Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 280353
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
853 PM PDT THU AUG 27 2015

.SYNOPSIS...A SIGNIFICANT WEATHER PATTERN CHANGE WILL BEGIN TONIGHT
INTO FRIDAY AS A LOW PRESSURE SYSTEM APPROACHES THE COAST. THE FIRST
WAVE OF RAIN IS NOW SPREADING INTO THE COASTAL WATERS AND WILL MOVE
ON TO THE COAST LATER TONIGHT AND FRIDAY. SOME LIGHT RAIN IS ALSO
EXPECTED TO SPREAD INLAND FRIDAY BEFORE LIFTING NORTH LATER IN
THE DAY. THE MOST SIGNIFICANT WAVE WILL LIFT NORTH THROUGH THE AREA
FRIDAY NIGHT AND SATURDAY MORNING FOR MORE RAIN. THE MODELS ARE
INCREASINGLY INDICATING THAT THIS WAVE WILL BE ASSOCIATED WITH A
RATHER STRONG SURFACE LOW THAT WILL BRING WINDY CONDITIONS TO NEARLY
ALL OF SOUTHWEST WASHINGTON AND NORTHWEST OREGON LATE FRIDAY NIGHT
AND SATURDAY MORNING. ANOTHER FRONT WILL SWEEP IN FROM THE WEST
SATURDAY NIGHT INTO EARLY SUNDAY FOR ANOTHER PERIOD OF RAIN.
UNSETTLED WEATHER WILL CONTINUE AT TIMES INTO NEXT WEEK AS A TROUGH
REMAINS NEAR THE COAST.
&&

.SHORT TERM...IT WAS ANOTHER MAINLY SUNNY AND WARM SUMMER DAY TODAY
ACROSS SW WASHINGTON AND NW OREGON. HIGHS OVER THE INTERIOR LOWLANDS
REACHED INTO THE UPPER 80S TO NEAR 90. HOWEVER IT APPEARS THAT THIS
WAS THE LAST SUMMER LIKE DAY FOR THE FORESEEABLE FUTURE...AS A
SIGNIFICANT WEATHER PATTERN CHANGE WILL BEGIN TO OCCUR TONIGHT AND
FRI. AN UPPER LEVEL TROUGH IS CENTERED OUT NEAR 41N/139W THIS
EVENING THAT WILL MOVE TOWARD THE REGION OVER THE NEXT COUPLE OF
DAYS. THERE IS ALSO A MOIST FRONTAL BOUNDARY WITH CONNECTIONS TO
SUBTROPICAL MOISTURE APPARENT ON IR SATELLITE SITTING JUST OFFSHORE.
NWS DOPPLER RADAR IS BEGINNING TO SHOW SOME SOLID ECHOES OVER THE
COASTAL WATERS ASSOCIATED WITH THIS FRONTAL BOUNDARY TONIGHT. A WEAK
SHORTWAVE TROUGH WILL LIFT NORTH TONIGHT INTO FRI...WHICH SHOULD
ALLOW LIGHT RAIN TO SPREAD INTO THE COAST AND COAST RANGE OVERNIGHT.
SOME LIGHT SHOULD ALSO MAKE IT EAST OF THE COAST RANGE INTO THE
INTERIOR VALLEYS AND THE CASCADE FOOTHILLS DURING THE DAY FRI...BUT
QPF TOTALS SHOULD BE LIMITED TO A FEW HUNDREDTHS OF AN INCH. PLACES
ALONG THE NORTH COAST MAY SEE UP TO 0.25 TO 0.5 INCHES THROUGH FRI
AFTERNOON.

AFTER A BRIEF LULL LATE FRIDAY AFTERNOON AND FRIDAY EVENING...THE
STRONGEST WAVE OF THE SERIES WILL BE LIFTING NORTH ALONG THE COAST
AND THROUGH THE FORECAST AREA LATE FRIDAY NIGHT AND SATURDAY MORNING.
THE MODELS...ESPECIALLY THE GFS13 AND THE 12Z ECMWF... INDICATE A
RATHER STRONG SURFACE LOW TO LIFT NORTH ALONG THE COAST AND THROUGH
THE AREA LATE FRIDAY NIGHT AND SATURDAY MORNING. THE NAM HAS NOT BEEN
AS BULLISH ON THE DEVELOPMENT OF THE SURFACE LOW OVER THE PAST
SEVERAL CYCLES...BUT THE 00Z RUN IS NOW SHOWING SIGNS OF TRENDING
TOWARD THE STRONGER AND FURTHER NORTH GFS AND ECMWF SOLUTIONS. IF
THINGS PAN OUT AS CURRENTLY EXPECTED... THE LOW WOULD BRING SOLID
GALES TO THE COASTAL WATERS...HIGH WIND TO THE COAST AND POSSIBLY
THE COASTAL MOUNTAINS...AND WINDY CONDITIONS FARTHER INLAND. A HIGH
WIND WATCH IS IN EFFECT FOR THE COAST AND COASTAL MOUNTAINS FOR LATE
FRIDAY NIGHT AND SATURDAY MORNING.

