Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 242111
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
210 PM PDT FRI APR 24 2015

.SYNOPSIS...APRIL SHOWERS WILL CONTINUE THROUGH SATURDAY ACROSS
SOUTHWEST WASHINGTON AND NORTHWEST OREGON. COOL UPPER LEVEL LOW
PRESSURE WILL MOVE ACROSS WA SAT AND OFF TO THE E SUN. HIGH
PRESSURE WILL BUILD IN FROM THE SOUTH FOR DRIER AND MUCH WARMER
WEATHER MONDAY...POSSIBLY LINGERING INTO TUESDAY AS WELL. THE
NEXT COLD FRONT MAY BRING MORE SHOWERS BY THE MIDDLE OF NEXT WEEK.
&&

.SHORT TERM...SHOWERS WERE WIDESPREAD OVER THE FORECAST AREA FRI
AFTERNOON WITH WATER VAPOR PICTURES SHOWING AN UPPER LOW NEAR
VANCOUVER ISLAND. MODELS CONTINUE TO SHOW THIS LOW  DRIFTING SE
ACROSS WA TONIGHT AND SAT...BEFORE FINALLY MOVING E SUN. AS
SUGGESTED BY THE 12Z SLE SOUNDING...RADAR HAS SHOWN THE SHOWERS TO
BE RATHER SHALLOW WITH TOPS UNDER 20K FT. SNOW SHOWERS IN THE
CASCADES HAVE GENERALLY BEEN IN THE LIGHT SIDE...ON THE ORDER OF 1
TO 3 INCHES. A LOW LEVEL ONSHORE FLOW HELPED TO FEED THE
SHOWERS...BUT THE ONSHORE FLOW WEAKENS CONSIDERABLY TONIGHT AND SAT.
GFS AND ECMWF INDICATE DEEPER INSTABILITY FOR SAT AS THE COLD UPPER
LOW MOVES CLOSER. WHILE MODELS ALL SEEM TO SUGGEST THE SHOWERS
BECOMING LESS WIDESPREAD LATER TONIGHT AND SAT...THE DEEPER
INSTABILITY SUGGESTS INCLUDING A SLIGHT CHANCE FOR THUNDER SUN EVEN
AS POPS DIMINISH. WHAT APPEARS TO BE THE FINAL PROMINIENT SHORTWAVE
ASSOCIATED WITH THE CLOSED LOW MOVES ACROSS THE AREA EARLY SAT
AFTERNOON. FOLLOWING THIS WAVE POPS EXPECTED TO DROP OFF QUICKLY AS
THE UPPER RIDGE BEGINS TO BUILD IN AND AIR MASS STABILIZES.

MODELS OVER THE PAST FEW DAYS HAVE VARIED CONSIDERABLY ON HOW FAR S
THE IMPACTS OF A WARM FRONT WOULD EXTEND SUN AND SUN NIGHT. LATEST
RUNS OF GFS AND NAM JUST CLIP THE NW CORNER OF THE FORECAST AREA SUN
WITH QPF. EC AND UK EXTEND THE PRECIPITATION FURTHER S...BUT EVEN
THESE MODELS ON THE 12Z RUNS ARE TRENDING TOWARDS LOWER POPS. GIVEN
CURRENT TRENDS...WILL BACK OFF ON POPS A BIT MORE FOR SUN AND
SUN NIGHT ESP ACROSS THE S PART OF THE FORECAST AREA.

