Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 011608
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
908 AM PDT TUE PEP 1 2015

.SYNOPSIS...A WEAK COLD FRONT WILL BRING RAIN AT TIMES TO WESTERN
WASHINGTON TODAY. A LARGE UPPER LEVEL LOW WILL BE OVER THE REGION
WEDNESDAY THROUGH FRIDAY FOR COOL SHOWERY WEATHER. THE UPPER LEVEL
LOW WILL MOVE EAST THIS WEEKEND FOR A GRADUAL DRYING AND WARMING
TREND.

&&

.SHORT TERM...A WEAK COLD FRONT IS OVER W WA THIS MORNING...
EXTENDING FROM CENTRAL PUGET SOUND ACROSS THE SW WA COAST. THE FRONT
WILL CONTINUE MOVING VERY SLOWLY E AND SE TODAY AND SHOULD DISSIPATE
OVER THE CASCADES TONIGHT. RAIN FROM THE FRONT HAS BEEN LIGHT AND
NOT THAT EXTENSIVE...BUT THAT SHOULD CHANGE THIS AFTERNOON. AN UPPER
LEVEL SHORTWAVE TROUGH OFFSHORE NEAR 135W AND EMBEDDED IN THE W FLOW
ALOFT WILL MOVE OVER W WA THIS AFTERNOON. THE GFS AND NAM SHOW
PRECIP INCREASING THIS AFTERNOON AND CONTINUING INTO EARLY THIS
EVENING...PARTICULARLY ON AND E OF A LINE FROM THE N CASCADES ACROSS
PUGET SOUND AND OVER THE CENTRAL AND S COAST.

THE COLD UPPER LEVEL LOW OVER THE CENTRAL B.C. COAST THIS MORNING
WILL CONTINUE MOVING SE...REACHING SOUTHERN B.C. ON WEDNESDAY. THE
GFS AND NAM BRING A WEAK SHORTWAVE TROUGH...ROTATING AROUND THE S
QUADRANT OF THE LOW...OVER W WA LATE THIS EVENING FOR MORE SHOWERS.

COLDER MORE UNSTABLE AIR THAT IS CURRENTLY ON THE W SIDE OF THE LOW
WILL FOLLOW THE SHORTWAVE TROUGH...MOVING OVER THE COASTAL WATERS
AND W WA WEDNESDAY MORNING. GFS SHOWS LIFTED INDICES IN THIS COOL
UNSTABLE AIR MASS ARE BETWEEN -1 AND -2...SO THERE IS A CHANCE OF
THUNDERSTORMS FOR THE LOWLANDS AND OLYMPICS WEDNESDAY AFTERNOON AND
EVENING. THERE WILL LIKELY BE ISOLATED THUNDERSTORMS OVER THE
COASTAL WATERS AND PERHAPS THE COASTAL STRIP WEDNESDAY MORNING. THIS
WILL BE ADDED IN THE NEXT FORECAST PACKAGE.

ALL MODELS MOVE THE COLD UPPER LEVEL LOW SLOWLY S OVER W WA ON
THURSDAY. SCATTERED SHOWERS WILL CONTINUE. THE GFS SHOWS SMALL AREAS
WHERE LIFTED INDICES ARE JUST A BIT BELOW ZERO...NOT QUITE ENOUGH TO
ADD THUNDERSTORMS TO THE FORECAST. MAX TEMPERATURES WEDNESDAY AND
THURSDAY WILL BE IN THE LOWER TO MID 60S WHICH IS ABOUT 10 DEGREES
BELOW NORMAL.

WITH COLD AIR MOVING S OVER W WA WEDNESDAY AND THURSDAY...SNOW
LEVELS OVER THE MOUNTAINS WILL LOWER TO 5500 TO 6000 FEET WEDNESDAY
AND 5000-6000 FEET THURSDAY. ALONG WITH UNSEASONABLY COLD
TEMPERATURES THE SHOWERS COULD BRING SEVERAL INCHES OF SNOW TO
HIGHER MOUNTAIN ELEVATIONS...PARTICULARLY THE N CASCADES. A SPECIAL
WEATHER STATEMENT REMAINS IN EFFECT HIGH-LIGHTING THIS ISSUE. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 319 AM AFD...THE LONGER
RANGE MODELS HAVE FALLEN INTO BETTER AGREEMENT FOR THE EXTENDED
PERIOD FRIDAY THROUGH MONDAY. THE UPPER TROUGH WILL REMAIN OVER THE
REGION FRIDAY...THEN DRIER NORTHWEST FLOW WILL DEVELOP SATURDAY AS
THE TROUGH MOVES EAST OR SOUTHEAST AND CONTINUE INTO MONDAY. LIGHTER
SHOWERS FRIDAY WILL BECOME LIMITED TO THE CASCADES BY SATURDAY
NIGHT...WITH MOSTLY SUNNY AND WARMER WEATHER SUNDAY AND MONDAY.
MCDONNAL

&&

.AVIATION...A FRONTAL SYSTEM MOVING THROUGH WESTERN WASHINGTON THIS
MORNING WILL PRODUCE LIGHT RAIN AT TIMES THROUGH TONIGHT. CEILINGS
OVER MUCH OF THE LOWLANDS HAVE BEEN RANGING BETWEEN MVFR TO IFR WITH
THE LIGHT RAIN. IN ADDITION TO RAIN WITH THE FRONT THERE HAVE BEEN
SOME BREEZY CONDITIONS WITH GUSTS UP AROUND 20 KNOTS. EXPECT RAIN TO
TRANSITION TO SHOWERS LATER THIS MORNING AS THE FRONT EXITS THE
AREA. THE HIGHER TERRAIN WILL REMAIN OBSCURED TODAY. THE AREAS OF
BREEZY SOUTHERLY WIND WILL DECREASE OVERNIGHT AND TUESDAY MORNING AS
THE FRONT WEAKENS.

KSEA...RAIN BAND ASSOCIATED WITH THE FRONT OVER THE TERMINAL AS OF
16Z. THIS BAND WILL SLOWLY WORK EAST THIS MORNING ALLOWING CEILINGS
TO IMPROVE TO MVFR AND THEN VFR THIS AFTERNOON. RAIN WILL GIVE WAY
TO SHOWERS AS THE FRONT WORKS EAST. SOUTHERLY WINDS 6 TO 10 KNOTS.

&&

.MARINE...A FRONTAL SYSTEM MOVING THROUGH WESTERN WASHINGTON THIS
MORNING BRINGING RAIN TO AREA WATERS. INCREASING SOUTHWESTERLY WINDS
OVER THE COASTAL WATERS TODAY WILL BECOME WESTERLY THIS AFTERNOON
AND EVENING. A SMALL CRAFT ADVISORY REMAINS IN PLACE FOR PARTS OF
THE COASTAL WATERS AND GRAYS HARBOR BAR THROUGH WEDNESDAY MORNING.
A BROAD TROUGH IN THE NORTHEAST PACIFIC WILL GRADUALLY SAG OVER THE
PACNW AND WEAKEN OVER THE NEXT SEVERAL DAYS AND THEN WEAK HIGH
PRESSURE WILL BUILD LATE IN THE WEEK.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES NORTHERN AND CENTRAL OUTER COASTAL
WATERS...GRAYS HARBOR BAR.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS 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.