FXUS66 KPQR 102314 CCA
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
154 PM PST THU DEC 10 2009

.SYNOPSIS...AN ARCTIC AIR MASS WILL CONTINUE THROUGH THE MID PART OF
THE WEEKEND. A PACIFIC SYSTEM IS EXPECTED TO MOVE INTO CALIFORNIA
LATE FRIDAY AND SLOWLY TRANSITION SOME PRECIPITATION BANDS NORTH OVER
THE COLD AIR IN PLACE.THERE IS A GOOD CHANCE THAT THERE WILL BE A
COMBINATION OF FREEZING RAIN...SNOW AND RAIN DEPENDING ON WHERE YOU
LIVE HOWEVER THE DETAILS ARE VERY COMPLEX AND THERE STILL EXISTS A
HIGH DEGREE OF UNCERTAINTY IN HOW THIS SCENARIO WILL PLAY OUT. A
WARMER AND MORE ORGANIZED SYSTEM IS EXPECTED FOR EARLY NEXT WEEK.

&&

.SHORT TERM...ONE LAST REAL COLD NIGHT REMAINS...PERHAPS ONLY A
COUPLE OF DEGREES WARMER THAN LAST NIGHT. AFTER THAT ATTENTION
FOCUSES ON THE POTENTIAL FOR FROZEN PRECIPITATION BEGINNING AS EARLY
AS TOMORROW AFTERNOON.

MODELS HAVE DIVERGED DRASTICALLY ON THE DETAILS AND ARE FINALLY
BEGINNING TO SUGGEST SIMILAR SOLUTIONS BRINGING A DEFORMATION BAND
NORTH OVER THE FORECAST AREA HOWEVER THEY ARE STILL HAVING
DIFFICULTIES WITH TIMING...QPF AMOUNTS...AND PRECIPITATION TYPE.
PROBING NAM AND WRF BUFR SOUNDING...SHOWS THE HIGH RESOLUTION MODELS
ARE BEGINNING TO REALIZE THE SUBFREEZING COLD AIR LAYER WHICH WAS ALL
BUT SPECULATED ABOUT UNTIL THE LATEST RUNS...THEIR COMMON MISTAKE OF
WARMING IT UP TO FAST. REGARDLESS THIS MEANS COLD AIR WILL BE IN
PLACE FOR THE NORTHWARD MIGRATION OF THE DEFORMATION BAND AND ANY
PRECIP THAT FALLS INTO THIS LAYER WILL BE OF THE FROZEN NATURE.
CURRENT THOUGHTS SIMILAR TO THAT OF THIS MORNING WITH SNOW TO THE
NORTH AND FZRA TO THE SOUTH. EXPECT SUB FREEZING AIR TO SLOWLY FROM
THE SOUTH AND EVENTUALLY SWITCH THE PORTLAND METRO AREA OVER TO FZRA
EARLY SATURDAY MORNING. OUTFLOW FROM THE GORGE DUE TO THE LOWS
PROXIMITY IS EXPECTED TO MAINTAIN A SUBFREEZING AIR MASS OVER THE
METRO AREA THROUGH SAT NIGHT AND PERHAPS AS LATE AS SUNDAY MORNING.
FURTHER THIS FLOW SHOULD HELP SET UP SOME UPSLOPE FLOW ON THE EASTERN
PORTIONS OF THE COAST RANGE FOOTHILLS JUST WEST OF HILLSBORO WHICH
COULD QUICKLY BRING UP TO FOUR INCHES OF SNOW AS THE DEPTH OF COLD
AIR IS INCREASED BY POOLING AND SOME CONVERGENCE. MINUTE DIFFERENCES
IN THE DEPTH OF THE COLD AIR COULD CAUSE A PLETHORA OF OTHER
SCENARIOS.  FOR INSTANCE COLD AIR IS DEEPER...WE GET A DECENT BATCH
OF SNOW.  COLD AIR IS SHALLOW AND EASILY ERODES...WE GET RAIN. COLD
AIR IS OF MODERATE DEPTH...OUR FORECAST IS RIGHT. ANOTHER BIG
QUESTION MARK IS HOW MUCH QPF WILL THERE BE.  IF THE GFS IS RIGHT IN
BRINGING 0.40 TO 0.50 INCHES TO THE NORTH VALLEY...THIS FORECAST MAY
BE DRASTICALLY UNDERESTIMATING THE SNOW AND ICE AMOUNTS. IT IS
NOTEWORTHY TO MENTION THAT THE GFS HAS CONSISTENTLY BEEN DOING THIS.
THE GFS DOES APPEAR TO BE THE OUTLIER OF ALL THE MODELS AND OUR
FORECAST TRENDS MORE TOWARDS THE NAM WHICH BRING ABOUT 0.20 INCHES OF
QPF TO THE AREA THROUGH SUNDAY MORNING. 

