Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 061050
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
348 AM PDT MON JUL  6 2015

.SYNOPSIS...HOT WEATHER WILL CONTINUE OVER MOST OF THE REGION THROUGH
MIDWEEK AS A STRONG RIDGE OF HIGH PRESSURE ALOFT REMAINS OVER THE
AREA. THE EXCEPTION IS THE COASTAL REGION...WHERE COOLER MARINE AIR
WILL HUG THE COASTLINE THE NEXT SEVERAL DAYS. AN UPPER LOW OFF
CALIFORNIA MAY DRIFT FAR ENOUGH NORTH THIS WEEK TO BRING
THUNDERSTORMS UP THE CASCADE CREST IN LANE COUNTY. RELIEF FROM
THE HEAT MAY COME LATER THIS WEEK AS THE UPPER RIDGE BREAKS DOWN
ENOUGH TO ALLOW STRONGER ONSHORE FLOW.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY...WEATHER MAPS THIS MORNING
LOOK AWFULLY SIMILAR TO HOW THEY HAVE LOOKED THE PAST SEVERAL
DAYS...WITH SW WASHINGTON AND NW OREGON REMAINING LOCKED IN A HOT AND
STAGNANT WEATHER PATTERN. A COL PATTERN ESTABLISHED ITSELF OVER THE
REGION LATE LAST WEEK...WITH A CUTOFF LOW OFF THE CA COAST...UPPER
TROUGHS CLIPPING WESTERN CANADA...AND UPPER LEVEL HIGHS OVER THE
GREAT BASIN AND NE PACIFIC. THIS TYPE OF PATTERN TENDS TO LOCK ITSELF
IN FOR A WHILE AND THIS HAS BEEN NO EXCEPTION. 500 MB HEIGHTS REMAIN
WELL ABOVE NORMAL ACROSS THE REGION...EVEN WITHIN THE UPPER TROUGH
OVER SRN BC/NE WA.

THAT SAID...A DECENT SOUTHERLY WIND REVERSAL PUSHED UP THE COAST
SUNDAY...DEEPENING THE MARINE LAYER WITH STRATUS TOPS 1500-2000 FT
THIS MORNING. IF MEMORY SERVES ME CORRECT...THIS IS DEEPER THAN THE
MARINE LAYER HAS BEEN IN A COUPLE WEEKS. THE STRATUS IS PUSHING WELL
INTO THE COASTAL VALLEYS THIS MORNING...WITH A CEILING ALREADY IN
KELSO. THIS IS PROBABLY AN INDICATION THAT ENOUGH COOLING WILL OCCUR
WITH THE ONSHORE FLOW THIS AFTERNOON TO KEEP KELSO BELOW 90 DEGREES.
THEREFORE WE WILL BE CANCELING THE HEAT ADVISORY FOR THE LOWER
COLUMBIA...I-5 CORRIDOR IN COWLITZ COUNTY...AND S WA CASCADE
FOOTHILLS.

WITH 500 MB HEIGHTS REMAINING IN THE MID-580S...THE MARINE LAYER WILL
PROBABLY BE TOO SHALLOW TO HAVE MUCH OF AN IMPACT ON AREAS FURTHER
INLAND TODAY/TUE...AND A SHORTWAVE PASSING TO THE NORTH MAY WEAKEN
ONSHORE GRADIENTS WED. 850 MB TEMPS REMAIN NEAR +20 DEG C THROUGH
WED. THEREFORE WILL LEAVE THE HEAT ADVISORY IN EFFECT FOR THESE AREAS
AS VALLEY HIGHS ARE STILL EXPECTED TO BE IN THE 90S THROUGH WED. IF
THIS OCCURS AT PDX...IT WOULD TIE THE LONGEST STRETCH OF 90+ DEGREE
DAYS ON RECORD...JUL 25-AUG 3 2009.

