Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 300356
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
856 PM PDT TUE JUL 29 2014

.SYNOPSIS...AN UPPER LEVEL RIDGE REMAINS ANCHORED OVER THE GREAT
BASIN AND NORTHERN ROCKIES. UPPER LEVEL LOW PRESSURE LINGERS OFF THE
WEST COAST OF CANADA LEAVING THE PACIFIC NORTHWEST UNDER SOUTH TO
SOUTHWESTERLY FLOW ALOFT. SURFACE LOW PRESSURE EAST OF THE CASCADES
BRINGS VERY WEAK ONSHORE FLOW...ENOUGH TO AFFECT THE IMMEDIATE
COASTAL VALLEYS WHILE THE INTERIOR REMAINS VERY WARM. WEAK
DISTURBANCES LIFTING NORTH FROM CALIFORNIA WILL BRING A CHANCE FOR
THUNDERSTORMS AT TIMES TO THE CASCADES...ESPECIALLY LANE COUNTY.
LITTLE CHANGE EXPECTED IN THIS OVERALL PATTERN THE NEXT SEVERAL DAYS.

&&

.UPDATE...THE BULK OF THUNDERSTORM ACTIVITY AS DRIFTED EAST OF THE
CASCADE CREST AS THE AXIS FROM THE WEAK SHORTWAVE DESCRIBED BELOW
HAS LARGELY CROSSED THE CREST. ADD IN THE PREDOMINANT DRY AIR BEHIND
THE WAVE AND IT LOOKS LIKE CONCERN FOR OUR SIDE HAS ENDED. STILL
MAINTAINED THE SLIGHT CHANCE FOR THE REST OF THE
EVENING...HOWEVER...AS IT APPEARS A FINAL ROUND OF DEVELOPMENT
COULD CLIP THE WILLAMETTE PASS AREA UNDER A STRONG STORM LEFT MOVER
SCENARIO DURING THE NEXT HOUR OR TWO. ELSEWHERE...AM SEEING A
STRONGER MARINE PUSH THIS EVENING NOTED BY TEMPERATURES AT KELSO AND
CORVALLIS AIRPORTS LOWERING NEAR TO THE 70 DEGREE MARK ALREADY. THUS
HAVE PRETTY GOOD CONFIDENCE THERE WILL BE AT LEAST SOME STRATUS PUSH
UP THE COLUMBIA LIKELY REACHING THE PORTLAND METRO BY OR SLIGHTLY
AFTER SUNRISE. PREVIOUS FORECAST PACKAGE HANDLED THIS PRETTY WELL.
IN ALL...THE GRID PACKAGE IS IN VERY REASONABLE SHAPE WITH MINIMAL
CHANGES REQUIRED FOR THE EVENING UPDATE. /JBONK

.PREV DISC... /ISSUED 246 PM PDT TUE JUL 29 2014/

SHORT TERM...TODAY THROUGH THURSDAY NIGHT...THUNDERSTORMS HAVE
DEVELOPED ALONG THE CASCADE CREST THIS AFTERNOON...WITH ONE
PARTICULARLY LARGE CELL WHICH WAS WARNED ON NEAR MCKENZIE PASS.
RADAR HAIL SIZE ESTIMATES MAXED OUT AT 1.75 INCHES...APPROACHING
PING PONG BALL SIZE...THOUGH ACTUAL HAIL SIZE WAS LIKELY A BIT LOWER
THAN THAT. 0-6 KM BULK SHEAR REALLY NOT ALL THAT IMPRESSIVE...SO
THIS STORM APPEARS TO HAVE FED A BIT OFF OF CONVERGING UPSLOPE WINDS
ALONG THE CASCADE CREST AS IT DRIFTED NORTHWARD. PERHAPS ONE OR TWO
MORE STRONG CELLS COULD DEVELOP SIMILARLY THIS AFTERNOON...BUT WE
ARE NOT ANTICIPATING THIS TO BE A WIDESPREAD OCCURRENCE.

ANOTHER DRIVER FOR THE THUNDERSTORM DEVELOPMENT THIS AFTERNOON WAS A
WEAK DISTURBANCE AND JET MAX PUSHING INTO THE OREGON CASCADES FROM
THE SOUTHWEST. THIS ALSO MAY HAVE HELPED PUSH THE ABOVE MENTIONED
CELL TO SEVERE LIMITS. AS THE JET MAX MOVES ON AND THE SUN GOES DOWN
EXPECT ANY THUNDERSTORM ACTIVITY TO DECREASE RAPIDLY THIS EVENING.

