FXUS66 KSEW 062240
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
340 PM PDT SAT SEP 6 2008

.SYNOPSIS...AN UPPER LEVEL RIDGE CONTINUES TO BRING FAIR WEATHER TO 
THE PACIFIC NORTHWEST. A THERMALLY INDUCED TROUGH OF LOW PRESSURE 
WILL BUILD UP THE WASHINGTON COAST SUNDAY TURNING THE SURFACE FLOW 
OFFSHORE. SUNDAY AND MONDAY WILL BE WARMER WITH TEMPERATURES RUNNING 
ABOVE SEASONAL NORMALS. TEMPERATURES WILL COOL AS A DISSIPATING 
WEATHER SYSTEM BRUSHES THE AREA MONDAY NIGHT AND TUESDAY. HIGH 
PRESSURE WITH OFFSHORE FLOW WILL BRING WARMER TEMPERATURES WEDNESDAY 
AND THURSDAY.

&&

.SHORT TERM...FOG IN THE SOUTHWEST AND SOUTHERN PUGET SOUND HAS 
CLEARED OUT NICELY THIS AFTERNOON...AND TEMPERATURES ARE GENERALLY 
RUNNING IN THE MID 60S TO LOWER 70S. SOME LEFTOVER 040-060 
STRATOCUMULUS NEAR ARLINGTON WILL LIKELY NOT FULLY SCATTER OUT BY 
THIS EVENING...AND IS DRIFTING TO THE SOUTHWEST AS THE FLOW BEGINS 
TO TURN OFFSHORE. RIDGE AXIS CONTINUES TO HOLD INSIDE OF 140W 
OFFSHORE...AND A THERMALLY INDUCED TROUGH OF LOW PRES WILL BUILD UP 
THE WASHINGTON COAST SUNDAY. THE POSSIBILITY REMAINS FOR FOG 
TONIGHT. HAVE INCLUDED PATCHY FOG FOR MANY OF THE SAME AREAS AS LAST 
NIGHT WITH DEWPOINTS IN THE LOWER TO MID 50S AND NAM BUFR SOUNDING 
SHOWING A TEMPERATURE INVERSION TO AROUND 925 MB AT 12Z SUNDAY. ANY 
FOG OR STRATUS THAT DOES FORM WILL BURN OFF QUICKLY...AS 
TEMPERATURES WARM INTO THE MID 70S TO MID 80S ON SUNDAY. HAVE 
DROPPED A FEW DEGREES OFF AREAS NEAR THE SOUND WHERE A NORTHERLY 
BREEZE WILL KEEP THINGS SLIGHTLY COOLER.  

A DISSIPATING FRONT WILL APPROACH THE COASTAL WATERS MONDAY 
AFTERNOON...AND THE FLOW WILL TURN ONSHORE ON THE COAST MONDAY 
AFTERNOON AS THE THERMAL TROUGH SHIFT INLAND. GFS AND NAM SHOW THE 
PUSH TRENDING SLIGHTLY LATER IN THE DAY THEN PREVIOUS MODEL RUNS. 
WEAK NORTHWEST PUSH WILL MOVE CLOUDS IN MONDAY NIGHT...AND HEIGHTS 
WILL DROP FURTHER ON TUESDAY AS A SHORTWAVE TROUGH DIGS INTO 
SOUTHERN BRITISH COLUMBIA.   

.LONG TERM...STILL NO QPF FORECASTED THROUGH THE ENTIRE FORECAST 
PERIOD...AS THE TROUGH QUICKLY MOVES INTO THE ID/MT BORDER BY WED 
MORNING...AND THE RIDGE BEGINS TO BUILD AGAIN AROUND 140W. GRADIENTS 
BRIEFLY GO OFFSHORE AGAIN WEDNESDAY BEFORE THE NEXT FRONTAL SYSTEM 
ATTEMPTS TO BREAK DOWN THE RIDGE ON THURSDAY...LIKELY RESULTING IN 
ONLY SOME HIGH CLOUD COVER IN THE LATE AFTERNOON/EVENING. WEAK 
FRONTAL SYSTEM WASHES OUT TO OUR EAST ON FRIDAY...AND THE RIDGE 
BUILDS BACK IN ON SATURDAY. DAMICO 

