Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 270512
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
901 PM PST WED NOV 26 2014

.SYNOPSIS...A WEAK COLD FRONT WILL PUSH SLOWLY INLAND TONIGHT AND
EARLY THU. THE FRONT WILL THEN STALL OVER WESTERN OREGON THU NIGHT
AND FRI...BEFORE ANOTHER STRONGER COLD FRONT WILL MOVE S THROUGH THE
REGION FRI NIGHT USHERING COLDER WEATHER FOR THE WEEKEND. HIGH PRES
OVER THE INTERIOR NW WILL TURN THE FLOW OFFSHORE BY SUN FOR DRY BUT
COLD WEATHER. SUN NIGHT AND MON A SYSTEM COMING UP FROM THE S WILL
ATTEMPT TO SPREAD SOME PRECIPITATION UP OVER THE COLD AIR MASS LEFT
OVER FROM THE WEEKEND.
&&

.UPDATE...NWS DOPPLER RADAR DEPICTS PRECIPITATION BEGINNING TO
SPREAD ONSHORE ACROSS THE REGION...THROUGH OBSERVATIONS
INDICATE THAT ACCUMULATIONS HAVE BEEN LIMITED THUS FAR...GENERALLY
ONLY A TRACE OR FEW HUNDREDTHS OF AN INCH AT BEST. FORECAST REMAINS
GENERALLY ON TRACK...BUT INCREASED POPS A BIT ALONG THE CENTRAL
OREGON COAST THROUGH THE NEAR TERM PER RADAR AND SATELLITE TRENDS.
THE FRONTAL BAND OF PRECIPITATION APPEARS SOMEWHAT DISJOINTED IN
APPEARANCE AND EXPECT RAINFALL TO BE INITIALLY LIGHT FOR THE NEXT FEW
HOURS...BEFORE INCREASING LATER TONIGHT THROUGH EARLY THU. LATEST
MODEL GUIDANCE SUGGESTS THAT THE SYSTEM MAY SPLIT N AND S...LEAVING
MANY PORTIONS OF THE AREA WITH ONLY OCCASIONAL LIGHT RAIN FROM MIDDAY
THU THROUGH THU EVENING. ALSO NUDGED FORECAST LOW TEMPERATURES FOR
TONIGHT A FEW DEGREES LOWER IN LINE WITH OBSERVATIONS AND GUIDANCE.
CULLEN
&&

.PREVIOUS DISCUSSION... /ISSUED 200 PM PST WED NOV 26 2014/

SHORT TERM...A WEAK COLD FRONT WAS OFFSHORE WED AFTERNOON...WITH
LAYERED CLOUDS SPREAD OUT AHEAD OF THE FRONT OVER THE PACIFIC NW. AS
THE UPPER RIDGE OVER THE REGION SHIFTS E TONIGHT AND THU THE FLOW
WILL TURN MORE TO THE SW...WITH THE FRONT SLOWLY PUSHING INLAND.
MODEL SOUNDINGS AGREE IN SHOWING MOISTURE INITIALLY IN THEMID AND
HIGH LEVELS...ABOVE 700MB. BY LATE TONIGHT THOUGH MOISTURE BEGINS TO
SPREAD IN IN THE LOWER LEVELS. DYNAMICS WITH THIS FRONT HOWEVER ON
THE WEAK SIDE...SO WILL BE SLOW TO INCREASE POPS OVERNIGHT INLAND
AREAS...WHILE THE COAST AND COAST RANGE WILL BENEFIT FROM AN
INCREASING LOW LEVEL SSW FLOW. WITH CLOUDS LIMITING RADIATIONAL
COOLING TONIGHT AND MUCH OF THE AREA STILL IN THE WARM SECTOR...
SHOULD BE ANOTHER UNSEASONABLY MILD NIGHT. THU THE FRONT APPEARS TO
STALL OVER THE REGION AS THE LOW OFFSHORE DIGS IN A BIT MORE. WITH
BAROCLINIC ZONE STALLED AND LOW LEVEL FLOW A LITTLE MORE ONSHORE
WILL TAKE POPS BACK UP TO LIKELY TO CATEGORICAL FOR MOST OF THE
REGION. ALTHOUGH THERE IS ONLY MODEST COOLING TO AIR MASS WITH THE
FRONT...CLOUDS AND EXPECTED OCCASIONAL LIGHT RAIN WILL LIMIT HIGH
TEMPS TO THE 50S MOST LOW ELEVATION AREAS.

