Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 301627
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
921 AM PDT SAT APR 30 2016

.SYNOPSIS...CLOUDS WILL DISSIPATE THIS MORNING AS STRONG HIGH PRESSURE
BUILDS INTO BRITISH COLUMBIA AND WASHINGTON STATE TODAY. AS THE UPPER
HIGH BUILDS TO THE NORTH...DRIER NORTH TO NORTHEASTERLY FLOW
DEVELOPS. THIS WILL CAUSE A SIGNIFICANT WARMUP COMMENCING THIS
AFTERNOON AND CONTINUING THROUGH MONDAY. HIGH TEMPERATURES WILL
JUMP 15 TO 20 DEGREES ABOVE NORMAL SUNDAY...COOLING ALONG THE COAST
MONDAY BUT REMAINING WARM INLAND. AS THE UPPER HIGH MOVES INTO
ALBERTA MONDAY...LOW TO MID LEVEL FLOW TURNS SOUTHERLY/SOUTHWESTERLY
BRINGING A CHANCE OF THUNDERSTORMS MAINLY TO THE CASCADES MONDAY
AFTERNOON/EVENING. SHOWER CHANCES WILL INCREASE ACROSS THE ENTIRE
AREA BY TUESDAY...AS A SLOW MOVING COLD FRONT APPROACHES FROM THE
PACIFIC. COOLER AND SHOWERY WEATHER IS EXPECTED TO CONTINUE FOR THE
REMAINDER OF THE WEEK.

&&

.UPDATE...MORNING SATELLITE TRENDS SHOW MARINE LAYER CLOUDINESS
MAINLY ALONG THE NORTH COAST...COLUMBIA RIVER LOWLANDS/NORTHERN
WILLAMETTE VALLEY...AND EASTERN WILLAMETTE VALLEY/CASCADES. AS
INITIAL MIXING DEVELOPS STRATUS HAS EXPANDED OVER THE PAST HOUR OR
TWO...BUT FORECAST SOUNDINGS SHOW LOWER TROPOSPHERIC FLOW TURNING
OFFSHORE AND WARMING BEGINNING BY 18Z. MIXED LAYER THEN DEEPENS
SUFFICIENTLY THEREAFTER FOR CLEARING THROUGHOUT THE AREA. HRRR RUNS
DEPICT TREND NICELY WITH MAINLY SUNNY /ALBEIT THROUGH CIRRUS/
BETWEEN 19-20Z. REMAINDER OF WEEKEND UNDER NORTHERLY/NORTHEASTERLY
FLOW AND WARMER AIRMASS. BRIGHT

PREVIOUS SHORT/LONG TERM DISCUSSIONS FOLLOW...

SHORT TERM...TODAY THROUGH MONDAY...WATER VAPOR SATELLITE IMAGERY
SHOWS OUR UPPER LOW DIGGING S-SE ALONG THE CA/NV BORDER AND HEADED
TOWARD ARIZONA. LINGERING LOW-LEVEL MOISTURE CONTINUES TO BANK UP
AGAINST THE CASCADES AND COAST RANGE...PRODUCING ENOUGH DRIZZLE OR
LIGHT RAIN TO MEASURE AT A FEW RAWS SITES HERE AND THERE. TOUGH TO
DISCRIMINATE BETWEEN ACTUAL PRECIPITATION AND MELTING SNOW AT SOME OF
THE HIGHER ELEVATION SITES...BUT AM FAIRLY CONFIDENT SOME AREAS OF
DRIZZLE WILL CONTINUE IN THE HIGHER TERRAIN BEYOND 12Z THIS MORNING.
WILL KEEP POPS LOW...AROUND 10 PERCENT...BUT ADDED MENTION OF DRIZZLE
ACCORDINGLY.

OTHERWISE...THE MAIN STORY THE NEXT FEW DAYS WILL BE YET ANOTHER WARM
SPELL ACROSS SW WA/NW OR. THIS WILL LIKELY BE THE THIRD WARM SPELL
WITH HIGHS IN THE 80S THIS SEASON FOR INLAND VALLEYS...AND POSSIBLY
THE COAST AS WELL. TODAY WILL BE THE TRANSITION DAY WITH DECREASING
CLOUDS AND A FEW DEGREES OF WARMING VERSUS FRIDAY. FLOW ALOFT TURNS
DECIDEDLY EASTERLY TONIGHT AND SUNDAY AS THE UPPER LOW OVER THE
SOUTHWESTERN UNITED STATES TRIES TO GET INTO A REX BLOCK WITH A
STRENGTHENING UPPER RIDGE OVER WESTERN CANADA AND WASHINGTON. THIS
WILL CAUSE THE WARMING TREND TO BEGIN IN EARNEST FOR SUNDAY AND
MONDAY. AS FLOW TURNS OFFSHORE THE AIR MASS WILL DRY CONSIDERABLY.
THIS SHOULD BRING PLENTY OF SUNSHINE FOR SUNDAY AND MONDAY.