AFTER THE PRECIPITATION TURNS TO SHOWERS AND EASES SATURDAY
AFTERNOON...ANOTHER FRONT WILL SWING IN FROM THE WEST SATURDAY NIGHT
FOR A ANOTHER PERIOD OF STEADY RAIN. SHOWERS WILL FOLLOW BEHIND ON
SUNDAY...ESPECIALLY ACROSS THE NORTHERN FORECAST ZONES.

THESE SYSTEMS...ESPECIALLY THE ONE LATE FRIDAY NIGHT AND SATURDAY
MORNING...WILL HAVE SUBSTANTIAL DYNAMICS WITH THEM. PRECIPITABLE
WATER VALUES FEEDING IN FRIDAY NIGHT AND SATURDAY CONTINUE TO BE
FORECAST TO BE NEAR 1.5 INCHES...ACCOMPANIED BY A 110 KT 300 MB JET
STREAK LATE FRIDAY NIGHT AND SATURDAY MORNING. 850 MB INFLOW IS
AROUND 25 KT WITH THE INITIAL SURGE OF MOISTURE TONIGHT AND
FRIDAY...THEN IS AROUND 60 KT ON THE GFS AND ECMWF AS THE SURFACE LOW
MOVES THROUGH...GIVING SUPPORT TO THE HIGH WIND. ALL IN ALL...THIS
LOOKS QUITE WET...THOUGH THE WINDY SYSTEM FRIDAY NIGHT AND SATURDAY
MORNING MIGHT NOT BE QUITE AS WET AS PREVIOUS EXPECTED.

RAINFALL ACCUMULATIONS THROUGH THE ENTIRE WEEKEND ARE LIKELY TO BE
OVER 1 INCH ALONG THE COAST...IN THE COAST RANGE...AND IN
THE SOUTH WASHINGTON CASCADES...0.5 TO 1.25 INCHES IN THE OREGON
CASCADES...AND IN THE 0.25 TO 0.75 INCH RANGE IN THE VALLEYS. THE
HEAVIES AMOUNTS WILL TEND TO BE ON THE SOUTH WASHINGTON COAST...AND
THE LOWER AMOUNTS IN THE CENTRAL OREGON CASCADES. THIS WILL LIKELY
PUT A HUGE DENT IN THE FIRE WEATHER SEASON FOR OUR AREA FOR AT LEAST
THE NEXT COUPLE OF WEEKS. PYLE/TOLLESON

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY. FALL-LIKE WEATHER PATTERN
CONTINUES INTO NEXT WEEK WITH PRIMARILY COOLER THAN NORMAL
TEMPERATURES...CLOUDY CONDITIONS...AND CHANCES FOR ADDITIONAL RAIN.
ON MONDAY A SHORTWAVE MOVING THROUGH TO OUR NORTH MAY CLIP US WITH
SOME RAIN MAINLY ON THE COAST AND INLAND NORTH WHILE THE REST OF THE
AREA SHOULD REMAIN MOSTLY DRY. HAVE LEFT A SLIGHT CHANCE FOR RAIN
ACROSS MOST OF THE AREA JUST IN CASE THE MODELS DON`T QUITE HAVE THE
RIGHT TRACK FOR THIS SHORTWAVE SINCE IT`S A FEW DAYS OUT. MODELS ARE
HONING IN ON ANOTHER LOW PRESSURE SYSTEM THAT WILL MOVE THROUGH
TUESDAY NIGHT INTO WEDNESDAY WHICH COULD PRODUCE ANOTHER SOAKING RAIN
ACROSS THE AREA. BEHIND THIS SYSTEM TEMPERATURES COOL DOWN A BIT MORE
WITH MAYBE A FEW SHOWERS LINGERING INTO THURSDAY. -MCCOY
&&

.AVIATION...DRY SOUTHWEST FLOW WILL BECOME INCREASINGLY MOIST
THROUGH LATE FRIDAY PRODUCING LOWER CEILINGS ACROSS THE REGION.
EXPECT MVFR STRATUS AND LIGHT RAIN TO PUSH ONTO THE COAST OVER
THE NEXT SEVERAL HOURS AND LIKELY LINGER FOR MUCH OF THE DAY
FRIDAY. THIS COULD ALSO BRING BRIEF PERIODS OF IFR STRATUS TO THE
COAST. A WEAK SURFACE TROUGH SHIFTING INLAND ON FRIDAY MAY ENABLE
SOME OF THE STRATUS ALONG THE COAST TO PUSH INTO THE WILLAMETTE
VALLEY LATE FRIDAY MORNING/MIDDAY...ESPECIALLY ACROSS THE NORTH.
THIS MAY PRODUCE A PERIOD OF MVFR CONDITIONS ACROSS THE
INTERIOR...BUT CONFIDENCE REMAINS LOW. EXPECT RAIN CHANCES TO
INCREASE ACROSS THE INTERIOR THROUGH THE DAY FRIDAY...WITH A BRIEF
LULL POSSIBLE FRIDAY EVENING.