LATE THU NIGHT...AND ESP FRI BETTER MOISTURE ARRIVES AS A NORTHERN
STREAM SHORT WAVE DROPS DOWN THROUGH BC WITH A TRUE COLD FRONT
DROPPING DOWN THE COAST AHEAD OF IT. MOIST ISENTROPIC LIFT IN THE
LOWER LEVELS IMPROVES AHEAD OF THE COLD FRONT AS WELL...BEST
DEPICTED IN MODEL 290K ISENTROPIC FIELDS. AS SUCH...POTENTIAL FOR
RAIN PICKS UP CONSIDERABLY BY FRI.

MODELS IN RELATIVELY GOOD AGREEMENT IN DEPICTING THE WESTERN
CANADIAN TROUGH DIGGING DOWN INTO THE PACIFIC NW STATES FRI NIGHT
AND SAT. ALL MODELS AT THIS POINT SHOWING A VIGOROUS CONTINENTAL
TYPE COLD FRONT MOVING S THROUGH SW WA AND NW OREGON FRI NIGHT.
PATTERN IS REMINISCENT OF A COLD FRONT FROM BACK ON 19 NOVEMBER 2003
THAT BROUGHT LOW ELEVATION SNOW TO INTERIOR N PARTS OF THE FORECAST
AREA. KEYS TO DOING SOMETHING SIMILAR RELY ON SOME OF THE
PRECIPITATION FALLING OVER AND BEHIND THE FRONT AS WELL AS STRONG
FRONTOGENETIC FORCING TO ALLOW FOR DYNAMIC COOLING. MODEL SOUNDINGS
AT THIS POINT INDICATE SNOW LEVEL FALLING RAPIDLY BEHIND THE FRONT
FRI NIGHT SUGGESTING AT LEAST A MIX OF RAIN AND SNOW POSSIBLE DOWN
TO FAIRLY LOW LEVELS. WHETHER IT WOULD BE COLD ENOUGH TO MIX SNOW AT
LOWEST ELEVATIONS IS ANYBODYS GUESS AT THIS POINT...BUT GIVEN THE
AGREEMENT IN MODELS AT THIS POINT WILL CARRY A MENTION OF MIXED RAIN
AND SNOW POSSIBLE FOR THE N PART OF THE AREA FRI NIGHT. SAT SEES A
RATHER COLD AIR MASS SETTLING IN OVER THE REGION BEHIND THE FRONT...
WITH A LINGERING CHANCE FOR SHOWERS...POTENTIALLY MIXED WITH SNOW IN
THE N...AS THE UPPER TROUGH MOVES THROUGH.

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...MOST GUIDANCE
SUGGESTS THE UPPER TROUGH AXIS RESPONSIBLE FOR SATURDAYS MIXED
RAIN/SNOW SHOWERS WILL BE MOVING ACROSS THE CASCADES SAT NIGHT...
WITH ANY LINGERING SNOW SHOWERS COMING TO END OVERNIGHT. EXPECT SOME
CLEARING SAT NIGHT AS COLD HIGH PRESSURE BUILDS DOWN FROM BRITISH
COLUMBIA...WITH LOW TEMPS LIKELY GETTING WELL INTO THE 20S FOR MOST
SPOTS. WITH HIGH PRESSURE STRENGTHENING EAST OF THE CASCADES...
EXPECT STRONG EAST WINDS TO RAMP UP THROUGH THE GORGE SUNDAY MORNING
AND PERSIST FOR MUCH OF THE PERIOD THROUGH WEDNESDAY...WITH BREEZY
CONDITIONS SPILLING INTO THE PORTLAND/VANCOUVER METRO. MONDAY MAY BE
A BRIEF BREAK FROM THE WINDS AS A SYSTEM PASSES BY TO OUR NORTH.

