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000
FXUS66 KSEW 241021
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT THU MAY 23 2013

.SYNOPSIS...A SLOW MOVING COLD UPPER-LEVEL LOW WILL CONTINUE TO
PRODUCE SHOWERS ACROSS THE REGION TODAY. THE UPPER LOW WILL NOODLE
AROUND THE NORTHWEST INTO THE MEMORIAL DAY WEEKEND AS IT SLOWLY
FILLS AND WEAKENS. A WEAK FRONTAL SYSTEM WILL APPROACH THE REGION ON
MEMORIAL DAY BUT MAY SHIFT SOUTH INTO OREGON.

&&

.SHORT TERM...THE CLOSED UPPER LEVEL LOW THAT HAS BEEN SPINNING OVER
WESTERN WA WILL SHIFT INTO EASTERN WA TODAY. MODELS STILL GENERATE
ISOLATED TO SCATTERED SHOWERS ACROSS THE REGION...BUT PRECIP AMOUNTS
LOOK PRETTY LIGHT. POPS ARE HIGHEST OVER THE COAST AND SOUTH PART.
THE RADAR COMPOSITE SHOWS RAIN ALONG THE WA/OR BORDER THIS MORNING.
THE THREAT OF T-STORMS IS LOW AND MAINLY EAST OF THE CREST TODAY.
TEMPERATURES ARE STILL COOL ALOFT WITH 500 MB TEMPS IN THE -20S.
SURFACE TEMPS IN THE MID TO UPPER 50S LOOKS GOOD...WITH A FEW LOW
60S POSSIBLE.

THIS SYSTEM WILL ROTATE NORTH INTO B.C./ALBERTA OVER THE WEEKEND FOR
A MODEST WARM-UP...TEMPS ARE CLOSER TO NORMAL. THE MODELS STILL SHOW
A WEAK TROUGH OVER WESTERN WA FOR A CHANCE OF SHOWERS...BUT LOOKS
LIKE JUST ISOLATED COVERAGE. SNOW LEVELS WILL RISE TO 5000-6000 FT
IN THE MOUNTAINS.

MODELS ARE BACKING OFF ON THE NEXT INCOMING SYSTEM SLATED FOR
MEMORIAL DAY. THE ECMWF IS PUSHING THIS NEXT SYSTEM FARTHER SOUTH
WHICH WILL MAINLY AFFECT OREGON. BUT THE 00Z GFS AND NAM STILL SOME
MOISTURE REACHING THE AREA DURING THE DAY. SO WILL STICK WITH A
BLEND FOR NOW...CLOUDY WITH A CHANCE OF RAIN. BUT IF EVERYTHING
TRENDS TOWARD THE EURO THEN LOOK FOR A MAINLY DRY HOLIDAY.

.LONG TERM...COOL ONSHORE FLOW WILL PREVAIL THROUGH THE REST OF THE
WEEK FOR MOSTLY CLOUDY SKIES AND TEMPS NEAR NORMAL. MODELS SHOW A
LONG WAVE TROUGH OVER THE PAC NW FOR ADDITIONAL SHOWERS ACROSS THE
REGION...AT LEAST THROUGH MIDWEEK. WEAK RIDGING MAY BRING DRIER
WEATHER BY THU OR FRI. 33

&&

.AVIATION...AN UPPER LEVEL TROUGH OVER WA WILL SLOWLY MIGRATE EWD
LATER TODAY AND TONIGHT. LIGHT VARIABLE FLOW BECOMING SWLY THIS
AFTERNOON. MOIST AND SLIGHTLY UNSTABLE. SHOWERS...DECREASING LATER
TONIGHT. LESS THAN A 10 PERCENT CHANCE OF ISOLATED THUNDERSTORMS
THIS AFTERNOON/EARLY EVENING.

KSEA...VARIABLE OR N WIND TO 5 KT...BECOMING S 5 TO 8 KT AFTER 13Z.
A MIX OF LOW VFR...OR MVFR DURING SHOWERS. MAINLY VFR CIGS AFTER 18Z.

&&

.MARINE...LIGHTER GRADIENTS AND WINDS OVER THE WA WATERS TODAY AS
LOW PRESSURE OFF ASTORIA FILLS AND MOVES INLAND. WEAK ONSHORE FLOW
LATER TODAY INCREASES A BIT TONIGHT THROUGH THE WEEKEND. THERE WILL
BE A RISK FOR LOW END SMALL CRAFT WINDS IN THE CENTRAL/E STRAIT THE
NEXT COUPLE EVENINGS.

THE NEXT ORGANIZED FRONT REACHES THE WATERS ON MONDAY WITH SMALL
CRAFT WINDS PROBABLE OVER THE COASTAL WATERS AND POSSIBLY SOME OF
THE INTERIOR WATERS.

&&

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

&&

$$

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