Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 041605
AFDPQR

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

.SYNOPSIS...A WEAK FRONTAL SYSTEM IS EXPECTED TO REACH THE COAST LATE
THIS AFTERNOON AND THEN INLAND TONIGHT. A MUCH COOLER AIR MASS
ASSOCIATED WITH AN UPPER LEVEL LOW WILL BE OVER THE REGION TUESDAY
AND WEDNESDAY. THE COOLER AND UNSETTLED PATTERN WILL RESULT IN A RISK
OF THUNDERSTORMS...PRIMARILY ON TUESDAY. DRIER NORTH FLOW ALOFT MOVES
IN THURSDAY. DRY AND SEASONAL CONDITIONS ARE EXPECTED FRIDAY AND
THROUGH THE WEEKEND.
&&

.SHORT TERM...FIRST VISIBLE SATELLITE IMAGES SHOWS STRATUS WELL INTO
THE COASTAL VALLEYS AND THROUGH THE CENTRAL COAST RANGE TO KEUG AND
SLIGHTLY BEYOND. NOT AS MUCH INTRUSION DOWN THE COLUMBIA RIVER.
COASTAL PIREPS INDICATED TOPS TO AROUND 4K FT. THE LOW-LEVEL ONSHORE
FLOW WILL CONTINUE TO INCREASE THROUGH THE DAY. 12Z NAM AND HI-RES
ARW SHOW 90 PCT OR GREATER 975 MB MOISTURE RETREATING BACK TO THE
COASTLINE THIS AFTERNOON...WITH SOME CUMULUS OR HIGH-LEVEL
STRATOCUMULUS OVER THE CASCADES. MODELS THEN SHOW RAPID INCREASE IN
THE 975 MB MOISTURE THIS EVENING.

INITIAL PRECIP THREAT WILL BE ALONG THE COAST THIS AFTERNOON AS THE
FRONT MOVES ACROSS THE AREA. HAVE ADDED DRIZZLE WORDING TO THE COAST
THIS AFTERNOON. AS 850 MB TEMPS DROP THIS EVENING AND TONIGHT AND THE
AIR MASS BECOMES SLIGHTLY MORE UNSTABLE...WILL SEE AN INCREASING
SHOWER THREAT FROM NW TO SE. GFS 850 MB CASCADE TEMPS FALL FROM
AROUND 10C 18Z MON TO 0C BY 12Z TUE. LOWERED SNOW LEVELS A BIT
TONIGHT TO BETTER MATCH 1000-500 MB THICKNESS VALUES AND FORECAST 850
MB TEMPS.

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...WITH A
COUPLE INCHES ACCUMULATION POSSIBLE ABOVE THE PASSES. THUNDER THREAT
CONTINUES WED...ALTHOUGH NAMM SOUNDING FOR KPDX WOULD SUGGEST THE
BETTER THREAT LOOKS TO BE LATE TUE AFTERNOON THROUGH THE EVENING.
NAMM KPDX SOUNDING SHOWS VERY SKINNY CAPE PROFILE LATE WED
MORNING...WITH DIMINISHING CAPE IN THE AFTERNOON AS THE INVERSION TOP
GRADUALLY LOWERS.  WEISHAAR

.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...MVFR STRATUS ALONG THE COAST HAS PUSHED INTO THE
SOUTHERN WILLAMETTE VALLEY AND UP THE COLUMBIA RIVER TO NEAR KPDX
UNDER A WEAK SOUTHWEST PUSH. EXPECT INTERIOR STRATUS TO BURN BACK
TO THE COAST RANGE TOWARDS MIDDAY...BEFORE PUSHING BACK INLAND
THIS EVENING AS AN UPPER LEVEL TROUGH PUSHES TOWARDS THE REGION.
LOW LEVEL COLD ADVECTION MAY KEEP VFR CONDITIONS GOING AT INTERIOR
TAF SITES THROUGH APPROXIMATELY 09 TO 12Z TUESDAY BEFORE HIGH END
MVFR CIGS TO LOW END VFR CIGS BEGIN TO TAKE HOLD. EXPECT ANY
PERSISTENT FLIGHT RESTRICTIONS TUESDAY MORNING TO DISSIPATE
TOWARDS 18Z TUESDAY

KPDX AND APPROACHES...EXPECT VFR CONDITIONS THROUGH THIS EVENING.
INCREASING ONSHORE FLOW AND LOW LEVEL MOISTURE WILL LEAD TO A MIX
OF HIGH END MVFR CIGS AND LOW END VFR CIGS BETWEEN 09Z AND 18Z
TUESDAY. /NEUMAN

&&

.MARINE...AN UPPER LEVEL TROUGH WILL SAG OVER THE REGION TONIGHT
THROUGH WEDNESDAY BRINGING RELATIVELY LITTLE IN THE WAY OF
MEANINGFUL WINDS. HOWEVER...AN INCOMING SWELL WILL BRING SEAS UP
TO AROUND 10 FT FOR A 6-18 HOUR PERIOD TONIGHT AND EARLY TUESDAY
BEFORE SEAS RELAX TUESDAY AFTERNOON OR EVENING. HIGH PRESSURE
BUILDING OVER THE NORTHEAST PACIFIC MID TO LATE IN THE WORK WEEK
WILL BRING INCREASING NORTH WINDS TO THE WATERS DURING THIS
PERIOD. THE GUSTIEST WINDS...AROUND 25 KT OR SO...WILL LIKELY
REMAIN OVER THE CENTRAL OREGON WATERS...AND BE STRONGEST DURING
THE LATE AFTERNOON AND EVENING HOURS. THE NORTHERLY WINDS MAY
STRENGTHEN A BIT LATE IN THE WEEKEND SO SEAS MAY BECOME A BIT
MORE CHOPPY AND WIND WAVE DOMINATED ACROSS ALL THE WATERS. /NEUMAN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 PM THIS
     AFTERNOON 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 11 PM THIS EVENING
     TO 9 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.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 5 AM TO
     9 AM PDT TUESDAY.

&&

$$

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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