Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 301102
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
400 AM PDT TUE JUN 30 2015

.SYNOPSIS...SOUTHWESTERLY FLOW ALOFT WILL BECOME WESTERLY TODAY AS A
WEAK UPPER LEVEL TROUGH MOVES INLAND NORTH OF THE AREA. THE LOW
LEVEL FLOW WILL REMAIN ONSHORE WITH HIGH TEMPERATURES A LITTLE
COOLER THAN MONDAY. HIGH PRESSURE ALOFT WILL REBUILD OVER THE
PACIFIC NORTHWEST ON WEDNESDAY FOR A RETURN TO HOT AND DRY
CONDITIONS THROUGH THE HOLIDAY WEEKEND.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS STRATUS ALONG THE
COAST...THROUGH THE CHEHALIS RIVER VALLEY INTO THE KITSAP PENINSULA
AND DOWN THE STRAIT OF JUAN DE FUCA TO WHIDBEY ISLAND. CLEAR SKIES
OVER THE REMAINDER OF THE AREA. TEMPERATURES AT 3 AM WERE IN THE MID
50S TO LOWER 60S.

TODAY WILL BE THE COOLEST DAY IN THE NEXT SEVEN FOR WESTERN
WASHINGTON. A WEAK TROUGH MOVING BY WELL TO THE NORTH OF THE AREA
TODAY WILL MAINTAIN THE LOW LEVEL ONSHORE FLOW PATTERN THROUGHOUT
THE DAY. THE STRATUS WILL CONTINUE TO EXPAND EASTWARD FOR THE NEXT
COUPLE OF HOURS BUT WITH THE ONSHORE GRADIENTS WEAKENING OVERNIGHT
TO NOT THINK THE STRATUS WILL GET AS FAR EAST AS THE FOOTHILLS. THE
MARINE LAYER IS SHALLOW WITH ESTIMATED TOPS AROUND 1500 FEET. EXPECT
THE STRATUS TO BURN BACK TO THE COAST BY MIDDAY AND EVEN OFF THE
COAST BY LATE THIS AFTERNOON. WITH THE ONSHORE FLOW HIGH
TEMPERATURES WILL BE A LITTLE COOLER WITH 60S ALONG THE COAST AND
70S TO LOWER 80S OVER THE INTERIOR.

UPPER LEVEL TROUGH AXIS MOVING EAST OF THE AREA TONIGHT WITH YET
ANOTHER UPPER LEVEL RIDGE BUILDING OVER WESTERN WASHINGTON. BY 12Z
WEDNESDAY 500 MB HEIGHTS BACK UP IN THE MID 580 DMS. LOW LEVEL
ONSHORE FLOW WEAKENS OVERNIGHT AS THE RIDGE BUILDS OVERHEAD. THIS
WILL CONFINE THE STRATUS TO THE COAST LATER TONIGHT. LOWS WILL BE IN
THE MID 50S TO LOWER 60S.

ANOTHER WARM DAY ON WEDNESDAY WITH THE UPPER LEVEL RIDGE CONTINUING
TO BUILD OVER THE AREA. 500 MB HEIGHTS BY 00Z THURSDAY PUSHING 590
DMS. FLAT SURFACE GRADIENTS BECOMING NORTHWESTERLY ONSHORE IN THE
AFTERNOON. THE RESULTING SEABREEZE WILL KEEP LOCATIONS NEAR THE
WATER COOLER THAN THE INLAND LOCATIONS. WITH THE LACK OF ANY ONSHORE
FLOW FOR MOST OF THE DAY HIGH TEMPERATURES WILL WARM BACK INTO THE
80S AND LOWER 90S OVER THE INTERIOR WITH 70S AND LOWER 80S ALONG THE
COAST.

