Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 190331
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
831 PM PDT MON AUG 18 2014

.SYNOPSIS...A SMALL WEAK UPPER LEVEL TROUGH AND STRONGER ONSHORE
FLOW TONIGHT WILL BRING PARTLY TO MOSTLY CLOUDY SKIES AND COOLER
CONDITIONS ON TUESDAY. A LARGE UPPER LEVEL TROUGH WILL FORM OVER
EASTERN WASHINGTON WEDNESDAY THROUGH FRIDAY...AND COMBINED WITH
STRONGER ONSHORE FLOW...WILL BRING PARTLY TO MOSTLY CLOUDY AND
COOLER WEATHER...WITH SHOWERS AT TIMES OVER THE MOUNTAINS. AN UPPER
LEVEL RIDGE WILL GRADUALLY BUILD OVER THE REGION NEXT WEEKEND.

&&

.SHORT TERM...A WEAK UPPER LEVEL TROUGH OVER B.C. IS SPREADING
MID/HIGH LEVEL CLOUDS OVER WESTERN WA THIS EVENING. THIS TROUGH WILL
CROSS THE AREA EARLY TUE MORNING. OVERALL THIS FEATURE IS LOOKING
DRY IN THE MODELS ALTHOUGH MAY SEE SOME DRIZZLE ALONG THE COAST. THE
INCREASE IN CLOUDS AND DIP IN 500 MB HEIGHTS WILL LEAD TO COOLER
TEMPS TUE AFTERNOON...ABOUT 5-10 DEGREES COOLER COMPARED TO TODAY.
LOW LEVEL ONSHORE FLOW WILL INCREASE TUE AFTERNOON AND MAY SEE A
PSCZ FORM OVER KING COUNTY...WITH AN ISOLATED SHOWER POSSIBLE. BOTH
THE NAM12 AND UW WRF GFS SHOW THE PSCZ WEAKENING LATE TUE EVENING.

AN UPPER LEVEL RIDGE OVER THE NE PAC WILL MAINTAIN NORTHWEST FLOW
THROUGH WESTERN WA ON WED. A WEAK UPPER LEVEL DISTURBANCE MAY CLIP
THE NORTH CASCADES FOR A FEW SHOWERS...OTHERWISE THE REST OF THE CWA
WILL BE DRY. MOS KEEPS TEMPS BELOW NORMAL WITH HIGHS IN THE
INTERIOR IN THE LOWER 70S. THERE IS LITTLE CHANGE IN THE PATTERN ON
THURSDAY SO LOOK FOR A REPEAT.  33

.LONG TERM...PREVIOUS DISCUSSION...THE GFS AND ECMWF BOTH HAVE THE
UPPER LEVEL LONGWAVE TROUGH SHIFTING E OVER THE ROCKIES ON
SATURDAY...ALLOWING AN OFFSHORE RIDGE TO BUILD WEAKLY INLAND OVER
THE AREA. ONE COMPLICATION IS THAT BOTH MODELS SHOW ANOTHER
SHORTWAVE TROUGH BRUSHING THE AREA SATURDAY NIGHT OR SUNDAY AS IT
HEADS SE ACROSS THE B.C. INTERIOR. BASED ON MODELS RUN-TO-RUN
CONSISTENCY...CONFIDENCE IS NOT VERY HIGH WITH THIS FEATURE...AND
ONLY SLIGHTLY BETTER WITH THE STRENGTH OF THE RIDGE BUILDING INLAND.
HOWEVER THE GRADUAL WEAK WARMING AND DRYING TREND FOR THE LATER
WEEKEND HAS BEEN KEPT. KAM

&&

.AVIATION...A BROAD UPPER LEVEL TROUGH WILL SETTLE OVER THE PACIFIC
NORTHWEST TONIGHT AND TUESDAY WITH WEST TO NORTHWEST FLOW ALOFT. AT
THE SURFACE...ONSHORE FLOW WILL PREVAIL WITH HIGH PRESSURE OFFSHORE
AND LOWER PRESSURE INLAND. AIR MASS DRY AND STABLE...BECOMING MOIST
AT THE LOW LEVELS LATER TONIGHT.

HIGH CLOUDS WILL BE MOVING THROUGH THE AREA THIS EVENING. STRATUS IS
EXPECTED TO FORM AT THE COAST THIS EVENING AND SPREAD INLAND AFTER
MIDNIGHT TONIGHT. ONSHORE GRADIENTS ARE NOT VERY STRONG WHICH
SUGGESTS THE LOW CLOUDS WILL ONLY PUSH PARTIALLY INLAND TUESDAY
MORNING. A STRONGER PUSH WITH MORE EXTENSIVE LOW CLOUDS FOR THE
INTERIOR IS EXPECTED TUESDAY NIGHT.

KSEA...HIGH CLOUDS THIS EVENING. COASTAL STRATUS PUSHING INTO THE
INTERIOR THROUGH THE CHEHALIS GAP TONIGHT COULD REACH THE TERMINAL
FOR A FEW HOURS TUESDAY MORNING. HOWEVER...THE ONSHORE FLOW IS NOT
VERY STRONG AND THERE IS A DECENT CHANCE THE STRATUS WILL NOT MAKE
IT TO THE TERMINAL. NORTHERLY WIND 5-10 KNOTS BECOMING SOUTHERLY 3-6
KNOTS LATE TONIGHT. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL PREVAIL FOR THE NEXT SEVERAL DAYS WITH
HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. A PAIR OF WEAK
UPPER LEVEL DISTURBANCES PASSING TO THE NORTH TONIGHT AND TUESDAY
WILL CAUSE AN INCREASE TO THE ONSHORE FLOW.

SMALL CRAFT ADVISORY WEST WINDS ARE LIKELY EACH EVENING FOR THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA. THERE IS A CHANCE WINDS
COULD HIT GALE TUESDAY EVENING WHEN THE ONSHORE FLOW IS STRONGEST.

THERE WILL ALSO BE SMALL CRAFT ADVISORY NORTHWEST WINDS OVER THE
OUTER COASTAL WATERS AT TIMES FOR THE NEXT COUPLE OF DAYS. SCHNEIDER

&&

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

&&

$$

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