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

000
FXUS66 KSEW 281716
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1016 AM PDT TUE OCT 28 2014

.SYNOPSIS...A COLD FRONT WILL SWEEP ACROSS THE AREA DURING THE DAY
TODAY...RESULTING IN LOCALLY WINDY CONDITIONS AND SHOWERY WEATHER.
HIGH PRESSURE ALOFT WILL BUILD OVER THE AREA TONIGHT THROUGH
WEDNESDAY FOR IMPROVING CONDITIONS. ANOTHER MOIST PACIFIC STORM
WILL IMPACT THE REGION ON THURSDAY.

&&

.SHORT TERM...
THE AIR MASS HAS DESTABILIZED SLIGHTLY OVER THE CWA THIS
MORNING... RESULTING IN A FEW LIGHTNING STRIKES. HOWEVER...THE
COLD FRONT WAS JUST OFF THE COAST AT THIS TIME AND WILL MOVE
ONSHORE THIS MORNING. EXPECT THE FRONT TO MOVE ACROSS THE PUGET
SOUND REGION THIS AFTERNOON. THE HRRR INDICATED THAT THE AIR MASS
WILL BECOME MORE UNSTABLE THIS AFTERNOON...THUS THE GRIDDED
FORECAST WAS UPDATED TO INCLUDE ISOLATED TSTMS OVER MUCH OF THE CWA.

THE HRRR ALSO INDICATED THAT WINDS WILL INCREASE AGAIN LATE THIS
MORNING OR EARLY AFTERNOON OVER THE NORTHWEST INTERIOR. THE GFS
MOS GUIDANCE SEEMED TO SUPPORT THIS IDEA AS IT SHOWED 27-KNOT /31
MPH/ SUSTAINED WIND AT WHIDBEY ISLAND NAS AT 2100 UTC. FOR THIS
REASON...THE WIND ADVISORY FOR THE NORTHWEST INTERIOR WAS EXTENDED
UNTIL 5 PM PDT TODAY. WILL ALSO NEED TO KEEP AN EYE ON THE WIND
SPEEDS OVER THE PUGET SOUND REGION AND SOUTHWEST INTERIOR WITH THE
FRONTAL PASSAGE. THERE COULD BE BRIEF GUSTS NEAR 40 MPH.

OTHERWISE....LOOK FOR COOL...SHOWERY WEATHER TODAY ACROSS MUCH OF
THE CWA. IN FACT...IT WAS SNOWING IN STEVENS PASS /ELEVATION NEAR
4K FT/ THIS MORNING...WHERE 2 INCHES HAS FALLEN SO FAR. THE TEMP
WAS SLIGHTLY ABOVE FREEZING...SO THE SNOW WAS LIKELY VERY WET.
THE SNOW IS EXPECTED TO CHANGE OVER TO RAIN BY MIDDAY TODAY.

SOUTHWESTERLY FLOW ALOFT CONTINUING OVER WESTERN WASHINGTON TONIGHT
WITH SHOWERS EMBEDDED IN THE FLOW ALOFT MOVING THROUGH THE AREA.
WINDS EASING OVERNIGHT AS SURFACE PRESSURE GRADIENTS DECREASE. LOWS
WILL BE MOSTLY IN THE UPPER 40S TO MID 50S.

SHOWER ACTIVITY DECREASING WEDNESDAY MORNING AS A WEAK RIDGE OF HIGH
PRESSURE BUILDS INTO WESTERN WASHINGTON AND SURFACE PRESSURE
GRADIENTS GO OFFSHORE IN RESPONSE TO THE NEXT APPROACHING WEATHER
SYSTEM. STILL A FEW LINGERING SHOWERS WEDNESDAY MORNING WITH THE
BEST CHANCES FOR SHOWERS IN THE MOUNTAINS. HIGHS ON WEDNESDAY WILL
BE NEAR 60 DEGREES.

AN UPPER RIDGE WILL BUILD OVER THE REGION TONIGHT AND CONTINUE
THROUGH WED FOR IMPROVING OR MORE SETTLED CONDITIONS. IT LOOKS
LIKE THERE WILL BE A DRY PERIOD FOR MUCH OF THE CWA DURING THE
AFTERNOON AND EVENING TIME FRAME.

EXPECT AN OLD BAROCLINIC BAND OFF THE OREGON COAST TO BECOME RE-
ENERGIZED AND CONSOLIDATED WITH AN OCCLUDED FRONT EMANATING OUT
OF THE GULF OF AK WED NIGHT. THE OCCLUDED FRONT WILL SLOWLY MOVE
ACROSS THE CWA DURING THE DAY THU. THIS SYSTEM WILL ALSO BE QUITE
MOIST...THUS HEAVY RAIN IS POSSIBLE ON THE SOUTHWEST FACING SLOPES
OF THE OLYMPICS AND CASCADES.

