Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 121558
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SAT APR 12 2014

.SYNOPSIS...CLOUDS THIS MORNING WILL GIVE WAY TO MOSTLY SUNNY SKIES
IN THE AFTERNOON AS DRIER AIR ARRIVES FROM THE NORTH. A STRONG UPPER
LEVEL RIDGE AND OFFSHORE FLOW WILL GIVE WARMING AND DRYING SUNDAY
AND MONDAY. CLOUDS AND AN INCREASING CHANCE OF SHOWERS ARE EXPECTED
MONDAY NIGHT THROUGH THE MIDDLE OF NEXT WEEK AS THE UPPER RIDGE
MOVES OFF TO THE EAST AND PACIFIC SYSTEMS APPROACH FROM THE WEST.

&&

.SHORT TERM...VISIBLE SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES
THIS MORNING WITH SOME CLEARING IN THE NORTH. NORTHERLY FLOW WILL
SLOWLY CLEAR SKIES FROM NORTH TO SOUTH TODAY. HIGHS WILL BE MAINLY
IN THE 60S.

SUNDAY LOOKS WARMER AS THE UPPER RIDGE BUILDING OFFSHORE SHARPENS
AND MOVES EAST. AT THE SAME TIME NORTHERLY SURFACE FLOW GAINS A MORE
OFFSHORE COMPONENT. THIS WILL GIVE SUNNY SKIES WITH HIGHS 65 TO 70.
NOTE THE NEW NAM MOS HAS A HIGH OF 70 AT KSEA.

ON MONDAY AN UPPER LEVEL LOW MOVES BY TO THE NORTH. FLOW AT THE
SURFACE TURNS STRONGLY ONSHORE AND HEIGHTS FALL SIGNIFICANTLY. THIS
PROBABLY MEANS THERE WILL BE CLOUDS ON THE COAST WHILE REMAINING
MOSTLY SUNNY INLAND. HIGHS WILL BE 5-10 DEGREES LOWER THAN SUNDAY.
MODELS THEN BRING SOME LIGHT RAIN MONDAY NIGHT. BURKE

.LONG TERM...PREVIOUS DISCUSSION...A MORE ZONAL PATTERN BEGINS
MONDAY NIGHT AND CONTINUES THROUGH THE END OF NEXT WEEK...RETURNING
THE WEATHER TO A CLOUDIER ONE WITH COOLER HIGH TEMPERATURES AND A
CHANCE OF SHOWERS. THE LATEST GFS SOLUTION PROMISES A SHORT WAVE
RIDGE ON WEDNESDAY FOR A SUNNIER AND WARMER DAY...BUT THE ECMWF AND
CANADIAN SOLUTIONS BRING A FRONTAL WAVE IN FROM THE WEST. GIVEN THE
RATHER HIGH UNCERTAINTY ON FEATURES IMPACTING THE AREA AFTER MONDAY
NIGHT OR TUESDAY...THE EXTENDED FORECAST WAS NOT CHANGED EARLY THIS
MORNING. ALBRECHT

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY ON AREA RIVERS...EXCEPT THE
NORTH FORK OF THE STILLAGUAMISH EAST OF OSO...FOR THE NEXT 7 DAYS.

A FLOOD WARNING REMAINS IN EFFECT UNTIL FURTHER NOTICE FOR THE
NORTH FORK OF THE STILLAGUAMISH RIVER IN SNOHOMISH COUNTY JUST
UPSTREAM OF THE SR 530 LANDSLIDE. FLOODING CONTINUES AS A RESULT
OF WATER POOLED BEHIND THE DEBRIS DAM THAT PARTIALLY BLOCKS THE
RIVER.

THE NORTH FORK OF THE STILLAGUAMISH NEAR ARLINGTON AND THE POOL
UPSTREAM OF THE SR 530 SLIDE WILL CONTINUE FALLING THROUGH MONDAY AS
A STRONG UPPER LEVEL RIDGE BRINGS DRY WEATHER TO THE AREA. A SHIFT
TO A WESTERLY FLOW PATTERN MONDAY NIGHT AND TUESDAY WILL BRING A
CHANCE OF RAIN BACK INTO THE AREA. AT THIS TIME...RAINFALL WITH
SYSTEMS MONDAY NIGHT THROUGH THE END OF NEXT WEEK ARE NOT EXPECTED
TO BE HYDROLOGICALLY SIGNIFICANT. ALBRECHT

&&

.AVIATION...CLOUDS THIS MORNING WILL GIVE WAY TO MOSTLY SUNNY SKIES
THIS AFTERNOON. IT WILL BE MOSTLY CLEAR TONIGHT AND SUNDAY WITH DRY
AIR AND NORTHERLY FLOW ALOFT.

KSEA...MORNING CLOUDS WILL LIFT AND SCATTER OUT BY AFTERNOON. CLEAR
TONIGHT AND SUNDAY. NORTHERLY PRESSURE GRADIENTS WILL INCREASE THIS
AFTERNOON AND EVENING.

&&

.MARINE...NORTHERLY FLOW WILL INCREASE THIS AFTERNOON AND PEAK THIS
EVENING. THEN GRADIENTS WILL WEAKEN AND TURN MORE EASTERLY ON SUNDAY
OVER WESTERN WA AS THERMALLY INDUCED LOW PRESSURE SETS UP ALONG THE
OREGON COAST FOR A DAY. ONSHORE FLOW WILL DEVELOP MONDAY AFTERNOON
AND EVENING AS A WEATHER SYSTEM REACHES THE AREA. THE LATEST NAM
SHOWS 1028 MB HIGH PRESSURE OVER BRITISH COLUMBIA SUNDAY GIVING WAY
TO A 1005 MB LOW MONDAY EVENING WHICH GIVES THE ONSHORE FLOW.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNING REMAINS IN EFFECT FOR THE NORTH FORK OF THE
     STILLAGUAMISH RIVER EAST OF THE SR 530 LANDSLIDE.

PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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





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