TEMPS AT 850 MB DO NOT LOOK QUITE AS WARM AS THE LAST TWO EVENTS...
NOR WILL 500 MB HEIGHTS BE QUITE AS HIGH. SEEING FAIRLY GOOD MODEL
AGREEMENT REGARDING HOW WARM THE AIR MASS WILL BE...WITH BOTH THE 00Z
GFS AND ECMWF SHOWING 850 MB TEMPS PEAKING AT AROUND +15 DEG C OVER
THE WILLAMETTE VALLEY SUNDAY AND MONDAY. HAVING DIFFICULTY PULLING UP
ARCHIVED SOUNDING DATA AT THE MOMENT...BUT BASED ON MEMORY THIS
COMPARES TO +17 TO +20 DEG C FROM OUR PAST TWO WARM SPELLS. WITH DEEP
EASTERLY FLOW DEVELOPING JUST ABOVE THE SURFACE... ANY THERMAL TROUGH
WHICH DEVELOPS WILL LIKELY STAY OFFSHORE SUNDAY. THIS SHOULD ALLOW
THE COAST TO GET IN ON THE WARMING AS WELL... POSSIBLY EVEN BEING THE
WARMEST IN OUR CWA ON SUNDAY AS THEY TAKE ADVANTAGE OF THE
DOUBLE-DOWNSLOPE EFFECT OFF BOTH THE CASCADES AND COAST RANGE.
ALTHOUGH THE AIR MASS DOES NOT APPEAR WARM ENOUGH FOR 90S THIS TIME
AROUND...80S APPEAR TO BE A GOOD BET FOR JUST ABOUT ANYONE AT LOW
ELEVATION IN OUR CWA SUNDAY AND/OR MONDAY.

00Z/06Z NAM SHOW WHAT SEEMS TO BE A PRETTY REALISTIC EVOLUTION OF THE
THERMAL TROUGH INTO A THERMAL LOW JUST OFF THE COAST SUN NIGHT/ EARLY
MON...WHICH THEN LIFTS NORTH ALONG THE PAC NW COAST MONDAY. THIS
COULD PROMPT A S-SW SURGE OF MARINE AIR ALONG THE COAST MONDAY...
POSSIBLY TRICKLING INLAND ENOUGH TO KEEP TEMPS A LITTLE COOLER FOR
EUGENE. AS ONE PART OF THE THERMAL LOW LIFTS NORTH ALONG THE PAC NW
COAST...ANOTHER PORTION WILL LIKELY MIGRATE ACROSS THE WILLAMETTE
VALLEY AND CASCADES MONDAY AFTERNOON. THIS COULD ENHANCE
INSTABILITY...WITH THE LEADING EDGE OF COOLER MARINE AIR EFFECTIVELY
WORKING AS A COLD FRONT TO PROVIDE SOME ADDED LIFT FOR SFC-BASED
PARCELS. MODEL SOUNDINGS ARE SHOWING A DECENT AMOUNT OF INSTABILITY
FOR THE WILLAMETTE VALLEY MONDAY...WITH THE 06Z NAM NOW SHOWING ABOUT
1000-1500 J/KG OF ML CAPE AND ONLY WEAK CIN DURING THE AFTERNOON.
WILL HOLD OFF ON ADDING A THUNDER MENTION WEST OF THE CASCADE
FOOTHILLS FOR NOW...BUT FUTURE SHIFTS MAY NEED TO REVISIT THIS. IT IS
NOTABLE THAT THE 00Z GFS SHOWS CONSIDERABLY LESS CAPE FOR THE
WILLAMETTE VALLEY MON AFTERNOON...CLOSER TO 300-500 J/KG OF ML
CAPE...WHICH ALSO SWAYED US TOWARD HOLDING OFF ON THE THUNDER MENTION
ASIDE FROM THE CASCADES. EITHER WAY...SHOWER CHANCES START TO
INCREASE MONDAY...AND THE REMAINDER OF THE WEEK LOOKS CLOSER TO
NORMAL FOR SPRING WITH COOLER TEMPS AND SHOWERS AT TIMES.

