Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 262248 AAA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT TUE APR 26 2016

.SYNOPSIS...LOW PRESSURE WILL SPLIT OFFSHORE AND SHIFT SOUTHEAST INTO
OREGON TONIGHT AND WEDNESDAY. THERE IS A CHANCE OF SPOTTY LIGHT RAIN
REACHING THE COAST THIS EVENING...SPREADING INTO MOSTLY SOUTHERN
PARTS OF THE INTERIOR LATER TONIGHT AND WEDNESDAY. HIGH PRESSURE
WILL BRING A PERIOD OF DRY WEATHER THURSDAY. THE NEXT QUICK MOVING
FRONT WILL BRING SOME SHOWERS TO THE AREA FRIDAY WITH A POSSIBLE
CONVERGENCE ZONE LINGERING INTO FRIDAY EVENING. DRY WEATHER AND A
WARMING TREND IS EXPECTED SATURDAY THROUGH MONDAY. A RETURN TO
COOLER ONSHORE FLOW AND SHOWERS MAY DEVELOP TUESDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS MID AND HIGH CLOUD SPREADING
INTO WESTERN WASHINGTON WITH OVERCAST SKIES FILLING IN OVER PUGET
SOUND BY THIS EVENING. BRIGHTER CLOUD TOPS ON IR IMAGERY IMPLY THE
SURFACE LOW ALONG THE FRONT IS HEADING TOWARD OREGON WITH A WEAKER
NORTHERN PORTION OF THE FRONT STILL OFF THE WA COAST. THIS SPLIT IS
IN LINE WITH MOST MODEL SOLUTIONS WHICH TAKE THE BULK OF MOISTURE
AND DYNAMICS SOUTH OF OUR AREA. THE WEAKER NORTHERN PORTION OF THE
FRONT WILL WEAKEN AND GRADUALLY DRAG THROUGH THE AREA LATER TONIGHT
AND WEDNESDAY. MESO MODELS ARE IN AGREEMENT THAT ANY LIGHT RAIN WILL
BE SPOTTY WITH LESS THAN A TENTH OF AN INCH AT ANY GIVEN LOCATION
THE NEXT 24 HOURS. MANY SPOTS OVER THE PUGET SOUND METRO AREA FROM
TACOMA NORTH MAY END UP NO MORE THAN A TRACE. THE COAST AND SW
INTERIOR HAVE THE BEST CHANCE OF MEASURING.

A PERIOD OF MOSTLY DRY WEATHER IS EXPECTED WEDNESDAY NIGHT AND
THURSDAY. MODELS SHOW A BRIEF 500 MB RIDGE TRAVERSING THE REGION
WITH SLIGHT HEIGHT RISES AND LIGHT ONSHORE FLOW. PARTIAL SUNSHINE
SHOULD ALLOW TEMPERATURES ON THURSDAY TO WARM A FEW DEGREES COMPARED
TO WEDNESDAY.

THE NEXT PROGRESSIVE TROUGH AND WEAK FRONT PUSH INTO WESTERN
WASHINGTON LATE THURSDAY NIGHT AND FRIDAY MORNING. THIS FRONT IS
EXPECTED TO REMAIN MORE CONSOLIDATED BUT WILL PUSH THROUGH TOO QUICK
TO BRING MUCH APPRECIABLE RAIN. THE COAST AND MOUNTAINS COULD GET UP
TO A QUARTER INCH AND MAYBE A TENTH OF AN INCH ACROSS PORTIONS OF
THE INTERIOR. MODELS DO SHOW A FAVORABLE SURFACE FLOW PATTERN FOR A
PUGET SOUND CONVERGENCE ZONE TO FORM BETWEEN EVERETT AND NORTH
SEATTLE. A CONVERGENCE ZONE RAIN BAND MAY BE ACTIVE IN THIS CORRIDOR
FRIDAY AFTERNOON INTO THE EVENING WHILE SHOWERS BEGIN TO DECREASE
ELSEWHERE ACROSS THE AREA. HIGHS WILL COOL BACK DOWN TO THE 50S.

.LONG TERM...LONG RANGE MODELS REMAIN IN GOOD AGREEMENT THAT A
STRONG RIDGE OF HIGH PRESSURE BUILDS OVER THE PAC NW THIS WEEKEND
INTO AT LEAST MONDAY OF NEXT WEEK. 500 MB HEIGHTS BUILD OVER THE
WEEKEND BUT ONSHORE FLOW SATURDAY WILL INITIALLY HOLD BACK POTENTIAL
HIGHS. TEMPERATURES WILL STRUGGLE TO GET MUCH ABOVE 60 ALONG THE
COAST...STRAIT...AND NORTH INTERIOR NEAR THE WATER. FURTHER INLAND
AND AROUND PUGET SOUND IT SHOULD WARM INTO THE LOW TO MID 60S AFTER
MORNING CLOUDS BURN OFF.

THE POSITIVE TILT RIDGE BUILDS MORE DIRECTLY OVER WA ON SUNDAY
ALLOWING THERMALLY INDUCED LOW PRESSURE TO BUILD NORTH ALONG THE
OREGON COAST AND INTO SW WA. SOME MODELS SHOW THE HEAT LOW SHIFTING
ALONG THE WA COAST OR EVEN JUST OFF THE COAST MONDAY WHICH WOULD
INDUCE STRONG OFFSHORE FLOW AND USHER IN DRIER DOWNSLOPE FLOW.
FORECAST HIGHS WERE BOOSTED TO WELL ABOVE AVERAGE SUNDAY AND MONDAY
WITH WIDESPREAD 70S A GOOD BET. I WOULD NOT BE SURPRISED TO SEE SOME
LOW 80S BY THE END OF THIS NEXT ROUND OF WARM TEMPERATURES. THE
GFS/ECMWF/CANADIAN VARY ON WHEN THE NEXT SYSTEM ARRIVES OR AT LEAST
WHEN ONSHORE FLOW RESUMES. TUESDAY SEEMS THE MOSTLY LIKELY DAY WITH
GFS/CANADIAN SHOWING EITHER SW FLOW ALOFT INDUCING SOME LOW LEVEL
ONSHORE FLOW OR POSSIBLY SOME SHOWERS WITH A FRONT PER THE CANADIAN
SOLUTION. KEPT SOME LOW POPS IN THE FORECAST AND LOWERED HIGHS BY
ROUGHLY 10 DEGREES WHICH WOULD STILL BE ABOVE AVERAGE. THIS APRIL
COULD VERY WELL END AS THE WARMEST ON RECORD.  MERCER

&&

.AVIATION...MID AND HIGH CLOUDS WILL INCREASE AHEAD OF A WEAK FRONT
THAT IS STALLED JUST OFFSHORE AND WILL SHIFT INTO OREGON AND NRN
CALIF THRU WED. THE COAST HAS A CHANCE OF LIGHT RAIN TONIGHT AND WED
MORNING.


KSEA...MID LEVEL CLOUDS WILL INCREASE OVERNIGHT FROM A WEAK FRONT
THAT WILL MOVE SOUTH OF THE AREA WED.

&&

.MARINE...A WEAKENING FRONT OVER THE OFFSHORE WATERS WILL
DISSIPATE BEFORE REACHING THE COAST LATER TONIGHT AND WED. WEAK HIGH
PRESSURE OVER THE AREA THU AND FRI WILL STRENGTHEN FOR THE WEEKEND.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.


&&

$$

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