.LONG TERM FROM THE PREV DISCUSSION...
EXTENDED MODELS IN FAIRLY GOOD AGREEMENT EARLY ON IN THE PERIOD
WITH THE UPPER LEVEL TROUGH OFFSHORE DIGGING SOUTH AND STALLING
THE FRONT OVER WESTERN WASHINGTON THURSDAY NIGHT. THE UPPER LEVEL
TROUGH OFFSHORE WILL MOVE EAST ON FRIDAY...PUSHING WHAT IS LEFT
OF THE FRONT INTO EASTERN WASHINGTON. WITH THE TROUGH STILL
OFFSHORE...SHOWERS WILL REMAIN IN THE FORECAST. THE TROUGH AXIS
WILL MOVE THROUGH FRIDAY NIGHT INTO SATURDAY MORNING...WITH THE
BEST CHANCE FOR A BREAK IN THE PRECIPITATION SATURDAY AFTERNOON.
THE NEXT SYSTEM TO REACH THE AREA WILL MOVE DOWN FROM THE NORTHWEST
SATURDAY NIGHT INTO SUNDAY FOR ANOTHER ROUND OF RAIN.

SOME DIFFERENCES BEGAN TO SHOW UP IN THE MODELS ON MONDAY...WITH
THE ECMWF BUILDING A WEAK RIDGE OVER THE AREA WHILE THE GFS KEPT
THE ZONAL FLOW INTACT AND SHOWED YET ANOTHER SYSTEM MOVING INTO
THE AREA. FOR NOW...WILL STAY WITH THE LIKELY POPS FOR MONDAY.
FELTON

&&

.HYDROLOGY...
1.5 TO 2 INCHES OF RAIN HAS FALLING ON THE SOUTH SLOPES OF THE
OLYMPIC RANGE DURING THE 12-HOUR PERIOD ENDING AT 9 AM PDT. THIS
AMOUNT WAS LESS THAN PREDICTED BUT THE SKOKOMISH RIVER HAS STARTED
TO RESPOND TO THE ADDITIONAL RAINFALL. EXPECT THE RIVER STAGE TO
CONTINUE RISING BEFORE CRESTING THIS AFTERNOON. THERE IS STILL THE
POSSIBILITY THAT THE SKOKOMISH RIVER WILL COME CLOSE TO OR REACH
THE FLOOD STAGE OF 16.5 FEET THIS AFTERNOON. THEREFORE THE FLOOD
WATCH FOR THE SKOKOMISH WILL REMAIN POSTED.

RIVERS FLOODING IS NOT EXPECTED ON THE REMAINING RIVERS THE NEXT
7 DAYS.

&&

.AVIATION...A COLD FRONT IS PASSING THROUGH WESTERN WA THIS MORNING
WITH SHOWERS ACROSS THE REGION...WITH ISOLATED THUNDERSTORMS
POSSIBLE. THE FLOW ALOFT IS WESTERLY. MAY SEE MVFR CIGS IN -SHRA.
THE AIR MASS WILL REMAIN COOL..MOIST AND UNSTABLE THIS AFTERNOON AND
EVENING AS AN UPPER LEVEL TROUGH MOVES THROUGH - EXPECT MORE
SHOWERS. 33

KSEA...SHOWERS WILL REMAIN IN THE VICINITY TODAY. SURFACE WINDS WILL
REMAIN SOUTHERLY AROUND 10 KT. CIGS ARE NEAR 3000 FT. 33

&&

.MARINE...SOUTH FLOW WILL INCREASE IN THE INTERIOR AS A COLD FRONT
PASSES THROUGH WESTERN WA THIS MORNING. GALES WERE EXTENDED THROUGH
00Z FOR ADMIRALTY INLET...EAST ENTRANCE AND THE NORTHERN INLAND
WATERS. ELSEWHERE...WIND SPEEDS WILL REMAIN IN SMALL CRAFT ADVISORY
RANGE. WINDS WILL EASE LATE TONIGHT AS A SURFACE TROUGH EXITS EAST.
WEAK HIGH PRES WILL SETTLE OVER THE REGION ON WED FOR A PERIOD OF
LIGHTER WINDS. THEN ANOTHER PAC FRONTAL SYSTEM WILL AFFECT WESTERN
WA WED NIGHT INTO THU. WILL LIKELY SEE SMALL CRAFT ADVISORY WINDS
OVER THE COASTAL WATERS WITH THIS SYSTEM. WEAK HIGH PRES WILL SHIFT
INLAND ON FRI. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY IN EFFECT UNTIL 5 PM THIS AFTERNOON FOR THE
     NORTHWEST INTERIOR.

     FLOOD WATCH IN EFFECT THROUGH LATE TONIGHT FOR MASON COUNTY.

PZ...GALE WARNING IN EFFECT UNTIL 5 PM THIS AFTERNOON FOR THE
     NORTHERN INLAND WATERS...EAST ENTRANCE TO THE STRAIT OF
     JUAN DE FUCA...AND ADMIRALTY INLET.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING
     WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH BAR UNTIL 11 AM
     WEDNESDAY FOR THE GRAYS HARBOR BAR.

&&

$$

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.