Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 040417
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
916 PM PDT MON AUG  3 2015

.SYNOPSIS...THE UPPER LEVEL DISTURBANCE WHICH GRAZED THE LANE COUNTY
CASCADES WITH A COUPLE THUNDERSTORMS IS NOW MOVING INTO CENTRAL
OREGON...AND WILL CONTINUE NORTHEAST OVERNIGHT. MEANWHILE A DRY COLD
FRONT IS PUSHING DOWN THE WASHINGTON COAST. THIS FRONT WILL MOVE
ACROSS THE FORECAST AREA TONIGHT AND TUESDAY...USHERING IN STRONGER
ONSHORE FLOW FOR MORE NIGHT AND MORNING LOW CLOUDS AND COOLER
TEMPS...WHILE KEEPING CONVECTION EAST OF THE AREA. AFTER A BRIEF
WARMUP LATE IN THE WEEK...ANOTHER UPPER TROUGH IS FORECAST TO DEVELOP
ALONG THE COAST NEXT WEEKEND INTO EARLY THE FOLLOWING WEEK.

&&

.SHORT TERM...A SLOW MOVING UPPER LEVEL DISTURBANCE COUPLED WITH SOME
RESIDUAL INSTABILITY TO PRODUCE SOME STRONG THUNDERSTORMS OVER
SOUTH-CENTRAL OREGON THIS AFTERNOON...GRAZING WILLAMETTE PASS AS THEY
BUILT NORTHWARD ALONG THE CASCADE CREST. LIGHTNING DETECTION SUGGESTS
ONLY A FEW STRIKES ACTUALLY OCCURRED IN OUR CWA...WITH THE BULK OF
THE ACTIVITY TO THE SOUTH AND EAST OF WILLAMETTE PASS. THE MAIN UPPER
DISTURBANCE ASSOCIATED WITH THIS ACTIVITY IS NOW MOVING INTO CENTRAL
OREGON...AND WILL CONTINUE NORTHEAST OVERNIGHT...ENDING THE THREAT
FOR OUR DISTRICT.

THE NEXT FEATURE TO KEEP AN EYE ON IS ACTUALLY DIFFICULT TO DISCERN
ON EARLIER VISIBLE AND NOW INFRARED SATELLITE IMAGERY...BUT IS MORE
APPARENT ON WATER VAPOR IMAGERY. A DRY COLD FRONT IS PUSHING SOUTH
ALONG THE WA COAST THIS EVENING...AND SHOULD REACH THE MOUTH OF THE
COLUMBIA BY MIDNIGHT. THE ASSOCIATED UPPER TROUGH WILL SETTLE INTO
THE PAC NW TUE/WED FOR GREATER ONSHORE FLOW AND COOLER TEMPS AS 500
MB HEIGHTS FALL INTO THE UPPER 570S. STRONGER ONSHORE FLOW MAY PUSH
MORE LOW CLOUDINESS UP THE COLUMBIA AND INTO THE PDX METRO TONIGHT/
TUE MORNING...BUT THERE IS SOME UNCERTAINTY AS SIGNIFICANT MIXING AND
CLEARING OF THE MARINE LAYER HAS DEVELOPED BEHIND THE FRONT. WILL
STICK WITH THE CURRENT FORECAST OF LOW CLOUDS RE-FORMING ALONG THE
COAST LATER TONIGHT AND SPREADING INLAND TUE MORNING AS THE BOUNDARY
LAYER COOLS...ESPECIALLY CONSIDERING HOW INSISTENT MODEL GUIDANCE IS
IN BRINGING THE STRATUS BACK.

THE UPPER TROUGH TO OUR NORTH WILL LINGER THROUGH WEDNESDAY WITH MORE
NORTHWEST ONSHORE FLOW AND MORE MORNING LOW CLOUDS ESPECIALLY
NORTH...POSSIBLY EVEN WORKING THEIR WAY MORE SOUTHWARD IN THE
WILLAMETTE VALLEY THAN ON TUESDAY. THE MODELS SHOW A WEAK PIECE OF
ENERGY ROTATING AROUND THE BASE OF THE UPPER TROUGH AND THROUGH
WESTERN WASHINGTON LATE TUESDAY NIGHT AND WEDNESDAY. THE MODELS
SUPPORT OUR CURRENT FORECAST OF SOME DRIZZLE ON THE NORTH COAST.
THERE IS A SMALL POSSIBILITY OF SOME LIGHT PRECIPITATION REACHING THE
NORTH INTERIOR ZONES WEDNESDAY EITHER DUE TO MORNING DRIZZLE OR
ISOLATED AFTERNOON SHOWERS AS THE MARINE LAYER MIXES INTO A
STRATOCUMULUS DECK. TEMPS INLAND IN THE NORTH WEDNESDAY WILL LIKELY
BE 75 TO 80 WITH 80 TO 85 NEAR EUGENE. THIS WILL BE THE COOLEST DAY
OF THE WORK WEEK.