FOR MOST OF THE FORECAST AREA...THE MAIN STORY IS AND WILL CONTINUE
TO BE THE VERY WARM TO HOT WEATHER INLAND. TEMPS ARE APPROACHING OR
HAVE ALREADY SURPASSED 90 DEGREES AT MANY INLAND LOCATIONS AS OF 2
PM. WHILE TEMPS HAVE COOLED OFF NICELY INTO THE 50S IN THE OUTLYING
VALLEYS...URBAN AREAS AND EXPOSED HILLSIDES HAVE SEEN LESS RELIEF
WITH TEMPS ONLY BOTTOMING OUT IN THE 60S. THERE WILL BE LITTLE CHANGE
IN THIS OVER THE NEXT FEW DAYS AS AN UPPER LEVEL RIDGE ONLY GRADUALLY
WEAKENS OVER THE GREAT BASIN AND NORTHERN ROCKIES. COASTAL AREAS WILL
REMAIN COOLER AS A WEAK ONSHORE COMPONENT TO THE FLOW CONTINUES.

RISK FOR THUNDER DECREASES TEMPORARILY WEDNESDAY AS MOST MODELS
DEPICT WEAK SHORTWAVE RIDGING TRANSITS THE REGION. STILL CANNOT
TOTALLY RULE OUT THUNDER ON THE CREST AS LAPSE RATES REMAIN DECENT.
MOISTURE APPEARS LESS ABUNDANT THOUGH...AND AGAIN THERE SHOULD BE
SUBSIDENCE FROM THE SHORTWAVE RIDGING. CHANCES INCREASE AGAIN THU/THU
NIGHT AS THE REMNANT MOISTURE OF POST-TROPICAL CYCLONE HERNAN LIFT
NORTH AND POSSIBLY COMBINE WITH ONE OF THE WEAK SHORTWAVES PRESENTLY
OFF THE CALIFORNIA COAST BEYOND 130W. FOR NOW...MOST MODELS SUGGEST
THIS ENERGY AND MOISTURE ARE TARGETING AREAS ALONG THE CASCADE CREST
AND POINTS EAST. HOWEVER IT IS NOT OUT OF THE QUESTION AREAS FURTHER
WEST COULD BE AFFECTED IF THE SHORTWAVE BECOMES STRONG ENOUGH TO PULL
IN SOME SE FLOW ALOFT. FOR NOW...JUST INCREASED POPS A BIT ALONG THE
CREST OF THE OREGON CASCADES THU/THU NIGHT.  WEAGLE

LONG TERM...FRIDAY THROUGH TUESDAY. OUR AREA IS ON THE WEST SIDE OF
AN UPPER-LEVEL RIDGE OVER THE WESTERN CONUS. SEVERAL SHORTWAVES ARE
FORECAST TO MOVE UP THIS RIDGE AND BRING CHANCES FOR THUNDERSTORMS
ALONG THE CASCADE CREST. THIS RIDGE WILL REMAIN STATIONARY THROUGH
TUESDAY. UNCERTAINTY REMAINS FOR TIMING AND LOCATION OF
THUNDERSTORMS...BUT LOOKS LIKE BEST CHANCE WILL STAY ALONG THE
CASCADE CREST.THE STATIONARY NATURE OF THIS WEATHER PATTERN WILL
KEEP HIGH AND LOW TEMPERATURES FAIRLY PERSISTENT UNTIL THIS UPPER-
LEVEL RIDGE EITHER BREAKS DOWN OR MOVES OFF TO THE EAST. -MCCOY

&&

.AVIATION...STRATUS AND FOG WILL CONTINUE TO HUG THE COASTLINE
WITH IFR AND LOCALIZED LIFR CONDITIONS PERSISTING INTO WED
MORNING. WITH NW FLOW IN PLACE...EXPECT THE COASTAL STRATUS TO
PUSH PARTIALLY UP THE LOWER COLUMBIA OVERNIGHT. THE STRATUS WILL
LIKELY MAKE IT TO KSPB...BUT CONFIDENCE IS LOWER THAT CLOUDS WILL
REACH AS FAR AS KPDX AND KTTD. THE OTHER INLAND AIRPORTS SHOULD
REMAIN VFR THROUGH TOMORROW. ANY INLAND STRATUS SHOULD CLEAR BY
ABOUT 16Z TOMORROW. EXPECT THE COAST TO IMPROVE TO VFR BY LATE
MORNING OR EARLY AFTERNOON. STRATUS WILL LIKELY RETURN TO THE
COAST DURING THE LATE AFTERNOON AND EVENING HRS TOMORROW.

