Issued by NWS Seattle/Tacoma, WA
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000 FXUS66 KSEW 131033 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 230 AM PST FRI FEB 13 2009 .SYNOPSIS...AN UPPER LEVEL LOW OFF THE SOUTHERN OREGON COAST WILL DROP SOUTHEAST INTO NORTHERN CALIFORNIA AND WEAKEN FRIDAY NIGHT. SURFACE HIGH PRESSURE OVER NORTHEAST BRITISH COLUMBIA AND NORTHERN ALBERTA WILL GIVE MAINLY DRY NORTHEAST LOW LEVEL FLOW TO WESTERN WASHINGTON THROUGH MUCH OF THE WEEKEND. A BROAD UPPER TROUGH OFF NORTHERN CALIFORNIA MAY DRIVE A LITTLE MOISTURE NORTH INTO THE AREA LATER SUNDAY INTO MONDAY BUT PRECIPITATION AMOUNTS WILL REMAIN WELL BELOW NORMAL FOR FEBRUARY. && .SHORT TERM...HIGH CLOUDS SPREAD ACROSS MOST OF THE AREA WITH MID CLOUDS OVER THE SOUTHERN MOST SECTIONS. RAIN HAS BEEN PRETTY MUCH CONFINED TO OREGON BUT OCCASIONALLY SPILLS INTO FAR SOUTHERN WASHINGTON. THIS TREND WILL CONTINUE THROUGH THE FIRST PART OF THE DAY AS MOISTURE CONTINUES TO STREAM NORTH ALOFT. HOWEVER WITH DRY LOW LEVEL FLOW AND UPPER SYSTEM CONTINUING TO MOVE SOUTH...DON`T EXPECT MUCH TODAY OVER SOUTHERN AREAS AND NONE ANYWHERE TONIGHT. AFTERNOON TEMPERATURES SIMILAR OR SLIGHTLY WARMER THAN YESTERDAY. FOR SATURDAY...THE ORIGINAL UPPER LOW HAS WEAKENED SIGNIFICANTLY WHILE ADDITIONAL ENERGY DROPS INTO THE MEANS TROUGH POSITION SATURDAY NIGHT INTO SUNDAY. ALL THIS HAPPENS FAR ENOUGH TO THE SOUTH THAT WE ARE LEFT WITH MID AND HIGH LEVEL MOISTURE AND VERY LITTLE FLOW AND LIFT. SO WENT WITH THE IDEA OF MOSTLY MID/HIGH CLOUDS AND LITTLE IF ANY PRECIPITATION. SUNDAY AND MONDAY...BACKED OFF SOME ON PRECIP THREAT AS WE REMAIN A LONG WAY FROM THE MAIN ACTION AS UPPER LOW LINGERS OFF NRN CALIF OR SRN OREGON COAST. NAM AND ECMWF ARE DRY WHILE GFS IS DAMP WITH MOISTURE STREAMING NORTHWARD. I AM LEANING TOWARD THE DRIER SOLUTIONS AND DRIED THINGS OUT AS MUCH AS I COULD WHILE STILL BLENDING WITH NEIGHBORS. BASICALLY IT LOOKS LIKE IT WILL BE DRY SUNDAY INTO MONDAY WITH VARIABLE AMOUNTS OF HIGH CLOUDS. AS A RESULT OF A BIT MORE EXPECTED SUNSHINE I BUMPED TEMPERATURES UP A NOTCH BUT WE WILL STILL BE A BIT BELOW NORMAL. CERNIGLIA .LONG TERM...LONG WAVE TROUGH POSITION WILL REMAIN ALONG THE WEST COAST THROUGH THE EXTENDED PERIOD BUT THAT ISN`T NECESSARILY A BAD THING AS MOST OF THE ENERGY IN THIS TROUGH WILL BE WELL TO THE SOUTH. CURRENTLY WE HAVE A CHANCE OF SHOWERS THROUGH THE EXTENDED PERIOD DUE TO THE UNCERTAINTY OF THE POSITION/STRUCTURE OF THE UPPER LOWS THAT WILL BE AFFECTING THE WEST COAST. HOWEVER WITH THE LIKELIHOOD THAT THEY WILL BE WELL TO THE SOUTH...OUR POP FORECAST IS LOWER THEN CLIMATOLOGY. IF THE CURRENT TREND CONTINUES...WE WILL LIKELY END UP MOSTLY DRY THROUGH THE EXTENDED PERIOD AND SLIGHTLY WARMER THAN WE HAVE IN THE CURRENT FORECAST. GIVEN THAT MODELS GENERALLY HANDLE CUTOFF UPPER LOWS RATHER POORLY THIS IS STILL A BIT UP IN THE AIR AT THIS POINT. CERNIGLIA && .AVIATION...AN UPPER LOW WILL REMAIN QUASISTATIONARY OFF THE FAR NRN CA COAST. CONTINUED SLY FLOW ALOFT AND LOW LEVEL OFFSHORE FLOW. PRIMARILY MID AND HIGH LEVEL MOISTURE WILL CONTINUE TO STREAM ACROSS THE AREA. PRECIPITATION WILL STAY MOSTLY OVER OREGON. KSEA...CONTINUED VFR CONDITIONS...WITH CIGS REMAINING AT OR ABOVE 7K FT. WINDS GENERALLY NELY AT 6-10 KNOTS. && .MARINE...HIGH PRES OVER BRITISH COLUMBIA AND LOWER PRES OFF THE OREGON COAST WILL KEEP THE FLOW OFFSHORE THROUGH SUNDAY. EXPECT THE PRES GRADIENT TO TIGHTEN ON SUNDAY FOR SOME INCREASE IN WIND. IT IS POSSIBLE THAT THE WIND SPEEDS IN THE FORECAST FOR SUNDAY MAY BE TOO LIGHT...ESPECIALLY OVER THE PUGET SOUND. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT ADVISORY FOR WINDS IN EFFECT FOR THE WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA TIL 20Z. $$ WEATHER.GOV/SEATTLE
