FXUS66 KSEW 201150 CCA
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST TUE JAN 20 2009
.SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC 
NORTHWEST THROUGH MID WEEK. THIS WILL MAINTAIN STAGNANT CONDITIONS 
OVER MUCH OF THE LOWLANDS WITH AREAS OF FOG AND LOW CLOUDS OVERNIGHT 
AND SOME MIDDAY CLEARING. THE UPPER LEVEL RIDGE WILL WEAKEN 
WEDNESDAY NIGHT AS A WEAK UPPER LEVEL TROUGH APPROACHES FROM THE 
WEST. WEAK UPPER LEVEL SYSTEMS WILL AFFECT THE REGION THROUGH THE 
END OF THE WORK WEEK...WITH COOLER CONDITIONS POSSIBLE OVER THE 
WEEKEND.
&&
.SHORT TERM...LITTLE CHANGE IN THE OVERALL FORECAST. IR SATELLITE 
SAYS IT ALL WITH THE ARC OF CLOUDS/JET STREAM LOCATED NORTH OF THE 
QUEEN CHARLOTTES AS THE STRONG UPPER LEVEL RIDGE REMAINS DOMINANT 
ACROSS THE ENTIRE WESTERN U.S. HIGH PRESSURE EAST OF THE CASCADES IS 
MAINTAINING DRY OFFSHORE FLOW ACROSS WESTERN WA...AS IT HAS BEEN 
OVER THE PAST SEVERAL DAYS. NO SURPRISE THAT WE ARE ONCE AGAIN 
SEEING PATCHY FOG ACROSS THE INTERIOR LOWLANDS WHERE THE STRONG LOW 
LEVEL INVERSION REMAINS. WITH LIGHT WINDS AT THE SURFACE AND LITTLE 
MIXING...THE FOG ALTHOUGH QUITE SHALLOW...WILL ONCE AGAIN SLOWLY 
ERODE LATE THIS MORNING OR POSSIBLY EARLY AFTERNOON IN SPOTS. SOME 
FREEZING FOG IS ALSO POSSIBLE ESPECIALLY WITH TEMPS THIS MORNING 
HOVERING IN THE UPPER 20S TO LOWER 30S. AS MENTIONED IN PREVIOUS 
DISCUSSIONS...AIR QUALITY REMAINS AN ISSUE ACROSS THE INTERIOR 
LOWLANDS AS AIR POLLUTANTS REMAIN TRAPPED NEAR THE SURFACE. THERE 
ARE SEVERAL BURN BANS IN EFFECT AND WILL MAINTAIN THE AIR STAGNATION 
ADVISORY. 
NEGATIVE TILT RIDGE AXIS REMAINS OVER WA ON WED WITH WHAT LOOKS LIKE 
AT LEAST ONE MORE DAY OF SUNNY TO MOSTLY SUNNY CONDITIONS. A DEEP 
UPPER LEVEL TROUGH OFFSHORE THAT IS APPROACHING WILL WEAKEN AS IT 
MOVES INLAND LATE WED...ALTHOUGH AT THIS POINT IT LOOKS LIKE WE WILL 
MAINLY JUST SEE AN INCREASE IN CLOUDS. CUTOFF LOW WILL DEVELOP ON 
THU BUT ALSO LOOKS LIKE IT WILL REMAIN OFFSHORE AND OFF THE CA 
COAST. LOW END CHANCE POPS ARE LEFT OVER IN THE GRIDS FOR THU NIGHT 
BUT MAY END UP BEING A DRY NIGHT AS WELL WITH WEAK RIDGING OVERHEAD. 
33
.LONG TERM...MODELS ARE SHOWING COOLER CONDITIONS OVER THE WEEKEND 
AS A BOUNDARY SLIDES SOUTH THROUGH B.C. AND INTO WA. HOWEVER IT 
STILL REMAINS UNCLEAR ON JUST HOW COLD WE WILL GET. THE GFS IS MUCH 