A CLIMATE NOTE TO FURTHER PUT THIS EXTREMELY WARM SPRING INTO
PERSPECTIVE...PDX HAS ALREADY HAD SIX 80-DEGREE DAYS THIS SEASON.
THIS IS AN ALL-TIME RECORD PACE FOR PDX...AND ONLY 2004 AND 1947 HAVE
HAD 5 80-DEGREE DAYS BY THE END OF APRIL SINCE RECORDS STARTED IN
1940. IN STARK CONTRAST...1954 HAD JUST 10 80-DEGREE DAYS THE ENTIRE
YEAR AT PDX. THE AVERAGE FOR AN ENTIRE YEAR AT PDX IS 51 DAYS. USING
PDX AS AN EXAMPLE AGAIN...THE MEAN TEMPERATURE FOR APRIL 2016 THROUGH
THE 28TH IS 57.9 DEG F...5.9 DEG F ABOVE NORMAL AND A STUNNING 1.6
DEG F ABOVE THE PREVIOUS RECORD OF 56.3 DEG F FROM APRIL 2004.
RECORDS ARE NOT JUST BEING BROKEN...THEY ARE BEING SHATTERED DUE TO
THE SERIES OF SUMMER-CALIBER UPPER RIDGES THAT HAVE AFFECTED THE PAC
NW THIS MONTH. MAY 2016 LOOKS TO BE STARTING NO DIFFERENTLY.  WEAGLE

LONG TERM...MONDAY NIGHT THROUGH FRIDAY...MODELS SEEM TO BE SHOWING
REASONABLE AGREEMENT THAT RELATIVELY COOLER MARINE AIR WILL PUSH
INLAND AND DEEPEN ON SW FLOW MONDAY NIGHT AND TUESDAY...AS THERMAL
LOW PRESSURE SHIFTS NORTH AND EAST OF THE FORECAST AREA. WITH LITTLE
TO NO EASTERLY COMPONENT TO THE FLOW ALOFT AND INCREASINGLY STABLE
MARINE AIR IN THE LOWER LEVELS...DECIDED TO REMOVE THUNDERSTORMS FROM
THE LOWLANDS TUESDAY AND WEDNESDAY. THE BETTER CHANCE FOR THUNDER IN
THE LOWLANDS MAY ACTUALLY BE MONDAY AS THE LEADING EDGE OF MARINE AIR
ACTS AS A LIFTING MECHANISM ON A SOMEWHAT UNSTABLE AIR MASS. ASSUMING
THE EARLY WEEK UPPER RIDGE DOES NOT FORM A STRONG AND PERSISTENT REX
BLOCK...MODELS SUGGEST THE RIDGE WILL MIGRATE EASTWARD ENOUGH TO
ALLOW AN UPPER TROUGH TO TAKE RESIDENCE OVER THE PAC NW MID TO LATE
WEEK. THIS SOLUTION WOULD BRING A COOLDOWN CLOSER TO NORMAL TEMPS FOR
EARLY MAY ALONG WITH PLENTY OF SHOWERS.  WEAGLE

&&

.AVIATION...SCATTERED HIGH MVFR CIGS THIS MORNING AS STRATUS
CONTINUES TO BACK BUILD FROM THE CASCADE FOOTHILLS. STRATUS WILL
CONTINUE TO EXPAND WEST IN COVERAGE THROUGH 17Z-18Z AND THEN BREAK
UP THROUGH ABOUT 20Z. THEN THE TREND SHOULD BE VFR CONDITIONS WITH
DISSIPATING CLOUDS THROUGH THE AFTERNOON AS DRIER NORTHERLY FLOW
DEVELOPS.

KPDX AND APPROACHES...CIG AROUND 2500 TO 3000 FT THROUGH 19Z-20Z
THEN BREAKING UP AND CLOUD DISSIPATING WITH VFR CONDITIONS THROUGH
THE AFTERNOON.

&&

.MARINE...A THERMAL TROUGH OVER THE SOUTH OREGON COAST WILL
STRENGTHEN TODAY BRINGING INCREASING WINDS ACROSS THE WATERS
LATER THIS MORNING AND THROUGH THE AFTERNOON. THE STRONGEST WINDS
ARE EXPECTED SOUTH OF ABOUT CASCADE HEAD. WINDS NEAR SHORE SHOULD
EASE LATER THIS EVENING...BUT CONTINUE OVER THE OUTER MARINE ZONES
INTO SUN MORNING. THE THERMAL TROUGH EXPANDS NORTH SUNDAY THEN
SHIFTS OVER THE COASTAL WATERS SUN NIGHT AND CONTINUES TO THE
WASHINGTON COASTAL WATERS MON.

SEAS HAVE BEEN GENERALLY RUNNING 7 TO 8 FT THIS MORNING WITH
DOMINANT PERIOD INCREASING TO 10 TO 11 SECONDS. HAVE LET THE SMALL
CRAFT ADVISORY FOR SEAS EXPIRE BUT WILL KEEP A CLOSE EYE ON SEAS
IN CASE PERIODS DECREASE WITH INCREASING WINDS TODAY TO CAUSE A
RETURN OF SQUARE SEAS. BOWEN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 9 AM PDT THIS
     MORNING FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS FROM 2 PM THIS AFTERNOON TO
     MIDNIGHT PDT TONIGHT FOR COASTAL WATERS FROM CAPE
     SHOALWATER WA TO CASCADE HEAD OR OUT 10 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL MIDNIGHT PDT TONIGHT FOR
     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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