Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 251020
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT FRI JUL 25 2014

.SYNOPSIS...MOIST WESTERLY FLOW WILL CONTINUE TODAY AS A WEAK
WEATHER SYSTEM MOVES ONTO THE BRITISH COLUMBIA COAST. THERE COULD BE
SOME LIGHT SHOWERS OVER THE COAST AND MOUNTAINS...OTHERWISE CLOUDY
SKIES WILL GIVE WAY TO PARTIAL AFTERNOON SUNSHINE. HIGH PRESSURE
ALOFT WILL BUILD OVER THE REGION THIS WEEKEND...BRINGING SUNNY
WARMER WEATHER THAT SHOULD CONTINUE NEXT WEEK.

&&

.SHORT TERM...WV/IR SATELLITE IMAGERY SHOWS A WEAK SHORT WAVE
EMBEDDED IN WESTERLY FLOW ALOFT MOVING ONTO THE B.C. COAST AND
BRUSHING WRN WA. THERE ARE SOME MID AND HIGH LEVEL CLOUDS ASSOCIATED
WITH THIS SYSTEM BUT THE MAIN AFFECT IS TO MAINTAIN MOIST LOW LEVEL
ONSHORE FLOW. THERE WAS ALREADY PLENTY OF MOISTURE IN THE LOW LEVELS
FROM EARLIER TODAY WHICH ALLOWED STRATUS TO REFORM AND EXPAND ACROSS
MUCH OF THE AREA. THE EXCEPTION IS THE SW INTERIOR ODDLY WHICH IS
MOSTLY CLOUDY FREE SO FAR EARLY THIS MORNING. THE FORECAST TODAY
INDICATES A CLOUDY START TO THE DAY...THEN BECOMING PARTLY SUNNY. I
RELUCTANTLY KEPT SOME LOW POPS ON THE COAST AND MOUNTAINS AS A MOS
BLEND STILL SHOWS A CHANCE OF SHOWERS IN THESE AREAS. CURRENT OBS DO
SHOW LIGHT RAIN ALONG VANCOUVER ISLAND SO IT IS POSSIBLE A BIT OF
THIS PRECIPITATION COULD SKIRT OUR AREA THIS MORNING. THE INTERIOR
LOWLANDS SHOULD BE DRY OUTSIDE OF A FEW LIGHT SPRINKLES FROM THE
STRATUS LAYER THIS MORNING. WITH SOME SUN BREAKING OUT THIS
AFTERNOON...HIGHS SHOULD REACH INTO THE LOW TO MID 70S AROUND PUGET
SOUND BUT STILL IN THE 60S COAST AND STRAIT.

HEIGHTS SLOWLY RISE TONIGHT BUT THE LOW LEVEL FLOW WILL STILL BE
ONSHORE. THIS MAY ALLOW SOME STRATUS TO REFORM OVER THE AREA BUT IT
SHOULD BE MORE PATCHY IN NATURE. THE FOUR CORNERS HIGH BUILDS NWD
INTO THE NRN ROCKIES SATURDAY AND SUNDAY WITH 500 MB HEIGHTS ABOVE
5800 M OVER WRN WA. THIS SUPPORTS A DRY AND WARMING TREND WITH HIGHS
IN THE UPPER 70S TO LOW 80S ON SATURDAY...WARNING TO THE LOW AND MID
80S SUNDAY UNDER SUNNY SKIES.

