Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 171634
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
930 AM PDT WED SEP 17 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM CURRENTLY OFF THE CALIFORNIA COAST
WILL MOVE PRODUCE OCCASIONAL SPRINKLES AND LIGHT RAIN SHOWERS ACROSS
THE AREA THROUGH THURSDAY. COASTAL LOCATIONS ARE LIKELY TO SEE MORE
FREQUENT BOUTS OF WET WEATHER DURING THIS PERIOD. WHILE HAZY SKIES
WILL CONTINUE TO LINGER OVER THE WILLAMETTE VALLEY...ONSHORE FLOW
WILL KEEP THE WORST OF THE SMOKE FROM THE 36 PIT AND DECEPTION
COMPLEX FIRES OVER THE CASCADES AND POINTS EAST. HIGH PRESSURE AND
OFFSHORE FLOW WILL BUILD OVER THE REGION TOWARDS THE WEEKEND SO
EXPECT SMOKIER CONDITIONS TO RETURN TO THE WILLAMETTE VALLEY AND
TEMPERATURES POSSIBLY APPROACHING 90F AGAIN.

&&

.UPDATE...WATER VAPOR SATELLITE IMAGERY REVEALS A LARGE UPPER LEVEL
TROUGH OFF THE OREGON/CALIFORNIA COAST...PLACING THE REGION IN DEEP
SOUTH TO SOUTHWESTERLY FLOW ALOFT. INFRARED AND VISIBLE SATELLITE
IMAGERY SHOW PLENTY OF MID TO UPPER LEVEL CLOUDS STREAMING
NORTHEASTWARD ACROSS THE REGION. A COUPLE ROUNDS OF HIGH BASED
SHOWERS HAVE MOVED NORTHWARD ACROSS WESTERN OREGON THIS MORNING.
SURFACE OBSERVATIONS AND DOPPLER RADAR INDICATE MOST OF THESE SHOWERS
CONSIST OF VIRGA. HOWEVER...EVERY NOW AND AGAIN...A STRONGER BAND OF
SHOWERS IS PRODUCES SPRINKLES AT THE SURFACE. THESE HIGH BASED
SHOWERS HAVE BEEN SLIGHTLY MORE PERSISTENT CLOSER TO THE COAST WHERE
AN OCCASIONAL HUNDREDTH OF AN INCH HAS BEEN MEASURED SO FAR.
OVERALL...EXPECT THIS GENERAL PATTERN TO CONTINUE THROUGH AT LEAST
EARLY TO MID AFTERNOON. WX GRIDS WERE ADJUSTED ACCORDINGLY.

THIS MORNINGS KSLE SOUNDING INDICATES A LAYER OF INSTABILITY ALOFT.
THIS IS LIKELY RESPONSIBLE FOR THE HIGH BASED SHOWERS OBSERVED SO
FAR. WHILE IT HAS NOT BEEN DEEP ENOUGH FOR THUNDERSTORMS...CANNOT
RULE OUT A STRAY LIGHTNING STRIKE OR TWO THIS AFTERNOON OR
EVENING...ESPECIALLY ACROSS OUR SOUTHEASTERN ZONES SO WILL CONTINUE
THE SLIGHT CHANCE MENTION INHERITED.

