Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | 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 261120
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST MON JAN 26 2015

.SYNOPSIS...HIGH PRESSURE OVER THE REGION AND LIGHT SURFACE FLOW
WILL RESULT IN WIDESPREAD LOW CLOUDS AND FOG THIS MORNING BEFORE
CLEARING. A WEAK FRONT WILL DISSIPATE OVER WESTERN WASHINGTON
TUESDAY THROUGH EARLY WEDNESDAY. ANOTHER RIDGE WILL BUILD OVER THE
REGION FRIDAY AND SATURDAY GIVING DRY AND MILD WEATHER. THE NEXT
FRONT BRINGS A CHANCE OF RAIN BACK INTO THE AREA SUNDAY AND EARLY
NEXT WEEK. NEAR OR ABOVE TEMPERATURES ARE EXPECTED.

&&

.SHORT TERM...HIGH PRESSURE ALOFT WILL CONTINUE OVER THE REGION
TODAY. LIGHT SURFACE FLOW AND NEAR SURFACE BASED MOISTURE ALLOWED
FOR WIDESPREAD FOG TO DEVELOP ACROSS THE LOWLANDS THIS MORNING.
SATELLITE FOG PRODUCT IMAGERY IS OBSCURED BY HIGH CLOUDS BUT MOST OB
SITES ARE REPORTING FOG WITH VISIBILITY BELOW ONE QUARTER MILE
COMMON. WILL ISSUE A DENSE FOG ADVISORY FOR MOST THE LOWLANDS
THROUGH LATE THIS MORNING. GFS/NAM BUFFER SOUNDINGS BOTH SHOW THE
INVERSION CAP BREAKING DURING THE AFTERNOON SO CLEARING SKIES ARE
EXPECTED. PER USUAL...THE SW INTERIOR/S PUGET SOUND WILL BE ONE OF
THE LAST PLACES TO LOSE THE FOG WHICH COULD LINGER INTO THE EARLY TO
MID AFTERNOON HOURS. 500 MB HEIGHTS FALL THROUGH THE DAY BACK BELOW
5700M RESULTING IN SLIGHTLY COOLER TEMPERATURES.
REGARDLESS...EXPECTED HIGHS IN THE MID TO UPPER 50S MAY BREAK
RECORDS IN SOME PLACES. THE RECORD HIGH FOR SEA-TAC IS 58 AND THE
FORECAST IS FOR 59.

THE UPPER RIDGE WEAKENS FURTHER AND STARTS TO SHIFT E OF THE AREA
TONIGHT. AN ELONGATED AND DIFFUSE LOOKING FRONTAL SYSTEM SEEN ON IR
SATELLITE IMAGERY WILL SLOWLY MIGRATE TOWARD WRN WA. 00Z MODEL RUNS
HAVE TRENDED A BIT WEAKER AND SLOWER WHICH IS NOT SURPRISING GIVEN
THE SATELLITE TRENDS. DEEPER MOISTURE ARRIVES AT THE COAST BY LATER
TONIGHT WITH A CHANCE OF RAIN. MODELS SHOW THE FRONTAL BAND
DISSIPATING AS IT PUSHES INLAND SO THERE IS ONLY A CHANCE OF SOME
SPOTTY LIGHT RAIN ON TUESDAY. LESS THAN A TENTH OF AN INCH IS
EXPECTED AND SOME INTERIOR LOCATIONS MAY NOT EVEN MEASURE. IT WILL
BE COOLER WITH HIGHS IN THE LOW TO MID 50S...STILL ABOVE AVERAGE.

MODELS ARE HAVING A DIFFICULT TIME RESOLVING THE WEAK TRAILING SHORT
WAVE THAT MOVES THROUGH ON WEDNESDAY. EVEN WITH THE
INCONSISTENCIES...MOST MODELS INDICATE SOME SPOTTY LIGHT QPF AROUND
WRN WA. IT SEEMS PRUDENT TO KEEP THE SLIGHT RISK OF SHOWERS IN THE
FORECAST FOR THE TIME BEING.

