Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 011645
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
845 AM PST SUN MAR 1 2015

.SYNOPSIS...AN UPPER RIDGE AND OFFSHORE LOW LEVEL FLOW WILL BRING
ANOTHER DAY OF FAIR WEATHER TO WESTERN WASHINGTON TODAY. A WEAK
WEATHER SYSTEM WILL MOVE SOUTHEAST THROUGH THE AREA TONIGHT
FOR AREAS OF LIGHT PRECIPITATION. DRY WEATHER WILL PREVAIL
THE REMAINDER OF NEXT WEEK UNDER THE INFLUENCE OF AN UPPER
RIDGE AND LOW LEVEL OFFSHORE FLOW.

&&

.SHORT TERM...DRY NORTHERLY FLOW ALOFT WILL PREVAIL TODAY WITH A FEW
PASSING HIGH CLOUDS.

A WEAK UPPER LEVEL DISTURBANCE WILL DROP DOWN FROM THE NORTHWEST
TONIGHT. THIS WILL BRING CLOUDS WITH A LITTLE RAIN AT THE COAST AND
A CHANCE OF RAIN FARTHER INLAND.

RAIN CHANCES WILL END QUICKLY MONDAY MORNING AS THE UPPER LEVEL
DISTURBANCE MOVES SOUTH OF THE AREA. LOW LEVEL NORTH TO NORHTEAST
OFFSHORE FLOW WILL INCREASE AS A 1040 MB SURFACE HIGH DROPS SOUTH
INTO BRITISH COLUMBIA. THIS WILL HELP DRY THE LOW LEVELS OUT AND
CLOUDS SHOULD BE ON THE DECREASE LATER IN THE DAY. THERE WILL ALSO
BE SOME BREEZY NORTH WINDS DURING THE DAY... ESPECIALLY OVER THE
NORTH INTERIOR.

AN UPPER RIDGE OVER THE NORTHEAST PACIFIC WILL BRING DRY AND MAINLY
SUNNY WEATHER TUESDAY ALTHOUGH THERE COULD BE SOME HIGH CLOUDS AT
TIMES. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...NORTHERLY FLOW ALOFT AND DRY
WEATHER WILL CONTINUE WEDNESDAY...AS THE UPPER RIDGE WEAKENS AND
MOVES TO THE PACIFIC NORTHWEST COAST. THE RIDGE WILL MOVE INLAND
WEDNESDAY NIGHT AND THURSDAY...WITH WEST OR NORTHWEST FLOW ALOFT
OVER WESTERN WASHINGTON IN ITS WAKE.

A WEAK UPPER SHORTWAVE COULD BRING SOME LIGHT PRECIPITATION TO PARTS
OF THE FORECAST AREA THURSDAY AND THURSDAY NIGHT...AND THE MOST
RECENT RUNS OF THE GFS AND CANADIAN MODELS SHOW THIS. HOWEVER
THE ECMWF AND EARLIER RUNS OF THE OTHER MODELS INDICATED DRY
WEATHER. I WILL STAND PAT WITH THE DRY FORECAST FOR NOW...AND
HOPEFULLY THE MODEL RUNS TODAY WILL HELP US PIN THIS DOWN.

ANOTHER UPPER RIDGE WILL BUILD OFFSHORE FRIDAY AND SATURDAY FOR MORE
DRY WEATHER.   MCDONNAL

&&

.HYDROLOGY...FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

&&

.AVIATION...A LARGE UPPER LEVEL RIDGE CENTERED OFFSHORE ALONG 140W
WILL MAINTAIN DRY NW FLOW ACROSS W WA THROUGH 00Z. AREAS OF HIGH
CLOUDS WILL SPREAD S THROUGH 00Z AHEAD OF AN APPROACHING UPPER LEVEL
SHORTWAVE TROUGH. GOOD VFR CONDITIONS ARE EXPECTED THROUGH 00Z.

AN UPPER LEVEL SHORTWAVE TROUGH OVER THE CENTRAL B.C. COAST AT 16Z
WILL MOVE SE OVER W WA BY 06Z. MID LEVEL CLOUDS WILL BEGIN SPREADING
OVER W WA AHEAD OF THE TROUGH AFTER 00Z WITH CIGS LOWERING TO AROUND
BKN050 WITH SOME LIGHT RAIN OVER THE N AFTER 03Z. LOWERING CIGS AND
AREAS OF RAIN WILL SPREAD S WITH THE SHORTWAVE TROUGH...WITH AREAS
OF MVFR CIGS POSSIBLE 06Z-15Z.

KSEA...UNRESTRICTED VFR CONDITIONS THROUGH 03Z WITH JUST SOME HIGH
CLOUDS OVER THE AREA AT TIMES. CIGS BKN050-100 INCREASING AFTER 03Z.
SURFACE WINDS WILL BE S-SW 4-7 KT. KAM

&&

.MARINE...A WEAK SURFACE TROUGH WILL REMAIN OVER W WA
TODAY...EMBEDDED IN A BROAD SURFACE RIDGE THAT EXTENDS BETWEEN A
LARGE SURFACE HIGH OFFSHORE AND ANOTHER CENTERED OVER MT. PRESSURE
GRADIENTS ACROSS W WA WILL REMAIN WEAK...SO WINDS WILL BE GENERALLY
LIGHT.

AN UPPER LEVEL SHORTWAVE TROUGH OVER THE CENTRAL B.C. COAST THIS
MORNING WILL MOVE SE ACROSS W WA TONIGHT. MESOSCALE MODELS CONTINUE
TO INDICATE MODERATE N WINDS DEVELOPING OVER THE COASTAL WATERS
TONIGHT WITH THE SHORTWAVE TROUGH...SO A SCA HAS BEEN ISSUED WITH
THE MORNING UPDATE.

BEHIND THE UPPER LEVEL TROUGH...A 1044 MB SURFACE HIGH WILL MOVE S
ACROSS INTERIOR B.C. ON MONDAY. RISING PRESSURES OVER B.C. WILL
INCREASE THE NORTHERLY PRESSURE GRADIENT ACROSS THE NORTHERN
INTERIOR OF W WA STARTING MONDAY MORNING. THE CURRENT FORECAST LOOKS
OK WITH AREAS OF SCA WINDS EXTENDING FROM THE N INLAND WATERS DOWN
THROUGH PUGET SOUND.

AS THE B.C. SURFACE HIGH MOVES SE THE PRESSURE GRADIENT ACROSS W WA
WILL SHIFT MORE E-NE AND STRENGTHEN MONDAY NIGHT AND TUESDAY. THIS
SHOULD ALLOW MODERATE TO STRONG E-NE FLOW TO DEVELOP ACROSS THE N
INLAND WATERS...EXTENDING OUT THROUGH THE STRAIT AND ACROSS THE
NORTHERN COASTAL WATERS. THE FLOW COULD BE STRONG ENOUGH TO REACH
GALE FORCE MONDAY NIGHT AND TUESDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS TONIGHT.

&&

$$

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









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