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248
FXUS66 KSEW 301101
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
400 AM PDT THU OCT 30 2014

.SYNOPSIS...A WET PACIFIC FRONTAL SYSTEM WILL BRING SIGNIFICANT
RAINFALL AMOUNTS TO WESTERN WASHINGTON LATER TODAY THROUGH FRIDAY
MORNING. THE FRONT WILL MOVE THROUGH THE AREA FRIDAY MORNING WITH
THE STEADY RAIN CHANGING TO SHOWERS. PARTLY SUNNY SKIES AND JUST A
CHANCE OF SHOWERS ON SATURDAY. A WEAK SYSTEM WILL ARRIVE SUNDAY FOR
MORE RAIN...AND GENERALLY WET WEATHER WILL BE THE RULE FOR AT LEAST
THE FIRST PART OF NEXT WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLOUDY SKIES OVER WESTERN
WASHINGTON EARLY THIS MORNING. DOPPLER AREAS PICKING UP JUST SOME
ISOLATED AREAS OF RAIN OVER THE INTERIOR WITH MOST OF THE
PRECIPITATION ECHOES OFF THE COAST AT 10Z/3 AM. TEMPERATURES WERE
MOSTLY IN THE LOWER TO MID 50S.

COLD FRONT OFF THE COAST THIS MORNING NEAR 132W WITH MOIST
SOUTHWESTERLY FLOW ALOFT AHEAD OF THE FRONT. THE SOUTHWESTERLY FLOW
ALOFT HAS TAPPED INTO SOME SUB TROPICAL MOISTURE SOUTH OF 30N OFF
THE CALIFORNIA COAST BUT TPW IMAGERY SHOWS THE TAP IS THINNING OUT
EARLY THIS MORNING. NARROW CORE OF 1 TO 1.5 TPW VALUES EMBEDDED IN
THE SOUTHWESTERLY FLOW ALOFT WITH MOST OF THE AREA OUT AHEAD OF THE
FRONT IN THE 0.75 TO 1 INCH RANGE. MODEL 850 MB WINDS PICKING UP
OVER THE AREA THIS MORNING TO NEAR 40 KNOTS ALONG THE SOUTH SLOPES
OF THE OLYMPICS BUT THEN DIMINISH DOWN TO 20-25 KNOTS THIS
AFTERNOON. THIS COMBINED WITH THE THINNING SUB TROPICAL TAP WILL
RESULT IN LESS RAINFALL OVER THE MOUNTAINS THAN PREVIOUSLY
ANTICIPATED TODAY. CURRENT OBSERVATIONS SHOW IT IS STILL NOT RAINING
ALONG THE NORTH OREGON COAST AND WITH THE DOPPLER RADARS SHOWING
PRETTY DISORGANIZED PRECIPITATION ECHOES WILL WORD THE FORECAST AS
RAIN AS TIMES THIS MORNING WITH THE STEADY RAIN AFTER THE MORNING
COMMUTE LATE THIS MORNING OR INTO THE EARLY AFTERNOON HOURS. HIGH
TEMPERATURES WILL BE NEAR 60.

FRONT SLOWLY MOVING EAST TONIGHT WITH RAIN OUT AHEAD OF THE FRONT
OVER THE ENTIRE AREA. THE FRONTS EASTWARD MOVEMENT IN THE LAST
COUPLE OF RUNS HAS PICKED UP WITH THE FRONT RIGHT ALONG THE COAST BY
12Z/5AM FRIDAY. MODEL 850 MB WINDS CONTINUE TO BE RATHER WEAK...15
TO 25 KNOTS OUT OF THE SOUTH SO WILL CUT BACK ON THE QPF AMOUNTS IN
THE OLYMPICS AND CASCADES OVERNIGHT. WITH THE RAIN AND CLOUD COVER
TEMPERATURES WILL REMAIN IN THE LOWER TO MID 50S OVERNIGHT.

FRONT MOVING THROUGH WESTERN WASHINGTON FRIDAY MORNING WITH THE
STEADY RAIN GIVING WAY TO SHOWERS. STORM TOTAL RAINFALL IN THE
LOWLANDS IS EXPECTED TO BE IN THE 0.75 TO 1.50 INCH RANGE WITH 1.5
TO 3 INCHES IN THE MOUNTAINS. THERE IS A GOOD CHANCE SEATTLE WILL
PICK UP ENOUGH RAIN FOR THIS OCTOBER TO BREAK INTO THE TOP 10
WETTEST AT SEA-TAC. THERE WILL BE LITTLE TEMPERATURE SPREAD ON
FRIDAY WITH THE COOLER AIR MASS ALOFT MOVING IN BEHIND THE FRONT
WITH HIGHS REMAINING IN THE 50S.

UPPER LEVEL TROUGH REMAINING OVER WESTERN WASHINGTON FRIDAY NIGHT
KEEPING A CHANCE OF SHOWERS IN THE FORECAST. THE AIR MASS WILL BE
RATHER COOL WITH SNOW LEVELS LOWERING DOWN TO AROUND 4500 FEET BUT
THE MOISTURE WILL BE LIMITED SO NOT EXPECTING MUCH IN THE WAY OF NEW
SNOW IN THE MOUNTAINS. LOWS SATURDAY MORNING WILL BE ON THE COOL
SIDE WITH THE COLDER LOCATIONS DIPPING INTO THE UPPER 30S.

