Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 120252
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
755 PM PDT FRI JUL 11 2014

.SYNOPSIS...MOIST AND UNSTABLE SOUTH FLOW ALOFT WILL CONTINUE
TONIGHT INTO SAT. THIS WILL RESULT IN THE THREAT OF THUNDERSTORMS TO
THE CASCADES AND SAT. AN UPPER LOW OFF THE NORTH CALIFORNIA COAST
SATURDAY IS EXPECTED TO MOVE NORTH TO NORTHEAST AND INLAND INTO
EXTREME SW OREGON SUNDAY FOR ANOTHER THREAT OF THUNDERSTORMS...
EXTENDING FROM THE COAST RANGE...THE VALLEYS AND TO THE CASCADES.
WELL-ABOVE NORMAL DAYTIME TEMPERATURES CAN BE EXPECTED THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...WATER VAPOR IMAGERY SHOWED A COUPLE OF UPPER LOW
CENTERS OFFSHORE NEAR 42N 130W AND FURTHER SW NEAR 35N 133W.
FORECAST AREA WAS IN AN AREA OF UPPER DIFFLUENCE TO THE NE OF THE
LOWS...WITH A BAND OF MID AND HIGH LEVEL MOISTURE MOVING UP THROUGH
THE FORECAST AREA. BEST INSTABILITY HOWEVER REMAINS WELL TO THE S...
AND RADAR ECHOES WITH THE BAND OF MOISTURE LIFTING UP OVER THE
REGION HAVE BEEN DIMINISHING. WITH THE SHORTWAVE OUTRUNNING THE
INSTABILITY IT APPEARS THE THREAT FOR ANY FURTHER SHOWERS OVER THE
REGION ARE GREATLY DIMINISHED AND SO WILL DROP POPS FOR THE REST OF
THE NIGHT AND SAT MORNING.

REMAINDER OF SHORT TERM DISCUSSION UNCHANGED...
SATURDAY LOOKS TO BE AN IN-BETWEEN DAY AS A TRANSITORY 500 MB RIDGE
MOVES OVER THE AREA IN THE WAKE OF TONIGHTS SHORT-WAVE. MODEL
SOUNDINGS FOR SAT AFTERNOON...PARTICULARLY THE GFS...ARE SOMEWHAT
DRY...POSSIBLY INDICATING DECENT SUBSIDENCE BEHIND THE DEPARTING
SYSTEM...BUT MORE LIKELY THAT THE AIR MASS WILL BE SO WARM AND CAN
HOLD MUCH MORE MOISTURE THAN AN AIR MASS UNDER SEASONAL CONDITIONS.
MAIN ISSUE SATURDAY WILL BE THE RISING 850 MB TEMPS...CLIMBING TO
AROUND 22C OVER KPDX. THIS WILL BE THE START OF A MULTI-DAY HOT
SPELL. WILL ISSUE A HEAT ADVISORY FOR THIS EPISODE. HAVE KEPT ANY
THUNDERSTORM MENTION SAT TO THE CASCADES WHERE MID-LEVEL LAPSE RATES
CLOSE TO 8C/KM ARE FORECAST BY THE GFS MODEL SOUNDING.

