Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 030459
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
857 PM PST MON MAR  2 2015

.SYNOPSIS...DRIER NORTH FLOW ALOFT WILL SETTLE OVER SW WASHINGTON AND
NW OREGON LATER TODAY AND TONIGHT. HOWEVER...ANOTHER WEAK DISTURBANCE
SLIDES SOUTH ALONG THE EASTERN CASCADE SLOPES TONIGHT. HIGH PRESSURE
WILL THEN DOMINATE THE WEATHER PATTERN MID-WEEK THROUGH THE WEEKEND.
THERE IS THE POSSIBILITY OF A PATTERN CHANGE EARLY NEXT WEEK.

&&

.UPDATE...INHERITED FORECAST APPEARS ON TRACK SO FEW CHANGES WERE
MADE TO THE FORECAST THIS EVENING. FOG COVERAGE WAS REDUCED A
BIT...WITH RIVER VALLEYS OF THE COAST RANGE AND THE SOUTHERN
WILLAMETTE VALLEY MOST LIKELY TO SEE SOME PATCHY FOG TUESDAY MORNING
BASED ON CURRENT DEWPOINTS. LOW TEMPERATURES WILL BOTTOM OUT NEAR
FREEZING FOR MANY LOCATIONS TONIGHT...AND LOOK TO BE EVEN A COUPLE
DEGREES COOLER TUESDAY NIGHT. MODELS CONTINUE TO SUGGEST A SHORTWAVE
TROUGH WILL SLIDE OVER THE TOP OF THE RIDGE OF HIGH PRESSURE INTO
SOUTHWEST BC LATE THURSDAY INTO FRIDAY. RAIN CHANCES LOOK TO REMAIN
NORTH OF OUR FORECAST AREA...BUT THIS SYSTEM MAY ALLOW MARINE CLOUDS
TO INCREASE ACROSS THE AREA...PARTICULARLY IF A SOUTHWEST MARINE
PUSH MATERIALIZES AS SOME MODELS SUGGEST. OTHERWISE...EXPECT DAYTIME
TEMPERATURES TO GRADUALLY WARM WELL ABOVE NORMAL INTO THE UPCOMING
WEEKEND AS HIGH PRESSURE LOOKS TO DOMINATE OUR WEATHER. /NEUMAN

PREVIOUS DISCUSSION BELOW...

.SHORT TERM...TONIGHT THROUGH THURSDAY...WATER VAPOR LOOP SHOWS A
SMALL AND COMPACT UPPER LEVEL LOW DIVING SOUTH ALONG THE CENTRAL
CALIFORNIA COAST EARLY THIS AFTERNOON. OTHER LARGE-SCALE FEATURES
INCLUDE A HIGH-AMPLITUDE RIDGE CENTERED NEAR 140W AND AN UPPER TROUGH
OVER THE NRN ROCKIES. VISIBLE SHOWS AN EXTENSIVE STRATOCUMULUS CLOUD
FIELD FROM THE W SLOPES OF THE COAST RANGE TO THE COAST AND ALSO OVER
THE CASCADE CREST AND INTO THE S WA CASCADE FOOTHILLS.

BRISK NLY FLOW ALOFT WILL BE OVER THE FORECAST AREA TONIGHT AND TUE.
THE LATEST NAM AND ECMWF HINT AT A WEAK BACK-DOOR SYSTEM SLIDING S
ALONG THE ERN CASCADE SLOPES TONIGHT WITH SOME VERY SPOTTY QPF
ASSOCIATED WITH IT. WILL KEEP THE MINIMAL POPS FOR THE HIGHER
CASCADES TONIGHT...BUT NOT OVERLY CONFIDENT ANYTHING WILL OCCUR. THE
BIGGER STORY FOR TONIGHT WILL BE WIDESPREAD FREEZING TEMPS. MAY ALSO
SEE A LITTLE EAST WIND DEVELOP IN THE GORGE LATE TONIGHT AS THE NAM
SHOWS A -3 TO -4 KTTD-KDLS GRADIENT BY 12Z TUE.

AN UPPER RIDGE WILL THEN BE THE DOMINANT FEATURE FOR THE REMAINDER OF
THE SHORT TERM...AS IT HAS BEEN FOR MOST THE WINTER. SOME LOW-LEVEL
OFFSHORE FLOW PERSISTS THROUGH WED SO NIGHT AND MORNING FOG WILL BE
RATHER LOCALIZED. OVERNIGHT LOWS WILL DROP TO NEAR OR BELOW FREEZING
TUE NIGHT...WITH THE LATEST GUIDANCE SHOWING LOWS IN THE MID TO UPPER
20S FOR MANY INLAND VALLEYS. LATEST GFS AND NAM SHOW A WEAK
SHORT-WAVE MOVING ACROSS THE AREA 00Z-12Z TUE. WOULD EXPECT JUST HIGH
CLOUDS WITH THIS FEATURE. THE GFS AND ECMWF RUNS ALSO SHOW THE UPPER
RIDGE FLATTENING A BIT WED NIGHT AND THU. NAM CROSS-SECTION FROM NEAR
KAST THROUGH THE COLUMBIA GORGE HINTS AT SOME HIGH LEVEL
MOISTURE...ABOVE 450 MB...WED NIGHT AND THU SO WOULD SUSPECT ANOTHER
SURGE OF CIRRUS CLOUDS. MAX TEMPS WED WILL BE NEAR SEASONAL
NORMALS...BUT WARM TO SLIGHTLY ABOVE NORMAL THU. SOME FAR SRN AREAS
COULD GET TO NEAR 60 DEG AS EARLY AS THU AFTERNOON. WEISHAAR