&&

.AVIATION...AN UPPER RIDGE ALONG ABOUT 138W IS BRINGING NW FLOW 
ALOFT. AS A RIDGE OF HIGH PRESSURE DEVELOPS OVER SOUTHEAST BRITISH 
COLUMBIA AND EASTERN WASHINGTON SUNDAY THROUGH MONDAY BEHIND A 
DEPARTING UPPER LEVEL DISTURBANCE IN THE CANADIAN ROCKIES...A 
THERMALLY INDUCED TROUGH OF LOW PRESSURE OVER SOUTHERN OREGON WILL 
DEVELOP NORTHWARD ALONG THE WASHINGTON COAST LATE SUNDAY. 

OFFSHORE FLOW WILL GRADUALLY DEVELOP AND INCREASE SUN MORNING. 
UNFORTUNATELY...IT APPEARS THAT THERE WILL BE SUFFICIENT TIME 
TONIGHT IN LIGHT NE GRADIENTS TO ALLOW THE BOUNDARY LAYER TO INVERT 
FOR THE FORMATION OF A SHALLOW BUT MODERATELY EXTENSIVE AREA OF FOG 
AND VERY LOW STRATUS...INCLUDING SOME LAKE WASHINGTON STRATUS EAST 
OF I-5 MOVING TOWARD SEATAC AIRPORT. MANY OF THE TERMINALS WILL 
LIKELY SEE A 2-4 HOUR PERIOD OF STRATUS AND FOG SUN MORNING...AND 
SOME VISIBILITIES WILL LIKELY BE 1/2SM OR LESS IN FG. 

BECAUSE OF THE INCREASING OFFSHORE GRADIENTS SUNDAY MORNING... 
INSOLATION SHOULD LIFT OUT AND BURN OFF LOW LEVEL MOISTURE 
EARLY...BY 17Z. SEVERE CLEAR WILL FOLLOW SUN AFTERNOON AND SUN 
NIGHT. 

KSEA...JUST A FEW MID CLOUDS ARE EXPECTED MOST OF THE NIGHT. WINDS 
NORTH 8 KT AT THE TERMINAL THIS EVENING WILL TREND NE OVERNIGHT. 
SHALLOW VERY LOW STRATUS AND FOG WILL DEVELOP IN THE VALLEY E OF I-5 
LATE TONIGHT AND WILL LIKELY WAFT SW INTO THE TERMINAL DURING THE 
MORNING HOURS. LOW LEVEL MOISTURE WILL RAPIDLY EVAPORATE AFTER 17Z. 
VISIBILITIES BETWEEN 14Z AND 17Z MAY OCCASIONALLY DROP BELOW 1/2SM 
FG. ALBRECHT

&&

.MARINE...STRONG HIGH PRESSURE ALONG ABOUT 138W WILL GIVE N-NW FLOW 
TO THE COASTAL WATERS THROUGH EARLY NEXT WEEK. WINDS WILL RANGE FROM 
10 TO 20 KT BUT MAY OCCASIONAL REACH SMALL CRAFT ADVISORY LEVELS IN 
THE OUTER WATERS AT TIMES LATER SUN INTO MON. 

NORTHERLY FLOW IN THE INTERIOR WILL INCREASE TO 10 TO 20 KT AND 
POSSIBLY TO SMALL CRAFT ADVISORY LEVEL MIDDAY SUN THROUGH SUN 
EVENING AS A THERMALLY INDUCED TROUGH OF LOW PRES FORMS OVER SW 
OREGON DEVELOPS NORTH INTO WESTERN WASHINGTON. WINDS WILL BECOMING 
LIGHT IN THE INTERIOR MON AS THE TROUGH SHIFTS E...THEN WILL BECOME 
MODERATELY ONSHORE MON EVENING AS THE TROUGH SHIFTS E OF THE 
CASCADES AND WEAKENS. 

&&

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

$$
WEATHER.GOV

ZSE ARTCC WEATHER HAZARDS

Issued: 9/6/2008 2:09:25 PM

AREAS

Click here for ZSE Area Map