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AREA FORECAST DISCUSSION

 
 FXUS66 KSEW 191538
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
838 AM PDT SUN APR 19 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL REMAIN OVER THE REGION
THROUGH MONDAY. THE HIGH WILL MOVE EAST ON TUESDAY...ALLOWING A
LOW PRESSURE SYSTEM TO APPROACH FROM THE WEST. THE MAIN IMPACTS
WILL BE COOLER TEMPERATURES AND INCREASED CLOUD COVER. ANTICIPATE
AN UNSETTLED WEATHER PATTERN WEDNESDAY THROUGH THE END OF THE
WEEK.

&&

.SHORT TERM...
SMOKE FROM LARGE WILDFIRES IN SIBERIA AND CIRROSTRATUS WERE
STREAMING ACROSS THE CWA THIS MORNING...RESULTING IN FILTERED
SUNSHINE. THERE WAS ALSO SHALLOW FOG PRESENT IN THE SNOHOMISH
RIVER VALLEY AND LOWER CHEHALIS RIVER VALLEY /EXTENDING PARTIALLY
INTO GRAYS HARBOR/ THIS MORNING. THE FOG SHOULD BURN OFF IN ABOUT
AN HOUR OR TWO.

AN UPPER RIDGE WILL REMAIN OVER THE REGION THROUGH MONDAY. THE
RIDGE WILL MOVE INTO THE INTERMOUNTAIN WEST ON TUESDAY. THIS WILL
ALLOW A SPLITTING UPPER TROF TO APPROACH THE WEST COAST DURING THE
DAY TUE. THE MAIN FORECAST PROBLEM IN THE SHORT TERM WILL BE THE
TIMING OF THE ONSHORE PUSH. THIS...IN TURN...WILL HAVE AN IMPACT
ON DAYTIME TEMPS. UNSURPRISINGLY...THE 1200 UTC GFS SOLUTION
INDICATED THAT THE PUSH WILL OCCUR MON AFTERNOON...WHICH IS
EARLIER THAN ITS PREVIOUS SOLUTION. THE NAM HOLDS THE PUSH OFF
UNTIL TUE. THIS WILL BE THE FORECASTER DILEMMA...DETERMINING WHICH
MODEL TO BELIEVE.

.LONG TERM FROM THE PREV DISCUSSION...
UPPER TROUGHING PASSES TO THE EAST OF THE AREA LATE WEDNESDAY.
THE ECMWF IS STRONGER WITH ANOTHER SHORT WAVE TROUGH AND
ASSOCIATED FRONTAL SYSTEM ON THU THAN THE GFS...BUT BOTH MODELS
SHOW A FEATURE MOVING THROUGH IN THE THU TIME FRAME. A RATHER DEEP
TROUGH SETS UP JUST OFFSHORE FOR NEXT WEEKEND WITH A FRONTAL
SYSTEM OVER OR JUST TO THE WEST OF THE AREA. WILL MAINTAIN THE
CURRENT FORECAST OF MOSTLY CLOUDY AND A CHANCE OF SHOWERS WITH
TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL. ALBRECHT

&&

.AVIATION...AN UPPER LEVEL RIDGE IS OVER THE PACNW. FAIR SKIES WITH
A DRY STABLE AIR MASS WILL REMAIN IN PLACE. THE FLOW ALOFT IS NW
WITH JUST A LITTLE CIRRUS.

KSEA...A LITTLE CIRRUS...NORTHERLY BREEZE.

&&

.MARINE...HIGH PRESSURE EXTENDS NORTH ALONG 130W...THROUGH QUEEN
CHARLOTTE SOUND...AND INTO CENTRAL BRITISH COLUMBIA. THERE IS
THERMALLY INDUCED LOW PRESSURE OVER CALIF AND THAT EXTENDS NORTH
ALONG THE COAST. ONSHORE FLOW SHOULD DEVELOP MONDAY EVENING AND THEN
INCREASE TUESDAY AS A FRONT REACHES THE AREA...WITH WLY GALES
POSSIBLE IN THE STRAIT. ONSHORE FLOW WILL CONTINUE THROUGH THE END
OF THE WEEK.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&




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