Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 040333
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
833 PM PDT MON AUG 3 2015

.SYNOPSIS...AN UPPER TROUGH WILL BE OVER THE AREA THROUGH MIDWEEK.
WEAK HIGH PRESSURE ALOFT WILL MOVE OVERHEAD LATE IN THE
WEEK...FOLLOWED BY ANOTHER UPPER TROUGH NEXT WEEKEND.

&&

.SHORT TERM...AN UPPER TROUGH WILL BE OVER THE PACIFIC NORTHWEST
THROUGH WEDNESDAY WITH LOW LEVEL ONSHORE FLOW. EXPECT LOW CLOUDS
TO DEVELOP AND SPREAD INLAND TONIGHT WITH AFTERNOON SUNSHINE
TUESDAY FOR INLAND AREAS. WEDNESDAY LOOKS A BIT CLOUDIER AS THE
UPPER TROUGH DEEPENS OVER THE REGION. THERE MIGHT ALSO BE SOME
SHOWERS ON WEDNESDAY. HIGHS WILL BE NEAR NORMAL TUESDAY...AND
PROBABLY COOL AT LEAST A FEW DEGREES TO A LITTLE BELOW NORMAL ON
WEDNESDAY.

A WEAK UPPER RIDGE WILL MOVE OVER THE AREA ON THURSDAY. THIS
SHOULD EFFECTIVELY END THE SHOWER THREAT AND THERE SHOULD BE MORE
SUNSHINE AGAIN BY AFTERNOON. HIGHS WILL LIKELY WARM BACK TO NEAR
NORMAL. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...WEAK HIGH PRESSURE ALOFT IS
ANTICIPATED TO PREVAIL OVER THE REGION ON FRI. THIS COMBINED WITH
WEAK LOW LEVEL ONSHORE FLOW WILL LEAD TO SLIGHTLY ABOVE NORMAL
TEMPS.

BEYOND FRI...THE MEDIUM RANGE SOLUTIONS WERE IN FAIRLY GOOD
AGREEMENT THAT AN UPPER TROF WILL DOMINATE THE WEATHER PATTERN
OVER THE PACIFIC NORTHWEST. THE MAIN DIFFERENCES WERE IN THE
DETAILS. THE MODELS PREDICTED MAX TEMPS APPEARED TOO WARM IN
LIGHT OF THE PATTERN BEING ADVERTISED...THUS TOOK A RISK AND
UNDERCUT GUIDANCE. THE CURRENT FORECAST INDICATED BELOW NORMAL
DAYTIME TEMPS FOR SATURDAY THROUGH MON.

&&

.AVIATION...A LARGE UPPER LEVEL LOW WILL REMAIN CENTERED OVER
CENTRAL BRITISH COLUMBIA THROUGH TUESDAY WITH AN UPPER LEVEL
TROUGH EXTENDING S OVER W WA. FLOW ALOFT WILL BE WESTERLY.

STRONG LOW LEVEL ONSHORE FLOW HAS DEVELOPED ACROSS W WA THIS
EVENING...ASSOCIATED WITH A WEAK DRY FRONT THAT IS CROSSING THE
AREA. THE ONSHORE FLOW WILL SPREAD MARINE MOISTURE INLAND IN A
RATHER DEEP MARINE LAYER OVERNIGHT. THIS SHOULD ALLOW AREAS OF MVFR
STRATUS TO FORM EARLY TUESDAY MORNING. THE AIR MASS OVER W WA AT
0230Z DID NOT HAVE A LOT OF CLOUD COVER...WITH ONLY PATCHY STRATUS
PRESENT ALONG THE COAST. THE LACK OF VISIBLE MOISTURE SUPPORTS LESS
EXTENSIVE STRATUS TUESDAY MORNING AND A LITTLE EARLIER BURN-OFF.

KSEA...GOOD VFR CONDITIONS TONIGHT WITH ONLY SCATTERED CIRRUS. MVFR
STRATUS WILL FORM LATE TONIGHT WITH BASES AROUND OVC015. THE STRATUS
IS EXPECTED TO LIFT THROUGH MID MORNING THEN CLEAR OUT AROUND 18Z-
19Z. SURFACE WINDS WILL BE A LITTLE SQUIRRELLY THIS EVENING BECAUSE
KSEA IS IN-BETWEEN THE SW FLOW COMING UP FROM TACOMA AND THE N FLOW
COMING S FROM SEATTLE. THE WINDS SHOULD BE PREDOMINANTLY W-SW 4-8 KT
BUT COULD HAVE BRIEF PERIODS OF NW TO N WINDS. KAM

&&

.MARINE...A LARGE PERSISTENT SURFACE RIDGE CENTERED WELL OFFSHORE...
COMBINED WITH LOWER PRESSURE OVER E WA WILL PRODUCE MODERATE TO
STRONG ONSHORE FLOW THROUGH THIS WEEK. THE WESTERLY ONSHORE FLOW
WILL BE STRONGEST DURING THE LATE AFTERNOON AND EVENING HOURS IN THE
CENTRAL AND E STRAIT OF JUAN DE FUCA. THE 18Z GFS SHOWS THE UIL-BLI
PRESSURE GRADIENT PEAKING NEAR 4 MB TONIGHT AND TUESDAY
EVENING...THEN PEAKING A LITTLE LOWER AROUND 3 MB WEDNESDAY AND
THURSDAY. THIS WOULD PUT THE WINDS IN THE STRAIT IN GALE FORCE RANGE
TUESDAY NIGHT AND IN BORDERLINE GALE RANGE AFTER THAT.

FOR TONIGHT...A GALE WARNING IS IN EFFECT UNTIL 5 AM PDT TUE FOR THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA. GALES ARE POSSIBLE TUE
NIGHT AS WELL. SMALL CRAFT ADVISORY NW WINDS ARE EXPECTED IN
ADJACENT ADMIRALTY INLET.

SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS BEYOND
10 NM FROM THE COASTLINE AS NW FLOW INCREASES THIS EVENING THROUGH
TUESDAY MORNING. WINDS IN THE COASTAL WATERS WILL RELAX MIDDAY
TUESDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 11 AM PDT TUESDAY FOR COASTAL WATERS
     FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
     WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
     COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10
     TO 60 NM.

     GALE WARNING UNTIL 5 AM PDT TUESDAY FOR CENTRAL U.S. WATERS
     STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF
     JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 3 AM PDT TUESDAY FOR ADMIRALTY INLET.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS 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.