FXUS66 KPQR 041724
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
925 AM PST FRI DEC  4 2009

.SYNOPSIS...AN UPPER TROUGH DROPPING DOWN FROM BRITISH COLUMBIA WILL
SLIDE SOUTH INTO THE PACIFIC NORTHWEST TODAY. ANY MOISTURE WITH THIS
SYSTEM WILL BE QUITE SPARSE BUT COULD FALL IN THE FORM OF A FEW SNOW
FLURRIES TONIGHT. A SECOND STRONGER SYSTEM DROPPING SOUTH ON SUNDAY
WILL BRING COLDER ARCTIC AIR AND INCREASING NORTHEASTERLY WIND INTO
THE AREA SUNDAY AND SUNDAY NIGHT. ISOLATED SNOW SHOWERS ARE POSSIBLE 
AS WELL BUT ANY ACCUMULATIONS ARE EXPECTED TO BE MINIMAL. COLD 
WEATHER WILL LIKELY PERSIST THROUGH EARLY NEXT WEEK. 

&&

.SHORT TERM...THE OFFSHORE FLOW WEAKENED OVERNIGHT AND HAS SHIFTED TO
LIGHT ONSHORE THIS MORNING. WITH AN UPPER TROUGH IN SOUTHEASTERN
BRITISH COLUMBIA CONTINUING DIG TO THE SOUTH THE ONSHORE GRADIENT
WILL INCREASE A COUPLE OF MILLIBARS BY EARLY AFTERNOON. SATELLITE
IMAGERY SHOWS AN ARCH OF MARINE STRATUS...CURRENTLY ALONG THE NORTH
OREGON COAST...PUSHING SOUTH DOWN THE COAST IN RESPONSE TO THE UPPER
LEVEL FORCING. WATER VAPOR IMAGERY ALSO SHOWS AN IMPRESSIVE DRY SLOT
ASSOCIATED WITH THIS UPPER TROUGH OVER WESTERN WASHINGTON THIS
MORNING.  AS THIS DRY AIR ALOFT MOVES INTO OREGON LATER TODAY...RHS
IN THE MOUNTAINS WILL DROP AND NORTHWESTERLY WINDS WILL INCREASE
PARTICULARLY AT RIDGE LEVEL AND ABOVE. 

WINDS WILL SHIFT MORE NORTHERLY THIS EVENING AND THEN TURN TO THE
NORTHEAST BY SATURDAY MORNING AS A COOLER MODIFIED ARCTIC AIR MASS
FILTERS INTO EASTERN WASHINGTON AND OREGON.  WEST OF THE MOUNTAINS
TEMPERATURE DROPS WILL BE MORE SUBTLE BUT SLOWLY TREND DOWNWARD
TONIGHT THROUGH SATURDAY NIGHT.  THE COAST WILL BE THE EXCEPT TO THIS
DURING THE DAY SATURDAY WITH AN INVERTED SURFACE TROUGH ALONG THE
COAST AND OFFSHORE DOWNSLOPE FLOW WARMING TEMPERATURES TO THE UPPER
40S AND LOW 50S AT THE BEACHES...FURTHER INLAND HIGH TEMPERATURES
WILL DO WELL TO BREAK 40 AT THE LOWER ELEVATIONS AND REMAIN IN THE
20S AND 30S IN THE MOUNTAINS.

THE MORE IMPRESSIVELY COLD ARCTIC AIR MASS WILL ARRIVE ON SUNDAY WITH
A DEEPER UPPER LEVEL LOW DIGGING SOUTH OVER OREGON.  MODELS SUGGEST A
BRIEF OVERWATER TRAJECTORY FOR THE COLD AIR AND SHOW THE UPPER LOW
PARTIALLY CUTTING OFF. GIVEN THESE FACTORS AND THE STRENGTH OF THE
UPPER LOW...ISOLATED TO SCATTERED SNOW SHOWERS ARE A POSSIBILITY ON
SUNDAY.  AT THE MOMENT MOISTURE LOOKS TO BE THE LIMITING FACTOR WHICH
SHOULD KEEP ANY SNOW ACCUMULATIONS MINIMAL.  MY ONE CONCERN ABOUT
THIS ASSUMPTION HOWEVER WOULD BE IF EXTRA FRONTAL DEVELOPMENT OCCURS
ALONG THE ARCTIC FRONT JUST OFFSHORE FUELED BY THE CONTRAST BETWEEN
THE VERY COLD AIR MASS AND THE WARMER MARINE AIR TO TE SOUTH. THE
DEGREE TO WHICH THE UPPER LOW STARTS TO CUT OFF COULD ALSO SUPPORT
THIS WITH THE ARCTIC FRONT STALLING 100 OR 150 MILES FURTHER NORTH
WHICH WOULD PUT IT OVER OUR CWA.

