Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KSEW 020440
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
940 PM PDT MON JUN 1 2015

.SYNOPSIS...AN UPPER LEVEL TROUGH OVER WESTERN WASHINGTON TONIGHT
WILL REMAIN OVER THE REGION THROUGH WEDNESDAY NIGHT. SHOWERS WILL
CONTINUE TONIGHT AND TUESDAY THEN GRADUALLY DIMINISH THROUGH
WEDNESDAY NIGHT AS THE TROUGH WEAKENS. AN UPPER LEVEL RIDGE WILL
BUILD OVER THE REGION LATE THIS WEEK FOR SUNNY AND WARMER WEATHER
THROUGH THIS WEEKEND.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS WEAK UPPER LEVEL LOW OVER THE
SOUTH PUGET SOUND EMBEDDED IN A BROAD UPPER LEVEL TROUGH OVER THE
AREA. DOPPLER RADARS SHOW SHOWER ACTIVITY FROM SNOHOMISH COUNTY
NORTHWARD AND IN THE VICINITY OF THE UPPER LEVEL LOW. WITH CLOUDY
SKIES OVER THE AREA TEMPERATURES RANGED FROM THE MID 50S TO THE
LOWER 60S AT 9 PM.

NOTHING NEW IN THE 00Z MODEL RUNS WITH THE BROAD UPPER LEVEL
TROUGH OVER WESTERN WASHINGTON REMAINING PLACE OVER THE AREA THROUGH
WEDNESDAY BEFORE WEAKENING AND EVENTUALLY DISSIPATING WEDNESDAY
NIGHT. HRRR MODEL RUNS SHOW SHOWER ACTIVITY CONTINUING ACROSS
WESTERN WASHINGTON OVERNIGHT WITH JUST LIGHT PRECIPITATION AMOUNTS.
IN THE LOWER LEVELS WEAK ONSHORE FLOW CONTINUING THROUGH TUESDAY
KEEPING THE AIR MASS MOIST. LIFTED INDEXES OVER WESTERN WASHINGTON
STAY POSITIVE IN THE LOWLANDS THROUGH TUESDAY WITH THE CONVECTIVE
TEMPERATURES NEAR 60 DEGREES. EXPECT AN INCREASE IN THE SHOWER
ACTIVITY LATE IN THE DAY WITH SOME DAYTIME HEATING. HIGHS WITH
PLENTY OF CLOUD COVER AND SHOWER ACTIVITY WILL ONLY CREEP INTO THE
LOWER 60S AT BEST...5 DEGREES OR SO BELOW NORMAL FOR THIS TIME OF
YEAR.

LOW LEVEL ONSHORE FLOW CONTINUING TUESDAY NIGHT INTO WEDNESDAY WITH
THE TROUGH SLOWLY WEAKENING. SHOWER ACTIVITY WILL DECREASE BUT AS
LONG AS THE TROUGH IS OVERHEAD WILL HAVE TO KEEP A CHANCE OF SHOWERS
IN THE FORECAST. TEMPERATURES WITH THE PLENTY OF MOISTURE IN THE
LOWER LEVELS WILL ONCE AGAIN BE BELOW NORMAL...JUST A COUPLE OF
DEGREES WARMER THAN WEDNESDAY.

UPPER LEVEL TROUGH DISSIPATING WEDNESDAY NIGHT WITH THE FLOW
ALOFT BECOMING NORTHWESTERLY AND 500 MB HEIGHTS RISING INTO THE LOW
570 DMS THURSDAY. HIGHS ON THURSDAY WILL BE AT LEAST 5 DEGREES
WARMER THAN WEDNESDAY WITH THE WARMER LOCATIONS GETTING BACK UP INTO
THE 70S. THURSDAY MARKS THE BEGINNING OF A WARMING TREND OVER THE
AREA. THE TREND WILL PEAK ON SUNDAY WITH THE POSSIBILITY OF THE
WARMEST DAY OF THE YEAR SO FAR.

CURRENT FORECAST HAS THE TRENDS COVERED. NO UPDATE THIS EVENING.
FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. MODELS ARE IN GOOD
AGREEMENT THAT A FAIRLY STRONG UPPER LEVEL RIDGE WILL BUILD JUST
OFFSHORE FRIDAY THROUGH THIS WEEKEND. 500 MB HEIGHTS WILL CLIMB
ABOVE 5800 METERS SATURDAY AFTERNOON THROUGH MONDAY. WEAKER NW
ONSHORE FLOW WILL DEVELOP THURSDAY EVENING THEN CONTINUE THROUGH
SATURDAY...ALLOWING MAX TEMPS TO WARM INTO THE 70S TO LOWER 80S.
NORTHERLY OFFSHORE FLOW WILL DEVELOP SATURDAY NIGHT WHICH SHOULD
PUSH THE WARMEST SPOTS INTO THE MID 80S AND POSSIBLY THE UPPER 80S
ON SUNDAY. KAM

&&

.CLIMATE...THE AVERAGE TEMPERATURE FOR MAY IN SEATTLE WAS 59.1
DEGREES. THIS TIED LAST YEAR FOR THE 5TH WARMEST MAY AT
SEATTLE-TACOMA AIRPORT. THIS IS THE THIRD YEAR IN A ROW WITH A TOP
TEN WARMEST MAY. 2013 WAS THE 7TH WARMEST MAY AT SEA-TAC WITH 58.6
DEGREES.

IN ADDITION TO THE WARM TEMPERATURES MAY WAS ALSO VERY DRY WITH ONLY
0.58 INCHES OF RAIN AT SEA-TAC. THIS IS THE 5TH DRIEST MAY ON RECORD
AND THE DRIEST MAY SINCE THE RECORD WAS SET BACK IN 1992 WITH 0.12
INCHES. FELTON

&&

.AVIATION...THE AIR MASS WILL REMAIN MOIST AND SLIGHTLY UNSTABLE
TONIGHT AS AN UPPER LEVEL TROUGH AXIS MOVES NORTH THROUGH
WASHINGTON. EXPECT SCATTERED SHOWERS ACROSS THE REGION WITH A FEW
THUNDERSTORMS OVER THE CASCADES. THE FLOW ALOFT IS SOUTHERLY.
MEANWHILE...LOW LEVEL ONSHORE FLOW WILL CONTINUE WITH MVFR CIGS
EXPECTED THROUGH TUE MORNING. SHOWERS WILL CONTINUE ON TUESDAY AS
THE UPPER LEVEL LOW SPINS OVERHEAD. 33

KSEA...MVFR CIGS EXPECTED TONIGHT WITH SHOWERS IN THE VICINITY.
SURFACE WINDS WILL REMAIN SOUTHERLY TO 10 KT. 33

&&

.MARINE...LOW LEVEL ONSHORE FLOW WILL PREVAIL ACROSS WESTERN WA THIS
WEEK WITH HIGH PRES OFFSHORE AND LOWER PRES EAST OF THE CASCADES.
HIGHEST WIND AND WAVES WILL BE FOUND THROUGH THE CENTRAL AND EASTERN
STRAIT OF JUAN DE FUCA DURING THE AFTERNOON AND EVENING HOURS. THE
LOW LEVEL FLOW WILL TURN MORE NORTHERLY THIS WEEKEND AS LOW PRES
FORMS ALONG THE COAST. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL STRAIT...EASTERN STRAIT...AND
     NORTHERN INLAND WATERS.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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













USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.