Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 300341
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT TUE JUL 29 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...A STRONG UPPER RIDGE EXTENDS NORTHWARD ALONG THE ROCKY
MOUNTAINS FROM A 5940 HIGH PRESSURE CENTER OVER THE DESERT
SOUTHWEST. DRY SOUTHWEST FLOW ALOFT CONTINUES OVER WESTERN
WASHINGTON. LOW LEVEL ONSHORE FLOW IS STILL GENERALLY WEAK...BUT
THERE IS A STRONGER SEABREEZE THIS EVENING WITH GALE WESTERLIES
BLOWING IN THE STRAIT OF JUAN DE FUCA. THE FORECAST AREA HAS MAINLY
CLEAR SKIES EXCEPT FOR THE MARINE STRATUS HUGGING THE COAST.

THE LARGE SCALE PATTERN WILL CHANGE LITTLE WEDNESDAY THROUGH FRIDAY.
STRATUS WILL PUSH WEAKLY INLAND TONIGHT -- THROUGH THE STRAIT OF
JUAN DE FUCA TO WHIDBEY ISLAND AND THE SAN JUANS...AND THROUGH THE
CHEHALIS GAP TO THE SOUTH PUGET SOUND REGION AND PARTS OF THE
SOUTHWEST INTERIOR. THE SEATTLE AREA SHOULD REMAIN MOSTLY CLEAR...
AND THE STRATUS THAT DOES MOVE INLAND SHOULD BURN OFF MID TO LATE
MORNING. SO WEDNESDAY WILL BE ANOTHER GENERALLY SUNNY DAY WITH HIGHS
IN THE LOWER 70S AT THE COAST AND MID 70S TO MID 80S INLAND.
THURSDAY AND FRIDAY SHOULD BE VERY SIMILAR...WITH THE POSSIBLE
EXCEPTION NOTED BELOW.

MONSOON MOISTURE ROTATING NORTHWARD ALONG THE WEST SIDE OF THE UPPER
HIGH HAS RESULTED IN ISOLATED THUNDERSTORMS AS NEAR AS THE OREGON
CASCADES THE LAST COUPLE DAYS. AND THIS EVENING SOME CONVECTION
DEVELOPED JUST EAST OF THE CASCADES ALONG THE BORDER OF BRITISH
COLUMBIA AND WASHINGTON. WE CAN BE FAIRLY CONFIDENT THAT THIS
ACTIVITY WILL CONTINUE TO JUST MISS OUR FORECAST AREA WEDNESDAY AND
THURSDAY. HOWEVER SOME MODEL RUNS DO SHOW ISOLATED THUNDERSTORMS
OVER THE WASHINGTON CASCADES FRIDAY AFTERNOON AND EVENING.   MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE AFTERNOON
FORECAST DISCUSSION -- THE ECMWF/GFS/AND TO SOME EXTENT THE CANADIAN
ARE SLOW TO SHIFT THE SHORT WAVE OUT OF THE AREA. JUST ENOUGH
MOISTURE AND LIFT OVER THE MOUNTAINS COULD PRODUCE SOME LIGHTNING
NEAR THE CREST. HOWEVER...LOOKING AT THE WRFGFS AND EXTENSION MODEL
MOST THE QPF DOES INDEED STAY ALONG THE CREST OR ON THE EAST SIDE
THROUGH MONDAY. WITH MOST THE ACTIVITY LIKELY TO BE JUST OUTSIDE OUR
FORECAST AREA WILL INDICATE INCREASING AFTERNOON/EVENING CLOUDS OVER
THE MOUNTAINS AND LEAVE IT AT THAT FOR NOW.

OTHERWISE...NOT MUCH IMPACT ON THE LOWLANDS. THE ONSHORE FLOW WILL
BRING CLOUDS IN FURTHER OVER THE WEEKEND BUT SHOULD BURN OFF BY
MIDDAY. HIGHS MAY STILL TOP OUT NEAR 80 GIVEN THE 500 MB HEIGHTS
STILL ABOVE 5800M EVEN IF THE WEAK UPPER LOW LIFTS ACROSS.