SHORT TERM MODEL GUIDANCE SUGGESTS CURRENT SHOWER ACTIVITY OVER THE
NORTHERN CALIFORNIA COAST WILL RIDE NORTHWARD INTO THE FORECAST AREA
LATE THIS AFTERNOON. AS A RESULT...THE WX MENTION WAS SWITCHED OVER
FROM BRIEF SPRINKLES TO A MENTION OF SHOWERS FOR LATE THIS AFTERNOON
AND EVENING WHEN IT APPEARS INTERIOR LOCATIONS WILL STAND A BETTER
CHANCE OF SEEING MEASURABLE RAIN. HOWEVER...RAIN CHANCES WILL
CONTINUE TO BE HIGHEST TOWARD THE COAST...AND LIKELY LOWEST TOWARDS
THE CASCADES. THE NAM AND GFS CONTINUE TO SUGGEST A LOW LEVEL FRONT
WILL FOCUS MOISTURE AND RAIN CHANCES THURSDAY MORNING ACROSS OUR
NORTHWESTERN ZONES SO POPS WERE NUDGED UPWARDS DURING THIS PERIOD.
IT SHOULD BE NOTED THAT THE EC PRODUCES SIGNIFICANTLY LESS QPF
ACROSS THE AREA OVER THE NEXT 24 HOURS THAN THE GFS AND NAM...WHICH
IS NOT TERRIBLY SURPRISING GIVEN THE SPLITTING NATURE OF THIS STORM
SYSTEM. THIS REMAINS THE MAIN REASON WE DO NOT HAVE HIGHER POPS IN
THE FORECAST THAN PERHAPS IT WOULD APPEAR WE SHOULD GIVEN NAM AND
GFS QPF FIELDS. /NEUMAN

PREVIOUS DISCUSSION BELOW...

.SHORT TERM...A LOW PRESSURE SYSTEM IS CENTERED OFF THE SOUTHERN
OREGON AND NORTHERN CALIFORNIA COAST THIS MORNING. IT HAS SPREAD SOME
LIGHT MOISTURE AND A FEW SHOWERS ACROSS PARTS OF NORTHWEST OREGON AND
SOUTHWEST WASHINGTON OVERNIGHT. THE MODELS INDICATE SOME MORE LIGHT
MOISTURE AND A FEW SHOWERS WILL CONTINUE TO SPREAD IN FROM THE
SOUTHWEST ACROSS OUR FORECAST AREA TODAY...THOUGH AMOUNTS WILL BE
LIGHT. THE EXPECTED CLOUD COVER WILL TEND TO KEEP TEMPS IN THE 75 TO
80 RANGE AGAIN TODAY ACROSS THE INTERIOR.

THE LOW WILL APPROACH THE COAST THIS AFTERNOON...AND A STRONGER AREA
OF VORTICITY AND MOISTURE WILL LIKELY SPREAD IN MAINLY THIS EVENING
AND OVERNIGHT TONIGHT AS THE LOW BEGINS TO MOVE ONSHORE. WILL HAVE
THE HIGHEST POPS DURING THAT TIME WITH CHANCE IN MANY AREAS AND SOME
SMALL AREAS OF LIKELY POPS ESPECIALLY THE SOUTHERN MOUNTAIN AREAS.

THE MAIN LOW CENTER THEN TENDS TO MOVE SOUTH INTO CALIFORNIA AS IT
MOVES INLAND ON THURSDAY. HOWEVER THERE IS ENOUGH MOISTURE IN
COMBINATION WITH DAYTIME HEATING FOR AN INCREASE IN SHOWERS IN THE
AFTERNOON FROM THE COAST RANGE EASTWARD. HAVE DECIDED TO GO
SCATTERED ON THE SHOWER COVERAGE THURSDAY AFTERNOON EXCEPT LIKELY IN
THE OREGON CASCADES.

THE MODELS SHOW SOME INSTABILITY BOTH THIS AFTERNOON AND THURSDAY
AFTERNOON IN THE OREGON CASCADES...SO HAVE A SLIGHT CHANCE OF THUNDER
IN THAT AREA BOTH DAYS.

AN UPPER RIDGE BUILDS IN THURSDAY NIGHT AND FRIDAY FOR DRYING AND
SLOWLY WARMING WEATHER. THERE IS ENOUGH ONSHORE FLOW AND LEFT OVER
MOISTURE FOR A FAIR AMOUNT OF MORNING LOW CLOUDS FRIDAY MORNING...
THAT MAY HANG AROUND THROUGH MUCH OF THE DAY IN THE MOUNTAINS FROM
ABOUT PORTLAND NORTH...FINALLY CLEARING IN THE EVENING. TEMPS WILL
START TO RISE A BIT FRIDAY...BUT THE MORE SUBSTANTIAL WARMING WILL
HOLD OFF UNTIL THE WEEKEND.