MODELS HAVING A HARD TIME WITH THE TIMING OF THE TROUGH PASSAGE
THROUGH WESTERN WASHINGTON. LAST COUPLE OF RUNS OF THE GFS HAVE
SLOWED DOWN THE TROUGH PASSAGE TO MIDDAY SATURDAY WHILE THE ECMWF
DOES NOT BRING THE TROUGH THROUGH UNTIL LATE SATURDAY. BOTH MODELS
HAVE THE JET WELL TO THE SOUTH OF THE AREA WITH LITTLE IN THE WAY OF
DYNAMICS OVER WESTERN WASHINGTON. WILL STAY WITH THE CURRENT
FORECAST THAT HAS THE SHOWER CHANCES CONFINED TO THE SOUTHERN
PORTION OF THE AREA AND THE CASCADES ON SATURDAY. HIGHS WILL BE IN
THE 50S.

.LONG TERM...CONFIDENCE NOT VERY HIGH IN THE EXTENDED PERIOD EARLY
ON WITH THE MODELS LOSING THEIR CONTINUITY BOTH RUN TO RUN AND
AMONG THEMSELVES ON THE 00Z RUN. THE ECMWF IS SLOWER IN EXITING THE
TROUGH ON SATURDAY WHICH SLOWS DOWN THE APPROACH OF THE NEXT SYSTEM
WHICH WAS TIMED INTO THE AREA ON SUNDAY. NOW IS IT SUNDAY NIGHT INTO
MONDAY. THE GFS IS A LITTLE FASTER WITH THIS SYSTEM BUT STILL SLOWER
THAN PREVIOUS MODELS. WITH THE GFS SOLUTION SHOWING THE MOST
CONTINUITY AT THIS POINT WILL STAY WITH THE LIKELY POPS ON SUNDAY.
MODELS COME INTO BETTER AGREEMENT WITH A WET DAY ON MONDAY WITH A
SYSTEM MOVING THROUGH THE AREA MONDAY NIGHT/TUESDAY MORNING. BOTH
THE GFS AND THE ECMWF ARE SHOWING AN ATMOSPHERIC RIVER SCENARIO
SETTLING UP FOR THE MIDDLE OF NEXT WEEK WITH THE ECMWF BEING THE
STRONGER AND THE WETTER OF THE TWO MODELS KEEPING RAIN IN THE
FORECAST THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. FELTON

&&

.HYDROLOGY...A RATHER SLOW MOVING FRONTAL SYSTEM WILL BRING STEADY
PRECIPITATION WESTERN WASHINGTON THROUGH FRIDAY MORNING. THE LARGEST
AMOUNTS WILL FALL OVER THE OLYMPIC AND NORTH CASCADES WITH UP TO 3
INCHES OF RAIN IN THE NEXT 24 HOURS. THE SNOW LEVEL WILL REMAIN HIGH
7000 TO 8000 FEET. THIS AMOUNT OF RAIN COULD ONCE AGAIN DRIVE THE
EXCEPTIONALLY FLOOD-PRONE SKOKOMISH RIVER ABOVE FLOOD STAGE. THE
FLOOD WATCH FOR THE SKOKOMISH WILL CONTINUE THROUGH THIS FORECAST
PACKAGE. IN ADDITION THE NOOKSACK RIVER WILL PROBABLY RISE
SIGNIFICANTLY. FLOODING THERE IS UNLIKELY BUT NOT OUT OF THE
QUESTION...AND A HYDROLOGIC OUTLOOK ADDRESSES THAT SITUATION.

AT THIS TIME FLOODING IS NOT EXPECTED ON THE OTHER RIVERS IN THE
FORECAST FOR THE NEXT 7 DAYS. FELTON

&&

.AVIATION...SW FLOW ALOFT. THE AIR MASS IS STABLE. MOISTURE WILL
INCREASE THIS MORNING AS RAIN BEGINS WITH CIGS EVENTUALLY LOWERING
THROUGH THE DAY....WITH LOW LEVEL SE FLOW OFF THE CASCADES IT MIGHT
TAKE QUITE AWHILE TO DROP UP AND DOWN THE I-5 CORRIDOR BUT THE
MOUNTAINS OUGHT TO BE OBSCURED IN PRECIP.

KSEA...RAIN WILL DEVELOP BEFORE DAYBREAK. WITH LOW LEVEL EASTERLY
FLOW CIGS SHOULD REMAIN FAIRLY HIGH TIL AFTERNOON WHEN THE FRONT
MOVES TROUGH THE INTERIOR OF WRN WA. CIGS WILL DROP FURTHER TONIGHT
IN LIGHT ONSHORE FLOW AND STABLE AIR.

&&

.MARINE...A FRONT WILL MOVE SLOWLY THROUGH WESTERN WA TODAY WITH
SMALL CRAFT ADVISORY LEVEL WINDS MOST WATERS. WEAK HIGH PRES WILL
BUILD INTO THE AREA FRI AND SAT. AN ACTIVE PERIOD OF WEATHER IS
EXPECTED NEXT WEEK AS A SERIES OF FRONTS MOVE THROUGH THE AREA.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH IN EFFECT FROM THURSDAY EVENING THROUGH LATE
     FRIDAY NIGHT FOR MASON COUNTY.

PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR ALL WATERS EXCEPT THE
     PUGET SOUND/HOOD CANAL.


&&

$$

WWW.WEATHER.GOV/SEATTLE

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









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