Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 040400
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
858 PM PDT THU SEP  3 2015

.SYNOPSIS...BROAD UPPER LEVEL LOW PRES WILL SLOWLY SAG SOUTH OVER THE
REGION THROUGH FRI...BRINGING CONTINUED CHANCES FOR SHOWERS AND
ISOLATED THUNDERSTORMS. THE WEATHER WILL IMPROVE ON SAT AS THE UPPER
LOW FINALLY BEGINS TO SLIDE EAST AND A SHORTWAVE RIDGE MOVES THROUGH
THE PAC NW. ANOTHER LOW IS EXPECTED TO MOVE THROUGH ON SUN...BRINGING
MORE SHOWER CHANCES MAINLY TO NORTHERN PORTIONS OF THE FCST AREA.
THEN WARMER AND DRIER WEATHER IS ON TAP FOR THE FIRST HALF OF NEXT
WEEK AS UPPER LEVEL HIGH PRES OVER THE NE PAC BEGINS TO PUSH INTO THE
PAC NW.

&&

.UPDATE...ISOLATED SHOWERS CONTINUE TO STREAM INLAND BUT ARE BECOMING
LESS INTENSE AFTER SUNSET. THE COLD POOL ALOFT WILL BE OVER THE AREA
TONIGHT AND THERE IS A DISTURBANCE HEADING TOWARD THE COASTAL
WATERS...SEEN AS COLD TOP CELLS ON THE INFRARED SATELLITE LOOP.
FRIDAY WILL ALSO BE UNSETTLED WITH THE UPPER LOW OVER THE AREA WITH
THE CENTER OF COLD POOL ALOFT NEAR THE COAST. THIS SHOULD PROVIDE
ENOUGH INSTABILITY TO MENTION A SLIGHT CHANCE OF THUNDERSTORM. BUT
NEW MODEL SOUNDINGS SHOW A DRIER VERTICAL PROFILE FRI AFTERNOON SO
DEVELOPMENT OF THUNDERSTORMS MAY LIMITED BY MOISTURE AVAILABILITY.

PREVIOUS SHORT TERM DISCUSSION FOLLOWS...
SHORT TERM...A BROAD UPPER LEVEL LOW REMAINS CENTERED OVER FAR
SW BRITISH COLUMBIA THIS AFTERNOON. THE LOW WILL GRADUALLY DROP
SOUTHWARD INTO WASHINGTON AND THEN OREGON TONIGHT AND FRIDAY...
BRINGING CONTINUED COOL AND SHOWERY WEATHER THROUGH THE END OF THE
WEEK. THE MOST SIGNIFICANT SHOWER ACTIVITY TODAY HAS BEEN OVER THE
HIGHER TERRAIN OF THE CASCADES AND COAST RANGE SO FAR...BUT BASED ON
THE LATEST NWS DOPPLER RADAR IMAGERY...A BATCH IS NOW BEGINNING TO
DRIFT INTO THE WESTERN PORTIONS OF THE VALLEY. SO FAR NO THUNDER HAS
BEEN DETECTED IN OUR FCST AREA TODAY...BUT THERE WERE A CONSIDERABLE
NUMBER OF STRIKES RECORDED IN NW WASHINGTON EARLIER WHERE THE COLDEST
AIR ALOFT RESIDES. CANNOT RULE OUT AN ISOLATED STRIKE OR TWO OVER THE
FAR NORTHERN PORTIONS OF THE FCST AREA LATER THIS AFTERNOON OR EARLY
EVENING. SHOWERS SHOULD TAPER OFF LATER THIS EVENING AND
OVERNIGHT...BUT EXPECT THERE WILL STILL BE SOME LIGHT ACTIVITY AS
SHORTWAVE ENERGY ROTATES AROUND THE BASE OF THE UPPER TROUGH.
OVERNIGHT LOWS SHOULD AGAIN BE ON THE CHILLY SIDE...POTENTIALLY A
DEGREE OR TWO COOLER THAN WE HAD LAST NIGHT.

THE UPPER LEVEL COLD POOL WILL MOVE DIRECTLY OVER NW OREGON ON FRI.
THIS WILL ALLOW FOR A LITTLE DEEPER INSTABILITY AND INCREASE THE
LIKELIHOOD THAT WE SEE A FEW THUNDERSHOWERS MIXED IN WITH THE SHOWER
DURING THE AFTERNOON. THE UPPER LOW WILL BEGIN TO SLIDE EAST FRI
NIGHT INTO SAT. EXPECT A FEW SHOWERS TO LINGER AS UPPER LEVEL ENERGY
ROTATES THROUGH ON THE BACKSIDE OF THE TROUGH.