18Z NAM STILL PULLS SOME COLD AIR TO THE EAST SIDE OF THE CASCADES
AND HINTS AT KEEPING SOME COLD AIR AROUND UNTIL SUNDAY MIDDAY. THEN
FINALLY THINGS SHOULD BEGIN TO WARM UP FOR THE NEXT SYSTEM ON
TUESDAY.

BOTTOM LINE...PLEASE PAY CLOSE ATTENTION TO THE PROGRESSION OF THIS
SYSTEM AS THERE STILL IS QUITE A BIT OF UNCERTAINTY IN TIMING... 
PRECIP TYPE...AND PRECIP AMOUNTS ALL OF WHICH CAN CHANGE THE END 
RESULT. WOLFE

.LONG TERM...EXTENDED MODELS SHOWING A LITTLE MORE CONSISTENCY TODAY 
AS OPPOSED TO PREVIOUS DAYS. GFS AND ECMWF OPERATIONAL RUNS CONTINUE 
TO SUGGEST THE E PAC RIDGE SHIFTING E ACROSS THE REGION MON... 
FOLLOWED BY WESTERLY FLOW ALOFT BREAKING THROUGH MON NIGHT WHICH 
PUSHES A PACIFIC FRONTAL SYSTEM INLAND BY TUE. WITH THE OFFSHORE 
FLOW AHEAD OF THIS SYSTEM...IT IS POSSIBLE THAT PRECIPITATION IN THE 
GORGE COULD BE A WINTERY MIX AT THE BEGINNING OF THE EVENT MON 
NIGHT. 

DETAILS ARE LESS CLEAR BEYOND TUE...BUT THE COMMON GROUND IN THE 
MODELS IS A CONTINUATION OF WESTERLY FLOW ALOFT. WILL TREND LATTER 
PERIODS TOWARDS CLIMATOLOGY POPS AND TEMPS.

&&

.AVIATION...OFFSHORE FLOW AND DRY AIR MASS WILL CONTINUE VFR 
CONDITIONS. NEXT SYSTEM APPROACHING FROM THE SOUTH IS EXPECTED TO
BRING FREEZING PRECIPITATION TO THE SOUTH INLAND AREAS FRIDAY
EVENING...POSSIBLY AS EARLY AS FRIDAY AFTERNOON. FREEZING
PRECIPITATION WILL CONTINUE TO SPREAD NORTH THROUGH FRIDAY NIGHT.

KPDX AND APPROACHES...VFR CONDITIONS FOR NEXT 24 HRS. 

&&

.MARINE...SEAS AND WINDS EXPECTED TO REMAIN BELOW ADVISORY
CRITERIA THROUGH AT LEAST SATURDAY. LOW PRES OFF THE NORTHERN
CALIFORNIA SWINGS TO NEAR SOUTH OREGON COAST SAT AND SHIFTS INLAND
SAT NIGHT AND SUN. SOUTHERLY WINDS OF 25 TO 30 KT WILL RETURN TO
THE AREA MON OR TUE AS THE JET STREAM LIFTS NORTH.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY 
     AFTERNOON FOR COAST RANGE OF NORTHWEST OREGON-GREATER 
     PORTLAND METRO AREA-LOWER COLUMBIA-UPPER HOOD RIVER VALLEY-
     WESTERN COLUMBIA RIVER GORGE.

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY 
     AFTERNOON FOR CENTRAL WILLAMETTE VALLEY-NORTHERN OREGON 
     CASCADE FOOTHILLS.

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY 
     NIGHT FOR CASCADE FOOTHILLS IN LANE COUNTY-CENTRAL COAST 
     RANGE OF WESTERN OREGON-SOUTH WILLAMETTE VALLEY.

WA...WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY 
     AFTERNOON FOR GREATER VANCOUVER AREA-I-5 CORRIDOR IN 
     COWLITZ COUNTY-WESTERN COLUMBIA RIVER GORGE.

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY 
     AFTERNOON FOR SOUTH WASHINGTON CASCADE FOOTHILLS.

PZ...NONE.

&&

$$

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.