Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 061617
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
917 AM PDT MON JUL 6 2015

.SYNOPSIS...THE STRONG UPPER LEVEL RIDGE OVER THE REGION WILL WEAKEN
GRADUALLY THIS WEEK ALLOWING DAILY TEMPERATURES TO COOL VERY SLOWLY.
A LARGE UPPER LEVEL TROUGH WILL DEVELOP JUST OFFSHORE ON FRIDAY
WHICH WILL PRODUCE MORE NORMAL SUMMER WEATHER THIS WEEKEND.

&&

.SHORT TERM...A FAIRLY STRONG UPPER LEVEL LONGWAVE RIDGE REMAINS IN
PLACE JUST W OF THE B.C. COAST THIS MORNING WITH NW FLOW ALOFT DOWN
THE E SIDE OF THE RIDGE OVER W WA. 500 MB HEIGHTS ARE STILL SOMEWHAT
HIGH AT CLOSE TO 5850 METERS. THE GFS AND ECMWF ARE IN GOOD
AGREEMENT THAT THE RIDGE WILL SLOWLY COLLAPSE THIS WEEK. THERE WILL
BE SLIGHT AIR MASS COOLING ON TUESDAY RESULTING FROM A COUPLE OF
WEAK UPPER LEVEL SHORTWAVE TROUGHS MOVING SE ACROSS THE AREA. ONE OF
THE TROUGHS WHICH SHOULD BE OVER THE YUKON THIS MORNING COULD
TRIGGER SOME ISOLATED CONVECTION OVER THE N CASCADES TUESDAY
AFTERNOON AND EVENING.

THE UPPER LEVEL RIDGE WILL CONTINUE COLLAPSING WEDNESDAY...BUT
PROGRESSES E OVER B.C. AND THE PACNW...FOR SLIGHTLY HIGHER 500 MB
HEIGHTS AND BRIEF AIR MASS WARMING. MAX TEMPS WILL PROBABLY BE IN
THE 80S TO NEAR 90.

ONSHORE FLOW THE NEXT COUPLE OF DAYS WILL BE A BIGGER FACTOR THAN
OVER THE WEEKEND. ONSHORE FLOW LAST NIGHT WAS A LITTLE STRONGER THAN
OVER THE WEEKEND AND WITH A WEAK SW COMPONENT MANAGED TO PUSH A
SHALLOW STRATUS LAYER INLAND OVER THE SW PART OF PUGET SOUND THIS
MORNING. IT LOOKS LIKE A REPEAT TONIGHT...AND BOUNDARY LAYER RH
PROGS FROM THE NAM AND ARW MODELS SUGGEST SLIGHTLY GREATER STRATUS
COVERAGE TUESDAY MORNING. THIS WILL HELP MAKE TUESDAY SLIGHTLY
COOLER...ALTHOUGH MAX TEMPS WILL STILL BE IN THE 80S.

ONSHORE FLOW TUESDAY NIGHT SHOULD BE WEAKER AND FROM THE NW...SO
STRATUS SHOULD BE MINIMAL OVER THE INTERIOR WEDNESDAY MORNING. AS
MENTIONED ABOVE...WITH THE WEAKENING RIDGE STILL OVER THE AREA...MAX
TEMPS WILL BE IN THE 80S TO NEAR 90.

THERE IS STILL SMOKE FROM THE B.C. FOREST FIRES OVER THE N HALF OF W
WA THIS MORNING. ON VISIBLE IMAGERY IT LOOKS LIKE IT IS SLOWLY
THINNING OUT. SW FLOW ALOFT TODAY BELOW 700 MB SHOULD HELP CLEAR THE
LOWER LEVELS...BUT AT ONLY 5-10 KT THE PROCESS WILL BE SLOW. FLOW
ABOVE 700 MB SHOULD BE NW 10-20 KT. NAM MODELS SHOWS THE LOWER LEVEL
FLOW TURNING E-NE ON TUESDAY...SO DEPENDING UPON HOW MUCH SMOKE THE
FIRES PUT OUT TONIGHT ANOTHER INCREASE IS POSSIBLE AGAIN ON TUESDAY.
KAM

.LONG TERM...THURSDAY WILL PROBABLY BE THE LAST HURRAH OF THE RECENT
EXTENDED WARM STRETCH. THE RIDGE WILL BE ALMOST GONE WITH 500 MB
HEIGHTS DOWN TO NEAR 5760 METERS THURSDAY AFTERNOON. HOWEVER THE AIR
MASS WILL STILL BE VERY WARM SO MAX TEMPS MAY ONLY BE A DEGREE OR SO
COOLER THAN WEDNESDAY. STRENGTHENING SW ONSHORE FLOW THURSDAY NIGHT
AS A LARGE UPPER LEVEL TROUGH APPROACHES FROM THE W WILL HASTEN THE
COOLING. SHALLOW STRATUS WILL PROBABLY COVER MOST OF THE INTERIOR
LOWLANDS FRIDAY MORNING. MOS GUIDANCE SHOWS MAX TEMPS RETREATING
INTO THE 70S. FOR THIS WEEKEND...CONTINUING SW ONSHORE FLOW AND THE
UPPER LEVEL TROUGH JUST W OF THE WA COAST SHOULD PRODUCE TYPICAL
SUMMER WEATHER...MORNING CLOUDS...SOME AFTERNOON SUNSHINE AND MAX
TEMPS IN THE 70S. KAM

&&

.AVIATION...THERE IS MARINE STRATUS AND FOG ON THE COAST AND OVER
PTNS OF SW WA THIS MORNING...THE LOW CLOUDS EXTEND THROUGH THE NORTH
COAST AND PARTLY IN THE STRAIT OF JUAN DE FUCA. ELSEWHERE THERE ARE
FAIR SKIES WITH SOME B.C. SMOKE...ESPECIALLY ACROSS THE NORTH
CASCADES. NOT MUCH CHANGE IS EXPECTED FOR THE NEXT COUPLE OF DAYS
WITH THE MARINE AIR MAINLY STAYING ON THE COAST AND THEN MORNING LOW
CLOUDS IN THE STRAIT AND SPILLING INTO PUGET SOUND FOR A FEW HOURS
AROUND DAYBREAK.


KSEA...THE MARINE AIR THAT SPILLED INTO PUGET SOUND OVERNIGHT IS
GIVING A SSW BREEZE THAT WILL BECOME LIGHT AND VARIABLE LATER TODAY.

&&

.MARINE...LOW CLOUDS AND FOG PATCHES FOR THE COAST AND WESTERN
STRAIT. THERE IS HIGH PRESSURE ALONG THE COAST AND LOWER PRES E OF
THE CASCADES WILL RESULTING IN ONSHORE FLOW THROUGH FRI. THE
AFTERNOON AND EVENING WLY IN THE STRAIT MAY GET UP TO GALE
FORCE...ESPECIALLY AROUND RACE ROCKS.

&&

.SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT
ADVISORY UNTIL 3 AM PDT TUESDAY FOR      CENTRAL U.S. WATERS STRAIT
OF JUAN DE FUCA-EAST ENTRANCE      U.S. WATERS STRAIT OF JUAN DE
FUCA.

&&

$$

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