MEANWHILE...A DISTURBANCE FROM THE ALEUTIANS IS EXPECTED TO CUT OFF
FROM THE MAIN PACIFIC JET AND SETTLE OFF THE CALIFORNIA COAST BY
SUNDAY...WHERE IT WILL LIKELY LINGER FOR A COUPLE DAYS. THERE IS A
CHANCE THIS SYSTEM COULD COME CLOSE ENOUGH TO SPREAD SOME PRECIP
NORTHWARD INTO OUR FORECAST AREA SUN NIGHT OR MON. THE 12Z GFS AND
CANADIAN MODELS ARE MORE AGGRESSIVE WITH THIS THAN THE ECMWF. IF
THIS OCCURS...THERE MAY BE SOME LIGHT FREEZING RAIN IN PORTIONS OF
THE WILLAMETTE VALLEY WITH SOME SNOW OR LIGHT FREEZING RAIN IN THE
GORGE. CUTOFF LOWS SUCH AS THIS ONE ARE NOTORIOUSLY DIFFICULT TO
FORECAST...AS MODELS STRUGGLE WITH THEM IN THE EXTENDED FORECAST
PERIOD. WHERE THIS UPPER LOW GOES WILL DICTATE THE WEATHER THROUGH
MIDWEEK...BUT TEMPS ARE EXPECTED TO SLOWLY MODERATE TUESDAY AND
WEDNESDAY.  WEAGLE
&&

.AVIATION...VFR CONTINUES FOR NOW EXCEPT FOR KAST WHERE PASSING
RAIN BANDS HAVE BRIEFLY LOWERED THE CIGS TO AROUND 029. EXPECT THE
OVERALL CONDITIONS TO CONTINUE DETERIORATING OVER THE NEXT SEVERAL
HOURS AS THE OFFSHORE COLD FRONT CONTINUES ITS APPROACH. EVEN THEN
LATEST GUIDANCE IS NOT TERRIBLY PESSIMISTIC WITH FLIGHT
CONDITIONS AHEAD OF AND WITH THE FRONTAL PASSAGE. RADAR BACKS THIS
UP AS RETURNS ARE FAIRLY DISJOINTED IMPLYING A LACK OF
ORGANIZATION. AS SUCH...WILL CONTINUE THE PREVIOUS PACKAGES INTENT
OF SHOWING A LOWER AND WEAKLY CONVECTIVE DECK AFTER THE FRONT AND
LASTING THROUGH MOST OF THURSDAY. THIS APPEARS TO RESULT IN IFR
CIGS AT THE COAST AND MVFR CIGS AROUND 020 INLAND.

KPDX AND APPROACHES...VFR CONDITIONS TO PREVAIL THROUGH AT LEAST
12Z THU WITH VISUAL APPROACHED BECOMING IMPACTED SHORTLY
THEREAFTER AS THE DECK LOWERS BEYOND 040. WILL LIKELY SEE CIGS
BOTTOM OUT AROUND 020 CLOSER TO 18Z WITH LITTLE LIFT FOR THE
REMAINDER OF THE LOCAL CALENDAR DAY. /JBONK

&&

.MARINE...WINDS HAVE BEEN UNDER PERFORMING THUS FAR TONIGHT WITH
THE HRRR MODEL HAVING AS GOOD OF A HANDLE AS ANYTHING. DO EXPECT
COASTAL JET ENHANCEMENT AS THE FRONT NEARS TONIGHT BUT LAST FEW
RUNS OF THE HRRR ONLY INDICATE A VERY MARGINAL GALE GUST SCENARIO
FROM ABOUT 15 NM OUT TOWARDS SHORE. BEST WINDS WILL STAY WELL
ELEVATED OFF THE WATER SURFACE AS BROAD ATMOSPHERIC LIFT IS NOT
SUPPORTING THE HIGHER SPEEDS GETTING MIXED TO THE SURFACE. WILL
MAINTAIN THE GALE WARNING SINCE IT HAS ALREADY BEEN ISSUED.

BEHIND THE FRONT...HIGH-END SMALL CRAFT ADVISORY SPEEDS PERSIST
THU MORNING. LATEST MODEL RUNS SHOW 20-25 KT NW-N WIND DEVELOPING
OVER THE N WATERS FRI EVENING THEN SPREADING FURTHER S OVERNIGHT
AS A STRONG COLD FRONT DROPS SOUTH OUT OF CANADA. THE WIND TURNS
OFFSHORE SAT WITH POTENTIAL GUSTS 20 TO 30 KT NEAR GAPS IN THE
COASTAL TERRAIN. WIND SPEEDS RELAX SUN.

SEAS EXPECTED TO BUILD TO 10 FT THIS EVENING THEN REMAIN AT OR
ABOVE 10 FT THROUGH AT LEAST SAT MORNING. WAVE HEIGHTS DROP OFF
SAT AFTERNOON AS OFFSHORE FLOW DEVELOPS. JBONK/WEISHAAR

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...GALE WARNING UNTIL 4 AM PST THURSDAY FOR COASTAL WATERS FROM
     CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 4 PM
     PST THURSDAY.
&&

$$

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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