KPDX AND APPROACHES...VFR PREVAILING THROUGH THIS EVENING. LOW
MVFR OR IFR STRATUS MAY APPROACH THE TERMINAL FROM THE WEST AFTER
12Z...BUT CONDITIONS SHOULD RETURN TO VFR BY 16Z. PYLE

&&

&&

.MARINE...UPDATED MOSTLY JUST SHORT-TERM WINDS FOR THE EVENING
PACKAGE TO BETTER REFLECT CURRENT OBS. WITH BUOY 50 GUSTING TO
ONLY 10-15 KT...WILL CANCEL SCA FOR OFFSHORE CENTRAL OREGON
WATERS....BUT WILL LET NEAR SHORE SCA RIDE AS NOS STATIONS AT
TILLAMOOK BAY AND NEWPORT CONTINUE TO CONSISTENTLY GUST TO 20-30
KT. WILL LEAVE DECISIONS ABOUT SCA FOR WEDNESDAY UP TO THE
MIDNIGHT SHIFT AS NEAR SHORE WINDS LOOK MARGINAL WITH OFFSHORE
WINDS INCREASING LATER IN THE PERIOD.

ONLY OTHER CHANGE IS TO SHORTEN PERIODS TO 5-6 SECONDS THROUGH
THE OVERNIGHT HOURS BASED ON RECENT OBS FROM BUOYS 29 AND 50 AS
WELL AS LATEST GUIDANCE. THIS MEANS SEAS ARE QUITE STEEP WITH 4-5
FEET AT 5-6 SECONDS AND WILL REMAIN SO THROUGH AT LEAST THE EARLY
MORNING HOURS WEDNESDAY. LONGER TERM FORECAST LOOKS GOOD AND
PREVIOUS DISCUSSION FOLLOWS. BOWEN

SURFACE HIGH PRESSURE WILL REMAIN OVER THE NE PACIFIC AS A
THERMAL TROUGH HOLDS OVER NORTHERN CALIFORNIA. THE THERMAL TROUGH
WILL RISE SLIGHTLY NORTH IN THE AFTERNOON AND EVENINGS RESULTING
IN A TIGHTER PRESSURE GRADIENT OVER THE OREGON WATERS. GUSTY WINDS
CAN BE EXPECTED AT THESE TIMES...OCCASIONALLY REACHING OR
EXCEEDING 25 KT. THE GRADIENT WILL BE TIGHTEST SOUTH OF TILLAMOOK.

THE SEAS WILL PRIMARILY BE DRIVEN BY THE LOCAL WINDS. STEEP SEAS 3
TO 5 FEET WILL DOMINATE THROUGH THE WEEK. THERE ARE SOME
BACKGROUND LONGER PERIOD SEAS THAT MAY OCCASIONALLY SHOW UP ON
THE BUOYS...BUT THESE ARE VERY SMALL...1 FOOT OR LESS...AND LESS
SIGNIFICANT TO THE MARINER THAN THE 3 TO 5 FEET SEAS AT 6 TO 8
SECONDS. THE STEEP SEAS WILL BE A COMBINATION OF WIND WAVE AND
FRESH SWELL WHICH IS NEARLY IMPOSSIBLE TO DISTINGUISH AND HAVE
THEREFORE COMBINED THE SEAS IN THE FORECAST. THE SEAS WILL BE THE
STEEPEST WHEN THE WINDS ARE THE GREATEST...DURING THE AFTERNOONS
AND EVENING...AND ESPECIALLY SOUTH OF CASCADE HEAD AND NEAR SHORE.
TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THIS EVENING 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.

&&

$$

MORE WEATHER INFORMATION ONLINE AT...HTTP://WEATHER.GOV/PORTLAND

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.PORTLAND.GOV
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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