Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 180914
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
213 AM PDT FRI APR 18 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD OVER THE AREA TODAY. THE
NEXT FRONTAL SYSTEM LOOKS TO ARRIVE SOONER THAN PREVIOUSLY FORECAST.
PRECIPITATION SHOULD REACH THE COAST SHORTLY AFTER SUNRISE SATURDAY
MORNING THEN SPREAD INLAND. WEAK HIGH PRESSURE RETURNS SATURDAY
NIGHT...AND THEN STRENGTHENS A BIT SUNDAY. WARMER SOUTHWEST FLOW
ALOFT SUNDAY WILL ALLOW INLAND DAYTIME TEMPERATURES TO BE A FEW
DEGREES ABOVE NORMAL. THE DRY PERIOD IS EXPECTED TO HOLD THROUGH
SUNDAY NIGHT...POSSIBLY AS LONG AS MONDAY MORNING...AS THE MAIN COLD
FRONT STALLS OFF THE COAST. THE FRONT FINALLY MOVES ONSHORE MONDAY
AFTERNOON INTO TUESDAY. THE PATTERN WILL THEN REMAIN FAIRLY UNSETTLED
THROUGH MUCH OF THE WEEK.
&&

.SHORT TERM...FRIDAY THROUGH SUNDAY...THE SHARP UPPER TROUGH WAS NEAR
OR JUST EAST OF THE CASCADES AS OF 09Z. WATER VAPOR IMAGERY SHOWS AN
OBVIOUS DRY SLOT MOVING ACROSS THE FORECAST AREA. NWS DUAL-POL
DOPPLER RADAR SHOWING SCATTERED SHOWER ACTIVITY OVER THE HIGHER
TERRAIN...ESPECIALLY THE N OREGON COAST RANGE AND S WA CASCADES AND
FOOTHILLS. THIS ACTION WILL CONTINUE TO DIMINISH THE REST OF TONIGHT
AND FRI MORNING AS THE AIR MASS ALOFT GRADUALLY MODERATES...WHICH
WILL WEAKEN THE MID-LEVEL LAPSE RATES. NEED TO LEAVE SOME SLIGHT
CHANCE POPS FOR THE S WA CASCADES AND EXTREME N OREGON CASCADES THIS
MORNING WITH 10-15 KT WLY 850 MB OROGRAPHIC FLOW AND NW ONSHORE
LOW-LEVEL FLOW. LATEST NAM SHOWS THE SURFACE RIDGE AXIS SOUTH OF MT.
HOOD AT 18Z.

GFS AND ECMWF SHOW A VERY WEAK UPPER LEVEL WAVE MOVING THROUGH THE
500 MB RIDGE THIS AFTERNOON. THE FEATURE DAMPENS OUT AS IT MOVES
ONSHORE BUT STILL SHOULD PRODUCE SOME MID AND HIGH CLOUDS. THE DRY
PERIOD WILL BE SHORT-LIVED...AND EVEN SHORTER LIVED THAN EARLIER
FORECASTS INDICATED. MODELS CONTINUE TO SPEED UP THE TIMING OF THE
NEXT SYSTEM. MODELS LOOKING PRETTY CONSISTENT WITH THE OVERALL
DETAILS FOR THE SAT SYSTEM. PREVIOUS SHIFT BROUGHT RAIN TO THE COAST
IN THE 12Z-15Z SAT TIME FRAME AND THAT STILL LOOKS REASONABLE. RAIN
MAY EVEN PENETRATE A LITTLE FURTHER INLAND THAN THE CURRENT GRIDS
SHOW. THE FRONT MOVES THROUGH AT A DECENT PACE AND SHOULD BE EAST
OF THE CASCADES BY EARLY SATURDAY EVENING AS THE PARENT UPPER SHORT
WAVE IS ALREADY MOVING INTO CENTRAL OREGON BY 00Z SUNDAY.

SURFACE HIGH PRES STARTS TO BUILD AGAIN SAT NIGHT...WITH LINGERING
PRECIP GENERALLY N OF A MT. JEFFERSON TO KONP LINE. HIGHEST POPS WILL
BE IN THE S WA CASCADES AND FOOTHILLS...CLOSEST TO THE UPPER LEVEL
TROUGH AND COOL POOL ALOFT. ANY LEFT-OVER PRECIP 12Z SUN SHOULD BE
LIMITED TO THE SW WA. SUNDAY IS LOOKING NICER AS A TRANSITORY 500 MB
RIDGE MOVES OVER THE PAC NW. 850MB TEMPS WARM TO AROUND 5C IN THE FAR
N TO NEAR 10C IN THE FAR S. THIS TRANSLATES TO MAX TEMPS A FEW
DEGREES ABOVE NORMAL. WEISHAAR

