Gale Watch 26, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
914 AM PDT MON MAY 7 2012

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL BRING SUNSHINE AND ABOVE
NORMAL TEMPERATURES TO WESTERN WASHINGTON TODAY. AN UPPER LEVEL
TROUGH WILL GRADUALLY MOVE OVER THE PACIFIC NORTHWEST TUESDAY AND
WEDNESDAY FOR CLOUDIER AND COOLER WEATHER AND A FEW LIGHT SHOWERS.
ANOTHER UPPER LEVEL RIDGE WILL BUILD OVER THE REGION LATE THIS WEEK
WITH A RETURN TO SUNSHINE AND WARMER WEATHER THAT SHOULD LAST
THROUGH THE WEEKEND.

&&

.SHORT TERM...THE UPPER LEVEL RIDGE OVER W WA WILL YIELD THE WARMEST
TEMPERATURES TODAY FOR THIS CURRENT WARM SPELL. MAX TEMPS SHOULD BE
6-10 DEGREES WARMER THAN YESTERDAY WITH 60S IN AREAS ADJACENT TO THE
COAST AND SALISH SEA /A.K.A. ALL THE INLAND WATERS/...WITH LOWER TO
MID 70S ELSEWHERE. THIS WILL BE A GOOD VITAMIN D THERAPY DAY.

THE LARGE UPPER LEVEL TROUGH OVER THE NE PACIFIC CENTERED NEAR
50N/150W WILL WEAKEN AND SLIDE INLAND OVER THE PACIFIC NORTHWEST BY
WEDNESDAY...BRINGING MAINLY A COOLER AIR MASS TO THE REGION. IN THAT
TRANSITION...THE COLD FRONT CURRENTLY ALONG 140W WILL REACH THE
COAST TUESDAY MORNING AROUND 15Z. THE COLD FRONT IS FORECAST TO
WEAKEN RAPIDLY AS IT APPROACHES THE COAST...WITH ONLY A CHANCE OF
SHOWERS OVER THE COASTAL WATERS AND ADJACENT COASTAL AREAS...AND
POSSIBLY THE MOUNTAINS. IT SHOULD BE A DRY FRONT FOR THE INTERIOR
LOWLANDS...WITH LOWER LEVEL FRONTAL CLOUDS REACHING THE AREA LATE
TUESDAY MORNING AND AFTERNOON.

THE STRONG W-NW ONSHORE FLOW DEVELOPING JUST AHEAD OF AND BEHIND THE
TUESDAY MORNING FRONT WILL BRING COOLER MARINE AIR INLAND. HOWEVER
THE STRENGTH OF THIS MARINE PUSH COMBINED WITH THE W-NW DIRECTION
OF THE ONSHORE FLOW MEANS MOISTURE WILL BE MORE LIMITED AND THE
RESULTING MARINE LAYER INLAND WILL BE 4000-5000 FEET DEEP. COOLING
FROM THE MARINE PUSH AND THE FRONT WILL DROP MAX TEMPS BACK TO THE
50S TO MID 60S ON TUESDAY.

THE UPPER LEVEL TROUGH MOVES OVER W WA ON WEDNESDAY BRINGING MORE
COOLING. MAX TEMPS SHOULD TOP OUT IN THE 50S. THIS WILL MOST LIKELY
END UP BEING A DRY TROUGH FOR MOST AREAS. BOTH THE GFS AND NAM QPF
FIELDS ARE DRY. GFS MOS POPS ARE IN THE 20S WHICH IS WHAT THE
CURRENT FORECAST HAS...BUT THE 12Z NAM MOS POPS ARE LESS THAN 10.
THE NAM BUFR SOUNDINGS INDICATE THE LOWER AIR MASS WILL REMAIN
CAPPED BELOW 10000 FEET WHICH WILL LIMIT ANY CONVECTION. I WILL SEE
WHAT THE 12Z GRIDDED DATA HAS BUT AT THIS POINT I AM INCLINED TO
ATTEMPT FINESSING SOME DRY AREAS FOR WEDNESDAY. BECAUSE OF THE
DECREASED LOW LEVEL MOISTURE IN A W-NW PUSH AND THE DEEPER MARINE
LAYER THERE WILL LIKELY BE BREAKS IN THE CLOUDS AT TIMES FOR BRIEF
PERIODS OF SUNSHINE ON WEDNESDAY. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 3 AM AFD...THE WEAK
OFFSHORE UPPER RIDGE WILL MOVE OVER THE PACIFIC NORTHWEST THURSDAY.
THE RIDGE WILL BUILD OVER THE REGION FRIDAY AND SATURDAY...AND IT
SHOULD REMAIN OVER THE AREA ON SUNDAY.

THERE ARE MINOR DIFFERENCES IN THE MODELS OF COURSE. FOR EXAMPLE
SOME RUNS...ESPECIALLY OF THE EUROPEAN MODEL...TEND TO PROGRESS THE
RIDGE EAST OF THE AREA MORE QUICKLY THAN OTHERS WITH A WEAK SYSTEM
APPROACHING FROM THE WEST. THIS WILL PROBABLY BE A FORECAST QUESTION
FOR THE EARLY PART OF NEXT WEEK. AT THIS POINT THERE IS A FAIRLY
HIGH CONFIDENCE FORECAST FOR DRY WEATHER THROUGH THE WEEKEND.
MCDONNAL

&&

.AVIATION...AN UPPER RIDGE OVER THE AREA WILL SHIFT INLAND TONIGHT
WITH INCREASING SOUTHWEST FLOW ALOFT. AT THE SURFACE...WEAK HIGH
PRESSURE WILL CONTINUE OVER THE COASTAL WATERS WITH LOWER PRESSURE
INLAND. AIR MASS DRY AND STABLE.

JUST SOME PASSING CIRRUS TODAY. STRATUS IS EXPECTED TO DEVELOP NEAR
THE COAST LATER TONIGHT...POSSIBLE PUSHING DOWN THE STRAIT AND
REACHING SHELTON BY TUESDAY MORNING.

KSEA...NORTH WIND 3-6 KNOTS WILL BECOME NORTHWEST 4-8 KNOTS
THIS AFTERNOON...THEN SWITCH TO SOUTHWEST LATE TONIGHT. SCHNEIDER

&&

.MARINE...WEAK ONSHORE FLOW TODAY WITH HIGH PRESSURE OVER THE
COASTAL WATERS AND LOWER PRESSURE INLAND. ONSHORE FLOW WILL INCREASE
TONIGHT AND BECOME STRONG TUESDAY AFTERNOON AND EVENING AS A
DISSIPATING FRONT MOVES ONSHORE. GALE FORCE WEST WINDS ARE LIKELY
LATE TUESDAY IN THE STRAIT WITH SMALL CRAFT ADVISORY WINDS MOST
OTHER WATERS. SLIGHTLY WEAKER ONSHORE FLOW WILL CONTINUE WEDNESDAY.
THERE COULD BE ANOTHER LATE AFTERNOON/EVENING GALE IN THE STRAIT
WEDNESDAY BUT THIS IS LESS OF A SURE THING THAN TUESDAY. ONSHORE
FLOW WILL CONTINUE FOR THE REMAINDER OF THE WEEK...LESSENING A BIT
EACH DAY AS THE LOW LEVEL FLOW TURNS MORE NORTHERLY. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WATCH CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA LATE
       TUESDAY AFTERNOON AND TUESDAY NIGHT.

&&

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.