.LONG TERM...GLOBAL MODELS CONTINUE TO ADVERTISE A STRONG HIGH
PRESSURE RIDGE DOMINATING THE INTERIOR WRN U.S. THROUGH MUCH OF NEXT
WEEK. THERE IS SOME UNCERTAINTY AS TO HOW FAR WEST THE RIDGE WILL
SHIFT AND THIS WILL AFFECT WHERE THERMALLY INDUCED LOW PRESSURE
DEVELOPS. MOST MODELS RUNS KEEP THE RIDGE AXIS ORIENTED NWD OVER THE
GREAT BASIN WHICH WOULD KEEP LOWER PRESSURE EAST OF THE CASCADES AND
ALLOW FOR LIGHT ONSHORE FLOW OVER WRN WA. IT WILL STILL BE QUITE
WARM...WELL INTO THE 80S...BUT HOT TEMPERATURES INTO THE 90S MAY BE
AVERTED IF THE RIDGE AXIS REMAINS FURTHER EAST. THE MORE RELIABLE
ECMWF HAS VARIED FROM RUN TO RUN...SOME PUTTING THE RIDGE CLOSER TO
OUR AREA SO A PERIOD OF EVEN WARMER  WEATHER IS NOT OUT OF THE
QUESTION NEXT WEEK. HIGH TEMPERATURES SHOULD BE ABOVE AVERAGE
REGARDLESS OF THE EXACT RIDGE POSITION. MERCER

&&

.AVIATION...WEAK UPPER LEVEL RIDGING AND MODERATE WESTERLY FLOW
ALOFT WILL PERSIST OVER THE REGION TODAY. LOW LEVEL ONSHORE FLOW
WILL STRENGTHEN SOMEWHAT DURING THE AFTERNOON AND EVENING HOURS
BEFORE RELAXING LATE TONIGHT.

THE AIR MASS OVER WESTERN WASHINGTON HAS DRIED AND BECOME MORE
STABLE OVERNIGHT. LINGERING LOW LEVEL MOISTURE AND THE ONSHORE FLOW
HAS HELPED LOW CLOUDS ALONG THE COAST...STRAIT AND THROUGH THE
CENTRAL INTERIOR WHILE CLOUD COVER OVER THE NORTH AND SOUTHWEST
INTERIOR REMAINS SPOTTY AS OF 10Z. CEILINGS CURRENTLY 3-5K FT MOST
AREAS...EXPECTED TO LOWER TO MVFR LEVELS AT OR JUST AFTER SUNRISE
THIS MORNING. A WEAK UPPER LEVEL SYSTEM MOVING INTO BRITISH COLUMBIA
THIS MORNING WILL KEEP A CHANCE OF SHOWERS AND OR DRIZZLE OVER THE
COAST AND OLYMPICS THROUGH THIS AFTERNOON. OTHERWISE MORNING CLOUDS
WILL LIFT TO VFR LEVELS LATE MORNING...WITH CLEARING OVER MUCH OF
THE INTERIOR DURING THE AFTERNOON.

KSEA...VFR CEILINGS EXPECTED TO LOWER AROUND DAY BREAK TO MVFR
LEVELS NEAR 1.5K FT...THEN LIFT BY LATE MORNING AND CLEARING
DURING THE AFTERNOON. LIGHT NORTHEAST WINDS 4 TO 6 KT WILL BECOME
NORTHWESTERLY BY EARLY AFTERNOON.

&&

.MARINE...ONSHORE GRADIENTS AND FLOW HAVE RELAXED THIS MORNING. A
TYPICAL PATTERN OF HIGH PRESSURE OVER THE COASTAL WATERS AND LOWER
PRESSURE INLAND WILL SUPPORT ONSHORE FLOW THROUGH EARLY NEXT WEEK.
EXPECT STRONGEST WESTERLIES THROUGH THE STRAIT...WITH SMALL CRAFT
ADVISORY LEVEL WINDS POSSIBLE AT TIMES ESPECIALLY DURING THE
AFTERNOON AND EVENING HOURS. THE CURRENT FORECAST REFLECTS 10 TO 20
KT WESTERLIES THIS AFTERNOON AND NOMINAL SMALL CRAFT ADVISORY WINDS
DURING THE EVENING HOURS ON SATURDAY AND SUNDAY. ALL OTHER WATERS
WILL REMAIN 10 TO 20 KTS.

&&

.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











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