Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 221034
AFDSEW

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

.SYNOPSIS...AN UPPER LOW OVER THE AREA WILL MOVE INTO EASTERN
WASHINGTON BY MIDDAY TODAY. STRONG NORTHERLY FLOW ALOFT WILL
DEVELOP IN ITS WAKE. LOOK FOR HIGH PRESSURE ALOFT TO PREVAIL OVER
THE REGION THIS WEEKEND...ALTHOUGH A WEAK LOW PRESSURE SYSTEM
ALOFT WILL CLIP THE AREA AS IT PASSES BY TO THE EAST. THIS SYSTEM
WILL HAVE LITTLE IMPACT ON OUR WEATHER.

&&

.SHORT TERM...
THE SURFACE PRESSURE GRADIENT HAS DEVELOPED A NORTHERLY OR
OFFSHORE COMPONENT...THUS THERE WAS MARKEDLY LESS STRATUS EARLY
THIS MORNING COMPARED TO YESTERDAY MORNING. THE STRATUS MAY FILL
IN A LITTLE BIT BUT NOT EXPECTING IT TO BECOME WIDESPREAD ACROSS
THE LOWLANDS.

MEANWHILE...AN UPPER LOW OVER WESTERN WA WILL MOVE INTO EASTERN
WA AND EASTERN OREGON BY AFTERNOON. THIS WILL ALLOW STRONG
NORTHERLY FLOW ALOFT TO DEVELOP OVER THE CWA. THE BEST CHANCE OF
ANY SHOWERS TODAY WILL BE OVER THE CASCADES...WHERE THERE WILL
ALSO BE A RISK OF AFTERNOON AND EVENING TSTMS.

AN UPPER RIDGE WILL PREVAIL OVER THE AREA TONIGHT AND SATURDAY.
THIS COMBINED WITH LOW LEVEL OFFSHORE OR NORTHERLY FLOW WILL MAKE
FOR A MOSTLY CLEAR AND COOL NIGHT...ESPECIALLY IN THE SHELTERED
VALLEYS WHERE TEMPS COULD DIP INTO THE MID 40S. MAX TEMPS ON
SATURDAY WILL BE NEAR OR SLIGHTLY ABOVE NORMAL UNDER PLENTY OF
SUNSHINE.

EXPECT A SHORT WAVE UPPER TROF TO CLIP THE CWA ON SUNDAY AS IT
PASSES BY TO OUR EAST. THE MAIN IMPACT THIS WILL HAVE ON OUR
WEATHER WILL BE TURN THE LOW LEVEL FLOW ONSHORE. DAYTIME TEMPS
ON SUNDAY SHOULD BE SLIGHTLY COOLER THAN SATURDAY.

.LONG TERM...
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.

&&

.AVIATION...WEAK UPPER LEVEL TROUGH SHIFTING EAST OF THE AREA THIS
MORNING. NORTHERLY FLOW ALOFT. LOW LEVEL FLOW WILL REMAIN WEAKLY
ONSHORE.

SATELLITE IMAGERY AT 0930Z/230 AM SHOWS STRATUS ALONG THE COAST WITH
THE STRATUS ONLY AS FAR AS KSHN TO THE SOUTH AND WEST OF KCLM
THROUGH THE STRAIT. THE LAYER IS VERY SHALLOW WITH CEILINGS BELOW
1000 FEET WITH LOCAL VISIBILITIES BELOW A MILE. SURFACE GRADIENTS
ARE LIGHT NORTHERLY AND THE VAD WIND PROFILER AT KATX SHOWS
NORTHWESTERLY WINDS RIGHT OFF THE GROUND. THIS IS NOT A GOOD
COMBINATION FOR THE STRATUS TO GET MUCH FURTHER EAST THIS MORNING.
HAVE ALREADY AMENDED THE CENTRAL SOUND TAFS TO TAKE THE CEILINGS OUT
OF THE FORECAST. KOLM CLOSE ENOUGH TO THE LEADING EDGE OF THE
STRATUS FOR THE POSSIBILITY OF A LITTLE FOG BUT EVEN IF THE FOG
DEVELOPS AT THE TERMINAL IT WILL NOT LAST LONG. WITH THE UPPER LEVEL
TROUGH MOVING EAST AND NORTHERLY FLOW ALOFT ALONG WITH LIGHT
NORTHERLY SURFACE GRADIENTS CONTINUING GOOD CHANCE THERE WILL NOT BE
ANY CEILINGS AT THE INTERIOR TAFS SATURDAY MORNING. FELTON

KSEA...MOSTLY CLEAR SKIES WITH LIGHT WINDS BECOMING NORTHWESTERLY 4
TO 8 KNOTS MIDDAY. FELTON

&&

.MARINE...THE VERY STATIC ONSHORE FLOW PATTERN WILL CONTINUE FOR THE
NEXT SEVERAL DAYS. AS IS TYPICAL WITH THIS TYPE OF PATTERN...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. FELTON

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML



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