Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 160354
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
849 PM PDT FRI AUG 15 2014

.SYNOPSIS...AN UPPER LEVEL LOW WILL KEEP SKIES MOSTLY CLOUDY TONIGHT
AND SATURDAY MORNING WITH A LINGERING CHANCE OF SHOWERS MAINLY OVER
THE MOUNTAINS. WEAK HIGH PRESSURE WILL BUILD OVER THE AREA SATURDAY
AFTERNOON AND SUNDAY AS THE LOW MOVES EAST. CLOUDS WILL DECREASE
THROUGH SUNDAY MORNING. SUNDAY AFTERNOON AND MONDAY WILL SEE
MOSTLY SUNNY SKIES AND WARMER WEATHER. A TRANSITION TO WESTERLY FLOW
AND A SERIES OF WEAK UPPER LEVEL SYSTEMS TUESDAY ONWARD WILL BRING
CLOUDS AND A CHANCE OF SHOWERS THROUGH THE REMAINDER OF THE EXTENDED
PERIOD.

&&

.SHORT TERM...THE UPPER LEVEL LOW OVER THE REGION WILL CONTINUE TO
MOVE SLOWLY NE AND INTO W MT BY EARLY SATURDAY MORNING. SHOWER
ACTIVITY OVER W WA THIS EVENING REMAINS MINIMAL WITH A FEW SHOWERS
OVER THE HOOD CANAL AREA...NORTH COAST AND CASCADES. THERE REMAINS
ENOUGH INSTABILITY AND OR DYNAMICS WITH THE UPPER LEVEL LOW TO KEEP
A CHANCE OF SHOWERS OVER THE MOUNTAINS TONIGHT. A WEAK UPPER LEVEL
RIDGE WILL BUILD BRIEFLY OVER W WA SATURDAY BEHIND THE EXITING UPPER
LEVEL LOW. THIS WILL HELP DIMINISH SHOWERS...HOWEVER THE AIR MASS
WILL REMAIN RATHER MOIST...KEEPING SATURDAY MORNING CLOUDY WITH SOME
CLEARING TO PARTLY SUNNY SKIES SATURDAY AFTERNOON.

A WEAK UPPER LEVEL TROUGH OVER THE NORTHEAST PACIFIC AND ASSOCIATED
WEAK FRONTAL SYSTEM WILL APPROACH THE AREA SATURDAY. GUIDANCE
REMAINS IN GOOD AGREEMENT THAT THE WEAK FRONTAL SYSTEM WILL FALL
APART OFFSHORE SATURDAY WITH THE WEAK UPPER LEVEL TROUGH MOVING OVER
W WA SUNDAY MORNING. WHILE THIS SYSTEM IS EXPECTED TO BRING SOME
MID/HIGH LEVEL MOISTURE WITH IT...THE END RESULT WILL BE LITTLE MORE
THAN MOSTLY CLOUDY SKIES SUNDAY MORNING WITH CLEARING TO SUNNY SKIES
IN THE AFTERNOON.

MONDAY REMAINS A TRANSITION DAY AS THE WEAK UPPER LEVEL TROUGH
SHIFTS E AND S OF THE AREA AND WESTERLY FLOW ALOFT BEGINS TO SETTLE
OVER THE REGION FROM THE NORTH. A DRY AIR MASS COUPLED WITH SUNNY
SKIES WILL MAKE MONDAY THE WARMEST DAY OF THE WEEK WITH HIGH TEMPS
REACHING INTO THE LOWER 80S IN THE WARMEST SPOTS.

.LONG TERM...THE TRANSITION TO ZONAL FLOW TUESDAY WILL ALLOW A
SERIES OF WEAK UPPER LEVEL SYSTEMS TO AFFECT THE NORTHWEST. MEDIUM
RANGE MODEL RUNS CONTINUE TO SHOW THE FIRST OF THESE SYSTEMS MOVING
ONSHORE EARLY TUESDAY MORNING. EXPECT THIS SYSTEM TO REMAIN
GENERALLY DRY WITH INCREASED CLOUD COVER AND PRECIP OVER THE
MOUNTAINS. MODELS CONTINUE TO DIFFER ON THE TIMING AND EFFECT OF THE
TRAILING SHORTWAVE DISTURBANCES EMBEDDED IN THE WESTERLY FLOW BEYOND
TUESDAY. THE MODEL TO MODEL AND EVEN RUN TO RUN DIFFERENCES HAVE
BEEN SIGNIFICANT ENOUGH THAT CONFIDENCE IN ANY SINGLE SOLUTION
REMAINS LOW AT THIS POINT. THE CURRENT FORECAST TUESDAY ONWARD
REFLECTS A COMPROMISE...WITH CHANCE OF SHOWERS IN THE FORECAST FOR
EACH DAY.

&&

.AVIATION...WESTERLY FLOW ALOFT WILL PREVAIL TONIGHT AND SATURDAY
WITH A WEAK UPPER LEVEL RIDGE OVER THE PACIFIC NORTHWEST. AT THE
SURFACE...ONSHORE FLOW WILL CONTINUE WITH HIGH PRESSURE OFFSHORE AND
LOWER PRESSURE INLAND. THE AIR MASS IS MOIST AND STABLE. LOW CLOUDS
WILL FILL BACK IN TONIGHT AND SATURDAY MORNING...THEN MOSTLY BURN
OFF SATURDAY AFTERNOON.

KSEA...MID CLOUDS THIS EVENING WITH LOW CLOUDS RE-FORMING LATE
TONIGHT. LOW AND MID CLOUDS SHOULD BREAK UP AROUND MIDDAY ON
SATURDAY. LIGHT NORTHERLY WIND. SCHNEIDER

&&

.MARINE...HIGH PRESSURE WILL BE OFFSHORE WITH LOWER PRESSURE INLAND
FOR THE NEXT SEVERAL DAYS. THIS SHOULD PRODUCE SMALL CRAFT ADVISORY
WEST WINDS FOR THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA EACH
EVENING. AN UPPER LEVEL DISTURBANCE PASSING TO THE NORTH WILL CAUSE
LOW LEVEL ONSHORE FLOW TO INCREASE ON TUESDAY. THIS COULD BRING GALE
FORCE WEST WINDS TO THE CENTRAL AND EAST STRAIT TUESDAY NIGHT.
SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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













USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.