.LONG TERM...HIGH PRESSURE ALOFT BUILDS THURSDAY THROUGH SATURDAY
FOR A PERIOD OF DRY AND MILD WEATHER. INVERSIONS WILL LIKELY RESULT
IN SOME MORNING LOW CLOUDS AND FOG...OTHERWISE MOSTLY CLEAR
AFTERNOONS. HIGH TEMPERATURES WILL BE ABOVE AVERAGE IN THE LOW TO
MID 50S.

LONG RANGE MODELS SHOW THE RIDGE BREAKING DOWN SATURDAY NIGHT AND
SUNDAY AS A MOIST FRONTAL SYSTEM BRINGS RAIN BACK INTO WRN WA. A
TRAILING SYSTEM LIFTS INTO B.C. WHICH MAY BRING ADDITIONAL MOISTURE
INTO WRN WA BEYOND SUNDAY. THERE IS A CHANCE OF RAIN EARLY NEXT WEEK
AND ABOVE AVERAGE TEMPERATURES ARE LIKELY.  MERCER

&&

.HYDROLOGY...FLOODING IS NOT EXPECTED FOR THE NEXT 7 DAYS.

&&

.AVIATION...UPPER LEVEL RIDGE OVER WESTERN WASHINGTON TODAY.  RIDGE
AXIS EAST OF THE AREA WITH SOUTHWESTERLY FLOW ALOFT. RIDGE WEAKENING
TONIGHT AS SYSTEM MOVES INTO BRITISH COLUMBIA. AMS STABLE AND MOIST
BELOW 1500 FEET THIS MORNING.

WIDESPREAD VISIBILITIES 1/2 SM OR LESS AND CEILINGS 200 FEET OR LESS
AT 10Z. SURFACE GRADIENTS ARE LIGHT AND WILL CONTINUE TO BE LIGHT
THIS MORNING. NO TOP REPORTS YET THIS MORNING BUT SANDPOINT PROFILER
SHOWS THE BASE OF THE INVERSION AROUND 400 TO 500 METERS SO EXPECT
THE TOPS TO BE 1000-1500 FEET MSL. THE COMBINATION OF THE SHALLOW
MOIST LAYER AND THE SURFACE GRADIENTS BECOMING SOUTHERLY LATER THIS
MORNING SHOULD RESULT IN A LATE MORNING/MIDDAY BREAKOUT FOR MOST OF
THE AREA. IN THE FOG PRONE LOCATIONS LIKE KOLM THE FOG COULD LAST
INTO THE EARLY AFTERNOON HOURS. JUST SOME HIGH CLOUDS LATER THIS
AFTERNOON INTO TONIGHT AS A VERY WEAK SYSTEM APPROACHES THE AREA.

KSEA...CEILINGS AOB 200 FEET AND VISIBILITIES 1/2SM OR LESS UNTIL
MID MORNING. WITH THE SHALLOW LAYER RAPID IMPROVEMENT LATE MORNING
WITH JUST SOME HIGH CLOUDS BY MIDDAY. LIGHT WINDS. FELTON

&&

.MARINE...LIGHT LOW LEVEL FLOW THIS MORNING. A 1000 MB LOW WILL MOVE
NORTHEAST TO HAIDA GWAII LATER TODAY INCREASING THE SOUTHERLY WINDS
OVER THE COASTAL WATERS AND A FEW LOCATIONS OVER THE INLAND WATERS.
THE FRONT WILL DISSIPATE BEFORE IT MOVES INLAND MONDAY NIGHT INTO
TUESDAY MORNING. LOW LEVEL FLOW WILL TURN ONSHORE TUESDAY BEFORE
SWITCHING BACK AROUND TO LIGHT OFFSHORE WEDNESDAY. THE LIGHT LOW
LEVEL FLOW PATTERN WILL CONTINUE INTO FRIDAY. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...DENSE FOG ADVISORY THROUGH 10 AM PST FOR THE LOWLAND ZONES
     EXCLUDING THE STRAIT OF JUAN DE FUCA AND NORTH COAST.
PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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.