FXUS66 KSEW 092133 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 230 PM PDT SAT MAY 9 2009 .SYNOPSIS...A WEAK UPPER LEVEL RIDGE AND SURFACE HIGH PRESSURE JUST OFFSHORE WILL GIVE WAY TO A COLD FRONT SUNDAY NIGHT. THE FRONT WILL MOVE INLAND MONDAY FOLLOWED BY A COLD UPPER TROUGH ON TUESDAY. A BRIEF BREAK BETWEEN SYSTEMS IS EXPECTED WEDNESDAY WITH ANOTHER WEATHER SYSTEM ARRIVING THURSDAY. && .SHORT TERM...CLEAR SKIES BUT FOR A COUPLE OF SHOWERS CASCADES. NOT LIKELY TO SEE THE AREAS OF STRATUS LIKE WE SAW THIS MORNING FOR SUN MORNING...AIR MASS WARMER AND DRIER...MAYBE SOME PATCHY VALLEY FOG. MOSTLY SUNNY SUN MORNING THEN HIGH CLOUDS WILL SHOW UP AFTERNOON. AM BETTING THAT ANY CIRRUS IS THIN ENUF THAT WE SEE MAX HEATING AND HV FCST INLD WELL INTO THE 60S WITH LOWER 70S IN A FEW SPOTS SOUTH AND EAST OF SEATTLE. SURFACE HIGH PRES JUST OFFSHORE GIVES OUT THRU SUN AS SURFACE LOW PRES CENTER TRACKS TOWARD THE AREA. 12Z GFS HAS THE SFC LOW JUST OFFSHORE SUN EVE W/ A WINDY PUSH BEHIND IT AND AT 18Z MON A +9MB PDX-BLI GRADIENT. BUT THAT IS THE STRONGEST PRES GRADIENT AMONG THE MODELS AND WE ARE LEANING AWAY FROM THAT SOLN. THE NAM HAS MUCH LESS GRADIENT W/ JUST A COUPLE MB AND WEAK TROF HANGING BACK OVR COASTAL WATERS. THE STRONGER JET AND BETTER 500MB HEIGHT FALL/RISE COUPLET IS WELL OFFSHORE AT THE MAIN UPPER TROF EARLY MONDAY SO I DON'T THINK MON WILL BE THE BREEZY DAY. LOOK FOR BLUSTERY WEATHER MON NITE OR TUE AS THE MAIN COLD UPPER TROF AND SFC TROF PASS THRU. TUE WILL SEE THE LOWEST SNOW LEVELS WITH -4C AT 850MB...THE FCST READS 2500FT FOR NOW BUT EVEN THE FOOTHILLS COULD SEE A LITTLE WET SNOW IN THE MORNING AND W/ THE COLDEST AIR ALOFT FCST TO TRACK RIGHT OVER WRN WA TUE MORNING EVEN SHOWERS IN THE LOWLANDS COULD HAVE ICE PELLETS AND A BRIEF WINTRY MIX. 19 .LONG TERM...THERE SHOULD BE A PAUSE ON WEDNESDAY BETWEEN WEATHER SYSTEMS AND I THINK THERE IS ROOM TO PUT SOME MORE SUNSHINE AND LOWER POPS IN FOR THAT DAY. HOWEVER BY THURSDAY ANOTHER VIGOROUS SYSTEM FOR MAY WILL BE ARRIVING. THE MODELS ARE PROGRESSIVE AND THE TROF IS MOVING INLAND FRIDAY...HOWEVER THE TROF IS STILL BROAD ENUF TO KEEP THE SHOWERS GOING INTO FRIDAY. NEXT WEEKEND COULD BE SUNNY AND DRY WITH A WEAK UPPER RIDGE BUILDING INTO THE AREA. 19 && .AVIATION...A WEAK RIDGE ALOFT REMAINS JUST OFFSHORE WITH LIGHT NW FLOW FOR LITTLE IF ANY MID AND HIGH CLOUDS. HIGH PRESSURE AT THE SURFACE OUT NEAR 130W AND LOWER PRESSURE EAST OF THE CASCADES WILL MAINTAIN LIGHT ONSHORE FLOW THROUGH TONIGHT. SKIES ARE PRETTY MUCH CLEAR THIS MORNING WHICH WHEN COMBINED