Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 040327
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 PM PDT SUN MAY 3 2015

.SYNOPSIS...HIGH PRESSURE OVER THE PACIFIC NORTHWEST WILL PRODUCE
DRY WEATHER TONIGHT. A FRONT WILL APPROACH THE REGION MONDAY WITH
INCREASING CLOUDS. LOW PRESSURE WILL BRING SHOWERS AND COOLER
TEMPERATURES MONDAY NIGHT THROUGH WEDNESDAY. MOUNTAIN SHOWERS WILL
LINGER THROUGH FRIDAY BUT IT WILL BE MOSTLY DRY ACROSS THE LOWLANDS.

&&

.SHORT TERM...HIGH PRESSURE ALOFT WILL SHIFT INLAND TONIGHT AS AN
UPPER TROUGH APPROACHES FROM THE WEST. LOW LEVEL ONSHORE FLOW IS
STRONGER TONIGHT AND LOW CLOUDS SHOULD DEVELOP AT THE COAST BY
MORNING.

HIGHS WILL COOL SEVERAL DEGREES MONDAY WITH STRONGER LOW LEVEL
ONSHORE FLOW. THE COAST WILL BE CLOUDY WITH A LITTLE RAIN LIKELY BY
LATE AFTERNOON AS A RAGGED FRONT REACHES THE AREA. THE INTERIOR WILL
EXPERIENCE ANOTHER MOSTLY SUNNY DAY.

THE FRONT WILL MOVE INLAND MONDAY EVENING...BRINGING SHOWERS AND
CLOUDS. AN UPPER LOW WILL SETTLE OVER WESTERN WASHINGTON TUESDAY.
SHOWERS WILL REMAIN LIKELY AND HIGHS WILL COOL TO 55 TO 60 WHICH IS
SLIGHTLY BELOW NORMAL. SNOW LEVELS WILL LOWER TO AROUND 4000 FEET
AND THERE MIGHT BE SOME MINOR ACCUMULATIONS ABOVE THAT LEVEL. THERE
IS ALSO A THREAT OF THUNDERSTORMS TUESDAY WITH UNSTABLE AIR IN PLACE.

SHOWERS WILL TAPER AND MOSTLY END TUESDAY NIGHT WITH THE LOSS OF
DAYTIME HEATING AND AS THE UPPER LOW STARTS TO SHIFT EAST AND SOUTH.
THE UPPER LOW WILL REMAIN CLOSE ENOUGH ON WEDNESDAY THAT SHOWERS
WILL BUBBLE BACK UP ACROSS THE AREA WITH THE BEST CHANCES NEAR THE
CASCADES. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...AN UPPER LEVEL RIDGE WILL BUILD
OFFSHORE ON THURSDAY WITH FLOW ALOFT OVER WESTERN WA BECOMING
NORTHERLY. THE UPPER LEVEL LOW WILL SHIFT SOUTH INTO OREGON BUT
THERE REMAINS ENOUGH LIFT AND MOISTURE FOR A FEW SHOWERS IN WESTERN
WA...MAINLY IN THE CASCADES. THERE ARE 20 POPS FOR THE INTERIOR FOR
ISOLATED SHOWERS.

WEAK LOW PRESSURE IN EASTERN WA MAY TRIGGER A FEW MORE SHOWERS IN
THE CASCADES FRIDAY AND SATURDAY...OTHERWISE THE LOWLANDS ARE
LOOKING DRY. A WEAK FRONT MAY CROSS THE AREA SUNDAY OR SUNDAY NIGHT
HOWEVER THE TIMING IS OFF IN THE MODELS. THUS NO MAJOR CHANGES JUST
YET. 33

&&

.AVIATION...COASTAL LOW CLOUDS WILL FORM TONIGHT BUT THE MARINE
LAYER WILL BE SHALLOW AND THERE SHOULD ONLY BE A FEW PATCHES OF LOW
CLOUDS OR FOG PUSHING INTO THE INTERIOR OF WESTERN WA MONDAY
MORNING. AN UPPER TROUGH WILL SHIFT OVER THE PACIFIC NORTHWEST
THROUGH TUESDAY. SW FLOW ALOFT. ONSHORE FLOW WILL STRENGTHEN MONDAY
AND A WEAK COLD FRONT WILL BRING SOME RAIN TO THE COAST IN THE
AFTERNOON WITH SHOWERS PUSHING INTO THE INTERIOR OF WESTERN WA
MONDAY NIGHT AND TUESDAY AS THE UPPER TROUGH SHIFTS OVER THE AREA.

KSEA...PATCHES OF MORNING LOW CLOUDS SHOULD NOT AMOUNT TO MUCH
MONDAY MORNING. BUT THE CLOUDS WILL EVENTUALLY INCREASE BY ABOUT
MONDAY EVENING WITH AN INCREASING CHANCE OF SHOWERS THROUGH MONDAY
NIGHT AS A WEAK COLD FRONT AND THEN AN UPPER TROUGH PUSH INTO THE
AREA.

&&

.MARINE...A COLD FRONT JUST OFFSHORE SHOULD REACH THE COAST MONDAY
AFTERNOON. ONSHORE FLOW WILL STRENGTHEN TONIGHT AND MONDAY. A TROUGH
WILL MOVE GRADUALLY OVER THE AREA THROUGH TUESDAY FOR A COOL SHOWERY
DAY WITH EASING PRESSURE GRADIENTS.

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

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