BY MON MODELS IN GOOD AGREEMENT WITH BUILDING A FAIRLY STRONG IF
TRANSIENT RIDGE OVER THE REGION. H8 TEMPS ON THE ORDER OF 14 DEG C
ON BOTH GFS AND EC SUGGEST HIGH TEMPS MON MAY APPROACH 80 IN THE
INLAND VALLEYS.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY...MODELS ARE STILL SOMEWHAT
INCONSISTENT WITH THE TIMING OF SYSTEMS FORECAST TO MOVE THROUGH
NEXT WEEK.  RIDGE OVER THE PACIFIC NORTHWEST GETS PUSHED OFF TO THE
EAST MONDAY NIGHT INTO TUESDAY AS AN UPPER-LEVEL TROUGH MOVES
ONSHORE AND STALLS OVER THE AREA. A COLD FRONT ASSOCIATED WITH THIS
UPPER-LEVEL TROUGH MOVES THROUGH DURING THE DAY ON TUESDAY...WITH
THE ECMWF BRINGING THE FRONT THROUGH DURING THE MORNING ON TUESDAY
AND THE GFS BRINGING THE FRONT THROUGH LATER IN THE
AFTERNOON/EVENING ON TUESDAY. THE ECMWF SEEMS TO BRING THE FRONT IN
A LITTLE TOO FAST...WHILE THE GFS MIGHT BE TOO SLOW...SO EXPECT THE
FRONT TO MOVE THROUGH SOMETIME MIDDAY ON TUESDAY. COOLED TEMPS A BIT
ON TUESDAY AS EITHER AN INCREASE IN CLOUDS AHEAD OF THE FRONT...OR
CLOUDS AND RAIN WITH THE FRONTAL SYSTEM WILL KEEP TEMPERATURES FROM
REACHING AS WARM AS PREVIOUSLY FORECAST. UNSTABLE AIRMASS UNDER
UPPER LEVEL TROUGHING BEHIND THE FRONT TUESDAY NIGHT INTO WEDNESDAY
WILL LIKELY KEEP SCATTERED SHOWERS ACROSS THE AREA UNTIL WEDNESDAY
EVENING...WHEN SHOWERS SHOULD BEGIN TO TAPER OFF EXCEPT MAYBE IN THE
CASCADES AND NORTHERN COAST/COAST RANGE.

A SHORTWAVE ON THE BACK SIDE OF THE STALLED UPPER-LEVEL TROUGH OVER
OUR AREA WILL MOVE THROUGH LATER NEXT WEEK...WITH INCONSISTENCY
BETWEEN THE GFS AND ECMWF ON THE TIMING OF THIS SYSTEM AS WELL.
RIGHT NOW...MODELS SUGGEST THAT THIS FRONT WILL MOVE THROUGH
SOMETIME ON THURSDAY...BRINGING MORE RAIN FOR THURSDAY INTO FRIDAY.
-MCCOY
&&

.AVIATION...MOSTLY VFR CONTINUES NEXT 24 HRS IN SCATTERED
SHOWERS. OCCASIONAL MVFR CIGS AND VIS IN HEAVIER SHOWERS. SHOWERS
WILL BE MOST ACTIVE NORTH OF KSLE. THERE WILL BE A SLIGHT CHANCE
OF THUNDERSTORM IN THE KAST AREA AFTER 06Z SAT...AND OVER INLAND
VALLEYS AFTER 14Z SAT.

KPDX AND APPROACHES...VFR WILL PREVAIL IN POST FRONTAL SHOWERS
NEXT 24 HRS. BRIEF MVFR CIGS...AND OCCASIONALLY VIS...POSSIBLE
IN HEAVIER SHOWERS. THERE IS A THREAT FOR ISOLATED THUNDERSTORMS
TO BE IN THE VICINITY BETWEEN 14Z-20Z SAT MORNING. /27

&&

.MARINE...WEST WINDS HAVE FALLEN BELOW ADVISORY CRITERIA THIS
AFTERNOON WITH WINDS 10 TO 15 KT. WINDS WILL REMAIN BELOW SMALL
CRAFT ADVISORY CRITERIA THROUGH LATE SAT...THEN PICK UP AGAIN WITH
THE APPROACH OF AN INCOMING WARM FRONT BY SUN. THE FRONT STALLS
OVER THE NORTHERN MARINE ZONES BEFORE LIFTING NORTH EARLY MON...SO
THE MAIN THREAT FOR ADVISORY LEVEL WIND GUSTS WILL BE OVER THE
NORTHERN COASTAL WATERS. AFTER MONDAY MODEL DIFFERENCES GROW AND
FORECAST CONFIDENCE DECREASES.

SEAS PEAKED BETWEEN 15 TO 17 FT EARLIER TODAY...WITH THE US COAST
GUARD REPORTING 16 TO 18 FT SEAS AT THE MAIN CHANNEL OF THE
COLUMBIA RIVER BAR. SEAS WILL CONTINUE TO FALL THROUGH THIS
EVENING...HOVERING AROUND 10 FT THROUGH AT LEAST 04-06Z SAT. SEAS
REMAIN BELOW 10 FEET THROUGH EARLY NEXT WEEK. /27

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR COASTAL WATERS FROM CAPE SHOALWATER TO FLORENCE
     OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 11
     PM PDT THIS EVENING.
&&

$$

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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