COOLER THAN THE ECMWF WITH A FRAZER RIVER OUTFLOW DEVELOPING BY 06Z 
SUN...AND 850MB TEMPS -08 TO -10C WITH 1000-850MB THICKNESS DROPPING 
TO 1250S-1260S ACROSS W WA. A REX BLOCK WILL ALSO DEVELOP OFFSHORE 
OVER THIS TIME PERIOD WHICH MAY AFFECT THE STRENGTH AND TIMING OF 
THIS FEATURE. THUS WILL AVOID ANY MENTIONS OF SNOW THIS FAR OUT AND 
WILL KEEP TEMPS BELOW NORMAL BUT NOT AS COLD AS THE GFS...ESPECIALLY 
SINCE THERE ARE SOME INCONSISTENCIES WITH THE EURO. COOLER AIR MAY 
STICK AROUND INTO EARLY NEXT WEEK WITH NLY FLOW ALOFT AND OFFSHORE 
FLOW AT THE SURFACE. 33 
&&
.AVIATION...NOT MUCH CHANGE IN THE NEXT 24 HOURS AVIATION WISE WITH 
AN UPPER LEVEL RIDGE OVER WESTERN WASHINGTON AND LOW LEVEL OFFSHORE 
FLOW. SANDPOINT PROFILER SHOWS INVERSION RIGHT NEAR THE SURFACE LIKE 
IT HAS BEEN FOR THE PAST COUPLE OF DAYS AND LIGHT WINDS ALOFT UP TO 
NEAR 3000 FEET. OFFSHORE GRADIENTS WILL SLOWLY WEAKEN TODAY INTO 
WEDNESDAY WHILE THE WIND PROFILE ALOFT WILL REMAIN THE SAME...LIGHT. 
FOG COVERAGE THIS MORNING OVER THE WATER AS WELL AS FROM ABOUT 
EVERETT TO OLYMPIA. NO TOP REPORTS YET THIS MORNING BUT EXPECT TOPS 
LESS THAN 1000 FEET. EVEN WITH THIS SHALLOW A LAYER WITH THE LACK OF 
MIXING IN THE LOWER LEVELS AND THE WEAK LATE JANUARY SUN NOT LOOKING 
FOR BREAKOUT UNTIL THE AFTERNOON HOURS. SAME SCENARIO WEDNESDAY WITH 
A LITTLE MORE EXTENSIVE FOG COVERAGE AND A LATER BREAKOUT.  
KSEA...VISIBILITY AROUND 1/4 OF A MILE UNTIL EARLY AFTERNOON. EXPECT 
AN IMPROVING TREND BEGINNING AROUND 21Z AND LASTING UNTIL ABOUT 06Z 
WED WHEN THE VISIBILITIES WILL ONCE AGAIN DROP BACK DOWN TO NEAR 1/4 
OF A MILE. FELTON  
 
&&
.MARINE...HIGH PRES EAST OF THE CASCADES AND LOWER PRES OVER THE 
EASTERN PACIFIC WILL KEEP THE FLOW OFFSHORE THROUGH THU. THE HIGH 
WILL WEAKEN ON FRIDAY. ANOTHER SURFACE HIGH WILL BUILD OVER BRITISH 
COLUMBIA ON SAT. KUIL-KBLI EASTERLY GRADIENT SLOWLY DECREASING 
DURING THE DAY. TATOOSH ISLAND IN THE LOW 20S EARLY THIS MORNING SO 
WILL KEEP THE SMALL CRAFT FOR THE WEST ENTRANCE OF THE STRAIT GOING. 
FELTON
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...AN AIR STAGNATION ADVISORY REMAINS IN EFFECT FOR THE INTERIOR
     LOWLANDS THROUGH THU.
   
PZ...A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WEST ENTRANCE       
     OF THE STRAIT OF JUAN DE FUCA TODAY.        
    
$$
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