SUNDAY LOOKS TO BE QUITE INTERESTING. ANOTHER ROUND OF MOIST SOUTH
FLOW ALOFT BEGINS TO SPREAD INTO SWRN OREGON AS EARLY AS SAT EVENING.
GFS AND ECMWF SIMILAR WITH THE OVERALL DETAILS...BUT THE 12Z NAM
APPEARS TO BE AN OUTLIER. THE  12Z ECMWF AND 12Z GFS BRING THE NEXT
LOW CENTER TO NEAR 41N 129W BY 12Z SUN. THE NAM IS A LITTLE MORE SW
WITH THE FEATURE AND MUCH SLOWER MOVING IT THROUGH THE FORECAST AREA.
UNLIKE TODAYS SYSTEM...THIS NEXT ONE IS EXPECTED TO
HAVE JET SUPPORT. GFS AND ECMWF SHOW A 60-80 KT 300 MB JET SEGMENT
MOVING INTO SWRN OREGON SUN MORNING. FORECAST AREA WILL BE IN THE
FAVORED QUADRANT OF THE JET SEGMENT FOR ADDITIONAL CONVECTIVE
SUPPORT. GFS MODEL SOUNDINGS FOR KPDX AND FOR A POINT IN THE N OREGON
CASCADES VALID SUN AFTERNOON ARE QUITE IMPRESSIVE. THE KPDX SOUNDING
VALID 00Z MON HAS A SURFACE-BASED CAPE OF NEARLY 600 J/KG...LIFTED
INDEX OF -2...TOTAL TOTALS OF 51 AND PRECIPITABLE WATER OF 1.37
INCHES. THE CASCADE SOUNDING IS EVEN MORE IMPRESSIVE WITH A CAPE OF
OVER 900 J/KG...LI OF -4...TOTAL TOTALS OF 54...0-6KM BULK SHEAR OF
NEARLY 40 KT...PRECIPITABLE WATER 1.66 INCHES...AND A SWEAT INDEX OF
311 (WE USE 250 AS THE BENCHMARK FOR POSSIBLE SEVERE). THE SREF
CALIBRATED PROBABILITY OF THUNDERSTORMS VALID 00Z-03Z MON SHOWS A 50
PERCENT BULLS-EYE OVER THE CASCADES AND THE 30 PERCENT CONTOUR TO THE
COAST. ALL IN ALL...MODELS ARE SHOWING SEVERAL INGREDIENTS COMING
TOGETHER FOR A CLASSIC PAC NW THUNDERSTORM EVENT. THUNDERSTORM
ACTIVITY SHOULD CONTINUE THROUGH SUN NIGHT...ESPECIALLY IN THE NERN
ZONES. WILL ALSO TONE DOWN SUN MAX TEMPS AS THERE SHOULD BE EXTENSIVE
CLOUD COVER DESPITE 850 MB FORECAST TEMPS OF 21-23C.

WOULD EXPECT A FLOOD OF MARINE AIR SUN NIGHT AND MON MORNING BEHIND
THE DEPARTING SHORT-WAVE. THIS WILL QUICKLY STABILIZE THINGS SUCH
THAT BY MON AFTERNOON ANY CONVECTION SHOULD BE WELL EAST OF THE AREA.
850 TEMPS 00Z TUE TO REMAIN IN THE 21-23C RANGE AND A 1000-500 MB
THICKNESS RIDGE NEAR THE OREGON COAST RANGE. WEISHAAR

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. MONDAY NIGHT
THROUGH FRIDAY...MAIN EMPHASIS WILL BE ON THE UNSEASONABLY HOT
CONDITIONS THROUGH MUCH OF THE PERIOD. 12Z ECMWF MAINTAINS THE HOT
PATTERN THROUGH AT LEAST WED. IT DOES HINT AT THE POSSIBILITY OF A
LITTLE MARINE AIR SEEPAGE BEGINNING WEDNESDAY...BUT MORE SO ON
THURSDAY. DO NOT AGREE WITH THE GFS SOLUTION OF HAVING A DEEP UPPER
LOW SWING THROUGH LATE IN THE WEEK. 12Z ECMWF KEEPS THE AREA IN NWLY
FLOW ALOFT AND ONSHORE LOW-LEVEL FLOW...KEEPING DAYTIME TEMPERATURES
SLIGHTLY ABOVE AVERAGE. A PRIMARY CONCERN WILL BE THE HIGH DEW
POINTS...RESULTING IN UNCOMFORTABLE NIGHTTIME PERIODS. WEISHAAR

&&

.AVIATION...THE MARINE STRATUS WILL REMAIN ALONG THE COAST TONIGHT
WITH WIDESPREAD IFR AND LIFR CONDITIONS. THE MARINE STRATUS WILL
LIKELY REMAIN ALONG THE IMMEDIATE COAST ON SAT...THOUGH IT MAY
LIFT INTO MVFR CIGS IN THE AFTERNOON. INLAND...VFR CONDITIONS
TONIGHT AND SAT WITH MID LEVEL CLOUDS IN THE 12KFT TO 15KFT
THROUGHOUT EVENING AND BECOMING CLEAR LATE TONIGHT.

