Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 021213 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
513 AM PDT MON MAY 2 2016

CORRECTED A MINOR TYPO IN THE LAST PARAGRAPH OF THE LONG TERM
SEGMENT.

.SYNOPSIS...HIGH PRESSURE ALOFT WILL CONTINUE MOVING SLOWLY
EAST...ALLOWING LOW PRESSURE OFFSHORE TO APPROACH. EXPECT
ANOTHER DAY OF UNSEASONABLY WARM WEATHER TODAY BEFORE TEMPERATURES
COOL 10 TO 15 DEGREES ON TUESDAY. WEATHER CONDITIONS WILL ALSO BE
UNSETTLED TUESDAY AND WEDNESDAY DUE TO THE PROXIMITY OF THE LOW
PRESSURE SYSTEM OFFSHORE.

&&

.SHORT TERM...
AN UPPER LEVEL RIDGE OVER THE REGION WILL SHIFT SLOWLY EAST
THROUGH TUESDAY...ALLOWING AN UPPER LEVEL TROF OVER THE NORTHEAST
PACIFIC TO APPROACH THE WEST COAST. THIS WILL CAUSE THE FLOW ALOFT
TO BECOME SOUTHERLY AND STRENGTHEN DURING THIS TIME FRAME.

EXPECT MID AND HIGH CLOUDS TO BEGIN OVERSPREADING THE FORECAST
AREA DURING THE DAY TODAY. SOME MIDLEVEL INSTABILITY WILL ALSO
WORK ITS WAY NORTH ACROSS THE AREA TONIGHT FOR A RISK OF TSTMS
OVER THE FAR SOUTHWEST INTERIOR. THE TSTMS MADE IT AS FAR NORTH AS
NORTHERN CA YESTERDAY. WITH THE FLOW ALOFT BECOMING SOUTHERLY...
SHOULD EXPECT THE TSTMS TO BE OVER NORTHERN OREGON BY LATE THIS
AFTERNOON. THERE CONTINUED TO BE SOME UNCERTAINTY IN REGARDS TO
THE TSTM THREAT. THE SREF CONTINUED TO ADVERTISE A THREAT OF TSTMS
OVER MUCH OF THE INTERIOR CWA THIS EVENING. IT EVEN INDICATED A
RISK OVER THE SOUTHWEST INTERIOR THIS AFTERNOON BUT THIS TIMING
APPEARED TOO QUICK. AT ANY RATE...THE DAY SHIFT WILL NEED TO
REASSESS THE POTENTIAL FOR TSTMS AFTER THE 1200 UTC MODEL CYCLE
ARRIVES.

THE LOW LEVEL OFFSHORE FLOW WILL BECOME FLAT THIS AFTERNOON BEFORE
TURNING LIGHT ONSHORE TONIGHT. THE ONSHORE SURFACE PRESSURE
GRADIENT WILL TIGHTEN SIGNIFICANTLY DURING THE DAY TUESDAY. THE
GFS MODEL WAS PREDICTING THE KUIL TO KBLI PRESSURE GRADIENT TO BE
PLUS 4.1 MB AT 5 PM PDT TUESDAY. THIS COMBINED WITH INCREASED
CLOUD COVER AND A THREAT OF SHOWERS WILL RESULT IN MARKEDLY COOLER
TEMPS ON TUESDAY. IN OTHER WORDS...TODAY WILL BE THE LAST DAY OF
THE CURRENT HOT SPELL. IT WILL BE 10-15 DEGREES COOLER AT MOST
PLACES ON TUESDAY. ADDITIONAL COOLING WILL OCCUR ON WEDNESDAY...
WITH TEMPS FORECAST TO BE NEAR OR SLIGHTLY BELOW NORMAL.

ANTICIPATE THE UPPER LEVEL TROF OFFSHORE ON TUESDAY TO REMAIN
OFFSHORE ON WEDNESDAY WHILE SPLITTING. MUCH OF THE ENERGY WITH
THIS TROF WILL HEAD TOWARDS NORTHERN BRITISH COLUMBIA AND
CALIFORNIA.

.LONG TERM...
WA WILL LIE BETWEEN UPPER LEVEL RIDGES CENTERED OFFSHORE AND OVER
THE ROCKIES AND TROFS OVER BRITISH COLUMBIA AND CA ON THURSDAY.
THERE WILL BE A CONTINUED THREAT OF SHOWERS ON THURSDAY BUT THE
THREAT WILL BE DIMINISHING WITH TIME.

