Cold in Washington, December 5 to 6, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
206 PM PST THU DEC  5 2013

.SYNOPSIS...A COLD AIR MASS WILL REMAIN OVER THE FORECAST AREA FOR
THE NEXT SEVERAL DAYS...LIKELY INTO EARLY NEXT WEEK. AN UPPER LEVEL
DISTURBANCE DEVELOPING ALONG THE WASHINGTON COAST TODAY WILL DIVE
SOUTH ALONG THE OREGON COAST TONIGHT AND FRIDAY MORNING...MOVING
SOUTH OF THE FORECAST AREA FRIDAY NIGHT. THIS SYSTEM WILL BRING AREAS
OF SNOW TO THE OREGON COAST AND INLAND AREAS MOSTLY SOUTH OF SALEM. A
MUCH COLDER AIR MASS SETTLES OVER THE REGION FRIDAY NIGHT AND
SATURDAY. A SLOW MODERATION WILL OCCUR SUNDAY THROUGH EARLY NEXT
WEEK...FOLLOWED BY A TRANSITION TO MILDER AND WETTER CONDITIONS THE
LATTER HALF OF NEXT WEEK. THIS TRANSITION COULD START ICY FOR MANY
INLAND AREAS LATER TUESDAY INTO WEDNESDAY WITH COLD AIR IN PLACE.
&&

.SHORT TERM...TONIGHT THROUGH SUNDAY...MORNING LOW TEMPS FELL WELL
INTO THE TEENS AT MANY INLAND LOCATIONS...SINGLE DIGITS IN THE HIGHER
CASCADES...AND LOW TO MID 20S AT THE COAST. IT WILL CONTINUE TO BE
COLD INTO NEXT WEEK. THERE IS A DISTURBANCE THAT IS BEGINNING TO DROP
DOWN THE SOUTHERN B.C. AND WASHINGTON COASTS TODAY...AND MID AND HIGH
CLOUDS WERE SPREADING INTO OUR AREA FROM THE NORTH THIS AFTERNOON.
THE SURFACE LOW WITH THIS DISTURBANCE WILL MOVE TO OFF THE OREGON
COAST TONIGHT WITH CLOUDS THICKENING OVER OUR FORECAST
AREA...INCREASING THE OFFSHORE FLOW AND GRADIENT THROUGH THE GORGE.
THE MODELS CONTINUE TO SAY THE MOST LIKELY AREAS OF SNOW WILL BE
ALONG THE COAST INTO THE COASTAL MOUNTAINS...AND IN THE VALLEY FROM
ABOUT SALEM SOUTHWARD. THE MODELS SUGGEST THE SNOW WILL START AT THE
COAST OVERNIGHT TONIGHT AND IN THE SOUTH VALLEY EITHER LATE TONIGHT
OR MORE LIKELY FRIDAY MORNING. THE OFFSHORE FLOW WILL SUPPRESS THE
SNOW NEAR PORTLAND TO EITHER NOTHING OR PERHAPS SOME FLURRIES. SEE
THE LIST BELOW FOR ALL THE WARNINGS AND ADVISORIES BEING ISSUED WITH
THIS PACKAGE.

THE LOW MOVES SOUTH OF OUR FORECAST AREA FRIDAY NIGHT INTO EARLY
SATURDAY WITH DRYING AND DECREASING SNOW. HOWEVER...THE REINFORCING
SHOT OF COLD AIR AND OFFSHORE WINDS BEHIND THIS SYSTEM WILL KEEP IT
VERY COLD AGAIN OVER THE WEEKEND. THE INCREASING OFFSHORE GRADIENTS
FRIDAY NIGHT AND SAT WILL RESULT IN EXTREMELY COLD WIND CHILLS IN
EAST WIND PRONE AREAS. SATURDAY HIGHS WILL STRUGGLE TO GET OUT OF THE
20S FOR MANY INLAND AREAS.

IT APPEARS A SLOW MODERATION BEGINS SUNDAY...WITH 850 MB TEMPS IN THE
-7 TO -10C RANGE. IT WILL STILL BE COLD THOUGH. THERE IS A WEAK
DISTURBANCE THAT PASSES SOUTHWARD BUT WELL OFF THE COAST SUNDAY THAT
MAY GIVE US SOME CLOUDS BUT IT LOOKS DRY FOR NOW...MORE LIKE THE GFS
AND ECMWF THAN THE NAM12 MODEL. IT MAY TAKE UNTIL LATER NEXT WEEK TO
GET OUT OF THE COLD AIR ENTIRELY. TOLLESON

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY. FORECAST MODELS INDICATE
THAT THE COLD ARCTIC AIR MASS WILL REMAIN IN PLACE OVER THE REGION
THROUGH EARLY NEXT WEEK. 12Z ECMWF/GFS DEPICT AN AREA OF LIGHT
PRECIPITATION LATE MON INTO EARLY TUE ASSOCIATED WITH A WEAK IMPULSE
DROPPING SOUTH ALONG THE WEST COAST. GIVEN THE STRENGTH OF THE COLD
AIR FIRMLY IN PLACE...THIS COULD BRING SOME FREEZING RAIN...SNOW...
RAIN...OR SOME MIX OF THE ABOVE. CONFIDENCE IS SOMEWHAT LOW AND
AMOUNTS LOOK TO BE FAIRLY SMALL AT THIS TIME...SO KEPT POPS IN CHANCE
NORTH TO SLIGHT CHANCE SOUTH RANGES.

