Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 221744
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
940 AM PST THU JAN 22 2015

.SYNOPSIS...A WEAK WARM FRONT WILL SPREAD LIGHT RAIN TO WESTERN
WASHINGTON TODAY AND TONIGHT. A MOIST FLOW OF JET STREAM WIND WILL
BRING EVEN HEAVIER RAIN ON FRIDAY AND FRIDAY NIGHT...WHILE ALSO
MAINTAINING MILD TEMPERATURES ACROSS THE REGION. A STRONG UPPER
HIGH WILL EXPAND INTO WESTERN WASHINGTON LATER SATURDAY AND PERSIST
THROUGH TUESDAY...BRINGING DRY WEATHER.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS THE ENHANCED CLOUDS WITH ONE
WEAK WARM FRONT EXITING EAST OF THE CASCADES NOW...WHILE ENHANCED
CLOUDS WITH THE NEXT WARM FRONT WILL SOON CROSS INSIDE OF 130W. THE
SPACE IN BETWEEN WILL ACT AS A RELATIVE LULL IN RAINFALL THIS
AFTERNOON...AND PARTICULARLY THIS EVNG ALONG THE I-5 CORRIDOR.
RELATIVE IS THE KEY WORD...WITH KLGX RADAR SHOWING A LOT OF SHALLOW
SHOWER ACTIVITY CONTINUING TO SPREAD ONTO THE COAST RIGHT NOW IN
THIS SUPPOSED LULL. FROM A SENSIBLE STANDPOINT...MAY BE HARD TO
NOTICE MUCH BREAK BETWEEN SYSTEMS ALONG THE COAST TODAY...BUT THE
INTERIOR SHOULD GET A MORE NOTICEABLE BREAK IN THE RAIN OF A FEW
HOURS DURING THE LATE THIS AFTERNOON AND EARLY THIS EVENING.

THE FRONT CURRENTLY NEARING 130W WILL REACH THE COAST EARLY THIS
EVNG...DRIVEN ALONG AT THE NOSE OF A FAST AND MOIST FLOW OF JET
STREAM WINDS TO ITS WEST. EVEN AFTER THE INITIAL FRONT PASSES ON FRI
MORNING...STRONG JET STREAM FLOW AROUND AN UNSEASONABLY STRONG UPPER
HIGH TO OUR SOUTH WILL DRIVE A RICHLY MOIST AND MILD AIR MASS INTO
WRN WA...WITH PW`S WELL IN EXCESS OF ONE INCH AND SFC DEWPOINTS
EXCEEDING 50F ON FRI AND SAT. W-SW 850 MB WINDS OF 35-50 KT WILL
KICK IN FROM FRI THROUGH SAT MORNING...OROGRAPHICALLY LIFTING THE
MOIST AIR OVER THE MTNS. ALL THE WHILE...SNOW LEVELS WILL BE QUITE
HIGH FOR THE SEASON. THE 12Z GFS CONFINES THE HEAVIEST RAIN FROM FRI
THROUGH SAT MORNING TO THE NORTH CASCADES...WHILE THE 12Z NAM BRINGS
HEAVIER AMOUNTS FURTHER SOUTH OVER THE HEADWATERS OF THE SNOHOMISH
AND OVER THE OLYMPIC MTNS. THE NAM SOLUTION WOULD CAUSE ME SOME
CONCERN FOR MINOR RIVER FLOODING...WHILE THE MORE TYPICALLY RELIABLE
GFS DOES NOT CAUSE ME MUCH CONCERN.

ON SATURDAY...THE STRONG UPPER HIGH TO OUR SOUTH WILL START TO
EXPAND NORTHWARD...PUSHING THE FEED OF MOISTURE AND JET STREAM WINDS
NORTH TO THE CANADIAN BORDER ON SAT AFTN...THEN NORTH OF THE BORDER
ON SAT NIGHT.