THE UPPER TROUGH TO OUR NORTH MOVES EAST WEDNESDAY NIGHT AND
THURSDAY. THIS WILL ALLOW THURSDAY TO BE A WARMER DAY WITH MORE
SUNSHINE THAN THE PREVIOUS TWO DAYS...WITH THE MORNING LOW CLOUDS
MAINLY NORTH AND CLEARING EARLIER THAN ON TUESDAY OR WEDNESDAY.
WEAGLE/TOLLESON

.LONG TERM...BROAD UPPER-LEVEL TROUGH AND CONTINUED ONSHORE FLOW
SHOULD KEEP TEMPERATURES OUT OF THE 90S LATE THIS WEEK INTO THE
WEEKEND...BUT WEAKENING ONSHORE FLOW AND WINDS BECOMING MORE
SOUTHERLY ON FRIDAY WILL ALLOW TEMPERATURES TO BE A BIT WARMER ON
FRIDAY THAN EARLIER IN THE WEEK. SOUTHERLY FLOW ALSO INTRODUCES A
CHANCE FOR THUNDERSTORMS IN THE OREGON CASCADES...MAINLY ALONG THE
CREST. THE SHIFT TO MORE SOUTHERLY WINDS OCCURS AHEAD OF A UPPER
LEVEL LOW DIGGING DOWN OUT OF ALASKA OVER THE WEEKEND... BRINGING A
CHANCE FOR SHOWERS SATURDAY AND SUNDAY. THERE IS SOME DISAGREEMENT
BETWEEN THE MODELS ON TIMING AND AMOUNT OF RAIN WITH OF THIS
SYSTEM...CREATING UNCERTAINTY WHICH SHOULD BECOME RESOLVED AS WE
APPROACH THIS WEEKEND. HAVE KEPT TEMPERATURES A BIT CLOSER TO
CLIMATOLOGY ON SATURDAY AND SUNDAY...BUT IF SYSTEM PLAYS OUT AS
FORECAST RIGHT NOW TEMPERATURES WILL LIKELY BE A BIT COOLER THAN
CURRENTLY FORECAST. -MCCOY

&&

.AVIATION...A STABLE LOW LEVEL NORTHWESTERLY FLOW PATTERN WILL
BRING MVFR TO HIGH END IFR CONDITIONS TO THE COAST OVERNIGHT AND
TUESDAY MORNING WITH MAINLY VFR CONDITIONS INLAND. GIVEN CURRENT
STRATUS COVERAGE OFFSHORE IS MODEST AT BEST...CONFIDENCE IS NOT
ALL THAT HIGH IT WILL BE ABLE TO MAKE IT INTO THE PORTLAND METRO
TAFS. KPDX AND KTTD WILL BE SUSCEPTIBLE TO MVFR CONDITIONS
PRIMARILY BETWEEN 13Z AND 17Z TUESDAY. KHIO...KSLE AND KEUG SEEM
MORE THAN LIKELY TO REMAIN VFR THROUGH 06Z WEDNESDAY.

MVFR STRATUS REMAINS ALONG THE NORTH COAST...WITH VFR CIGS OVER
THE CENTRAL COAST. CIGS OVER THE NORTH COAST LOOK TO SCATTER OUT
BRIEFLY THIS AFTERNOON...BUT EXPECT WIDESPREAD MVFR CIGS TO
RETURN THIS EVENING. IFR CIGS AND VSBY POSSIBLE AFTER 06Z OVER THE
CENTRAL COAST. A BRIEF PERIOD OF VFR CIGS POSSIBLE TUE AFTERNOON.

KPDX AND APPROACHES...A STABLE NORTHWESTERLY FLOW PATTERN WILL
BRING PRIMARILY VFR CONDITIONS THROUGH 06Z WEDNESDAY. THERE IS A
CHANCE A BRIEF PERIOD OF MVFR CIGS WILL DEVELOP OVER THE TERMINAL
TUESDAY MORNING...MOST LIKELY BETWEEN 13Z AND 17Z TUESDAY.
GIVEN THE MINIMAL AMOUNT OF STRATUS OFFSHORE...CONFIDENCE HAS
LOWERED THAT IT WILL BE ABLE TO PUSH INLAND TO PDX. /NEUMAN

&&

.MARINE...HIGH PRESSURE WILL CONTINUE OVER THE NORTHEAST PACIFIC
AND CONTINUE OUR TYPICAL SUMMERTIME PATTERN OF NORTHERLY WINDS
ALONG THE COAST WITH OCCASIONAL STEEPER WIND DRIVEN SEAS FROM TIME
TO TIME THIS WEEK. WINDS AND SEAS WILL GENERALLY BE STRONGEST
ACROSS THE CENTRAL OREGON WATERS FOR THE NEXT SEVERAL DAYS.

THE FIRST ROUND OF WINDS AND HIGHER SEAS SHOULD ARRIVE TUESDAY
AFTERNOON AND EVENING. ALTHOUGH STEEP AND HAZARDOUS SEAS WILL BE
MARGINAL...OPTED TO ISSUE AN ADVISORY FOR THIS THREAT FOR THE
CENTRAL OREGON WATERS GIVEN MODEL GUIDANCE AND BIAS.

THE NEXT MAJOR UPTICK IN WINDS AND SEAS WILL LIKELY ARRIVE
THURSDAY AFTERNOON AND EVENING AS THERMAL LOW PRESSURE TEMPORARILY
STRENGTHENS OVER CALIFORNIA AND WE WILL LIKELY NEED ANOTHER ROUND
OF SMALL CRAFT ADVISORIES FOR THE CENTRAL OREGON WATERS.

AN UPPER LEVEL TROUGH SHOULD SETTLE INTO THE PACIFIC NORTHWEST
OVER THE WEEKEND...AND A WEAK FRONT MAY BRIEFLY TURN WINDS
SOUTHERLY...BUT WINDS LOOK TO REMAIN RELATIVELY BENIGN.
OTHERWISE...WE MAY SEE NORTHERLY WINDS STRENGTHEN AS THERMAL LOW
PRESSURE OVER CALIFORNIA RETURNS LATE IN THE WEEKEND INTO EARLY
NEXT WEEK. /NEUMAN


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 2 PM TUESDAY TO 3 AM PDT
     WEDNESDAY FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 PM TUESDAY TO 3
     AM PDT WEDNESDAY FOR COASTAL WATERS FROM CASCADE HEAD OR TO
     FLORENCE OR OUT 60 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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