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 202208
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT MON APR 20 2015

.SYNOPSIS...THE WARM SUNNY WEATHER TODAY WILL BE FOLLOWED BY COOL
MARINE AIR PUSHING INTO WESTERN WASHINGTON TUESDAY. AN UPPER TROUGH
AND COLD FRONT WILL REACH WESTERN WASHINGTON BY TUESDAY NIGHT.
ANOTHER FRONT FRONT WILL ARRIVE LATER THURSDAY. A STRONGER WEATHER
SYSTEM IS LIKELY TO REACH THE AREA OVER THE WEEKEND.

&&

.SHORT TERM...THE RIDGE IS WEAKENING AND WILL MOVE SLOWLY INLAND
THROUGH TUESDAY. AN UPPER TROUGH AND COLD FRONT ARE CROSSING 130W
THIS AFTERNOON. ONSHORE FLOW WILL INCREASE TONIGHT AND TUESDAY AND
AS THE TROUGH AND REMNANTS OF THE COLD FRONT ARRIVE THE CHANCE OF
SHOWERS WILL INCREASE TUESDAY AFTERNOON AND NIGHT. THERE IS A GOOD
CHANCE OF A PUGET SOUND CONVERGENCE ZONE TUESDAY NIGHT INTO
WEDNESDAY MORNING. ANOTHER FRONT SHOULD REACH WRN WA THU AFTERNOON.

.LONG TERM...THERE MAY BE A BRIEF PERIOD OF WEAK RIDGING TOWARD THE
END OF THE WORK WEEK BEFORE A COUPLE OF STRONGER FRONTAL WAVES REACH
THE AREA. A LARGE UPPER TROUGH WILL TAKE UP RESIDENCE IN THE NE
PACIFIC AND SPIN OUT SEVERAL SYSTEMS BETWEEN SATURDAY AND THE MIDDLE
OF NEXT WEEK. THE EXTENDED FORECAST IS JUST A BROADBRUSH FORECAST
FOR RAIN LIKELY AS IT IS TOO EARLY TO TIME THE BREAKS BETWEEN
FRONTS...FOR THE MOMENT SATURDAY NIGHT AND SUNDAY MORNING LOOK THE
WETTEST.

&&

.AVIATION...THE UPPER LEVEL RIDGE OVER WESTERN WASHINGTON THIS
AFTERNOON WILL WEAKEN AS IT MOVES EAST OF THE CASCADES TONIGHT. A
WEAK COLD FRONT WILL MOVE THROUGH THE FORECAST AREA TUESDAY...
FOLLOWED BY ITS UPPER TROUGH TUESDAY NIGHT. SOUTHWEST FLOW ALOFT
WILL DEVELOP TONIGHT AND CONTINUE TUESDAY. THE AIR MASS WILL BECOME
MOIST LATE TONIGHT AND TUESDAY AS LOW LEVEL ONSHORE FLOW INCREASES.

MARINE STRATUS ALONG THE COAST THIS AFTERNOON WILL DEEPEN AND PUSH
INLAND AT LEAST WEAKLY TONIGHT. THE MAIN FORECAST PROBLEM IS HOW
STRONG THE MARINE PUSH WILL BE...AND WHETHER THERE WILL BE MUCH
MORNING STRATUS OVER THE WESTERN WASHINGTON INTERIOR LOWLANDS
TUESDAY MORNING. AT THIS TIME THE PUSH LOOKS RATHER WEAK. STRATUS IS
LIKELY TO REACH OLYMPIA LATE TONIGHT...BUT IT WILL PROBABLY RATHER
THIN AND SHORT LIVED IN THE CENTRAL PUGET SOUND REGION TUESDAY
MORNING.

KSEA...NORTH WIND TO 10 KT...BECOMING SOUTHERLY TO 8 KT LATE
TONIGHT...AND SOUTHWEST 6-12 KT TUESDAY AFTERNOON. MARINE STRATUS
WILL PROBABLY REACH KSEA AROUND 13Z WITH SEVERAL HOURS OF SCT-BKN005
TUESDAY MORNING.   MCDONNAL

&&

.MARINE...ONSHORE FLOW WILL STRENGTHEN TONIGHT AS LOW PRESSURE OVER
WESTERN WASHINGTON MOVES EAST OF THE CASCADES. SMALL CRAFT ADVISORY
WINDS ARE LIKELY OVER THE COASTAL WATERS...WESTERN AND CENTRAL
STRAIT OF JUAN DE FUCA...ADMIRALTY INLET...AND NORTHERN INLAND
WATERS. THE STRONGEST WINDS SHOULD OCCUR IN THE CENTRAL AND EASTERN
STRAIT.

ONSHORE FLOW WILL INCREASE FURTHER TUESDAY AND TUESDAY NIGHT AS A
WEAK COLD FRONT MOVES INLAND. GALE WESTERLIES ARE A VERY GOOD BET
FOR THE CENTRAL AND EASTERN STRAIT...AND I HAVE UPGRADED THE GALE
WATCH TO A WARNING WITH THE AFTERNOON FORECAST PACKAGE. MARGINAL
GALES ARE POSSIBLE OVER THE NORTHWEST COASTAL WATERS TOO...BUT I
WILL LEAVE THAT AS A GALE WATCH FOR NOW. SMALL CRAFT ADVISORY WINDS
SHOULD OCCUR...OR CONTINUE...FOR ALL OTHER MARINE ZONES EXCEPT MAYBE
PUGET SOUND AND HOOD CANAL.

ANOTHER WEAK COLD FRONT WILL CROSS THE FORECAST AREA THURSDAY AND
THURSDAY NIGHT...WITH A STRONGER FRONTAL SYSTEM REACHING THE AREA
SATURDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS...CENTRAL AND EASTERN
       STRAIT OF JUAN DE FUCA...ADMIRALTY INLET...NORTHERN INLAND
       WATERS.
    .GALE WARNING FOR TUESDAY NIGHT CENTRAL AND EASTERN STRAIT.
    .GALE WATCH FOR TUESDAY NIGHT COASTAL WATERS ZONES 150 170 173.

&&

$$

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.