Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 230323
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
823 PM PDT FRI MAY 22 2015

.SYNOPSIS...AN UPPER LOW OFF THE NORTH OREGON COAST THIS EVENING
DIVES SOUTH TONIGHT AND SATURDAY...WHILE ANOTHER UPPER LOW SETTLES
OVER VANCOUVER ISLAND. THE MARINE LAYER WILL DEEPEN TONIGHT AND
SATURDAY. THE ONSHORE FLOW WEAKENS A LITTLE SUNDAY. THE UPPER LOW
MOVES OVER CENTRAL WASHINGTON MEMORIAL DAY THEN SHIFTS EAST TUESDAY.
A GRADUAL WARMING TREND IS EXPECTED MID TO LATE NEXT WEEK.

&&

.UPDATE...SOME SHOWERS ARE LINGERING OVER NW OREGON AND SW WASHINGTON
THIS EVENING AS AN UPPER LEVEL SHORTWAVE TROUGH MOVES OVER THE OREGON
COAST...AND GENERAL UPPER LEVEL TROUGH REMAINS OVER THE WESTERN
STATES. THE SHOWERS ARE MOVING NORTH TO SOUTH AND DECREASING WITH THE
LOSS OF DAYTIME HEATING. EXTENSIVE MARINE LAYER CONTINUES AND EXPECT
CLOUDY AND DRIZZLY CONDITIONS LATE TONIGHT INTO SATURDAY MORNING.
ONLY MADE MINOR CHANGES TO POPS AND WEATHER WITH THE EVENING UPDATE.
TJ

PREVIOUS SHORT TERM DISCUSSION...COMPLEX LARGE-SCALE PATTERN WILL
CONTINUE OVER THE PACIFIC NORTHWEST THROUGH THE SHORT TERM. AT 20Z
WATER VAPOR LOOP SHOWED A LARGE LOW PRESSURE AREA EXTENDING FROM
SOUTHERN OREGON TO SOUTHERN CALIFORNIA. ANOTHER UPPER LOW WAS
CENTERED OVER THE CENTRAL BRITISH COLUMBIA COAST...AND A THIRD BUT
MORE SUBTLE LOW CIRCULATION WAS NOTED OFF THE S WASHINGTON COAST. THE
FORECAST AREA LIES IN A BROAD DEFORMATION AREA...WITH EAST FLOW ALOFT
OVER THE FAR SOUTH AND S-SW FLOW ALOFT IN THE FAR NORTH. BULK OF THE
MOISTURE AND LIFT WAS OVER ERN OREGON. KRTX DUAL-POL DOPPLER RADAR
CONTINUES TO SHOW SCATTERED PRECIP ACTIVITY. BETWEEN 19Z AND 20Z
SEVERAL LIGHTNING STRIKES WERE NOTED NEAR BENNETT PASS.

NOT ANTICIPATING ANY THUNDERSTORMS LATE THIS AFTERNOON THROUGH THE
EVENING AS A GRADUAL SWITCH TO NWLY MID-LEVEL FLOW DEVELOPS. NOT
EXPECTING MUCH IN THE WAY OF LATE-AFTERNOON OR EARLY-EVENING CLEARING
TODAY...AS DEPICTED IN THE HI-RES WRF-ARW MODEL. AT 21Z THE KTTD-KDLS
GRADIENT WAS 4.7 MB...AND THE MORE SYNOPTIC KOTH-KGEG GRADIENT WAS
11.7 MB. THESE VALUES SUGGEST SUBSTANTIAL ONSHORE LOW-LEVEL
FLOW...WHICH IS READILY APPARENT IN VISIBLE IMAGERY.

THE SMALL UPPER LEVEL CIRCULATION SEEN IN WATER VAPOR OFF THE S WA
COAST THIS MORNING GRADUALLY SINKS SOUTH TONIGHT. GFS PICKS UP ON
THIS FEATURE AND DEVELOPS A CLOSED LOW OVER NRN CAL BY SAT AFTERNOON.
MEANWHILE...ANOTHER UPPER LOW ALONG THE BRITISH COLUMBIA COAST SLOWLY
DRIFTS SOUTH SAT. HOWEVER...THE MAIN WEATHER DRIVER FOR THE AREA
TONIGHT AND SAT WILL BE IN THE LOWER LEVELS. SURFACE HIGH PRES
STRENGTHENS OVER THE NE PAC TONIGHT AND SAT...INDUCING STRONGER
ONSHORE FLOW. MODEL SOUNDINGS FOR THE WILLAMETTE VALLEY VALID 12Z SAT
YIELD CLOUD TOPS TO NEARLY 5000 FT MSL. AM A LITTLE MORE CONFIDENT
THERE WILL BE DRIZZLE ALONG THE COAST AND WEST SLOPES OF THE COAST
RANGE AND INTO THE WILLAPA HILLS OF SW WA LATE TONIGHT AND SAT
MORNING. NAM TIME-HEIGHT SECTION FOR KPDX SHOWS 90 PCT OR GREATER RH
UP TO AROUND 850 MB SAT AFTERNOON. HAVE INCREASED SKY COVER IN THE
GRIDS...ESPECIALLY TONIGHT AND SAT.