KPDX AND APPROACHES...VFR TONIGHT AND SAT. MID LEVEL CLOUDS IN THE
12KFT RANGE EXPECTED THROUGH 09Z...THEN CLEARING. STRATUS IS NOT
EXPECTED TO REACH THE TERMINAL SATURDAY MORNING.

&&

.MARINE...HIGH PRES WILL REMAIN OVER THE NE PAC THROUGH THE
WEEKEND...KEEPING WINDS FROM THE N TO NW. THE GRADIENTS WILL
CONTINUE TO BE WEAK FOR LIGHTER WINDS TONIGHT THROUGH SATURDAY
NIGHT. THE OFFSHORE HIGH AND THE INLAND THERMAL LOW WILL
STRENGTHEN SUNDAY FOR INCREASING NORTHWEST WINDS BY AFTERNOON AND
LIKELY REACH SMALL CRAFT ADVISORY LEVELS...THEN REMAIN BRISK INTO
THE MIDDLE OF NEXT WEEK.

SEAS CONTINUE TO FALL TONIGHT AND SATURDAY. BY SATURDAY AFTERNOON
THE NORTHWEST FRESH SWELL ABATES UNDER LIGHT WINDS. NOAA WAVE
MODEL INDICATES WE WILL START TO SEE A LONG PERIOD WEST SWELL OF
2 TO 3 FT SAT AFTERNOON. ALL IN ALL THE SEAS WILL REMAIN BELOW 5
FT UNTIL THE NORTHWESTERLY WINDS INCREASE SUNDAY AFTERNOON.

THE COLUMBIA RIVER BAR WILL HAVE A VERY STRONG EBB EARLY SATURDAY
MORNING BUT WITH RELATIVELY LIGHT INCOMING SWELL...THE WAVES WILL
REMAIN BELOW SMALL CRAFT LEVELS. STILL MARINERS SHOULD BE
CAUTIOUS CROSS THE BARS DURING THIS VERY STRONG EBB. TW

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HEAT ADVISORY FROM 5 AM SATURDAY TO 2 PM PDT TUESDAY FOR CASCADE
     FOOTHILLS IN LANE COUNTY-CASCADES IN LANE COUNTY-CENTRAL
     COAST RANGE OF WESTERN OREGON-CENTRAL COLUMBIA RIVER GORGE-
     CENTRAL WILLAMETTE VALLEY-COAST RANGE OF NORTHWEST OREGON-
     GREATER PORTLAND METRO AREA-LOWER COLUMBIA-NORTHERN OREGON
     CASCADE FOOTHILLS-NORTHERN OREGON CASCADES-SOUTH WILLAMETTE
     VALLEY-UPPER HOOD RIVER VALLEY-WESTERN COLUMBIA RIVER GORGE.

WA...HEAT ADVISORY FROM 5 AM SATURDAY TO 2 PM PDT TUESDAY FOR CENTRAL
     COLUMBIA RIVER GORGE-GREATER VANCOUVER AREA-I-5 CORRIDOR IN
     COWLITZ COUNTY-SOUTH WASHINGTON CASCADE FOOTHILLS-SOUTH
     WASHINGTON CASCADES-WESTERN COLUMBIA RIVER GORGE-WILLAPA
     HILLS.

PZ...NONE.
&&

$$

MORE WEATHER INFORMATION ONLINE AT... HTTP://WEATHER.GOV/PORTLAND

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.PORTLAND.GOV
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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