BY SUNDAY...ALL OF THE RAIN AND MOST OF THE CLOUDS WILL HAVE BEEN
SHOVED NORTH OF THE CANADIAN BORDER...LEAVING WRN WA UNDER THE
INFLUENCE OF A MILD AIR MASS...EVEN BEFORE THE SUN APPEARS. THE
STRONG UPPER HIGH TO OUR SOUTH WILL PUMP WARMER AND DRIER AIR ALOFT
OVER THE AREA ON SUNDAY AND MONDAY...WITH 850 MB TEMPS OF +9C TO
+14C. ON SUNDAY AT LEAST...ENOUGH WIND WILL CONTINUE AT THE TOP OF
THE BOUNDARY LAYER TO MIX THE WARMTH TO THE SURFACE. AS A
RESULT...THE CURRENT FORECAST CALLS FOR A RECORD HIGH TEMPERATURE AT
SEA-TAC ON SUNDAY.   HANER

CONCERNING TIDES...THE OBSERVED TIDES HAVE BEEN RUNNING LOWER THAN
THE PREDICTION. THUS...THE PROBABILITY OF MINOR TIDAL OVERFLOW HAS
DIMINISHED. WILL STILL NEED TO MONITOR THE TIDES IN THE PUGET SOUND
REGION BECAUSE THE KING TIDES FRI MORNING WILL BE CLOSE TO THE LEVEL
AT WHICH MINOR TIDAL OVERFLOW BEGINS.

.LONG TERM...FROM PREVIOUS DISCUSSION...AN UPPER LEVEL RIDGE WILL
CONTINUE TO BRING DRY WEATHER TO WESTERN WA ON MON. A WEAK UPPER
LEVEL DISTURBANCE MAY CLIP THE REGION TUE NIGHT OR WED AS THE RIDGE
SHIFTS EAST AND INLAND. FOR NOW WILL STICK WITH A CHANCE OF RAIN
BOTH PERIODS. THE ECMWF SHOWS THE RIDGE REBUILDING LATE IN THE WEEK
FOR DRY WEATHER AGAIN. THE GFS HOWEVER SHOWS SOME MOISTURE CLIPPING
THE AREA. THE CURRENT FORECAST IS CLOSER TO A BLEND SINCE THE MODELS
ARE OFF. 33

&&

.HYDROLOGY...WILL NEED TO WATCH THE SKOKOMISH RIVER FROM FRIDAY
AFTERNOON THROUGH SATURDAY MORNING...WHERE THERE IS A LOW CHANCE OF
MINOR FLOODING. ELSEWHERE...SIGNIFICANT RISES ON RIVERS ARE EXPECTED
FRIDAY NIGHT AND SATURDAY...ESPECIALLY ON RIVERS FLOWING OFF THE
NORTH AND CENTRAL CASCADES. HOWEVER...FLOODING REMAINS UNLIKELY FOR
THE NEXT SEVEN DAYS.

&&

.AVIATION...A WEAK UPPER TROF OVER THE AREA WILL MOVE INTO ERN WA BY
2000 UTC. A WEAK UPPER RIDGE WILL FOLLOW IN ITS WAKE. WLY FLOW ALOFT
WILL CONT BUT WILL STRENGTHEN SOME OVERNIGHT. CONTD WEAK LOW LEVEL
OFFSHORE FLOW.

ANTICIPATE AREAS OF CIGS IN THE 1-3K FT RANGE THRU TONIGHT ALONG
WITH AREAS OF 4-6SM -RA BR. THE MTNS WILL BE MOSTLY OBSCD.

KSEA...CIGS ARE EXPECTED TO LIFT INTO THE VFR CATEGORY RANGE BY
2400 UTC. OTHERWISE...ANTICIPATE OCNL -RA TODAY.

&&

.MARINE...
LOW PRES OFFSHORE AND HIGHER PRES INLAND WILL RESULT IN E OR SE
FLOW THROUGH TONIGHT. EXPECT A FRONTAL SYSTEM TO AFFECT THE AREA
ON FRI...RESULTING IN INCREASED SOUTHERLY OR ONSHORE FLOW. ONSHORE
FLOW WILL PERSIST ON SATURDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FROM 6 PM THIS EVENING TIL 4
     PM FRIDAY FOR THE COASTAL WATERS.

&&

$$

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