SMOKE FROM THE 36 PIT AND DECEPTION COMPLEX FIRES WILL TEND TO SPREAD
OUT TO THE NORTH AND NORTHEAST TODAY...THEN MORE TO THE EAST THURSDAY
AND FRIDAY. EAST WINDS MAY RETURN THIS WEEKEND WHICH WOULD BRING THE
SMOKE BACK INTO THE WILLAMETTE VALLEY AGAIN. TOLLESON

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...FRIDAY NIGHT
THROUGH TUESDAY...THE GFS...DGEX...AND ECMWF MODELS ALL SHOW A
RETURN TO EASTERLY FLOW ON SATURDAY WHICH WILL WARM TEMPERATURES
ACROSS THE AREA. THIS WARM UP WILL ONLY LAST THROUGH SUNDAY...AS
WINDS SHIFT BACK TO THE WEST FROM AN UPPER-LEVEL TROUGH AND
ASSOCIATED CYCLONE DEEPENING OVER THE GULF OF ALASKA. THIS WILL COOL
TEMPERATURES AND BRING THE MARINE LAYER BACK IN AT NIGHT MONDAY AND
TUESDAY. -MCCOY
&&

.AVIATION...WIDESPREAD VFR PERSISTS UNDER LIGHT WINDS AND VARIABLE
MID AND HIGH CLOUDS. SOME LIGHT RAIN PUSHED ALONG THE COAST THIS
MORNING...BUT EXPECT AN INCREASED THREAT FOR SHOWERS THROUGH THIS
AFTERNOON AS MID LEVEL CLOUDS INCREASE.

SMOKE FROM THE 36-PIT FIRE CONTINUES TO DRIFT TO THE E AND NE.
WILL SEE SMOKE CONTINUE IN EAST COLUMBIA GORGE...UPPER HOOD RIVER
VALLEY AND AROUND MT HOOD...WITH SOME SMOKE TRAPPED SETTLING IN
VALLEYS TO E AND N OF THE FIRE. WITH S WINDS ALOFT OVER NEXT FEW
DAYS...SMOKE FROM FIRES OVER SW OREGON AND NW CALIFORNIA WILL
DRIFT N TO NE...AFFECTING SLANTWISE VISIBILITY FROM CASCADES
EASTWARD.

KPDX AND APPROACHES...VFR CONTINUES WITH VARIABLE HIGH CLOUDS THIS
MORNING. INCREASING MID LEVEL CLOUDS TODAY...WITH CIGS LIKELY
FORMING IN THE 4000-5000 FT RANGE THIS AFTERNOON/EVENING WITH
INCREASING CHANCES FOR A SHOWER OR TWO. CULLEN

&&

.MARINE...FAIRLY BENIGN CONDITIONS CONTINUE OVER THE WATERS FOR
THE NEXT FEW DAYS AS WEAK LOW PRES WILL MAINTAIN S TO SE WIND LESS
THAN 15 KT. THERE WILL BE A MIX OF WAVE TRAINS WITH VARYING
PERIODS...FROM THE NW...W AND SW. EXPECT NW SWELL TO DOMINATE
TODAY AT AROUND 15 SECONDS. OVERALL SEAS RUNNING 6 TO 8 FT...WITH
HIGHEST FURTHER OFFSHORE.

HIGH PRES WILL REBUILD OVER THE WATERS FRI AND SAT...WITH THERMAL
LOW PRES OVER THE COAST AND COASTAL WATERS. THIS WILL BRING
ANOTHER ROUND OF E TO NE WINDS TO THE WATERS THIS WEEKEND WITH
WINDS POSSIBLY GUSTING TO 25 KT ON SAT AND SAT NIGHT. CULLEN

&&

.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 AS THE FORECAST AREA.


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