AFTER THE LOW KICKS OUT THE RIDGE REMAINS FLAT AND THERE IS A CHANCE
OF WLY FLOW ALOFT DEVELOPING. THIS WOULD HELP MODERATE TEMPERATURES
AND BRING MARINE AIR FURTHER INLAND. BUT SOME MODELS MAINTAIN A
STUBBORNLY STRONG RIDGE AND WARMER TEMPERATURES. WILL GO WITH A
COMPROMISE AND KEEP DRY WEATHER AND HIGHS SLIGHTLY ABOVE AVERAGE
WHICH HAS BEEN THE DOMINATE PATTERN. MERCER

&&

.CLIMATE...TODAY MARKS 5 YEARS SINCE THE ALL TIME RECORD HIGH
TEMPERATURE WAS SET AT SEA-TAC WAS SET ALONG WITH OTHER RECORD
HIGHS. SEATTLE(SEA-TAC) 103...NWS SEATTLE 105...CENTRALIA
107...OLYMPIA 104...ELMA 104...EVERETT 100...BELLINGHAM
96...ABERDEEN 95.

IN ADDITION...A TOTAL OF 0.31 INCHES OF RAIN HAS BEEN REPORTED ON
THIS DAY SINCE RECORDS STARTED AT SEATTLE-TACOMA AIRPORT IN 1945
MAKING THIS THE DRIEST DAY OF THE YEAR IN TERMS OF TOTAL RAINFALL
FOR THE DAY AT SEA-TAC.

&&

.AVIATION...AN UPPER RIDGE IS IN PLACE OVER THE WESTERN U.S. WITH SW
FLOW ALOFT OVER WA. AT THE SURFACE THERE IS HIGH PRESSURE OFFSHORE
WITH THERMAL LOW PRESSURE EAST OF THE CASCADES. THE AIR IS DRY AND
STABLE EXCEPT FOR A SHALLOW COASTAL MARINE LAYER. SOME AREAS OF FOG
OR LOW CLOUDS HAVE PUSHED IN AS FAR AS WRN WHIDBEY ISLAND THIS
EVENING...SO AREAS OF MORNING FOG ARE A GOOD BET UP AROUND WHIDBEY
AND IN THE STRAIT. THERE MAY BE SOME FOG OR LOW CLOUDS INTO OLYMPIA
AND SHELTON AS WELL BY DAYBREAK...THAT WILL LAST A FEW HOURS.
OTHERWISE...MORE SUNNY WEATHER ON TAP ON WEDNESDAY EXCEPT FOR THE
LOW CLOUDS ALONG THE OCEAN BEACHES.

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
THROUGH SATURDAY. THE ONSHORE FLOW IS STRONGER THIS EVENING AND A
GALE WARNING IS IN EFFECT FOR THE CENTRAL AND EASTERN STRAIT OF JUAN
DE FUCA...WITH SMALL CRAFT ADVISORIES ADJACENT TO THE GALE WARNING
AREA...THE WEST ENTRANCE TO THE STRAIT...THE NORTHERN INLAND
WATERS...AND ADMIRALTY INLET. NORTHWESTERLY FLOW OVER THE COASTAL
WATERS WILL GIVE SMALL CRAFT ADVISORY WINDS THERE THIS AFTERNOON AND
EVENING. THE PATTERN IS EXPECTED TO CHANGE LITTLE WED THROUGH SAT.
SLIGHTLY WEAKER ONSHORE PRESSURE GRADIENTS WILL STILL GIVE SMALL
CRAFT ADVISORY CONDITIONS TO THE COASTAL WATERS AND THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA DURING THE LATE AFTERNOON AND EVENING
HOURS EACH DAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL STRAIT OF JUAN DE FUCA AND EAST
      ENTRANCE TO THE STRAIT.
     SMALL CRAFT ADVISORY COASTAL WATERS...WEST ENTRANCE STRAIT
      OF JUAN DE FUCA...ADMIRALTY INLET...AND NORTHERN INLAND
      WATERS.

&&

$$

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





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