WITH LINGERING LOW LEVEL MOISTURE IS RESULTING IN PATCHES OF FOG AND VERY LOW STRATUS FORMING...ESPECIALLY NEAR THE COAST. THIS WILL NOT BECOME WIDESPREAD AND WILL BURN OFF BY LATE MORNING...BUT IF YOUR FLYING EARLY THIS MORNING WILL NEED TO KEEP THAT IN MIND. SATURDAY NIGHT INTO EARLY SUN WILL BE A NEAR REPEAT OF THIS MORNING. KSEA...NOT EXPECTING FOG OR STRATUS TO AFFECT THE TERMINAL THIS MORNING ALTHOUGH THERE WILL BE PATCHES OF IT AROUND. NE BREEZE WILL BECOME MORE OF A N-NW BREEZE THIS AFTERNOON. CERNIGLIA && .AVIATION...OTHER THAN SOME CUMULUS BUILDUPS OVER THE MOUNTAINS...MOSTLY CLEAR CONDITIONS DOMINATE THIS AFTERNOON. EXPECT CONDITIONS TO CLEAR IN THE MOUNTAINS AS WELL AFTER SUNSET. LIGHT NLY FLOW WILL DOMINATE. THE AIR MASS IS DRYING SOMEWHAT SO EXPECT LESS STRATUS OR FOG SUNDAY THAN TODAY. AT THIS POINT EXPECT MOST TERMINALS TO BE CLEAR SUN MORNING WITH ONLY SOME CHEHALIS RIVER VALLEY FOG E OF KHQM MOVING INTO THAT TERMINAL 13Z-16Z...AND SOME PATCHY FOG AROUND KOLM. CIRRUS WILL MOVE INTO THE AREA FROM THE SW MIDDAY THEN THICKEN TO AN ALTOSTRATUS DECK AROUND 00Z MON. KSEA...EXPECT MOSTLY CLEAR CONDITIONS THROUGH MIDDAY SUN. NW WIND 7-10 KT WILL TURN 03006KT AFTER 04Z WITH LIGHT AND VARIABLE WIND DOMINATING SUN. ALBRECHT && .MARINE...HIGH PRES ALONG 130W WILL GRADUALLY SHIFT E INTO WESTERN WA SUN AND E OF THE CASCADES SUN NIGHT. EXPECT LIGHT ONSHORE FLOW THIS EVENING TO BECOME MAINLY LIGHT AND VARIABLE TONIGHT AND SUN. A WEAK LOW WILL FORM IN THE OREGON OFFSHORE WATERS SUN AND MOVE E OR NE ACROSS THE WATERS SUN. THE GFS HAS TRENDED FARTHER S AND WEAKER WITH THE LOW WHILE THE 18Z NAM HAS TRENDED A BIT FARTHER N. AT THIS POINT WILL TREND THE WINDS 30 PERCENT TOWARD THE ECMWF...A LIGHTER SOLUTION...AND MAINTAIN A TRACK TOWARD SOUTHERN VANCOUVER ISLAND. THIS WOULD BRING SOME POTENTIAL FOR SMALL CRAFT ADVISORY SOUTHERLY WINDS ALONG THE COAST AND IN THE N INLAND WATERS LATER SUN NIGHT INTO MON MORNING...BUT WITH A GOOD DEAL OF UNCERTAINTY. A MATURING LOW IN THE GULF OF ALASKA WILL OPEN UP INTO A STRONG TROUGH AND MOVE THROUGH THE WATERS LATER MON INTO EARLY TUE. THIS TROUGH WILL INCREASE SOUTH AND SW PRES GRADIENTS ACROSS THE REGION AND WILL GIVE SMALL CRAFT ADVISORY CONDITIONS TO MOST WATERS. A WEAK RIDGE OF HIGH PRES WILL MOVE THROUGH THE REGION WED GIVING LIGHT TO SLIGHTLY OFFSHORE FLOW. THEN ANOTHER FRONT WILL MOVE THROUGH THE WATERS THU BRINGING ANOTHER ROUND OF WIDESPREAD SMALL CRAFT ADVISORY CONDITIONS. ALBRECHT && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE PZ...NONE $$ WWW.WEATHER.GOV/SEATTLE