.LONG TERM...AND THE RIDGE CONTINUES. ECMWF ACTUALLY SHOWS THE RIDGE
AMPLIFYING FRI AS A SHORT-WAVE DROPS THROUGH THE NRN ROCKIES. 850  MB
TEMPS WARM A BIT MORE FRI...WHICH SHOULD BE ENOUGH TO PRODUCE MAX
TEMPS IN THE LOWER 60S FOR A GOOD PORTION OF THE SRN TWO-THIRDS OF
THE FORECAST AREA. UPPER RIDGE AXIS PUSHES A BIT CLOSER TO THE COAST
SAT FOR A LITTLE MORE WARMING. ECMWF WOULD SUGGEST A LITTLE LOW-LEVEL
OFFSHORE FLOW FRI NIGHT AND SAT. LITTLE CHANGE SUN... ALTHOUGH THE
GFS STARTS MOVING THE RIDGE EAST...WITH THE RIDGE AXIS ALONG A LINE
FROM KUIL-KREO. THE GEFS AND NAEFS MEAN CHARTS VALID 00Z MON SUGGEST
THE RIDGE AXIS WILL SHIFT EAST OF THE CASCADES. BIGGER MODEL
DIFFERENCES CROP UP MON...AS THE GFS TRIES TO BRING AN UPPER LOW
CLOSER TO THE COAST AND THE ECMWF MAINTAINS THE RIDGE. WOULD TEND TO
LEAN CLOSER TO THE ECMWF...SINCE THE RIDGE HAS BEEN THE DOMINANT
FEATURE THIS WINTER. EVEN IF THE GFS TURNS OUT MORE CORRECT...IT
TENDS TO BREAK DOWN THE RIDGE A LITTLE TOO FAST. INTRODUCED SOME
SLIGHT CHANCE POPS FOR THE THE SOUTH COAST AND COAST RANGE SECTIONS
MON NIGHT FOR NOW. WEISHAAR
&&

.AVIATION...WIDESPREAD VFR CONDITIONS IN CONTROL THIS EVENING AS
HIGH PRES BUILDS OVER THE REGION. DRIER NORTHERLY FLOW CLEARED
SKIES FROM NORTH TO SOUTH DURING THE AFTERNOON AND EARLY EVENING.
SOME STRATOCUMULUS CONTINUE TO OBSCURE THE CASCADES...BUT THESE
CLOUDS SHOULD DISSIPATE OVERNIGHT. CLEARING SKIES AND FAIRLY
LIGHT WINDS WILL LEAD TO GOOD RADIATIONAL COOLING OVERNIGHT...WITH
MANY VALLEY LOCATIONS FALLING NEAR OR JUST BELOW FREEZING.
HOWEVER...GIVEN THE RELATIVELY LOW DEW POINTS TO START IT IS
UNLIKELY THAT FOG WILL BE AN ISSUE. THE EXCEPTION MAY BE IN THE
SOUTHERN WILLAMETTE VALLEY...WHERE DEW POINTS ARE STARTING OUT A
BIT HIGHER. ANY FOG THAT DOES FORM SHOULD BURN OFF BY MID TO LATE
MORNING...WITH WIDESPREAD VFR THROUGH THE REST OF TUESDAY.

KPDX AND APPROACHES...VFR THROUGH TUESDAY. LIGHT-MODERATE N-NW
FLOW SFC AND ALOFT...DIMINISHING OVERNIGHT. PYLE

&&

.MARINE...WEAK HIGH PRES MOVING DOWN THE COAST EARLIER TODAY IS
NOW DISSIPATING OFF THE CA/OR BORDER. THIS HAS ALLOWED WINDS OVER
THE CENTRAL OR WATERS TO DROP BELOW 20 KT...SO LET THE SMALL
CRAFT ADVISORY FOR WINDS EXPIRE AT 8 PM. WINDS WILL CONTINUE TO
DECREASE OVERNIGHT AND TUE MORNING AS HIGH PRESSURE BUILDS OVER
THE REGION...TURNING LIGHT OFFSHORE. A THERMAL TROUGH BUILDING
NORTH FROM CA MAY CAUSE A MODEST INCREASE IN N WINDS
MIDWEEK...MAINLY FOR OUR SOUTHERN WATERS. OTHERWISE A STRONG UPPER
LEVEL RIDGE WILL KEEP CONDITIONS BENIGN FOR THE REST OF THE
WEEK...AS THE PACIFIC STORM TRACK STAYS WELL TO OUR NORTH.
PYLE/WEAGLE

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.
&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
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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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