THE UPPER LEVEL RIDGE OFFSHORE WILL BUILD OVER THE AREA ON FRIDAY
AND SIGNAL A TREND TOWARDS WARMER AND DRIER CONDITIONS. THERE MAY
BE A LINGERING THREAT OF SHOWERS OVER THE CASCADES ON FRIDAY...
OTHERWISE EXPECT DRY WEATHER THROUGH THIS WEEKEND. TEMPS WILL
LIKELY CLIMB ABOVE NORMAL. ALTHOUGH CONFIDENCE IN THE FORECAST
WAS NOT HIGH FOR DAY 7. THE ECMWF SOLUTION HAD THE REGION UNDER
THE INFLUENCE OF A DEEP TROF OVER WESTERN CANADA ON SUNDAY
WHEREAS THE GFS HAD A STRONG UPPER RIDGE CENTERED OVER WESTERN
CANADA. IF THE ECMWF IS CORRECT...THE FORECAST IS TOO WARM AND
SUNNY. THE CURRENT FORECAST REFLECTED MODEL CONSENSUS.

&&

.AVIATION...UPPER LEVEL RIDGE CENTERED OVER SOUTHERN BRITISH
COLUMBIA AND ALBERTA WITH EASTERLY FLOW ALOFT. LIGHT LOW LEVEL
OFFSHORE FLOW EXPECTED TODAY BEFORE GRADUALLY SHIFTING ONSHORE
LATE TONIGHT AND INTO TUESDAY.

THE COMBINATION OF THIS UPPER LEVEL RIDGE AND LOW LEVEL OFFSHORE
FLOW WILL RESULT IN CLEAR SKIES OVER THE AREA TODAY. AS LOW LEVEL
FLOW STARTS TO GRADUALLY TURN ONSHORE...HOWEVER...EXPECT HIGH CLOUDS
TO SLOWLY START TO FILTER IN LATE TONIGHT AND TOMORROW.  SMR

KSEA...CLEAR SKIES. EAST TO NORTHEAST WINDS THIS MORNING AND EARLY
AFTERNOON 7 TO 10 KNOTS. BY LATE AFTERNOON AND EARLY EVENING...WINDS
WILL SHIFT WESTERLY WITH ONLY A SLIGHT EASING DOWN TO 5-8 KNOTS. SMR

&&

.MARINE...LOW LEVEL OFFSHORE FLOW THIS MORNING WITH LOW
PRESSURE OVER THE COASTAL WATERS. A RETURN TO LOW LEVEL ONSHORE FLOW
WILL OCCUR TONIGHT AND CONTINUE INTO TUESDAY WITH VARYING DEGREES OF
ONSHORE FLOW THROUGH THE END OF THE WEEK. EARLIER MODEL RUNS WERE
SUGGESTING THAT GALE FORCE WINDS MIGHT BE POSSIBLE IN THE CENTRAL
AND EASTERN STRAIT OF JUAN DE FUCA TUESDAY NIGHT...BUT MOST RECENT
RUNS HAVE BACKED AWAY FROM THIS SOLUTION WITH ONLY SMALL CRAFT
ADVISORY LEVEL WINDS EXPECTED. WILL BE CURIOUS TO SEE WHAT NEXT RUN
COMES UP WITH...BUT AT LEAST SOME SORT OF HEADLINE WILL LIKELY
BE NEEDED FOR THAT TIME PERIOD.  SMR

&&

.CLIMATE...
APRIL 2016 WAS THE WARMEST APRIL ON RECORD ACROSS WESTERN
WASHINGTON. APRIL 2016 TEMPERATURES CRUSHED THE OLD RECORD
TEMPERATURES BY 1.5 DEGREES TO A LITTLE MORE THAN 3 DEGREES.
SEATTLE HAD THE BIGGEST DIFFERENCE WITH 56.7 DEGREES VERSUS THE
OLD RECORD OF 53.6 DEGREES SET IN 1977. OTHER RECORDS INCLUDE...
BUT ARE NOT LIMITED TO...OLYMPIA 53.2...OLD RECORD 50.9 (1989)...
BELLINGHAM 54.0...OLD RECORD 52.0 (1989)...HOQUIAM 53.8 DEGREES...
OLD RECORD 52.3 (1987)...AND QUILLAYUTE 51.9 DEGREES...OLD RECORD
50.3 (1989).

INCLUDING THE RECORD WARM APRIL...SEATTLE HAS HAD 7 RECORD WARM
MONTHS IN THE LAST 19 MONTHS...OCTOBER AND DECEMBER 2014 AND
FEBRUARY...MARCH... JUNE AND JULY...2015. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION CAN BE SEEN AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML


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