Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 270458
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST THU FEB 26 2015

.SYNOPSIS...A LOW PRESSURE SYSTEM WILL BRING RAIN TO MOST OF WESTERN
WASHINGTON THROUGH FRIDAY MORNING BEFORE CHANGING OVER TO SHOWERS. A
FEW INCHES OF SNOW WILL FALL IN THE MOUNTAINS AND POSSIBLY SOME OF
THE PASSES. AN UPPER RIDGE AND OFFSHORE FLOW WILL BRING SUNNY DAYS
AND COOL NIGHTS THIS WEEKEND. A WEAK SYSTEM WILL MOVE THROUGH SUNDAY
NIGHT AND MONDAY...WITH DRY WEATHER AGAIN TUESDAY AND WEDNESDAY.

&&

.SHORT TERM...RADAR SHOWS LIGHT TO MODERATE RAIN PUSHING INTO THE
INTERIOR OF WRN WA THIS EVENING AS A LOW PRESSURE SYSTEM APPROACHES.
CLOUD TOP BRIGHTENING ON IR SATELLITE IMAGERY INDICATES THE SYSTEM
IS IN A DEVELOPING PHASE. MSAS ANALYSIS PLACES A 1009 MB CLOSED
SURFACE LOW OFF THE N/CENTRAL WA COAST AT 04Z. MODELS SHOW THE 500
MB TROUGH CLOSING OFF OVERNIGHT AND BECOMING VERTICALLY ALIGNED WITH
A SLIGHTLY DEEPER 1005 MB LOW BY 12Z. THIS PROCESS WILL TEND TO SLOW
THE PROGRESSION OF THE SYSTEM AND HOLD RAINFALL OVER WRN WA LONGER.
HEAVIER RAINFALL AMOUNTS OF A HALF INCH TO ONE INCH WILL FALL WITHIN
THE FAVORED DEFORMATION ZONE TO THE E/NE OF THE CENTRAL LOW
CIRCULATION. HIGH RESOLUTION MODELS GENERALLY AGREE THIS WILL BE
FROM THE COAST THROUGH GREATER PUGET SOUND AND THE SW INTERIOR/S
CASCADES OVER THE NEXT 12 HOURS OR SO. THE N INTERIOR SHOULD HAVE
LIGHTER RAINFALL AMOUNTS. GIVEN THE CURRENT SATELLITE/RADAR
TRENDS...WILL UPDATE THE FORECAST TO CALL IT RAIN RATHER THAN
SHOWERS. WILL ALSO REMOVE THE THUNDERSTORMS GIVEN THE PRECIPITATION
IS MORE STRATIFORM ON RADAR.

SNOW WILL FALL IN THE MOUNTAINS THROUGH FRIDAY MORNING BUT THE
HEAVIEST PRECIPITATION WILL LIKELY BE TO THE W OF THE CASCADES. SNOW
LEVELS WILL FALL FROM ABOUT 4500 FEET TO 3500 FEET FRIDAY MORNING
WITH A FEW INCHES OF SNOW POSSIBLE. HIGHEST AMOUNTS UP TO 5
INCHES...JUST BELOW ADVISORY CRITERIA...WILL LIKELY OCCUR OVER THE
SRN CASCADE ZONE AROUND MT RAINIER.

RAIN TRANSITIONS TO SHOWERS LATE FRIDAY MORNING OR AFTERNOON
DEPENDING ON HOW QUICKLY THE SYSTEM SHIFTS SWD. IT WILL DRY OUT
FASTER ACROSS THE N. SURFACE HIGH PRESSURE BUILDING OVER SRN B.C.
WILL PROVIDE INCREASING NE OFFSHORE FLOW LATER IN THE DAY INTO
FRIDAY NIGHT. LOWER DEW POINT AIR MEANS SHOWERS WILL END. IT ALSO
WILL BECOME BREEZY...ESPECIALLY ACROSS THE N INTERIOR WHERE FRASER
OUTFLOW WILL DEVELOP. THE AIR MASS WILL ALSO BE COOLER AND LOWS WILL
PROBABLY BE IN THE 30S MOST SPOTS SATURDAY MORNING.

DRY WEATHER AND SUNSHINE WILL RETURN TO WRN WA OVER THE WEEKEND. NE
OFFSHORE FLOW WILL HOLD TEMPERATURES BACK SOMEWHAT...BUT STILL NEAR
AVERAGE IN THE LOW 50S. EXPOSED AREAS THAT HAVE BREEZY WINDS WILL
PROBABLY STAY JUST ABOVE FREEZING SATURDAY/SUNDAY MORNINGS.
HOWEVER...SHELTERED LOCATIONS AND THE TYPICAL COLD POCKETS WILL SEE
LOWS NEAR FREEZING AND POSSIBLY DIPPING INTO THE UPPER 20S IN A FEW
SPOTS. MERCER

.LONG TERM...NO UPDATE FROM PREVIOUS DISCUSSION...A WEAK WEATHER
SYSTEM WILL BRING A CHANCE OF RAIN SUNDAY NIGHT THROUGH MONDAY
NIGHT. THE STRENGTH OF THIS SYSTEM HAS BEEN WANING IN RECENT MODEL
RUNS. TUESDAY THROUGH THURSDAY IS LIKELY TO BE A DRY PERIOD...WITH A
CHANCE OF RAIN RETURNING FRIDAY. HIGHS AND LOWS WILL BE SLIGHTLY
BELOW NORMAL. BURKE

&&

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

&&

.AVIATION...A SURFACE AND UPPER LEVEL LOW ALONG WESTERN VANCOUVER
ISLAND WILL DROP SOUTH THROUGH THE COASTAL WATERS TONIGHT AND
THROUGH THE OREGON WATERS ON FRIDAY. THE AIR MASS AROUND THIS LOW IS
MOIST AND SOMEWHAT STABLE. RAIN WRAPPING AROUND THE LOW WILL GIVE
MVFR CIGS AND VSBYS TONIGHT INTO FRIDAY MORNING. CONDITIONS WILL DRY
FROM THE NORTH STARTING MIDDAY FRIDAY AS HIGH PRESSURE AT THE
SURFACE AND ALOFT BUILDS OVER BRITISH COLUMBIA. ALBRECHT

KSEA...EXPECT 3-5SM -RA BR BKN010-015 OVC025 THROUGH 18Z FRI. NE
WIND 3-6 KT WILL BECOME N 7-10 KT AFTER 15Z. ALBRECHT

&&

.MARINE...FORECAST MODELS ARE SHOWING RATHER GOOD CONSISTENCY AND
CONTINUITY THIS EVENING. A WEAK LOW W OF CENTRAL VANCOUVER ISLAND
WILL DROP SOUTH THROUGH THE COASTAL WATERS TONIGHT AND THE OREGON
COASTAL WATERS ON FRI. STRONG OFFSHORE FLOW WILL DEVELOP IN THE WAKE
OF THE LOW AS A 1030-1035 MB HIGH PRES SYSTEM OVER BRITISH COLUMBIA
BUILDS INTO THE AREA FROM THE NORTH.

WINDS WILL DIMINISH AND BECOME LIGHT ON SUN AS A RIDGE OF HIGH PRES
MOVES SE ACROSS THE WATERS. ANOTHER ROUND OF STRONG N TO NE WINDS
ARE EXPECTED LATER MON INTO TUE AS A 1040 MB HIGH BUILDS OVER
BRITISH COLUMBIA...THEN MOVES BY THE AREA TO THE NE.

EXPECT LIGHT WIND TONIGHT. N TO NE WIND WILL INCREASE 20-25 KT ALONG
THE CENTRAL AND SOUTHERN OUTER COASTAL WATERS EARLY FRI MORNING.
SMALL CRAFT ADVISORY N TO NE WINDS WILL SPREAD INTO THE REMAINDER OF
THE COASTAL WATERS AND TO ALL OF THE INLAND WATERS FRI NIGHT INTO
SAT. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY STARTING 15Z FRI FOR THE COASTAL WATERS
      FROM JAMES ISLAND TO CAPE SHOALWATER 10-60 NM OFFSHORE.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE 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.