WEAK TROUGH MOVING THROUGH THE AREA WEDNESDAY NIGHT IS NOT EVEN
STRONG ENOUGH TO LOWER THE 500 MB HEIGHTS BY 5 DMS. THE RIDGE POPS
RIGHT BACK UP DURING THE DAY ON THURSDAY. 850 MB TEMPERATURES
THURSDAY AFTERNOON NEAR PLUS 20C. SURFACE GRADIENTS ONCE AGAIN ARE
FLAT OVERNIGHT INTO THURSDAY MORNING THEN BECOME NORTHWESTERLY
ONSHORE THURSDAY AFTERNOON. WITH THE SLIGHT WARMING IN THE
TEMPERATURES ALOFT HIGHS ON THURSDAY A COUPLE OF DEGREES WARMER FOR
THE INTERIOR WITH THE WARMEST LOCATIONS IN THE LOWER 90S AND MOST OF
THE REMAINDER OF THE AREA IN THE 80S. TEMPERATURES ALONG THE COAST
WILL REMAIN IN THE 70S. FELTON

.LONG TERM...EXTENDED MODELS STILL IN GOOD GENERAL AGREEMENT KEEPING
THE UPPER LEVEL RIDGE OVER WESTERN WASHINGTON THROUGH THE PERIOD.
THE GFS IS A LITTLE MORE AGRESSIVE WITH THE SHORTWAVES MOVING OVER
THE TOP OF THE RIDGE OVER THE WEEKEND BUT EVEN WITH THIS 500 MB
HEIGHTS ON THE GFS DO NOT DROP BELOW THE LOWER 580 DMS. SOME SMALL
DIFFERENCES IN THE SURFACE PATTERN IN THE MODELS COME SUNDAY WITH
THE ECMWF FINALLY TURNING THE LOW LEVEL FLOW OFFSHORE WHILE THE GFS
KEEPS THE LOW LEVEL FLOW FLAT. CURRENT FORECAST FOLLOWS THE SLIGHTLY
COOLER GFS SOLUTION WHICH STAYS WITH THE IDEA OF HIGHS MOSTLY IN THE
80S OVER THE INTERIOR AND 70S ALONG THE COAST THROUGH THE WEEKEND.
IF THE ECMWF VERIFIES FORECAST MAX TEMPS WILL BE AROUND 5 DEGREES
TOO COOL ON SUNDAY WITH LOWER 90S COMMON FROM SEATTLE SOUTHWARD.
DIFFERENCES IN THE MODELS CONTINUE ON MONDAY WITH THE ECMWF HAVING A
MUCH HIGHER AMPLITUDE RIDGE OVER THE AREA AND GFS SHOWING MORE LOW
LEVEL ONSHORE FLOW. THE FORECAST FOR MONDAY IS A COMPROMISE OF THE
TWO SOLUTIONS. WITH THE DIFFERENCES IN THE MODELS WILL LEAVE THE
MONDAY FORECAST ALONE. FELTON

&&

.CLIMATE...WITH ONLY ONE DAY LEFT IN THE MONTH SEATTLE WILL END UP
WITH THE WARMEST JUNE ON RECORD. THROUGH THE 29TH THE AVERAGE HIGH
FOR THE MONTH IS 78.6 DEGREES. THE OLD RECORD FOR THE MONTH WAS 75.8
DEGREES IN 1992. WITH THE WARM LOW TEMPERATURES THE LAST FEW DAYS
SEATTLE IS NOW ON PACE TO BREAK THE RECORD FOR THE WARMEST AVERAGE
LOW TEMPERATURE FOR THE MONTH OF JUNE. THROUGH THE 29TH THE AVERAGE
LOW FOR THE MONTH HAS BEEN 56.3 DEGREES. THE RECORD WAS 55.7 DEGREES
SET IN 2013. THE AVERAGE TEMPERATURE FOR THE MONTH THROUGH THE 29TH
IS 67.5 DEGREES. THE OLD RECORD WAS 64.9 DEGREES SET IN 1992.

TO PUT THIS RECORD WARM JUNE IN PERSPECTIVE...THE CURRENT AVERAGE
MAX TEMPERATURE OF 78.6 DEGREES WOULD BE THE 12TH WARMEST JULY ON
RECORD AND THE 9TH WARMEST AUGUST ON RECORD. RECORDS STARTED AT SEA-
TAC IN 1945.

