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

000
FXUS66 KSEW 220003
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
400 PM PST WED JAN 21 2015

.SYNOPSIS...AN APPROACHING WILL CAUSE RAIN TO SPREAD ONTO THE COAST
AND MOVE INLAND THIS EVENING. ADDITIONAL FRONTS WILL MAINTAIN A WET
PATTERN THROUGH SATURDAY. AN UPPER LEVEL RIDGE WILL BRING MORE
SUNSHINE AND MILD WEATHER SUNDAY THROUGH TUESDAY.

&&

.SHORT TERM...THE START OF SW FLOW ALOFT TODAY HAS BROUGHT AN
INCREASE IN MID-HIGH LEVEL MOISTURE...WITH WARM ADVECTION LIFT
GETTING UNDERWAY AS WELL. LIGHT RADAR ECHOES ARE NOW SPREADING ONTO
THE COAST...WITH MORE SUBSTANTIAL AND MEASURABLE PRECIP JUST A
COUPLE OF HOURS AWAY FROM THE COAST. RAIN EXTENDS BACK TO NEAR
130W...SO RAIN WILL CONTINUE FAIRLY STEADILY INTO THU MORNING.
MODELS SHOW A RELATIVE LULL OR LIGHTENING OF THE RAINFALL ON THU
AFTN...AS THE EXIT OF A SHORTWAVE LESSENS THE AMOUNT OF LIFT.
ANOTHER WEAK SHORTWAVE WILL SPREAD MORE RAIN INTO WRN WA ON THU NGT.

ON FRI...WARM AND MOIST W-SW FLOW ALOFT WILL STRENGTHEN AT THE
PERIPHERY OF AN UNSEASONABLY STRONG UPPER RIDGE BUILDING INTO
CALIFORNIA. PW`S WILL RISE TO OVER 1 INCH FROM FRI AFTN THROUGH SAT
MRNG...AND SFC DEWPOINTS WILL EXCEED 50 DEGREES OVER THE LOWLANDS.
WITH W-SW 850 MB WINDS AROUND 35-45 KT...SOME MODERATE TO HEAVY RAIN
WILL RESULT OVER THE COAST AND MTNS. OVER THE WESTERN
OLYMPICS...24-HOUR RAINFALL OF 2-3 INCHES IS POSSIBLE. OVER THE
CASCADES FROM KING COUNTY NORTH...1.5-2.5 INCHES SHOULD BE COMMON.
ALL THE WHILE...SNOW LEVELS WILL RISE INTO THE 7000-9000 FOOT RANGE
DURING THIS TIME...WHICH IS QUITE HIGH FOR THE SEASON. RAINFALL
AMOUNTS DO NOT CAUSE MUCH CONCERN FOR FLOODING...THOUGH MANY RIVERS
WILL SEE RISES.

ON SATURDAY...THE CALIFORNIA UPPER RIDGE WILL EXPAND FURTHER
NORTH...SHOVING OUR RAINS NORTH OF THE CANADIAN BORDER BY SAT NGT.
LOOKING FOR INCREASING SUNSHINE ON SAT AFTN. THE AIR MASS WILL BE
QUITE WARM BY JANUARY STANDARDS...WITH LOWLANDS TEMPS WELL INTO THE
50S...EVEN BEFORE THE SUN COMES OUT.    HANER

CONCERNING KING TIDES...WILL NEED TO KEEP AN EYE ON THE TIDES THE
NEXT FEW DAYS. THE KING TIDES HAVE ALREADY BEGUN ON THE COAST AND
WILL BEGIN IN THE PUGET SOUND REGION ON THE 22ND OR 23RD...DEPENDING
ON SITE LOCATION. CANNOT COMPLETELY RULE OUT THE POSSIBILITY OF
MINOR TIDAL OVERFLOW IN THE PUGET SOUND REGION FRI MORNING.
NOTE...KING TIDES HAPPEN WHEN THE EARTH IS CLOSEST TO THE SUN IN ITS
ELLIPTICAL ORBIT AND THE MOON IS FULL. THIS INCREASES THE
GRAVITATIONAL EFFECTS ON THE EARTH...RESULTING IN HIGHER THAN USUAL
TIDES. WHEN UNUSUAL HIGH ASTRONOMICAL TIDES COINCIDE WITH LOW
PRESSURE...THE RESULT IS EVEN HIGHER TIDES. A LINK TO TIDE
PREDICTIONS FOR SITES IN WESTERN WASHINGTON CAN BE FOUND ON OUR
MARINE WEATHER PAGE.