THE NEXT SYSTEM LOOKS TO MOVE INTO THE AREA FOR WED OR THU WITH SOME
MORE SIGNIFICANT MOISTURE CONTENT. AS THIS MOIST AND MILD SYSTEM
APPROACHES THE PACIFIC NORTHWEST...SOME HEAVY RAINFALL LOOKS POSSIBLE
AS WELL AS SOME MODERATING TEMPERATURES BACK CLOSER TO /BUT STILL
BELOW/ SEASONAL NORMS. GIVEN THE LOWER LEVEL COLD AIR IN PLACE...THIS
MAY BEGIN AS FREEZING RAIN OR ICE FOR SOME LOCATIONS. THIS IS
ESPECIALLY TRUE FOR AREAS IN THE COLUMBIA RIVER GORGE AND VALLEYS IN
THE CASCADE FOOTHILLS. HOWEVER...THE PARTICULAR TRACK OF THE
DEVELOPING LOW AND TIMING DIFFERENCES REMAIN TO BE SORTED OUT BETWEEN
THE FORECAST MODELS...AND THESE FACTORS WILL INFLUENCE WHERE SNOW
LEVELS MAY BE ALONG WITH THE POTENTIAL FOR MIXED FROZEN PRECIP VERSUS
JUST RAIN FOR LOWLAND LOCATIONS.  CULLEN
&&

.AVIATION...EXPECT INCREASING MID LEVEL CLOUDS THIS AFTERNOON AND
EVENING AHEAD OF A LOW PRESSURE DROPPING INTO SOUTHWEST OREGON. LIGHT
SNOW SHOULD SPREAD INTO THE NORTHERN COASTAL ZONES AROUND 06Z
TONIGHT...POSSIBLY A TOUCH EARLIER...AND THEN BETWEEN 06Z AND 12Z
FRIDAY AT KONP. THIS SNOW SHOULD THEN SPREAD SOUTHEASTWARD INTO KEUG
AND KSLE BETWEEN 12Z AND 18Z FRIDAY. 2 TO 4 INCHES OF SNOW SEEM
LIKELY FOR KEUG...WHILE 1 TO 2 INCHES SEEM LIKELY FOR KSLE AND KONP.
THERE IS A DECENT CHANCE KHIO COULD ALSO SEE A PERIOD OF LIGHT SNOW
AROUND 18Z FRIDAY. A HALF INCH OR LESS OF SNOW IS MOST LIKELY AT KHIO
AND KAST. EXPECT VISIBILITIES TO RAPIDLY DETERIORATE AT LOCATIONS
WHERE SNOW FALLS. HOWEVER...IT APPEARS UNLIKELY SNOW WILL IMPACT KPDX
AND KTTD DUE TO DRY AIR SPILLING OUT OF THE COLUMBIA RIVER GORGE.

KPDX AND APPROACHES...OFFSHORE FLOW SHOULD PRODUCE VFR CONDITIONS AT
THE TERMINAL THROUGH 00Z SATURDAY. THERE IS A 20 PERCENT CHANCE SOME
LIGHT SNOW COULD SPREAD INTO THE TERMINAL BETWEEN 15Z AND 21Z FRIDAY.
/NEUMAN
&&

.MARINE...SEA CONDITIONS WILL REMAIN FAIRLY BENIGN THROUGH THE MIDDLE
OF NEXT WEEK. HOWEVER...EXPECT GUSTY EAST WINDS TO DEVELOP LATE
TONIGHT INTO FRIDAY AS A LOW PRESSURE SYSTEM DROPS SOUTHEASTWARD INTO
SOUTHWEST OREGON FRIDAY. AREAS NEAR COASTAL GAPS NEAR THE SHORE MAY
SEE SMALL CRAFT LEVEL WINDS FRIDAY EVENING SO AN ADDITIONAL ADVISORY
MAY BE NECESSARY. OTHERWISE...WE WILL CONTINUE TO WATCH A STRONGER
LOW PRESSURE SYSTEM THAT WILL ARRIVE TOWARDS THE MIDDLE TO LATTER
HALF OF NEXT WEEK...THAT COULD POSSIBLY BRING GALE FORCE WINDS TO THE
WATERS. /NEUMAN
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WARNING FROM 2 AM TO 4 PM PST FRIDAY FOR SOUTH
     WILLAMETTE VALLEY.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 2 PM PST
     FRIDAY FOR COAST RANGE OF NORTHWEST OREGON-NORTH OREGON COAST.

     WINTER STORM WARNING FROM 1 AM TO 4 PM PST FRIDAY FOR CENTRAL
     OREGON COAST.

     WINTER WEATHER ADVISORY FROM 2 AM TO 4 PM PST FRIDAY FOR
     CASCADE FOOTHILLS IN LANE COUNTY-CENTRAL COAST RANGE OF WESTERN
     OREGON-CENTRAL WILLAMETTE VALLEY-NORTHERN OREGON CASCADE
     FOOTHILLS.

WA...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 10 AM PST
     FRIDAY FOR SOUTH WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 1 AM FRIDAY TO 4 AM PST
     SATURDAY FOR WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD
     OR FROM 10 TO 60 NM-WATERS FROM CASCADE HEAD TO FLORENCE OR
     FROM 10 TO 60 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.