MODEL SOUNDINGS AND TIME-HEIGHT SECTIONS VALID SUN INDICATE LOWER
CLOUD TOPS AND A LITTLE WEAKER ONSHORE GRADIENTS. THUS...SHOULD SEE
MORE AFTERNOON CLEARING...ESPECIALLY IN THE SOUTH PART OF THE
FORECAST AREA. GFS AND ECMWF IN GENERAL AGREEMENT MON WITH THE UPPER
LOW NEAR THE SOUTH END OF VANCOUVER ISLAND AT 12Z...THEN OVER NRN WA
BY 00Z TUE. ECMWF CONTINUES TO BE A LITTLE MORE E WITH IT COMPARED TO
THE GFS. CYCLONIC 500 MB FLOW IN CONJUNCTION WITH STRONGER ONSHORE
LOW-LEVEL FLOW WILL RESULT IN A DEEPER MARINE LAYER MEMORIAL DAY
MORNING. THE NAM TIME-HEIGHT SECTION FOR KPDX BEARS THIS OUT. HAVE
ADDED A MENTION OF DRIZZLE SUN NIGHT AND MON MORNING TO ACCOUNT FOR
THIS. WEISHAAR

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY...BY MONDAY NIGHT AN UPPER
LEVEL LOW PRESSURE SYSTEM WILL BE SLIDING GENERALLY THROUGH THE
REGION...THOUGH CONFIDENCE IN THE PRECISE TIMING AND TRACK REMAIN
RELATIVELY LOW. MODELS SEEM TO BE CLUSTERING ON A SOLUTION THAT
DROPS THE LOW ALONG OR EAST OF THE CASCADES AS IT MOVES SOUTH FROM
CANADA...WHICH WILL PROVIDE FOR PLENTY OF MARINE CLOUDS BUT KEEP
MOST PRECIPITATION IN THE HIGHER TERRAIN OF THE CASCADES.
THEN...SHORTWAVE RIDGING WILL LIKELY BEGIN TO BUILD OVER THE REGION
FOR DRY CONDITIONS AND WARMING...PARTICULARLY FOR THE SECOND HALF OF
THE WEEK. WHILE MODEL SPREAD REMAINS SOMEWHAT LARGE WITH RESPECT TO
HOW HIGH HEIGHTS WILL RISE...HIGH TEMPERATURES COULD CLIMB INTO THE
LOWER 80S FOR THE INTERIOR ON FRIDAY.  CULLEN
&&

.AVIATION...A VARIETY OF FLIGHT CONDITIONS WILL CONTINUE TONIGHT
AS SCATTERED SHOWERS GRADUALLY DISSIPATE. MOSTLY A MIX OF VFR AND
MVFR CIGS WILL PERSIST THIS EVENING... THEN EXPECT CONDITIONS TO
LOWER TOWARDS A MIXTURE OF MVFR/IFR CIGS BETWEEN 05Z-07Z SAT.
AREAS OF DRIZZLE POSSIBLE BETWEEN 10Z-19Z SATURDAY MORNING. SHOULD
SEE CIGS LIFT TO VFR AFTER 21Z...WITH A FEW SUNBREAKS POSSIBLE
AFTERWARDS.

KPDX AND APPROACHES...MVFR CIGS WILL CONTINUE THROUGH SAT. PERIODS
OF DRIZZLE LIKELY TO IMPACT THE TERMINAL BETWEEN 10Z-17Z SATURDAY.
CIGS SHOULD LIFT TO VFR AFTER 21Z. /27

&&

.MARINE...A PERSISTENT WEATHER PATTERN WILL CONTINUE TO BRING
BENIGN CONDITIONS TO THE WATERS THROUGH EARLY NEXT WEEK. NW WINDS
ARE EXPECTED TO GENERALLY REMAIN BELOW ADVISORY LEVEL WITH HIGH
PRES WELL OFFSHORE. A FRESH SWELL OF 5 TO 6 FT WILL ALSO CONTINUE
OUT OF THE WNW.

&&

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

$$

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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