.LONG TERM...SUNDAY THROUGH AT LEAST TUESDAY LOOK DRY. AN
UNSEASONABLY STRONG UPPER HIGH WILL PASS ACROSS NRN CALIFORNIA ON
SUNDAY...WITH A WARM AIR MASS EXTENDING NORTH INTO WRN WA. THERE
WILL BE ENOUGH WIND ALOFT TO AVOID HAVING THE ATMOSPHERE SIMPLY
BECOMING INVERTED. INVERSIONS ARE MORE COMMON IN THE WINTER WITH
WARM AIR ALOFT. DUE TO THE LACK OF INVERSIONS ON SUDNAY...THE WARM
AIR ALOFT WILL MIX TO THE SFC...MOST EASILY ON SUNDAY AFTN. THE
FORECAST HIGH OF 59F AT SEA-TAC ON SUNDAY ALREADY WOULD BREAK THE
OLD RECORD HIGH FOR THE DATE...AND TEMPERATURES COULD EASILY BE
WARMER AND SURPASS 60F.

SHOULD FINALLY HAVE CLEAR SKIES ON SUNDAY NIGHT...WHICH WILL ALLOW
NIGHTTIME TEMPERATURES TO COOL OFF MORE EASILY. WITH A COOLER START
ON MONDAY...THE AFTN DOES NOT LOOK QUITE AS WARM AS SUNDAY.

UPPER HEIGHTS AND TEMPERATURES ALOFT WILL DROP ON TUESDAY...
SUPPORTING THE EASING OF THE WARM WEATHER. ON WEDNESDAY...SOUTHERLY
FLOW ALOFT AND A SHORTWAVE SCOOTING AROUND THE EDGE OF THE UPPER
RIDGE IS ENOUGH TO RE-INTRODUCE LOW POPS TO THE FORECAST NEXT WED.
TEMPS WILL STILL BE ABOVE NORMAL...BUT WILL NOT BE FLIRTING WITH
RECORD TERRITORY BY THAT TIME.     HANER

&&

.HYDROLOGY...WILL NEED TO WATCH THE SKOKOMISH RIVER FROM FRIDAY
AFTERNOON THROUGH SATURDAY MORNING...WHERE THERE IS A LOW CHANCE OF
MINOR FLOODING. ELSEWHERE...RISES ON RIVERS ARE EXPECTED FRIDAY
NIGHT AND SATURDAY...BUT FLOODING REMAINS UNLIKELY FOR THE NEXT
SEVEN DAYS.     HANER

&&

.AVIATION...A WEAK UPPER RIDGE OVER THE REGION WILL CONT MOVG E...
ALLOWING A WEAK UPPER TROF TO APPROACH FROM THE W. THIS SYSTEM
WILL MOVE ACROSS THE AREA THU MORNING. THE FLOW WILL BE WLY. CONTD
LOW LEVEL LIGHT OFFSHORE FLOW. VFR CONDITIONS ARE EXPECTED TO
PREVAIL ACROSS MUCH OF THE AREA. THERE WILL BE AREAS OF 4-6SM /DUE
TO -RA BR/ AND CIGS OF 1-3K FT MAINLY ON THE COAST AND MAINLY
AFTER 0300 UTC.

KSEA...VFR CONDITIONS ARE ANTICIPATED THROUGH MUCH OF TONIGHT.

&&

.MARINE...
LOW PRES OFFSHORE WITH HIGHER PRES E OF THE CASCADES WILL KEEP
THE FLOW E OR SE THROUGH THU. THE FLOW WILL BECOME SOUTHERLY OR
ONSHORE ON FRI. ONSHORE FLOW WILL CONTINUE ON SATURDAY. MEANWHILE...
A WEAK COLD FRONT WELL OFFSHORE WILL DISSIPATE AS IT MOVES ACROSS
THE COASTAL WATERS OVERNIGHT. A STRONGER FRONTAL SYSTEM WILL
AFFECT THE AREA ON FRI.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR MUCH OF THE COASTAL
     WATERS AND THE WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA.

&&

$$









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