IN ADDITION TO THE WARM WEATHER IT HAS ALSO BEEN A VERY DRY JUNE
WITH ONLY 0.23 INCHES OF RAIN AT SEA-TAC. THIS WILL BE THE 4TH
DRIEST JUNE ON RECORD. THE MAY 1ST THROUGH JUNE 30TH RAINFALL TOTAL
IS 0.81 INCHES. THIS WILL BE THE DRIEST ON RECORD. THE OLD RECORD
WAS 1.26 INCHES IN 1992.

NUMEROUS OTHER RECORDS WILL BE BROKEN ACROSS THE AREA THIS MONTH.
THE RECORDS WILL BE SUMMARIZED TOMORROW IN A PUBLIC INFORMATION
STATEMENT. FELTON

$$

.AVIATION...WESTERLY FLOW ALOFT OVER WESTERN WASHINGTON EARLY THIS
MORNING WILL CONTINUE THROUGH TONIGHT. LOW LEVEL ONSHORE FLOW WILL
INCREASE LATE TODAY AND CONTINUE TONIGHT. THE AIR MASS IS MAINLY DRY
EXCEPT FOR MOISTURE IN THE SHALLOW SURFACE-BASED MARINE LAYER.

MARINE STRATUS WITH BASES 500 TO 800 FT COVERS THE COASTAL WATERS
AND WASHINGTON COAST...AND BY 2 AM IT HAD MOVED THROUGH THE STRAIT
OF JUAN DE FUCA AS FAR AS BREMERTON AND THROUGH THE STRAIT OF JUAN
DE FUCA TO WHIDBEY ISLAND. STRATUS WILL LIKELY COVER MUCH OF THE
PUGET SOUND REGION FOR SEVERAL HOURS THIS MORNING WITH IFR CEILINGS.
IT SHOULD BURN BACK TO THE COASTAL WATERS THIS AFTERNOON. THERE WILL
PROBABLY BE LESS STRATUS TONIGHT AND WEDNESDAY MORNING.

KSEA...SOUTH TO SOUTHWEST WIND 4-10 KT THIS MORNING...SHIFTING TO
NORTHWEST LATE THIS AFTERNOON...THEN NORTH TO NORTHEAST TONIGHT.
STRATUS SHOULD REACH KSEA AROUND 12Z AND GIVE THE TERMINAL IFR
CEILINGS THROUGH AROUND 17Z.   MCDONNAL

&&

.MARINE...HIGH PRESSURE WELL OFFSHORE AND THERMALLY INDUCED LOW
PRESSURE EAST OF THE CASCADES WILL MAINTAIN ONSHORE FLOW TODAY. IT
SHOULD INCREASE LATE TODAY IN RESPONSE TO A WEAK UPPER LEVEL SYSTEM
MOVING THROUGH...AND GALE FORCE WESTERLIES ARE LIKELY LATE THIS
AFTERNOON AND TONIGHT IN THE CENTRAL STRAIT OF JUAN DE FUCA AND EAST
ENTRANCE STRAIT. IN ADDITION SMALL CRAFT ADVISORY WINDS ARE LIKELY
OVER THE OUTER COASTAL WATERS AND IN ADMIRALTY INLET.

ONSHORE FLOW WILL PROBABLY EASE SOMEWHAT ON WEDNESDAY AND STRENGTHEN
AGAIN THURSDAY. THEN IT SHOULD EASE AGAIN FRIDAY AND SATURDAY AS
THERMALLY INDUCED LOW PRESSURE DEVELOPS OVER WESTERN WASHINGTON.
MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...GALE WARNING LATE THIS AFTERNOON THROUGH LATE TONIGHT CENTRAL
     AND EAST STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY UNTIL 9 AM THIS MORNING CENTRAL AND EAST
     STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY THIS EVENING ADMIRALTY INLET.
     SMALL CRAFT ADVISORY NOON TODAY THROUGH WEDNESDAY MORNING OUTER
     COASTAL WATERS.

&&

$$

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



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