CONDITIONS LOOK TO IMPROVE SAT AS THE UPPER LOW MOVES FURTHER EAST
AND A SHORTWAVE RIDGE MOVES THROUGH THE PAC NW. EXPECT MORE SUN AND
HIGHS OVER THE INTERIOR LOWLANDS BACK INTO THE MID 70S. HOWEVER...IT
APPEARS THAT ANOTHER SHORTWAVE TROUGH WILL DIVE SOUTH OUT OF BRITISH
COLUMBIA ON SUNDAY. THIS IS EXPECTED TO BRING MORE CLOUDS AND SHOWER
CHANCES DURING THE DAY SUN...PARTICULARLY OVER THE NORTHERN HALF OF
THE FCST AREA. PYLE

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY. A SHORTWAVE DISTURBANCE
WILL BRING A THREAT FOR SHOWERS AND INCREASING CLOUDS LATE
SUNDAY INTO EARLY MONDAY MORNING AS AN UPPER LEVEL TROUGH DRIFTS
OVER THE PACIFIC NORTHWEST. 12Z EXTENDED MODELS HAVE BEEN SHOWING
NOTABLE RUN TO RUN VARIABILITY...BUT HINT AT BRIEF UPPER LEVEL
RIDGING LATE TUESDAY...BEFORE THE UPPER LEVEL FLOW BECOMES MORE
ZONAL BY WEDNESDAY. OVERALL...WITH ONLY WEAKER DISTURBANCES PASSING
NEAR THE AREA...HEIGHTS GRADUALLY WILL RISE TO SUPPORT TEMPERATURES
CLOSER TO SEASONAL NORMALS AND GENERALLY EXPECT DRIER AND WARMER
AGAIN FOR THE MIDDLE OF THE WEEK. /27
&&

.AVIATION...EXPECT MOSTLY VFR CONDITIONS THE NEXT 24 HOURS.
SCATTERED SHOWERS DISSIPATING THIS EVENING WITH LITTLE TO NO
ACTIVITY OVERNIGHT. MVFR CIGS POSSIBLE EARLY FRIDAY MORNING
ACROSS THE INTERIOR AS STRATUS BACK BUILDS OFF THE CASCADES...BUT
CONFIDENCE IS LOW. COULD SEE A REPEAT OF THIS MORNING DOWN IN
EUGENE WITH IFR CONDITIONS BUT CONFIDENCE IS PARTICULARLY LOW IN
THAT SCENARIO. WILL LIKELY SEE ANOTHER ROUND OF AFTERNOON SHOWERS
AND A SLIGHT CHANCE OF THUNDERSTORMS FRIDAY.

KPDX AND APPROACHES...VFR THE NEXT 24 HOURS. A FEW HOURS OF MVFR
CIGS POSSIBLE AFTER 14Z...BUT CONFIDENCE IS LOW. WILL SEE ANOTHER
ROUND OF AFTERNOON/EVENING SHOWERS AND A SLIGHT CHANCE OF
THUNDERSTORMS FRIDAY. BOWEN/64

&&

.MARINE...NO SIGNIFICANT UPDATES NEEDED TO THE FORECAST THIS
EVENING. WINDS ARE LIGHT AND OUT OF THE NORTHWEST. SEAS ARE AROUND
6 FT AND DROPPING SLOWLY. WINDS WILL PICK UP FRIDAY AFTERNOON BUT
LOOK AS MARGINAL AS POSSIBLE IN REACHING SMALL CRAFT ADVISORY
CRITERIA SO WILL NOT ISSUE. PREVIOUS DISCUSSION FOLLOWS. BOWEN

LOW PRESSURE ALOFT WILL CONTINUE TO BRING SHOWERS AND A SLIGHT
CHANCE OF THUNDERSTORMS TO THE WATERS THROUGH FRIDAY. SURFACE HIGH
PRESSURE OVER THE NORTHEAST PACIFIC AND A WEAK THERMAL TROUGH OVER
SOUTHERN OREGON COULD BRING MARGINAL SMALL CRAFT ADVISORY GUSTS
LATE FRIDAY. A WEAK FRONT LOOKS TO MOVE ACROSS THE WATERS ON
SUNDAY AND COULD BRING A BRIEF PERIOD OF SOUTHERLY WINDS...BUT
WINDS EXPECTED TO REMAIN UNDER 15 KT. HIGH PRESSURE LOOKS TO
REBUILD OVER THE WATERS LATE SUNDAY WITH THERMAL LOW PRESSURE
STRENGTHENING EARLY NEXT WEEK. THIS WILL BRING THE TYPICAL SUMMER
PATTERN OF GUSTY NORTHERLY WINDS.

MILD WINDS WILL ALLOW SEAS TO CONTINUE TO FALL TO AROUND 5 FT
LATE TONIGHT. SEAS EXPECTED TO REMAIN BETWEEN 5 TO 7 FT THROUGH
THE FORECAST PERIOD. HOWEVER...AS WINDS INCREASE NEXT WEEK WE
COULD SEE PERIOD OF STEEP AND CHOPPY CONDITIONS...ESPECIALLY OVER
THE CENTRAL OREGON WATERS. /64

&&

.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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