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 48 49 50

000
FXUS66 KSEW 290456
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
955 PM PDT THU AUG 28 2014

.SYNOPSIS...LOW LEVEL ONSHORE FLOW WILL HELP MAINTAIN MARINE
CLOUDINESS IN MUCH OF WESTERN WASHINGTON THE NEXT FEW DAYS. A
PACIFIC WEATHER SYSTEM IN THE NORTHEAST PACIFIC IS EXPECTED TO MOVE
ONSHORE LATER FRIDAY AND SATURDAY BRINGING SOME LIGHT SHOWERS TO THE
AREA. ANOTHER SYSTEM WILL FOLLOW ON SUNDAY. HIGHER PRESSURE IS
FORECAST TO BUILD FOR A DRIER LABOR DAY BEFORE ANOTHER WEAK WEATHER
SYSTEM WITH A THREAT OF SHOWERS MOVES ONSHORE BY THE MIDDLE OF NEXT
WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS THE MID AND HIGH LEVEL CLOUDS
ASSOCIATED WITH A WEAK SHORTWAVE HAVE MOVED INTO THE CASCADES THIS
EVENING. STRATUS ALONG THE COAST HAS NOT YET CONSOLIDATED WITH KUIL
STILL CLEAR AT 04Z WHILE KHQM IS OVERCAST. TEMPERATURES AT 9 PM WERE
IN THE UPPER 50S TO LOWER 70S.

00Z MODEL SOLUTIONS SHOWING GOOD CONSISTENCY WITH THE THE PREVIOUS
MODEL RUNS FOR THE FIRST COUPLE OF DAYS. MAIN STORY FOR WESTERN
WASHINGTON IS THE WARM WEATHER IS OVER WITH A SPELL OF COOLER AND
CLOUDIER WEATHER IN STORE FOR THE NEXT FEW DAYS. ONSHORE GRADIENTS
INCREASING A LITTLE OVERNIGHT IN RESPONSE TO THE NEXT
SHORTWAVE...CURRENTLY NEAR 135W...MOVING EASTWARD. THE INCREASING
ONSHORE FLOW WILL HELP THE STRATUS ALONG THE COAST SPREAD INLAND
EARLY FRIDAY MORNING. DEW POINTS ARE IN THE MID 50S TO LOWER 60S AT
9 PM SO EXPECT SOME OF THE STRATUS TO FORM IN PLACE EARLY FRIDAY
MORNING AS WELL. LOWS TONIGHT IN THE 50S AND LOWER 60S.

SHORTWAVE MOVING THROUGH WESTERN WASHINGTON LATE MORNING THROUGH
FRIDAY AFTERNOON WITH LOW LEVEL ONSHORE FLOW CONTINUING. SATELLITE
IMAGERY SHOWS CLOUD TOP TEMPERATURES WARMING WITH THE SHORTWAVE
WARMING. IN ADDITION THE PARENT LOW OF THE SHORTWAVE IS MOVING
NORTHEAST WHICH IS SPLITTING AND WEAKENING THE SHORTWAVE AS WELL.
EVEN WITH THE SHORTWAVE WEAKENING...IT WILL NOT WEAKEN ENOUGH TO
TAKE A CHANCE OF SHOWERS OUT OF THE FORECAST ON FRIDAY. HIGH
TEMPERATURES WILL CONTINUE TO COOL ON FRIDAY WITH MID 60S TO LOWER
70S.

LOW LEVEL ONSHORE FLOW WITH A CHANCE OF SHOWERS CONTINUING INTO
FRIDAY NIGHT. ANOTHER WEAK SHORTWAVE ARRIVING ON SATURDAY KEEPING AT
LEAST A CHANCE OF SHOWERS FORECAST. THE SHORTWAVE ON SATURDAY LOOKS
TO BE THE STRONGEST OF THE GROUP. IF THE MODEL TRENDS CONTINUE LOOK
FOR THE POPS TO BE INCREASED ON SATURDAY.

YET ANOTHER SHORTWAVE MOVING THROUGH THE AREA SOMETIME LATER SUNDAY
INTO SUNDAY NIGHT. 00Z MODEL CONSISTENCY BOTH RUN TO RUN AND WITHIN
THE MODELS BEGINS TO BREAK DOWN ON SUNDAY WITH THE NAM KEEPING THE
FASTER SOLUTIONS OF THE PREVIOUS RUNS WITH AT LEAST A CHANCE OF
SHOWERS OVER THE AREA BY SUNDAY AFTERNOON. THE 00Z GFS HAS SLOWED
THE SHORTWAVE DOWN MOVING IT THROUGH THE AREA LATE SUNDAY NIGHT INTO
MONDAY MORNING. WITH THE LACK OF CONSISTENCY WILL STAY WITH THE
CHANCE POPS FORECAST.

CURRENT FORECAST HAVE THE TRENDS COVERED. NO UPDATE THIS EVENING.
FELTON

.LONG TERM...THE PROGS DIVERGE QUITE A BIT STARTING ON TUESDAY WITH
THE GFS CLEARLY THE OUTLIER WEDNESDAY AND THURSDAY. THE CMC AND
ECMWF BOTH DIG THE NEXT TROUGH INTO THE PACIFIC NW LATER ON TUESDAY
INTO WEDNESDAY AND SHIFT IT INLAND BY THURSDAY WHILE THE GFS LAGS
BEHIND. AGREE WITH THE PMD DISCUSSION AND HAVE THE FIRST WEEK OF
SCHOOL FORECAST INCREASING THE THREAT OF SHOWERS AGAIN LATER TUESDAY
INTO WEDNESDAY WITH DRIER CONDITIONS THURSDAY. DAYTIME TEMPS DO NOT
REALLY GET MUCH OF CHANCE TO RECOVER FROM HOLIDAY WEEKEND READINGS.
BUEHNER

&&

.AVIATION...LOW LEVEL ONSHORE FLOW CONTINUES ACROSS WESTERN WA
TONIGHT. THE FLOW ALOFT IS WESTERLY. LOW CLOUDS WILL FILL IN
OVERNIGHT WITH MVFR CONDITIONS EXPECTED. A WEAK COLD FRONT WILL
CROSS WESTERN WA ON FRI WITH ISOLATED TO SCATTERED SHOWERS ACROSS
THE REGION. LOW CLOUDS WILL LIFT DURING THE AFTERNOON AND EVENING
FOR VFR CONDITIONS. 33

KSEA...LOW CLOUDS WILL LOWER INTO MVFR RANGE OVERNIGHT. SURFACE
WINDS WILL REMAIN LIGHT SLY. EXPECT SHOWERS IN THE VICINITY ON FRI
AS A COLD FRONT CROSSES WESTERN WA. CIGS WILL RAISE TO AROUND 3000
FT FRI AFTERNOON. 33

&&

.MARINE...POST-FRONTAL ONSHORE FLOW CONTINUES ACROSS WESTERN WA
TONIGHT WITH SMALL CRAFT ADVISORY WINDS THROUGH THE CENTRAL AND EAST
STRAIT OF JUAN DE FUCA. ANOTHER WEAK COLD FRONT WILL CROSS WESTERN
WA ON FRI WITH ONSHORE FLOW INCREASING FRI NIGHT. WILL LIKELY SEE
ANOTHER ROUND OF SMALL CRAFT ADVISORY WINDS THROUGH THE STRAIT. THEN
ANOTHER WEAK SURFACE TROUGH WILL MOVE INLAND ON SUNDAY. HIGH PRES
OVER THE NE PAC WILL MAINTAIN ONSHORE FLOW ACROSS WESTERN WA THROUGH
EARLY NEXT WEEK. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THE 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.