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 291051 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
351 AM PDT FRI AUG 29 2014

CORRECTED MINOR TYPOS IN THE SYNOPSIS AND SHORT TERM SEGMENTS.

.SYNOPSIS...LOW PRESSURE ALOFT WILL DOMINATE THE WEATHER PATTERN
OVER THE REGION THROUGH THIS WEEKEND FOR COOL AND UNSETTLED
CONDITIONS. LOOK FOR A WEAK COLD FRONT TO SWEEP ACROSS THE AREA
LATER THIS MORNING. A SLIGHTLY STRONGER FRONT IS EXPECTED TO IMPACT
THE REGION ON SUNDAY.

&&

.SHORT TERM...
THERE WAS SOME LIGHT PRECIP OCCURRING WELL OFFSHORE AT THIS TIME.
THE 0600 UTC GFS ARRIVED AND WAS WETTER THAN THE PREVIOUS CYCLE.
THE CURRENT FORECAST WAS BASED ON THE 0000 UTC RUN...AND MAY BE
A LITTLE ON THE DRY SIDE.

MEANWHILE...AN UPPER TROF WILL DOMINATE THE WEATHER PATTERN OVER
THE PACIFIC NORTHWEST THROUGH SATURDAY. EXPECT A WEAK COLD FRONT
TO SWEEP ACROSS THE CWA LATER THIS MORNING...FOLLOWED BY A SURFACE
TROF ON SATURDAY. THUS...EXPECT COOL AND UNSETTLED CONDITIONS FOR
THIS PERIOD.

CONCERNED THAT THE MODELS QUANTITATIVE PRECIP FORECASTS MIGHT BE
UNDERESTIMATING THE PRECIP AMOUNTS DURING THE SHORT TERM PERIOD. THE
SATELLITE-DERIVED PRECIPITABLE WATER /PWAT/ IMAGERY INDICATED
THAT...IN GENERAL...THE AIR MASS OVER THE NORTHEAST PACIFIC WAS
QUITE MOIST. PWAT VALUES WERE GENERALLY IN THE 1-2 INCH RANGE OR
OVER 100 PERCENT OF NORMAL. SOME OF THIS MOISTURE WAS ALREADY
BECOMING ENTRAINED IN THE SYSTEM OFF OUR COAST.

EXPECT ANOTHER LOW PRESSURE SYSTEM TO IMPACT THE AREA ON SUNDAY.
THERE WERE SOME DISAGREEMENTS IN THE TIMING AND...TO A LESSER
DEGREE...THE STRENGTH OF THIS SYSTEM. THE ECMWF AND GFS WERE FASTER
IN EJECTING THIS SYSTEM OUT OF THE AREA WHEREAS THE CANADIAN AND NAM
WERE A LITTLE SLOWER. HAVE CHOSEN TO COMPROMISE BETWEEN THE TWO
SOLUTIONS.

.LONG TERM...
IT APPEARED THAT THE REGION WILL BE MORE UNDER THE INFLUENCE OF AN
UPPER RIDGE ON MON. BEYOND MON...CONFIDENCE IN THE FORECAST WAS
SOMEWHAT LOW. IT LOOKS LIKE THE THE MEDIUM RANGE SOLUTIONS MIGHT
BE LEANING TOWARD HOLDING ONTO AN UPPER TROF OVER THE AREA LONGER
THAN THE PREVIOUS RUNS. DUE TO LACK OF CONFIDENCE...THE ONLY CHANGES
MADE TO THE EXTENDED WERE TO BLEND BETTER WITH NEIGHBORS.

&&

.AVIATION...LOW LEVEL ONSHORE FLOW CONTINUES ACROSS WESTERN WA
TODAY. THE FLOW ALOFT IS WESTERLY. A WEAK COLD FRONT WILL CROSS THE
REGION THIS MORNING WITH ISOLATED TO SCATTERED SHOWERS. CIGS ARE A
MIXED BAG BUT SHOULD SEE MAINLY MVFR CONDITIONS THIS MORNING. LOW
LEVEL CLOUDS WILL LIFT DURING THE AFTERNOON AND EVENING FOR VFR
CONDITIONS. 33

KSEA...EXPECT MVFR CONDITIONS THIS MORNING. SURFACE WINDS WILL
REMAIN LIGHT SLY. CIGS WILL RAISE TO AROUND 3000 FT THIS AFTERNOON.
33

&&

.MARINE...A WEAK COLD FRONT WILL CROSS WESTERN WA TODAY. ONSHORE
FLOW WILL INCREASE BEHIND THE FRONT THIS EVENING AND WILL LIKELY SEE
SMALL CRAFT ADVISORY WINDS THROUGH THE CENTRAL AND EAST STRAIT OF
JUAN DE FUCA. 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 IN EFFECT UNTIL 5 AM SATURDAY FOR THE
     CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

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.