Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 181612
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
912 AM PDT SAT APR 18 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL PREVAIL OVER THE REGION
THROUGH MONDAY FOR DRY WEATHER WITH ABOVE NORMAL TEMPERATURES.
UNSETTLED AND COOLER CONDITIONS ARE ANTICIPATED TUESDAY THROUGH
THE END OF NEXT WEEK.

&&

.SHORT TERM...
SKIES WERE MOSTLY SUNNY OVER THE CWA THIS MORNING. THERE WAS
PATCHY FOG IN THE LOWER CHEHALIS RIVER VALLEY EXTENDING INTO GRAYS
HARBOR AT THIS TIME. EXPECT THE FOG TO DISSIPATE DURING THE NEXT
HOUR OR TWO. MEANWHILE...AN UPPER RIDGE WILL PREVAIL OVER THE
REGION THROUGH MON FOR DRY WEATHER WITH ABOVE NORMAL TEMPS.

THE LATEST GFS AND NAM SOLUTIONS STARTED THE MARINE PUSH MON
AFTERNOON OR EARLIER THAN FORECAST...SO THERE IS A POSSIBILITY
THAT THE COAST WILL BE COOLER ON MON. THERE IS ALSO A POSSIBILITY
THAT THE NEXT NAM AND GFS CYCLE WILL DELAY THE MARINE PUSH TIL MON
NIGHT.

.LONG TERM FROM THE PREV DISCUSSION...
THE UPPER RIDGE SHIFTS EAST OF THE CASCADES MONDAY NIGHT AS A
FRONTAL SYSTEM MOVES INTO THE OFFSHORE WATERS. IT APPEARS LIKELY
THAT A GOOD MARINE PUSH WILL BEGIN MONDAY NIGHT OR TUESDAY.

THE 06Z GFS AND 00Z ECMWF ARE A SLIGHTLY SLOWER IN MAKING THE
TRANSITION TO ONSHORE FLOW...AND THAT MAKES THE CLOUD AND
TEMPERATURE FORECAST FOR TUESDAY CHALLENGING. LATE APRIL MARINE
PUSHES AFTER A WARM SPELL CAN BE QUITE DRASTIC HERE IN WESTERN
WASHINGTON WITH 24 HOUR TEMPERATURE FALLS OF 15 TO 20 DEGREES NOT
OUT OF THE QUESTION. THE LATEST WRFGFS FROM THE UNIVERSITY OF
WASHINGTON SHOWS HIGHS IN SEATTLE ON TUESDAY AROUND 70 WHILE THE
NAM12 SHOWS HIGHS IN THE MID TO UPPER 50S. THE CURRENT FORECAST OF
MID 60S WILL BE RETAINED FOR NOW. SHOWER CHANCES DO NOT APPEAR LARGE
WITH THE FRONT OR THE PASSING UPPER TROUGH...GUIDANCE VALUES IN THE
CHANCE CATEGORY ARE SIMILAR TO THE CURRENT FORECAST.

AFTER TUESDAY...THE MODEL RUN-TO-RUN CONSISTENCY IS NOT GREAT WITH
THE 06Z GFS SHOWING WEAK SHORT WAVE RIDGING ON WED WHILE THE ECMWF
SHOWS A STRONG PUSH TUE NIGHT THROUGH THU FOLLOWED BY THE APPROACH
OF A DEEP UPPER TROUGH LATE IN THE WEEK. NO SIGNIFICANT CHANGES
WERE MADE TO THE LONG TERM FORECAST EARLY THIS MORNING. ALBRECHT

&&

.AVIATION...AN UPPER LEVEL RIDGE OVER THE PAC NW WILL GIVE CLEAR
SKIES AND A DRY STABLE AIR MASS OVER WRN WA THIS WEEKEND. THE FLOW
ALOFT IS NORTHWEST.

KSEA...CLEAR SKIES WITH A NORTHERLY BREEZE.

&&

.MARINE...FOR THE COASTAL WATERS THERE WILL BE AFTERNOON AND EVENING
NW WIND 15 TO 25 KT BETWEEN HIGH PRESSURE OFFSHORE AND THERMAL LOW
PRESSURE CENTERED OVER CALIF. ELSEWHERE...WINDS ARE NOT EXPECTED TO
EXCEED 20 KTS. A COLD FRONT WILL ARRIVE TUESDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT TIL 11 PM TONIGHT FOR THE
     COASTAL WATERS.

     SMALL CRAFT ADVISORY FOR ROUGH BAR IN EFFECT TIL 9 PM
     TONIGHT FOR THE GRAYS HARBOR BAR.

&&

$$

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YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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