National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSEW 301330
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
355 AM PDT WED JUL 30 2014

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BRING WARM SUNNY DAYS TO
WESTERN WASHINGTON THROUGH EARLY NEXT WEEK. LIGHT ONSHORE FLOW WILL
RESULT IN SOME NIGHT AND MORNING LOW CLOUDS...ESPECIALLY ALONG THE
COAST.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLEAR SKIES OVER THE INTERIOR.
NORTHERLY WINDS RIGHT ABOVE THE SURFACE HAS BROKEN UP THE LOW CLOUDS
ALONG THE NORTH COAST WITH THE HIGHEST CONCENTRATION OF THE LOW
CLOUDS ALONG THE CENTRAL COAST AND LOWER CHEHALIS VALLEY (PIC0)
TEMPERATURES AT 3 AM RANGED FROM NEAR 50 AT FORKS AND FRIDAY HARBOR
TO THE MID 60S IN THE SEATTLE METRO AREA.

LITTLE CHANGE IN THE PATTERN BOTH SURFACE AND ALOFT FOR THE NEXT
THREE DAYS (PIC1)(PIC2)(PIC3) WITH LIGHT ONSHORE FLOW AT THE SURFACE
WITH SOUTHWESTERLY FLOW ALOFT WITH 500 MB HEIGHTS IN THE MID 580
DMS. THERE WAS A LITTLE SURGE OF MARINE AIR INTO THE INTERIOR LAST
NIGHT WITH GALE FORCE WINDS IN THE STRAIT OF JUAN DE FUCA. EVEN
THROUGH THE STRATUS DID NOT MAKE IT DOWN THE STRAIT OR MUCH FURTHER
EAST THAN SHELTON DEW POINTS THIS MORNING ARE 2 TO 6 DEGREES HIGHER
THAN LAST NIGHT OVER THE INTERIOR. MODEL 850 MB TEMPERATURES ARE A
TOUCH COOLER TODAY VERSUS THE LAST TWO DAYS. ADD THIS TO THE WEAK
MARINE AIR  INTRUSION WILL GO FOR A COUPLE OF DEGREES OF COOLING FOR
THE HIGHS ACROSS THE INTERIOR TODAY. MID 70S TO UPPER 80S WILL BE
COMMON. HIGH TEMPERATURES ALONG THE COAST AND NEAR THE STRAIT WILL
CONTINUE TO BE IN THE UPPER 60S TO MID 70S.

PRETTY MUCH A PERSISTENCE FORECAST TONIGHT THROUGH FRIDAY WITH THE
LOW CLOUDS FORMING ALONG THE COAST IN THE EVENING PUSHING INLAND
DOWN THE STRAIT AND THROUGH THE LOWER CHEHALIS VALLEY INTO THE VERY
SOUTHERN MOST PORTION OFT HE PUGET SOUND IN THE EARLY MORNING HOURS
EACH DAY. THE MARINE LAYER WILL BE SHALLOW WITH THE STRATUS BURNING
BACK TO THE COAST EACH MORNING. HIGHS ALONG THE COAST AND STRAIT
WILL REMAIN IN THE UPPER 60S TO MID 70S WITH HIGHS IN THE INTERIOR
IN THE MID 70S TO UPPER 80S.

A POSSIBLE EXCEPTION TO THE PERSISTENCE FORECAST IS OVER THE CENTRAL
WASHINGTON CASCADES. 00Z MODEL RUNS SHOW THE FLOW ALOFT BECOMING
SLIGHTLY MORE SOUTHERLY THURSDAY AFTERNOON THROUGH FRIDAY EVENING
OVER THE CENTRAL AND SOUTHERN WASHINGTON CASCADES. MONSOON MOISTURE
ROTATING NORTHWARD ALONG THE WEST SIDE OF THE UPPER LEVEL RIDGE  HAS
RESULTED IN ISOLATED THUNDERSTORMS AS NEAR AS THE OREGON CASCADES
THE LAST COUPLE DAYS. EVEN WITH THE SLIGHT CHANGE IN THE FLOW ALOFT
THE 00Z MODEL RUNS DO NOT HAVE ANY CONVECTION ON THIS SIDE OF THE
CASCADES THROUGH FRIDAY. FOR NOW WILL LEAVE THE FORECAST UNCHANGED.

