Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 041204
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
300 AM PDT MON MAY 4 2015

.SYNOPSIS...ONE MORE MILD DAY TODAY AFTER MORNING LOW CLOUDS. THEN
CHANGES AS COOLER AND MORE SHOWERY WEATHER ARRIVES TONIGHT AND LASTS
THROUGH WED. DRY AND MILDER WEATHER WITH BUILDING HIGH PRES IS ON TAP
FOR THE END OF THE WEEK...AND POSSIBLY INTO MOTHERS DAY WEEKEND.
&&

.SHORT TERM...LIGHT ONSHORE FLOW THIS AM WILL GRADUALLY INCREASE
TODAY. LOW CLOUDS ARE HUGGING THE COAST INTO THE COAST RANGE...AND
WILL CONTINUE MOVING INLAND THIS AM. BEST THREAT OF THESE WILL BE IN
THE COWLITZ...AND COLUMBIA RIVER VALLEY...THEN CURLING INTO THE N
WILLAMETTE VALLEY AFTER SUNRISE. OTHER AREAS OF THE INTERIOR WILL
ALSO SEE LOW CLOUDS FORM THIS AM...ESPECIALLY OVER CENTRAL AND SOUTH
WILLAMETTE VALLEY. BUT WILL SEE CLOUDS BREAK UP BY LATE MORNING INTO
THE AFTERNOON...WITH ANOTHER MILD DAY ON TAP. HOWEVER... DUE TO THE
ONSHORE FLOW...HIGHS TODAY LIKELY ONLY IN THE MID TO UPPER 60S FOR
THE INTERIOR. COASTAL AREAS WILL HAVE MORE CLOUDS PERSISTING WITH
HIGHS IN THE 50S TO NEAR 60.

FIRST THREAT OF RAIN WILL ARRIVE THIS EVENING AND TONIGHT AS A FRONT
APPROACHES FROM THE WEST. HOWEVER...THIS FRONT IS NOT HOLDING
TOGETHER ALL THAT WELL...SO RAIN WILL BE SPOTTY WITH BEST THREAT OVER
THE COASTAL AREAS INTO THE COAST RANGE LATER THIS EVENING.

THE MAIN UPPER LOW CENTER WILL INITIALLY BE LOCATED TO OUR NORTH...
BUT ENOUGH ENERGY WILL SWING AROUND THE SOUTHERN PERIPHERY OF THE LOW
TO SAG THE COLD POOL INTO OUR FORECAST AREA BY TUESDAY. LOOK FOR
INCREASING SHOWERS TO SPREAD INTO THE COAST LATE TONIGHT AND INLAND
TUESDAY IN THE INCREASING ONSHORE FLOW. SMALL HAIL...GUSTY
WINDS...AND HEAVY SHOWERS ARE POSSIBLE TUESDAY AND TUESDAY EVENING.
SNOW LEVELS WILL LOWER TO AROUND PASS ELEVATIONS ON TUESDAY...BUT
SNOW AMOUNTS WILL TEND TO BE ON THE LIGHTER SIDE. BASED ON EARLIER
SHIFTS MAP ANALYSIS...AND CURRENT MODEL TRENDS...WILL CUT BACK ON
THREAT OF THUNDER A BIT MORE FOR TUE AS INSTABILITY SEEMS TO BE
SLOWING ON ITS ARRIVAL. COLDEST AIR ALOFT ARRIVES LATE TUE NIGHT AND
WED...SO SEEMS THAT WILL BE OUR BEST THREAT FOR ANY THUNDERSTORMS.
STILL...JUST KEEPING AT A SLIGHT CHANCE FOR NOW ACROSS NORTHERN ZONES
ON TUE...THEN BUT FURTHER SOUTH AND INLAND TO CASCADES ON WED.

THE UPPER LOW MOVES INLAND AND EAST OF THE CASCADES BY WEDNESDAY...
WITH SOME ENERGY DIGGING SOUTH INTO CALIFORNIA AND NEVADA. THE FLOW
ALOFT AND AT LOW LEVELS BECOMES MORE NORTHERLY...BUT THERE IS STILL
AMPLE ENERGY DROPPING SOUTH ON THE BACK SIDE OF THE LOW TO KEEP A
THREAT OF SHOWERS GOING FROM THE COAST RANGE WESTWARD. THERE LOOKS TO
BE SOME INSTABILITY AS WELL. THE AFTERNOON HEATING OF THE DAY WILL
PROBABLY LEAD TO AN AFTERNOON AND EVENING PEAK IN THE SHOWER AND
THUNDERSTORM ACTIVITY ON WEDNESDAY. HOWEVER...THE COAST WILL SEE THE
THREAT OF SHOWERS DECREASE ON WEDNESDAY AS THE MAIN DRIVING FORCES
MOVE INLAND.