KPDX AND APPROACHES...DRY SOUTHWEST FLOW WILL BECOME INCREASINGLY
MOIST FRIDAY. THERE IS A CHANCE OF MVFR CONDITIONS DEVELOPING LATE
FRIDAY MORNING/MIDDAY...BUT CONFIDENCE IN THIS SCENARIO REMAINS
LOW AT THIS POINT. RAIN CHANCES INCREASE THROUGH THE DAY
FRIDAY...WITH A BRIEF LULL POSSIBLE FRIDAY EVENING. /NEUMAN/64

&&

.MARINE...NO SIGNIFICANT CHANGES. PREVIOUS DISCUSSION FOLLOWS...
EXPECT RELATIVELY BENIGN CONDITIONS ON FRIDAY TO ABRUPTLY CHANGE
FRIDAY NIGHT. WHILE UNCERTAINTY STILL EXISTS...ESPECIALLY IN
REGARDS TO DETAILS...CONFIDENCE IS GROWING THAT THE WATERS WILL
EXPERIENCE A VERY UNUSUAL FOR THIS TIME OF THE YEAR LOW PRESSURE
SYSTEM...SOMETHING THAT HAS NOT BEEN OBSERVED IN AT LEAST THE PAST
30 YEARS THIS EARLY IN THE SEASON. THIS LOW PRESSURE SYSTEM
APPEARS LIKELY TO DEVELOP OFF THE CALIFORNIA COAST AND MOVE
NORTHEASTWARD OFF THE OREGON COAST BEFORE MAKING LANDFALL NEAR THE
OLYMPIC PENINSULA. THIS WILL RESULT IN SOUTH WINDS INCREASING
ABRUPTLY ACROSS THE WATERS LATE FRIDAY NIGHT OR EARLY SATURDAY
MORNING FROM SOUTH TO NORTH. GALE FORCE WIND GUSTS OF 35 TO 40 KT
APPEAR LIKELY DURING THIS PERIOD...WITH EVEN 45 TO 50 KT WINDS NOT
OUT OF THE QUESTION. A GALE WATCH WAS ISSUED FOR NOW...BUT
DEPENDING ON DETAILS THAT STILL NEED TO BE IRONED OUT...A STORM
WARNING MAY BE NEED FOR AT LEAST A PART OF THE WATERS DURING THE
LATE FRIDAY NIGHT OR EARLY SATURDAY MORNING HOURS. EITHER
WAY...THIS UPCOMING STORM SYSTEM IS VERY UNUSUAL FOR THIS TIME OF
YEAR...AND IS SOMEWHAT REMINISCENT OF ONE OF OUR BIGGEST MARINE
EVENTS LAST YEAR...OCTOBER 25TH 2014...WHERE SEAS ROSE 15 TO 20
FT IN 3 TO 4 HOURS AT BUOYS OFF THE OREGON COAST.

ANYWAY...ONCE THE LOW PRESSURE PUSHES ASHORE IN THE PACIFIC
NORTHWEST...A SECOND UNUSUALLY STRONG FRONTAL STORM SYSTEM WILL
PUSH INTO THE WATERS SATURDAY AFTERNOON AND EVENING. THIS SHOULD
PRODUCE ANOTHER ROUND OF 15 TO 25 KT WINDS WITH GUSTS OF 30 TO 35
KT. WINDS AND SEAS SHOULD THEN RELAX ACROSS THE WATERS SATURDAY
NIGHT AND EARLY SUNDAY.

ADDITIONAL BOUTS OF SMALL CRAFT ADVISORY LEVEL WINDS OF 20 TO 30 KT
APPEAR LIKELY THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. TIMING IN
THESE ADDITIONAL SURGES IN WINDS REMAINS UNCERTAIN AT THIS
POINT...BUT SUNDAY NIGHT AND EARLY TUESDAY APPEAR THE PRIMARY
WINDOWS OF CONCERN. THESE PERIODS OF HIGHER WINDS SHOULD KEEP SEAS
FLIRTING WITH THE 10 FT MARK THROUGH THE MIDDLE OF NEXT WEEK. /NEUMAN

&&

$$

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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