Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 291616
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE JUL 29 2014

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BRING WARM SUNNY DAYS TO
WESTERN WASHINGTON THROUGH EARLY NEXT WEEK AT LEAST. WEAK ONSHORE
FLOW WILL ALLOW CLOUDS ALONG THE COAST TO INTRUDE THROUGH THE STRAIT
OF JUAN DE FUCA AND LOWER CHEHALIS GAP DURING THE LATE NIGHT AND
MORNING HOURS. TEMPERATURES ACROSS GREATER PUGET SOUND WILL REMAIN
ABOVE AVERAGE THROUGH AT LEAST THURSDAY.

&&

.SHORT TERM...DRY SOUTHWEST FLOW ALOFT WILL DOMINATE THE PATTERN
THROUGH THURSDAY WITH THE UPPER RIDGE AXIS CENTERED WELL INLAND OVER
THE GREAT BASIN AND NRN ROCKIES. THIS PATTERN TENDS TO RESULT IN
VARYING DEGREES OF MOSTLY WEAK ONSHORE GRADIENTS. LOW STRATUS ALONG
THE COAST INTRUDED INTO THE LOWER CHEHALIS GAP AS FAR AS SHELTON AND
ALSO DOWN THE STRAIT OF JUAN DE FUCA AND AREAS SURROUNDING THE EAST
ENTRANCE. THESE CLOUDS WILL EASILY BURN BACK TO THE COAST BY MIDDAY.
WITH LACK OF ANY REAL DEEP MARINE INFLUENCE OVER THE INTERIOR AND
LITTLE CHANGE IN 500 MB HEIGHTS OR 850 MB TEMPS...WILL STICK WITH
THE CURRENT FORECAST HIGHS WHICH SHOULD BE SIMILAR TO YESTERDAY.
TEMPERATURES TODAY SHOULD REACH THE LOW TO MID 70S ALONG THE
COAST...AND AROUND THE STRAIT DUE TO MARINE AIR. HIGHS ACROSS THE
INTERIOR AWAY FROM THE WATER INCLUDING THE GREATER PUGET SOUND
SHOULD BE IN THE MID TO UPPER 80S...WARMEST ACROSS THE SW INTERIOR
TO TACOMA AREAS.

THE WESTERLY PUSH IN THE STRAIT MAY BE A BIT STRONGER THIS EVENING
POSSIBLY ENOUGH TO INDUCE GALES. SEE THE MARINE SECTION BELOW. 500
MB HEIGHTS COME DOWN JUST ABOUT 20M WHICH IS NOT TOO SIGNIFICANT AND
850 MB TEMPS REMAIN FAIRLY CONSTANT. MARINE AIR MAY FLOOD A BIT
FURTHER INLAND TOWARD THE N PUGET SOUND AND AREAS SURROUNDING THE
STRAIT BY WEDNESDAY MORNING. THESE AREAS WILL SEE MORE COOLING.
CENTRAL AND S PUGET SOUND...AND THE SW INTERIOR WILL PROBABLY REACH
THE LOW TO MID 80S.

500 MB HEIGHTS REMAIN LITTLE CHANGED INTO THURSDAY AND ONSHORE FLOW
APPEARS WEAK. HIGHS IN THE UPPER 60S/LOW 70S COAST AND AROUND THE
STRAIT WILL CONTINUE WITH WARMER HIGHS IN THE LOW TO MID 80S ACROSS
THE INTERIOR AT SPOTS AWAY FROM THE WATERS. BEYOND THURSDAY THERE
COULD BE SOME UNCERTAINTY IN THE FORECAST DISCUSSED BELOW. WILL
EVALUATION THE FULL SUITE OF 12/18Z MODELS TODAY AND MAKE ANY
ADJUSTMENTS IF NEEDED TO THE LONG RANGE FORECAST THIS AFTERNOON.
MERCER

.LONG TERM...PREVIOUS 330 AM DISCUSSION...AFTER A FEW RUNS OF
GOOD AGREEMENT IN THE EXTENDED MODELS A COUPLE OF WRINKLES IN THE
PROGS THIS MORNING. THE GFS HAS CHANGED SLIGHTLY FRIDAY AND OVER THE
WEEKEND WITH SOME WEAK TROUGHINESS OVER THE AREA. 500 MB HEIGHTS ARE
STILL HIGH...MID 580S DMS SO THERE IS STILL NO PRECIPITATION
FORECAST. THE SLIGHT CHANGE IN THE FLOW ALOFT COULD RESULT IN A
LITTLE STRONGER ONSHORE FLOW AND SLIGHTLY COOLER TEMPERATURES THAN
CURRENTLY FORECAST. THE ECMWF BRINGS A SMALL LOW UP FROM THE SOUTH
ON SATURDAY WITH PRECIPITATION OVER THE NORTHERN PORTION OF THE
AREA. THE CANADIAN ALSO HAS THIS FEATURE ALTHOUGH IT IS MUCH MORE
DRIER THAN THE ECMWF SOLUTION. WITH THESE SOLUTIONS BEING NEW TO THE
MODEL RUNS WILL STAY WITH THE MORE CONSISTENT GFS SOLUTION WHICH
KEEPS THE WEAK ONSHORE FLOW PATTERN WITH TEMPERATURES A FEW DEGREES
ABOVE NORMAL GOING INTO THE FIRST PART OF NEXT WEEK. FELTON