INCREASING NORTH WINDS ON SUNDAY SHIFTING TO THE NORTHEAST SUNDAY
NIGHT WILL BE QUITE CHILLY AS THEY COINCIDE WITH TEMPERATURES IN THE
TEENS. EAST WINDS WILL LIKELY PERSIST IN THE WESTERN GORGE THROUGH
MIDWEEK. THE STRONG EAST WINDS COMBINED WITH TEMPERATURES WELL BELOW
FREEZING WILL MAKE FREEZING SPRAY A DEFINITE CONCERN FOR GORGE
MARINERS. RUTHFORD

.LONG TERM...THE LONGER TERM MODELS ARE NOW INDICATING A MORE
SOUTHERN TRACK TO THE JET AS IT UNDERCUTS THE RIDGE. THIS IS
LESSENING THE THREAT OF ANY SIGNIFICANT SNOW EVENT FOR MID WEEK BUT
THE ECMWF SHOWS SEVERAL SHORTWAVES MOVING DOWN FROM THE NORTH WHICH
REINFORCE THE COLDER AIR KEEPING NEXT WEEK VERY COOL. SCHNEIDER

&&

.AVIATION...EXPECT AREAS OF LIFR IN FREEZING FOG THIS MORNING IN THE 
SOUTH WILLAMETTE VALLEY...AND IN THE CASTLE ROCK AREA. REMNANTS OF A 
WEAK FRONT BRINGING MVFR CIGS TO THE NORTH COAST AND INLAND TO THE 
KPDX AREA. EXPECT MVFR CIGS TO SLIDE DOWN THE COAST TODAY...AND 
LINGER IN THE NORTH INLAND AREAS INTO EARLY AFTERNOON.
A BACKDOOR COLD FRONT SWINGS THROUGH TONIGHT BUT CLOUDS LOOKING A 
BIT SPARSE. IF THE CLOUDS GET MORE ORGANIZED THAT THE MODELS 
SUGGEST...WE COULD GET LOCAL MVFR CIGS WITH SOME FLURRIES ESPECIALLY 
INLAND BUT THIS IS NOT CERTAIN.

KPDX AND APPROACHES...MVFR ON WESTERN APPROACHES THROUGH LATE 
AFTERNOON AND POSSIBLY TO KPDX THROUGH EARLY AFTERNOON.  GENERALLY 
VFR BUT SOMEWHAT UNCERTAIN FOR MVFR CIGS DEVELOP AGAIN LATER TONIGHT 
AS A BACK DOOR COLD FRONT MOVES THROUGH. 
&&

.MARINE...WINDS ARE TURNING NORTHERLY THIS MORNING AND WILL CONTINUE 
TODAY AS OFFSHORE FLOW WEAKENS DUE TO A SYSTEM PASSING BY TO OUR 
NORTH. THE ASSOCIATED FRONT WILL DROP SOUTH THROUGH THE WATERS LATE 
TODAY AND TONIGHT. SMALL CRAFT LEVELS ALREADY IN THE NORTHERN OUTER 
WATERS WILL EXPAND ACROSS ALL WATERS TODAY THEN DECREASE BRIEFLY 
LATE TONIGHT...BUT CONTINUE SATURDAY IN THE FAR OUTER WATERS. AN 
ARCTIC FRONT WILL SWEEP IN FROM THE NORTHEAST SUNDAY AND SHOULD SEE 
SOLID SMALL CRAFT WINDS THEN...WHICH LOOK TO LAST INTO MONDAY. SEAS 
HAVE DROPPED BELOW 10 FT EARLY THIS MORNING...BUT SHOULD RISE TO 
NEAR 10 FT IN THE OUTER WATERS MAINLY THIS AFTERNOON AND EVENING. 
WILL NEED TO WATCH IF SEAS WILL APPROACH 10 FT SUNDAY AND MONDAY BUT 
FOR NOW IT MAY STAY JUST BELOW. TOLLESON

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR AROUND EBB
      LATE THIS AFTERNOON.
     SMALL CRAFT ADVISORY FOR WINDS CAPE SHOALWATER TO
      FLORENCE 10 TO 60 NM OFFSHORE THROUGH ABOUT MIDNIGHT.
     SMALL CRAFT ADVISORY FOR WINDS CAPE SHOALWATER TO FLORENCE
      OUT 10 NM THIS AFTERNOON AND EVENING.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE SHOALWATER
      TO FLORENCE 10 TO 60 NM OFFSHORE THROUGH THIS EVENING.

&&

$$

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

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.