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MADE SOME CHANGES TO THE
SUN NIGHT AND MONDAY TIME FRAME. A DEVELOPING GULF OF ALASKA UPPER
TROUGH WILL DEEPEN SUN NIGHT ALLOWING THE DOWNSTREAM UPPER RIDGE TO
AMPLIFY. AS A RESULT...WENT DRY SUN NIGHT EXCEPT FOR SLIGHT CHANCE
POPS NEAR THE S WA COAST. A STRENGTHENING COLD FRONT FROM NEAR
VANCOUVER ISLAND TO 40N 133W WILL PIVOT INTO A MORE NORTH-TO-SOUTH
ORIENTATION SUN NIGHT AND MON MORNING. THUS...DRY CONDITONS MAY HOLD
THROUGH AT LEAST 18Z MON. THE FRONT FINALLY GETS FORCED INLAND MON
AFTERNOON AS THE DEEP GULF OF ALASKA UPPER TROUGH DIVES TO THE SE.
WILL NEED TO WATCH FOR THUNDERSTORM POTENTIAL MON AFTERNOON FOR THE
CASCADES WITH INCREASING S-SWLY FLOW...POSSIBLE SHORT-WAVES ROTATING
AROUND THE DEEP UPPER TROUGH AND STEEP AND MID-LEVEL LAPSE RATES.

LOOKS LIKE TUE AND WED WILL BE CHARACTERIZED BY COOL AND DAMP
CONDITIONS AS THE DEEP UPPER LOW MIGRATES ACROSS THE PAC NW AND INTO
THE NRN ROCKIES. LARGER MODEL DIFFERENCES CROP UP WED AND THU FOR
DIMINISHED FORECAST CONFIDENCE. THE ECMWF MAINTAINS A FAIRLY
PROGRESSIVE PATTERN THE LATTER HALF OF NEXT WEEK. WEISHAAR
&&

.AVIATION...PRIMARILY VFR ACROSS THE REGION AT THIS HOUR WITH MANY
LOCATIONS REPORTING A SCT CLOUDS AROUND 3000-4000 FT. JUST A FEW
LINGERING SCATTERED SHOWERS REMAIN...PRIMARILY N OF THE COLUMBIA
RIVER AND ALSO IN THE N OREGON COAST RANGE. PARTIAL CLEARING AND
DECREASING WINDS WILL LEAD TO LOW STRATUS OR FOG DEVELOPMENT WITH
THE BEST CHANCES OVER THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY.
CONDITIONS SHOULD IMPROVE BY 16Z TO 18Z AND REMAIN VFR FRI AS HIGH
PRES MOVES INTO THE REGION. INCREASING CLOUDS AFT 06Z SAT AHEAD OF
NEXT FRONTAL SYSTEM.

KPDX AND APPROACHES...EXPECT VFR THROUGH AT LEAST 09Z. LOW
STRATUS OR FOG LIKELY DEVELOPS AROUND 12Z. THIS SHOULD DISSIPATE
BY 16Z TO 18Z WITH VFR CONDITIONS FOLLOWING FOR THE REST OF FRI.
INCREASING MID CLOUDS AFT 06Z SAT AHEAD OF NEXT FRONTAL SYSTEM.
CULLEN

&&

.MARINE...WINDS HAVE GENERALLY DIMINISHED AS AN AREA OF HIGH PRES
BEGINS TO TAKE HOLD OVER THE WATERS. A FEW LOCALIZED GUSTS AROUND
20 KT POSSIBLE FOR THE NEXT FEW HOURS...PARTICULARLY ACROSS THE
FAR N OREGON AND S WASHINGTON WATERS WHERE THE SURFACE PRES
GRADIENT REMAINS A LITTLE STRONGER. AFTER THIS...A FAIRLY QUIET
PERIOD ON TAP OVER THE WATERS TODAY THROUGH EARLY SAT UNDER HIGH
PRES.

THE NEXT FRONT WILL MOVE ACROSS THE WATERS ON SAT...WITH ANOTHER
ROUND OF HIGH END SMALL CRAFT WINDS EXPECTED STARTING AROUND 5 AM
SAT THROUGH EARLY SUN. A LARGE SWELL TRAIN WILL FOLLOW THE FRONT
LATE SAT AND SUN. WHILE THE 00Z GUIDANCE HAS COME IN ABOUT 1 FT
LOWER... SEAS WILL RAPIDLY BUILD TO 17 TO 20 FT AT 16 SECONDS FROM
AROUND 11 PM SAT NIGHT THROUGH AROUND TO 5 PM SUN. WILL NEED TO
MONITOR FOR POTENTIAL HIGH SURF ADVISORY FOR SUN. SEAS WILL
GRADUALLY DECREASE SUN AFTERNOON...BUT LIKELY REMAIN ABOVE 10 FT
THROUGH AT LEAST WED. CULLEN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 5 AM
     TO 9 AM PDT THIS MORNING.

&&

$$

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..



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