Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 280410
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
910 PM PDT SAT SEP 27 2014

.SYNOPSIS...WHILE THERE WILL BE AREAS OF LOW CLOUDS AND FOG AROUND
THE LOWLANDS SUNDAY MORNING...A WEAK UPPER RIDGE WILL KEEP THE
WEATHER DRY THROUGH SUNDAY. A FRONT WILL BRING SOME RAIN TO THE AREA
MONDAY. SCATTERED SHOWERS WILL LINGER INTO THE MIDDLE OF THE WEEK. A
STRONGER UPPER RIDGE WILL BUILD BY THE END OF NEXT WEEK.

&&

.SHORT TERM...AN UPPER LOW SITS OVER THE DESERT SW WITH A FRONTAL
SYSTEM OVER THE EASTERN PACIFIC ALONG ABOUT 140W. WESTERN WA IS IN A
COL OR WEAK RIDGE IN BETWEEN THESE SYSTEMS WITH NEARLY CLEAR SKIES.
DEFORMATION ZONE MID AND HIGH CLOUDS ROTATING AROUND THE UPPER LOW
TO THE SE CAN BE SEEN OVER THE CASCADES...BUT THESE ARE DISSIPATING
AS THEY MOVE WESTWARD INTO THE AREA.

FOR TONIGHT...A STRENGTHENING INVERSION AROUND 1500 FEET COMBINED
WITH A SURFACE BASED NOCTURNAL INVERSION...RADIATIONAL COOLING...
RESIDUAL LOW LEVEL MOISTURE...AND LIGHT LOW LEVEL OFFSHORE FLOW ALL
POINT TO AREAS OF FOG AND LOW STRATUS FORMING AROUND THE LOWLANDS
AND PERSISTING UNTIL ABOUT MIDDAY SUNDAY. FOG AND LOW STRATUS IS
ALREADY FORMING OVER THE NORTHERN COASTAL AREAS. THE FOG AND LOW
STRATUS WILL BE MORE PERSISTENT THAT IT WAS ON SATURDAY
MORNING...BUT IT SHOULD BE SHALLOW ENOUGH TO BURN OFF MIDDAY. A VERY
NICE LATE SEPTEMBER AFTERNOON IS EXPECTED ON SUNDAY WITH HIGHS IN
THE 60S TO LOWER 70S ACROSS THE AREA.

A QUICK UPDATE FOR FOG AND STRATUS COVERAGE TONIGHT INTO SUNDAY
MORNING...MAINLY ALONG THE COAST...WAS SENT OUT THIS EVENING.

THE OFFSHORE FRONTAL SYSTEM WILL MOVE TO 130W EARLY SUN EVENING AND
WILL INDUCE A MARINE PUSH THAT WILL SPREAD STRATUS INLAND OVERNIGHT
SUNDAY. THE FRONT WILL PUSH ONSHORE MONDAY MORNING AND INLAND DURING
THE DAY GIVING SOME RAIN TO THE AREA. THE 00Z NAM12 SHOWS THE FRONT
MOVING ACROSS THE AREA A FEW HOURS FASTER THAN CURRENTLY INDICATED
IN THE FORECASTS. MAY NEED TO INCREASE CLOUDS FASTER SUNDAY NIGHT
AND SPEED THE TIMING OF THE FRONT ON MONDAY...BUT WILL AWAIT THE
FULL SUITE OF 00Z GUIDANCE BEFORE MAKING THOSE CHANGES.

CONVERGENT ONSHORE FLOW WITH SHOWERS AND A POTENTIAL CONVERGENCE
ZONE IS EXPECTED BEHIND THE FRONT MONDAY NIGHT AND TUESDAY. ALBRECHT

.LONG TERM...FROM THE PREVIOUS LONG TERM DISCUSSION...CLOUDS AND A
CHANCE OF SHOWERS MAY LINGER WED AND THU BUT UPPER HEIGHTS ARE
LIKELY TO RISE TOWARD THE END OF NEXT WEEK. THE 12Z GFS HAS 500MB
HEIGHTS RISING FROM AROUND 5700M LATE WED TO AROUND 5850M OVER THE
WEEKEND SO FOR NOW THE MODELS ARE TRENDING TOWARD WARM AND SUNNY
WEATHER TOWARD THE END OF NEXT WEEK.

&&

.AVIATION...A WEAK UPPER RIDGE WILL PREVAIL OVER THE REGION
OVERNIGHT. LIGHT NLY FLOW ALOFT WILL BECOME MORE ELY. LIGHT NLY LOW
LEVEL FLOW.

FOG /VSBYS 4-6SM/ WAS DEVELOPING AT THIS TIME...ESPECIALLY OVER THE
AREA WHERE WINDS WERE LIGHT AND SKIES WERE CLEAR. LOOK FOR THE FOG
TO BECOME MORE WIDESPREAD OVERNIGHT. BY 1200 UTC...ANTICIPATE AREAS
OF VSBYS AOB 1SM AND CIGS AOB 300 FT.

KSEA...CIRRUS BLANKETED THE TERMINAL AT THIS TIME. ALSO NLY WINDS
HAVE KICKED UP A BIT. THIS MAY PREVENT FOG FROM DEVELOPING OVER THE
TERMINAL OVERNIGHT...ESPECIALLY IF THIS PERSISTS. HOWEVER CANNOT
COMPLETELY RULE OUT THE POSSIBILITY OF FOG DEVELOPING EVEN WITH WITH
A NLY WIND NEAR 10 KNOTS.

&&

.MARINE...A 1020 MB HIGH OVER BRITISH COLUMBIA WITH LOWER PRES OVER
OREGON WILL RESULT IN LIGHT NORTHERLY FLOW OVERNIGHT. THE FLOW WILL
BECOME ONSHORE ON SUNDAY IN RESPONSE TO HIGH PRES BUILDING ALONG THE
COAST AND LOWER PRES E OF THE CASCADES. A WEAK COLD OR OCCLUDED
FRONT WILL MOVE ACROSS THE AREA ON MON.

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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