Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 221603
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
905 AM PDT FRI AUG 22 2014

.SYNOPSIS...AN UNSTABLE AIR MASS ASSOCIATED WITH AN UPPER LOW OVER
THE INTERIOR OF THE PACIFIC NORTHWEST WILL GENERATE AND CIRCULATE A
FEW SHOWERS AND LATE DAY THUNDERSTORMS OVER THE CASCADES TODAY.
OTHERWISE HIGHER PRESSURE ALOFT WILL NOSE INTO THE REGION THIS
WEEKEND FOR MORE SUNSHINE AND WARMER DAYTIME TEMPERATURES. THIS
WARMING TREND IS EXPECTED TO CONTINUE INTO THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...IN THE BIG PICTURE THE UPPER RIDGE IS NOW NEAR 140W
WITH THE UPSTREAM UPPER TROUGH NEAR THE DATELINE. THE SHORTWAVE THAT
WAS DIGGING DOWN THE EAST SIDE OF THE UPPER RIDGE HAS NOW SLID SE
INTO THE PACIFIC NW INTERIOR. RAOBS AT KUIL, KOTX AND KSLE THIS
MORNING SHOW THE AIR MASS IS QUITE UNSTABLE. SO THE CONTINUED THREAT
OF CONVECTION OVER THE CASCADES LATER TODAY LOOKS ON TRACK. THE BULK
OF CONVECTION SHOULD BE EAST OF THE CASCADES THOUGH.

LOW LEVEL ONSHORE FLOW CONTINUES THIS MORNING THOUGH WEAKER THAN
THURSDAY. THE MORE UNSTABLE AIR MASS RESULTED IN MORE LIMITED MARINE
CLOUDS IN WESTERN WA THIS MORNING. TOPS ARE SHALLOW - NO MORE THAN
1500 FT. SO THE CLOUDS AND FOG SHOULD DISSIPATE BY MIDDAY. TODAY
WILL MARK THE GRADUAL REBOUND OF DAYTIME TEMPERATURES WITH MORE
SUNSHINE AND A WARMER AIR MASS.

THE 12Z PROGS IN THUS FAR CONTINUE THE TREND OF NOSING IN HIGHER
PRESSURE ALOFT AS THE UPPER LOW CONTINUES FURTHER INLAND AND HEIGHTS
ALOFT RISE. ANOTHER VERY WEAK SHORTWAVE IS SET TO SLIDE SE INTO THE
NORTHERN ROCKIES SUNDAY IN THE NW FLOW ALOFT. THE PRIMARY IMPACT
SHOULD BE TO SLOW THE WARM UP AND KEEP LOW LEVEL ONSHORE FLOW GOING.

NO UPDATES TO THE FORECAST PACKAGE THOUGH DID MASSAGE THE SKY GRIDS
A BIT FOR TODAY AND THIS EVENING. BUEHNER

.LONG TERM...FROM THE PREVIOUS DISCUSSION...AN UPPER RIDGE WILL
PREVAIL OVER THE REGION DURING THIS PERIOD...HOWEVER IT WILL
GRADUALLY WEAKEN WITH TIME. IN FACT...THE LATEST GFS SOLUTION SHOWED
AN UPPER TROF OVER THE PACIFIC NORTHWEST ON DAY 7. THE INHERITED
FORECAST SHOWED TEMPS COOLING OFF LATE IN THE PERIOD AND THAT LOOKS
FINE. NC

&&

.AVIATION...A WEAK UPPER LEVEL TROUGH OVER THE AREA THIS MORNING
WILL SHIFT SOUTHEAST INTO SOUTHERN IDAHO BY SATURDAY MORNING. LIGHT
NORTHERLY FLOW ALOFT WILL BECOME NORTHWESTERLY AS THE LOW MOVES
SOUTHEAST. LOW LEVEL FLOW WILL REMAIN ONSHORE AND WEAK.

MARINE STRATUS THAT FORMED THIS MORNING OVER THE COAST...SOUTHWEST
INTERIOR...STRAIT AND WESTERN SKAGIT/SNOHOMISH COUNTIES REMAINS
SHALLOW WITH CEILINGS BELOW 1000 FEET AND LOCAL VISIBILITIES BELOW A
MILE. LIGHT NORTHERLY SURFACE GRADIENTS HELPED LIMIT THE EXTENT OF
THE LOW CLOUDS OVER THE INTERIOR...WITH MUCH OF THE CENTRAL SOUND
AND WESTERN WHATCOM COUNTY REMAINING CLEAR. THOSE AREAS WITH LOW
CLOUDS AND FOG WILL SEE CEILINGS AND CONDITIONS IMPROVE THROUGH THE
MORNING...SCATTERING OUT OVER THE INTERIOR BY 18Z/11 AM AND THE
COAST BY 20Z/1 PM. WARMING AND WITH THE NORTHERLY FLOW BOTH ALOFT
AND AT LOW LEVELS TODAY WILL MAKE IT MORE DIFFICULT FOR LOW CLOUDS
AND OR STRATUS TO REFORM OVER THE INTERIOR SATURDAY MORNING.

KSEA...MOSTLY CLEAR SKIES TODAY WITH VFR CONDITIONS PERSISTING
THROUGH SATURDAY. LIGHT WINDS WILL BECOME NORTHWESTERLY 4 TO 8 KNOTS
BY EARLY AFTERNOON AND PERSIST THROUGH THE EVENING...THEN BECOME
LIGHT AND NORTHEASTERLY AFTER 06Z/11 PM.

&&

.MARINE...THE VERY PERSISTENT ONSHORE FLOW PATTERN WILL CONTINUE FOR
THE NEXT SEVERAL DAYS. THE STRENGTH OF THE ONSHORE FLOW WILL VARY
DIURNALLY. EXPECT THE STRONGEST WESTERLY WINDS IN THE CENTRAL AND
EASTERN STRAIT DURING THE EVENING AND EARLY MORNING HOURS WITH SMALL
CRAFT ADVISORIES POSSIBLE AT THAT TIME EACH DAY INTO THE FIRST PART
OF NEXT WEEK. OVER THE COASTAL WATERS SURFACE HIGH PRESSURE BUILDING
INSIDE OF 140 W WILL TIGHTEN UP SURFACE GRADIENTS SATURDAY EVENING
OVER THE OUTER COASTAL WATERS...BOOSTING THE NORTHWESTERLIES ABOVE
SMALL CRAFT CRITERIA. WEST TO NORTHWESTERLY SWELL 4 TO 5 FEET WITH A
PERIOD AROUND 8 SECONDS WILL PERSIST THROUGH THE WEEKEND.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA
TONIGHT.

&&

$$

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