.LONG TERM...ALL OF THE EXTENDED MODELS SHOWING A VERY WEAK FEATURE
MOVING UP OVER WESTERN WASHINGTON ON SATURDAY. THE ONLY POSSIBLE
CHANGE IN THE FORECAST THIS FEATURE COULD CAUSE WOULD BE AN INCREASE
IN THE CONVECTION OVER THE CASCADES. THE GFS SHOWS A LITTLE
SOMETHING OVER THE NORTH CASCADES ON SATURDAY (PIC4) WHILE THE REST
OF THE MODELS KEEP THE ACTIVITY NORTH AND EAST OF THE AREA. CURRENT
FORECAST JUST SHOWS AN INCREASE IN CLOUD COVER OVER THE MOUNTAINS ON
SATURDAY. GIVEN THE UNCERTAINTY IN THE MODELS THIS IS A GOOD WAY TO
GO AT THIS POINT. SOME MORE DIFFERENCES IN THE MODEL ON SUNDAY WITH
THE GFS (PIC5)(PIC6) AND CANADIAN KEEPING THE WEAK FEATURE IN THE
AREA WHICH WOULD KEEP A CHANCE OF CONVECTION IN THE MOUNTAINS. THE
ECMWF HAS THE FEATURE FURTHER EAST. GFS MAINTAINS SOME WEAK
TROUGHINESS INTO MONDAY (PIC7) WHILE THE ECMWF TURNS THE FLOW ALOFT
WESTERLY. CURRENT FORECAST JUST HAS INCREASING CLOUD COVER OVER THE
MOUNTAINS IN THE AFTERNOON. WILL STAY WITH THIS IDEA FOR THIS
FORECAST PACKAGE.

LITTLE CHANGE IN THE FORECAST FOR THE LOWLANDS. 500 MB HEIGHTS ARE A
LITTLE LOWER...IN THE LOWER 580 DMS AND ONSHORE GRADIENTS ARE A
LITTLE STRONGER FOR A CHANCE OF THE MORNING LOW CLOUDS GETTING
FURTHER INLAND BUT THE ONSHORE FLOW DOES NOT LOOK STRONG ENOUGH TO
KEEP THE STRATUS FROM BURNING BACK TO THE COAST EACH DAY. 00Z RUNS
MAX TEMPERATURE GUIDANCE IS A DEGREE OR TWO COOLER VERSUS THE RUNS
YESTERDAY MORNING. IF THIS TREND CONTINUES LOOK FOR THE MAX TEMPS TO
BE KNOCKED DOWN A COUPLE OF DEGREES FOR THE WEEKEND. EVEN WITH THE
COOLER MAX TEMPERATURES HIGHS SHOULD STILL BE NEAR TO A COUPLE OF
DEGREES ABOVE NORMAL FOR THE INTERIOR...MID 70S TO MID 80S...THE
COAST AND STRAIT WILL REMAIN NEAR 70 FOR HIGHS EACH DAY. FELTON

&&

.AVIATION...AN UPPER RIDGE IS IN PLACE OVER THE WESTERN U.S. WITH SW
FLOW ALOFT OVER WA (PIC15). AT THE SURFACE THERE IS HIGH PRESSURE
OFFSHORE WITH THERMAL LOW PRESSURE EAST OF THE CASCADES (PIC11). THE
AIR IS DRY AND STABLE EXCEPT FOR AREAS OF LOW CLOUDS AND
FOG...MAINLY COAST AND STRAIT. OTHERWISE...MORE SUNNY WEATHER ON TAP
TODAY.

KSEA...CLEAR WITH NLY BREEZE.

&&

.MARINE...HIGH PRESSURE OVER THE COASTAL WATERS WITH LOWER PRESSURE
EAST OF THE CASCADES WILL GIVE VARYING DEGREES OF ONSHORE FLOW EACH
DAY. THE PATTERN IS EXPECTED TO CHANGE LITTLE...HERE IS THE GFS SEA
LEVEL PRESSURE FORECAST LATE EACH AFTERNOON FOR THE NEXT FOUR DAYS
(PIC11) (PIC12) (PIC13) (PIC14). WEAKER ONSHORE PRESSURE GRADIENTS
THROUGH TONIGHT WILL GIVE SMALL CRAFT ADVISORY CONDITIONS TO THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

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


&&

$$

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML