Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 240454
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST MON FEB 23 2015

.SYNOPSIS...A WEAK UPPER TROUGH WILL BRING A RETURN TO ONSHORE FLOW
ON TUESDAY. MOIST NORTHWEST FLOW ALOFT WILL PREVAIL WEDNESDAY
THROUGH FRIDAY WITH A CHANCE OF LIGHT PRECIPITATION. DRIER NORTHERLY
FLOW ALOFT WILL DEVELOP NEXT WEEKEND.

&&

.SHORT TERM...SKIES ARE CLEAR THIS EVENING WITH A RIDGE OF HIGH
PRESSURE MAINTAINING DRY WEATHER ACROSS THE REGION. DEW POINT AND
TEMPERATURE SPREADS ARE LARGE SO FOG SHOULD NOT BE PREVALENT TUESDAY
MORNING. THE COLDER AREAS AROUND THE SW INTERIOR/S SOUND MAY SEE
SOME PATCHY FORMATION BUT EVEN THIS WILL LIKELY FROST OUT. LOWS
TONIGHT WILL RANGE FROM NEAR FREEZING IN COLDER POCKETS TO AROUND 40
FOR EXPOSED LOCATIONS NEAR THE WATER.

THE UPPER RIDGE WEAKENS ON TUESDAY AS A WEAK UPPER LEVEL SYSTEM
BRUSHES BY THE AREA IN NW FLOW. THE MAIN AFFECT WILL BE INCREASE THE
LOW LEVEL ONSHORE FLOW AND BRING MARINE STRATUS INLAND FROM THE
COAST BY EVENING. THERE COULD BE JUST ENOUGH LIFT WITH THE INITIAL
PUSH FOR SOME SPRINKLES ALONG THE COAST BUT IT WILL BE DIFFICULT TO
MEASURE GIVEN THE LACK OF DEEP MOISTURE AND LIFT. HIGHS WILL MOSTLY
BE IN THE LOW 50S.

MOISTURE SHOULD INCREASE TUESDAY NIGHT AND WEDNESDAY AS ANOTHER
SOMEWHAT BETTER ORGANIZED SHORT WAVE MOVES SE THROUGH THE AREA.
THIS SYSTEM LACKS MUCH SURFACE STRUCTURE BUT DOES HAVE A SHARPER 500
MB TROUGH AXIS AND DECENT VORT MAX PROVIDING SOME EXTRA LIFT. BOTH
THE NAM/GFS TIME-HEIGHTS SHOW SHOW THE BEST DYNAMICS LATER WEDNESDAY
INTO WEDNESDAY NIGHT. MOST THE AREA SHOULD GET WET ALTHOUGH QPF
AMOUNTS WILL BE ON THE LIGHT SIDE.

A THIRD EVEN STRONGER SYSTEM DIVES SE JUST OFF THE B.C. COAST ON
THURSDAY. MODELS ARE ADVERTISING A CLOSED UPPER LOW AND STACKED
SURFACE LOW FEATURE REACHING VANCOUVER ISLAND BY LATE IN THE DAY.
MOISTURE AND INSTABILITY WILL INCREASE WITH RAIN OR SHOWERS LIKELY
TO PICK UP ACROSS WRN WA. IT WILL BE A BIT COOLER AND CLOUDY WITH
HIGHS CLOSE TO AVERAGE IN THE LOWER 50S.  MERCER

.LONG TERM...NO UPDATES FROM PREVIOUS DISCUSSION...FRIDAY WILL BE A
SHOWERY DAY AS AN UPPER LOW MOVES SOUTH THROUGH THE REGION. DRIER
NORTHERLY FLOW WILL DEVELOP BEHIND THE LOW NEXT WEEKEND WITH JUST A
FEW SHOWERS LINGERING OVER THE SOUTH PART INTO SATURDAY. SUNDAY
LOOKS LIKE THE NICEST DAY OF THE WEAK WITH PLENTY OF SUNSHINE AND
DRY LOW LEVEL OFFSHORE FLOW. ANOTHER WEAK WEATHER SYSTEM WILL DROP
DOWN FROM THE NORTH/NORTHWEST ON MONDAY FOR A CHANCE OF RAIN.
SCHNEIDER

&&

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

&&

.AVIATION...AN UPPER LEVEL RIDGE EXTENDING FROM SOUTHWESTERN
VANCOUVER ISLAND INTO A HIGH CENTERED NEAR 38N 132W WILL SHIFT
SOUTHEAST INTO OREGON TUE MORNING AND WEAKEN. LIGHT LOW LEVEL FLOW
WILL TURN WEAKLY ONSHORE TUE MORNING AS THE RIDGE SHIFTS SE. THE AIR
MASS IS DRY AND STABLE. AREAS OF LOW LEVEL MOISTURE WILL MOVE ONTO
THE COAST AROUND 12Z...THEN WILL LIFT INTO A STRATUS DECK WITH BASES
AROUND 035 AS IT SHIFTS INLAND TUE AFTERNOON.

GOOD VFR CONDITIONS WILL DOMINATE TONIGHT THROUGHOUT THE AREA AND IN
THE INTERIOR THROUGH 18Z TUE. AREAS OF IFR CONDITIONS IN LOW STRATUS
AND FOG WILL DEVELOP ON THE NORTH COAST ABOUT 12Z AND SPREAD S TO
THE KHQM TERMINAL ABOUT 15Z. THE LOW STRATUS AND FOG IS NOT EXPECTED
TO MOVE INLAND. ALBRECHT

KSEA...EXPECT JUST A FEW ALTOCUMULUS AND CIRRUS CLOUDS OVERNIGHT
THROUGH MIDDAY TUE. SCT-BKN035 WILL PUSH INTO THE TERMINAL AREA
AROUND 21Z TUE. EXPECT LIGHT WINDS THROUGH MIDDAY TUE WITH WIND
BECOMING SW 10-15 KT AFTER 21Z TUE. ALBRECHT

&&

.MARINE...HIGH PRES OVER THE WATERS WILL GIVE LIGHT PRES GRADIENTS
THROUGH MIDDAY TUE. ONSHORE FLOW WILL DEVELOP TUE AFTERNOON AS A
WEAK FRONTAL SYSTEM MOVES ACROSS THE AREA AND PRESSURES FALL E OF
THE CASCADES. BY LATE TUE AFTERNOON INTO TUE EVENING...SMALL CRAFT
ADVISORY WESTERLY WINDS CAN BE EXPECTED OVER THE CENTRAL AND EASTERN
STRAIT OF JUAN DE FUCA.

A WEAK RIDGE OF HIGH PRES WILL GIVE LIGHT PRES GRADIENTS TO THE
WATERS LATE TUE NIGHT INTO WED. ANOTHER WEAK FRONTAL SYSTEM WILL
MOVE SE ACROSS THE WATERS LATE WED NIGHT INTO THU AND WILL BE
FOLLOWED BY A WEAK LOW MOVING SE THROUGH THE COASTAL WATERS THU
NIGHT INTO FRI.

HIGH PRES WILL BUILD OVER BRITISH COLUMBIA LATER FRI INTO FRI NIGHT
OR SAT GIVING STRONGER N TO NE FLOW OVER THE WATERS. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.


&&

$$

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