.LONG TERM...WEDNESDAY NIGHT THROUGH SATURDAY. THE UPPER LOW PRESSURE
WILL SLOWLY CONTINUE SLIDING TOWARDS THE GREAT BASIN OR PERHAPS INTO
CENTRAL CALIFORNIA...WITH SOME SIGNIFICANT DIVERGENCE AMONG MODEL
SOLUTIONS. MEANWHILE HIGH PRESSURE WILL BEGIN TO BUILD OVER THE
EASTERN PACIFIC. WILL DRY OUT THU AND FRI FOR MOST AREAS...BUT WILL
HOLD ON TO A MINOR CHANCE OF SHOWERS ON THE OREGON CASCADES FOR THE
AFTERNOON/EVENINGS. OTHERWISE...HIGH PRES OFFSHORE WILL BUILD AND
BRING DRIER WEATHER WITH A RETURN TO MILD TEMPERATURES. ANOTHER
WEAKENING FRONT WILL ARRIVE NEXT WEEKEND. LIKELY TO BE DRY...BUT NOT
CERTAIN YET. WILL KEEP A VERY MINOR THREAT OF SHOWERS IN FORECAST AT
THIS POINT.
&&

.AVIATION...LOW END MVFR CIGS HAVE SET IN ALONG THE COAST AND ARE
TRYING HARD TO PUSH INLAND AT THIS HOUR BUT ARE MOSTLY FILLING THE
COASTAL VALLEYS. EXPECT SOME RETREATING TO PERHAPS JUST OFFSHORE
BUT DONT FEEL IT WILL LAST SIGNIFICANTLY LONG ENOUGH FOR PILOTS
NOT TO CARRY EXTRA FUEL AS SEA BREEZE WINDS DEVELOP RELATIVELY
EARLY UNDER CLEARER SKIES ALOFT. AN APPROACHING FRONT WILL
REINFORCE THE LOWER DECK ALLOWING IT TO PERSIST THROUGH 05/12Z.
A STRAY THUNDERSTORM MAY APPEAR AFTER 05/06Z BUT HAVE FAR TOO LOW
OF CONFIDENCE FOR TAF INCLUSION AT THIS POINT.

FOR INLAND TERMINALS...SATELLITE FOG PRODUCT APPEARS TO BE
HINTING AT SOME STRATUS TRYING TO DEVELOP IN THE CENTRAL AND
SOUTHERN WILLAMETTE VALLEY BUT AM NOT SEEING ANYTHING DEFINITIVE
JUST YET. WILL CONTINUE TO CARRY THE HINTS OF A LOW END MVFR DECK
FOR THE NORTHERN INLAND TAFS AND A BROKEN DECK FOR KSLE AND KEUG.
EXPECT PEAK COVERAGE WILL DEVELOP AROUND 13Z NEAR SUNRISE THEN
SCATTERING AROUND 17Z EXCEPT PERHAPS CLOSER TO 19Z FOR KEUG.
EXPECT TO SEE A LOW END VFR CIG START PUSHING IN FROM AN
APPROACHING WEAK FRONT AROUND 00Z THEN LOWERING TO AROUND 025
CLOSER TO 06Z WITH LIGHT SHOWERS BECOMING POSSIBLE.

KPDX AND APPROACHES...VFR THROUGH 05/06Z. APPROACHING FRONT LOWERS
CIGS TO AROUND 040 AFTER 00Z THEN DOWN TO AROUND 025 AFTER 06Z
WITH INCREASING SHOWER ACTIVITY. /JBONK
&&

.MARINE...HIGH PRES EXITS THE AREA TODAY. APPROACHING FRONT
CONTINUES TO WEAKEN PER MODELS WITH ONLY AN OUTSIDE CHANCE OF
GUSTS EXCEEDING 21 KT SMALL CRAFT ADVISORY CRITERIA OVER THE NEXT
24 HOURS. MAY GET SPORADIC GUSTS 25 TO 30 KT UNDER SHOWERS AND
POSSIBLE THUNDERSTORMS MONDAY NIGHT THROUGH TUESDAY.
OTHERWISE...MODELS
KEEP WINDS SOMEWHAT BELOW 20 KT UNTIL SURFACE HEAT LOW DEVELOPS
ALONG THE SW OREGON COAST THURSDAY AND FRIDAY. MAY GET NORTHERLY
20 TO 25 KT GUSTS FOR THE CENTRAL WATERS THEN.

BIGGER CONCERN WILL BE A COMPLICATED SET OF SWELLS CROSSING THE
WATERS FOR THE NEXT FEW DAYS. DYNAMIC FETCH UNDER EASING WINDS
BRINGS A WNW SWELL OF 8 TO 10 FT IN MONDAY NIGHT AND TUESDAY. ALL
THE WHILE... A PAIR OF LONG PERIOD 2 AND 3 FT SWELLS...PERIODS 17
AND 22 SECONDS RESPECTIVELY...CROSS FROM THE SOUTH. ADD IN SOME
WIND WAVE AND THE CONFUSED SEAS WILL ADD UP AND EXCEED 10 FEET FOR
THE BETTER PART OF THIS EVENING THROUGH TUESDAY EVENING. THE LONG
PERIOD SOUTHERLIES WILL CONTINUE THROUGH WEDNESDAY BEFORE EASING
BACK TO THE TYPICAL BACKGROUND VALUES. OVERALL SEAS WILL THEN
REMAIN 6 FEET OR LESS BUT CONTINUE TO SHOW MULTIPLE DISTANT
SOURCES IN ADDITION TO LOCALLY INDUCED WIND WAVES. /JBONK
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 8 PM THIS EVENING
     TO 9 PM PDT TUESDAY FOR WATERS FROM CAPE SHOALWATER WA TO
     CASCADE HEAD OR FROM 10 TO 60 NM-WATERS FROM CASCADE HEAD
     TO FLORENCE OR FROM 10 TO 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 AM TO 8 PM PDT
     TUESDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     CASCADE HEAD OR OUT 10 NM-COASTAL WATERS FROM CASCADE HEAD
     TO FLORENCE OR OUT 10 NM.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.



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