000 FXUS66 KSEW 080348 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 845 PM PDT SUN SEP 7 2008 .SYNOPSIS...AN UPPER LEVEL RIDGE COMBINED WITH LOW LEVEL OFFSHORE FLOW WILL PROVIDE WARM TEMPERATURES AND MOSTLY CLEAR SKIES THROUGH MONDAY. A WEAK FRONTAL SYSTEM WILL PASS THROUGH WESTERN WASHINGTON MONDAY NIGHT...TURNING THE FLOW ONSHORE AND USHERING IN MARINE MOISTURE. THE RIDGE WILL BUILD BACK IN AROUND 140W ON WEDNESDAY AFTERNOON THROUGH THURSDAY FOR DRY AND WARMER WEATHER AGAIN. && .SHORT TERM...DECENT OFFSHORE FLOW THIS EVENING WITH MOSTLY CLEAR SKIES AS THE RESULT. THIS PATTERN IS EXPECTED TO BASICALLY MAINTAIN ITSELF THROUGH THE 1ST HALF OF MONDAY WITH THE THERMALLY INDUCED TROUGH OF LOW PRESSURE AT THE SURFACE REMAINING ALONG THE COAST. THIS MODERATE OFFSHORE FLOW SHOULD ALSO KEEP THE FOG/STRATUS TO A MINIMUM OVERNIGHT...WITH ONLY THE MOST FOG PRONE AREAS HAVING ANY POTENTIAL DEVELOPMENT OVERNIGHT. THE SURFACE TROUGH WILL SHIFT INLAND MIDDAY...THEN EAST OF THE CASCADES DURING THE AFTERNOON WITH ONSHORE FLOW DEVELOPING ON ITS BACKSIDE. AT THIS POINT AM EXPECTING A NICE WARMUP ALONG THE COAST UNTIL EARLY AFTERNOON THEN THE WESTERLY WINDS WILL COOL THINGS OFF THERE. OVER THE INTERIOR...THE ONSHORE FLOW WILL KICK IN LATE ENOUGH IN THE DAY THAT IT WILL GO UNNOTICED AND TEMPERATURES WILL BE RATHER MILD ONCE AGAIN WITH MOSTLY SUNNY SKIES. OVERNIGHT...MARINE PUSH WILL CONTINUE WITH THE MAIN EFFECT BEING SOMEWHAT COOLER TEMPERATURES. ALL GUIDANCE HINTS AT A RELATIVELY DRY PUSH...THAT IS LIMITED MOISTURE FOR STRATUS FORMATION...SO IT WILL LIKELY BE A MOSTLY CLEAR PUSH WITH THE EXCEPTION OF THE COAST WHERE MORNING LOW CLOUDS IS A SURE BET. CERNIGLIA .LONG TERM...FROM PREVIOUS DISCUSSION...LONG RANGE MODELS ARE IN GOOD AGREEMENT...FLOW ALOFT TURNS WESTERLY AS THE RIDGE FLATTENS SOMEWHAT THURSDAY WITH ANOTHER DISSIPATING FRONTAL SYSTEM. ONSHORE FLOW FOLLOWS FRIDAY...AND THEN RIDGE QUICKLY AMPLIFIES SATURDAY AS A THERMAL TROUGH ATTEMPTS TO SET UP ALONG THE COAST FOR ANOTHER DRY AND WARM WEEKEND. DAMICO && .AVIATION...A WEAKENING UPPER LEVEL RIDGE OVER W WA WILL MOVE E MONDAY MORNING AS A WEAK UPPER LEVEL TROUGH AND DISSIPATING FRONT APPROACH THE AREA. THE REMNANTS OF THE FRONT WILL REACH THE COAST MONDAY NIGHT. THE AIR MASS WILL REMAIN DRY AND STABLE WITH RESIDUAL DRY NORTHERLY OFFSHORE FLOW ALLOWING ONLY ISOLATED MORNING STRATUS AND FOG AT BEST. KSEA...CLEAR. AIR MASS IS A LITTLE DRIER THAN LAST NIGHT. NO STRATUS OR FOG EXPECTED MONDAY MORNING. N SURFACE WINDS WILL CONTINUE THROUGH MONDAY. KAM && .MARINE...OBS AND LATEST MODELS INDICATE THE SCA FOR THE COASTAL WATERS ISN'T WORKING OUT. WILL DROP IT ON THE 9 PM PACKAGE. B.C. SURFACE HIGH IS WEAKENING AND THE SURFACE TROUGH ALONG THE WA/OREGON COASTS WILL SHIFT EAST OF THE CASCADES BY MONDAY AFTERNOON...AS A WEAK UPPER LEVEL TROUGH AND DISSIPATING FRONT APPROACH THE AREA...AND THE BIG NE PACIFIC SURFACE HIGH BECOMES DOMINANT. WESTERLY ONSHORE GRADIENTS WILL BE GOING UP MONDAY AFTERNOON...BUT LATEST MODELS SUGGEST THAT SCA WINDS IN THE STRAIT MONDAY AFTERNOON MAY BE TOO QUICK. WILL RE-EVALUATE THIS FOR THE 3 AM PACKAGE. SCA WINDS FOR THE OUTER COASTAL WATERS MAY WORK OUT. W ONSHORE FLOW CONTINUES FOR THE MOST PART FOR THE REST OF THE WEEK... BUT ANOTHER UPPER LEVEL RIDGE WEDNESDAY/THURSDAY MAY PROVIDE ANOTHER REALLY BRIEF SHOT AT OFFSHORE OR JUST SLACK FLOW. KAM && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...NONE. $$ WEATHER.GOV/SEATTLE