INLAND WATERS.

     SMALL CRAFT ADVISORY FOR ROUGH BAR IN EFFECT TIL 4 AM TUESDAY
     FOR THE GRAYS HARBOR BAR.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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.