ONE CAVEAT IS THE SOUTH WILLAMETTE VALLEY...WHERE THE HEAT ADVISORY
LOOKS BORDERLINE DUE TO A PROLIFIC W-SW PUSH OF MARINE AIR...
CONTINUING THIS MORNING WITH 10-20 MPH WINDS AT CVO AND EUG. WOULD
NOT BE SURPRISED TO SEE HIGH TEMPS STICK NEAR OR EVEN BELOW 90
TODAY...BUT WILL LEAVE THE HEAT ADVISORY UP AS THE AIR MASS REMAINS
WARM ENOUGH FOR LOW-MID 90S SHOULD THE ONSHORE FLOW SHUT OFF.

THE OTHER THING TO WATCH FOR THE NEXT FEW DAYS IS THE POTENTIAL FOR
THUNDER IN THE OREGON CASCADES. MODELS ARE A LITTLE MORE BULLISH
ABOUT THE POTENTIAL FOR THUNDER THIS AFTERNOON ALL THE WAY UP THE
OREGON CASCADES TO NEAR MT HOOD. THIS SEEMS A LITTLE OVERDONE AS THE
AIR MASS ALOFT REMAINS RATHER WARM AND MODEL SOUNDINGS SEEM TO BE
EXAGGERATING SFC-BASED CAPE AS USUAL WITH SFC DEWPOINTS THAT ARE
PROBABLY TOO HIGH. ALSO THERE IS NO OBVIOUS SYNOPTIC TRIGGER ON
LATEST GFS/EC GUIDANCE. MODELS HAVE BEEN A BIT TOO FAR NORTH WITH
TSTM COVERAGE THE PAST COUPLE DAYS...SO HOLDING WITH THE CURRENT FCST
OF SLIGHT CHANCE AFTN/EVE THUNDER IN THE LANE CASCADES THE NEXT FEW
DAYS LOOKS REASONABLE.WEAGLE

.LONG TERM...THURSDAY THROUGH SUNDAY...FINALLY AN END IS IN SIGHT TO
THIS HISTORIC HEAT WAVE...AS THE BLOCKING PATTERN WHICH HAS KEPT US
UNDER ANOMALOUSLY HIGH 500 MB HEIGHTS BREAKS DOWN. THE HIGH 500 MB
HEIGHTS HAVE KEPT THE MARINE LAYER SHALLOW...ROBBING ONSHORE FLOW OF
ITS COOLING INFLUENCE BEFORE IT REACHES THE INLAND VALLEYS. THE MOST
IMPORTANT CHANGE EXPECTED DURING THE EXTENDED FORECAST PERIOD WILL
LIKELY BE THE SLOW LOWERING OF OVERALL 500 MB HEIGHTS OVER THE
WESTERN UNITED STATES AND THE NE PACIFIC...AS THE CA CUTOFF LOW OPENS
UP MIDWEEK AND THE MEAN UPPER RIDGE POSITION SLOWLY SHIFTS EASTWARD
INTO THE GREAT PLAINS. AS OVERALL HEIGHTS LOWER...EXPECT THE MARINE
LAYER TO BECOME DEEPER...THUS BECOMING MORE EFFECTIVE IN COOLING THE
INTERIOR GIVEN ONSHORE FLOW.