&&

.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 LEVEL RIDGE CENTERED OVER THE INTERMOUNTAIN
WEST COMBINED WITH A TROUGH ALONG ABOUT 140W WILL GIVE SOUTHWEST
FLOW ALOFT THROUGH WEDNESDAY. AT THE SURFACE...A RIDGE OF HIGH
PRESSURE OVER THE OFFSHORE WATERS COMBINED WITH LOWER PRESSURE EAST
OF THE CASCADES WILL GIVE LOW LEVEL ONSHORE FLOW. THE AIR MASS IS
DRY AND STABLE...EXCEPT FOR A SHALLOW MARINE LAYER ALONG THE COAST.

AT 8 AM THE SHALLOW MARINE LAYER OVER THE COASTAL WATERS EXTENDS
INLAND OVER THE COASTAL ZONES AND EASTWARD THROUGH THE CHEHALIS GAP
TO ABOUT SHELTON. SOME FOG AND VERY LOW STRATUS IS ALSO SEEN
EXTENDING EASTWARD THROUGH THE STRAIT OF JUAN DE FUCA TO NORTHERN
WHIDBEY ISLAND AND THE SOUTHERN SAN JUAN ISLANDS. WHERE THE FOG AND
STRATUS ARE SEEN...IFR TO LIFR CONDITIONS ARE BEING OBSERVED. OTHER
LOCATIONS ARE CLEAR. THE FOG AND STRATUS WILL RAPIDLY BURN BACK TO
THE COASTLINE BY ABOUT 20Z.

LATEST FORECAST MODELS SHOW ONSHORE GRADIENTS INCREASING RAPIDLY
LATE THIS AFTERNOON AS STRONG HEATING TAKES PLACE EAST OF THE
CASCADES. THE ONSHORE FLOW WILL BE STRONGER THAN LAST EVENING AND
WILL LIKELY RESULT IN STRATUS AND FOG PUSHING INLAND FARTHER THAN
THIS MORNING. THE TERMINAL MOST LIKELY TO BE IMPACTED WILL BE
KPAE...BUT KOLM MAY ALSO GET SOME FOG AND STRATUS WED MORNING. ANY
LOCATION GETTING STRATUS WILL LIKELY SEE IFR TO LIFR CONDITIONS FOR
A FEW HOURS WED MORNING WHILE OTHER AREAS WILL REMAIN CLEAR.
ALBRECHT

KSEA...EXPECT CLEAR SKIES THROUGH TONIGHT. LIGHT WINDS WILL BECOME
NW 6 TO 9 KT AROUND 20Z THEN WILL VEER TO NE 5-7 KT AFTER 04Z THIS
EVENING. ALBRECHT

&&

.MARINE...A RIDGE OF HIGH PRESSURE OVER THE COASTAL WATERS COMBINED
WITH LOWER PRESSURE EAST OF THE CASCADES WILL GIVE VARYING DEGREES
OF ONSHORE FLOW THROUGH SATURDAY. THE ONSHORE FLOW IS EXPECTED TO BE
STRONGER LATE THIS AFTERNOON AND TONIGHT THAN IT HAS BEEN OVER THE
PAST FEW DAYS. SO...A GALE WARNING HAS BEEN ISSUED FOR THE CENTRAL
AND EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA FROM 5 PM THIS
AFTERNOON UNTIL 5 AM WEDNESDAY MORNING. SMALL CRAFT ADVISORIES HAVE
BEEN ISSUED FOR AREAS 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. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL STRAIT OF JUAN DE FUCA AND EAST ENTRANCE
     TO THE STRAIT 5 PM THIS AFTERNOON UNTIL 5 AM WEDNESDAY.
     SMALL CRAFT ADVISORY COASTAL WATERS 2 PM THIS AFTERNOON THROUGH
     TONIGHT.
     SMALL CRAFT ADVISORY WEST ENTRANCE TO THE STRAIT OF JUAN DE
     FUCA...NORTHERN INLAND WATERS...AND ADMIRALTY INLET 5 PM THIS
     AFTERNOON UNTIL 5 AM WEDNESDAY.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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










USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.