THERMAL LOW PRESSURE WILL LIKELY LINGER OVER THE WILLAMETTE VALLEY
THURSDAY...ALLOWING ONE MORE FAIRLY HOT DAY...THOUGH THE OVERALL AIR
MASS WILL BE COOLING AS 500 MB HEIGHTS LOWER. THU NIGHT APPEARS TO BE
THE BIG COOLDOWN AS THE THERMAL TROUGH MOVES INTO ERN WA AND
ENCOURAGES A STRONG SW PUSH OF MARINE AIR TO PUSH INTO THE DISTRICT.
THIS WILL AT LEAST PUSH TEMPERATURES CLOSER TO NORMAL WITH NIGHT AND
MORNING LOW CLOUDS EXTENDING INLAND BY THE WEEKEND...HOWEVER MODELS
DIVERGE ON WHETHER OR NOT AN INCOMING UPPER TROUGH CAN REMAIN STRONG
ENOUGH TO PRODUCE SHOWERS. DECIDED TO KEEP POPS VERY LOW...AS MODELS
HAVE A TENDENCY TO BE TOO AGGRESSIVE IN PUSHING THESE PACIFIC SYSTEMS
ONSHORE AFTER BEING UNDER A STRONG UPPER RIDGE. A MORE FAVORED
SOLUTION FOR THE WEEKEND IS THE 00Z ECMWF SOLUTION...WHICH LEAVES THE
UPPER TROUGH AXIS OFFSHORE AND SOUTHERLY FLOW OVER THE FORECAST AREA
KEEPING TEMPS CLOSE TO NORMAL RATHER THAN GOING BELOW NORMAL.
THEREFORE WE CONTINUE TO BE ON THE CONSERVATIVE SIDE OF GUIDANCE IN
THE MAGNITUDE OF COOLING EXPECTED WITH THIS PATTERN CHANGE.  WEAGLE

&&

.AVIATION...IFR STRATUS OVER THE COASTAL WATERS ALL THE WAY INTO
THE WESTERN SLOPES OF THE COAST RANGE AND THE LOWER COLUMBIA RIVER TO
KKLS. THE STRATUS SHOULD BURN BACK TO THE BEACHES TODAY...THEN
RETURN TO THE COASTAL AREAS LATE THIS AFTERNOON. THIS MEANS KONP MAY
REMAIN UNDER THE STRATUS OR ONLY BRIEFLY BREAK OUT LATER THIS
MORNING.  INLAND AREAS WILL BE VFR. SCATTERED TO BROKEN MID AND HIGH
CLOUDS WILL MOVE OVER LANE COUNTY THROUGH TODAY.

KPDX AND APPROACHES...VFR WILL CONTINUE THROUGH MONDAY NIGHT. CIGS
AROUND 1300 FT AT KKLS AS OF 09Z MON MAY EXTEND TO NEAR KSPB
BUT DO NOT EXPECT IT TO REACH TAF SITES. /MH

&&

.MARINE...SURFACE TROUGH WEST OF THE COASTAL WATERS AND A SURFACE
RIDGE NEAR THE COAST WILL CONTINUE TODAY THROUGH TUE. WINDS WILL
BE SOUTHERLY TODAY AND GENERALLY LESS THAN 15 KT. THE THERMAL
TROUGH WILL WEAKEN TONIGHT FOR LIGHT AND VARIABLE WINDS THROUGH
TUESDAY MORNING. THE SURFACE TROUGH WILL DISSIPATE TUE NIGHT AND
WED AND HIGH PRES OVER THE NE PAC WILL SHIFT BACK OVER THE
WATERS...RETURNING SEASONAL NW WINDS.

SEAS SUBSIDED TO AROUND 5 FT...AND WILL CONTINUE TO SUBSIDE
ANOTHER FOOT OR SO TODAY. SEAS SHOULD REMAIN 5 FT OR LOWER FOR
MUCH NEXT WEEK. /MH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HEAT ADVISORY UNTIL MIDNIGHT PDT WEDNESDAY NIGHT FOR CENTRAL
     COLUMBIA RIVER GORGE-CENTRAL WILLAMETTE VALLEY-GREATER
     PORTLAND METRO AREA-NORTHERN OREGON CASCADE FOOTHILLS-SOUTH
     WILLAMETTE VALLEY-UPPER HOOD RIVER VALLEY- WESTERN COLUMBIA
     RIVER GORGE.

WA...HEAT ADVISORY UNTIL MIDNIGHT PDT WEDNESDAY NIGHT FOR CENTRAL
     COLUMBIA RIVER GORGE-GREATER VANCOUVER AREA-WESTERN COLUMBIA
     RIVER GORGE.

PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM
     6 AM TO 10 AM PDT THIS MORNING.

&&

$$

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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