Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 310417
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
917 PM PDT WED JUL 30 2014

.SYNOPSIS...AN UPPER LEVEL RIDGE OVER THE ROCKIES AND GREAT BASIN
REMAINS OUR MOST DOMINANT WEATHER FEATURE...KEEPING TEMPERATURES A
FEW DEGREES ABOVE NORMAL INLAND. THIS RIDGE WILL SLOWLY ERODE OVER
THE NEXT SEVERAL DAYS...EVENTUALLY ALLOWING MORE ONSHORE FLOW AND
SLIGHTLY COOLER TEMPERATURES BY EARLY NEXT WEEK. IN THE MEANTIME
SOUTH-SOUTHWESTERLY FLOW ALOFT CONTINUES TO GUIDE WEAK DISTURBANCES
INTO OUR AREA FOR OCCASIONAL THUNDERSTORM CHANCES IN THE CASCADES.
ONE SUCH DISTURBANCE SHOULD PROMOTE ANOTHER DAY OF ENHANCED CASCADE
THUNDERSTORM ACTIVITY THURSDAY...WITH ANOTHER POSSIBLE SATURDAY.

&&

.UPDATE...A FAIRLY REPETITIVE PATTERN CONTINUES. ANOTHER ROUND OF
CONVECTION OVER THE CENTRAL OREGON CASCADES OCCURRED THIS EVENING
WITH AREAS SOUTH OF OREGON HIGHWAY 58 BEARING THE BRUNT ONCE AGAIN.
ONE CELL IN PARTICULAR MOVED OFF THE CREST WITH RADAR INDICATED HAIL
EXCEEDING AN INCH. WE WERE UNABLE TO VERIFY A WARNING ISSUED FOR THE
STORM NEAR WILLAMETTE PASS BUT THE PASS WEBCAM DID SHOW A COUPLE
FRAMES OF HAIL ACCUMULATION. SO AM VERY CONFIDENT THERE WAS AT LEAST
SOME TREACHEROUS DRIVING FOR SOME TIME ALONG THE HIGHWAY AS THE CORE
OF THE STORM WAS A FEW MILES DOWNHILL FROM THERE. THE REST OF THE
CONVECTIVE ACTIVITY HAS PUSHED EAST OF THE CREST WITH THE
REMAINING DEBRIS CLOUDS SLOWLY ERODING OVERNIGHT.

IN OTHER NEWS...HAVE OPTED TO PULL THE STRATUS MENTION ALONG THE
COAST TONIGHT AS HIGH RESOLUTION MODELS AND SATELLITE IMAGERY DO NOT
SUPPORT ANYTHING MUCH BEYOND SOME PATCHY FOG ALONG THE IMMEDIATE
COAST OVERNIGHT. LOOKING OFFSHORE...THERE IS THE SHORTWAVE
MENTIONED BELOW THAT HAS MOVED TO ABOUT 40N 133W AS OF THIS WRITING.
THIS LOOKS LIKE IT COULD BRING ENOUGH UPPER LEVEL TROPOPAUSE FOLD
LIFT AND ACT ON PARCELS AROUND 600 MB. IF EVERYTHING COMES TOGETHER
JUST RIGHT WE MAY SEE A HIGH BASED THUNDERSTORM NOT TERRIBLY LONG
AFTER SUNRISE TOMORROW MORNING. BEST CHANCES WOULD BE MAINLY SOUTH
AND EAST OF EUGENE THROUGH THE EARLY AFTERNOON. SURFACE HEATING
SHOULD BE THE DRIVING TRIGGER UNDER THE ASSUMPTION THE SKY IS NOT
ALREADY COVERED WITH DEBRIS FROM EARLIER. UPDATES WILL BE AVAILABLE
SHORTLY. /JBONK


&&

./PREV DISC ISSUED 250 PM PDT WED JUL 30 2014/

SHORT TERM...TONIGHT THROUGH SATURDAY...MORE OR LESS A PERSISTENCE
PATTERN THIS WEEK OVER THE FORECAST AREA...WITH ONLY SMALL VARIANCES
FROM DAY TO DAY. THE LARGE WEATHER PICTURE CONTINUES TO INCLUDE AN
EXPANSIVE UPPER LEVEL RIDGE OVER THE FOUR CORNERS...GREAT BASIN...
AND NORTHERN ROCKIES. MEANWHILE AN UPPER LEVEL LOW PERSISTS IN THE
GULF OF ALASKA. THESE TWO FEATURES HAVE BEEN CAUSING THE UPPER LEVEL
FLOW TO VARY FROM SOUTHWESTERLY TO SOUTHERLY AT TIMES...DEPENDING ON
WEAK DISTURBANCES RIDING ALONG THE SOUTHEAST PERIPHERY OF THE GULF
OF ALASKA UPPER LOW. THE PROXIMITY OF THE UPPER RIDGE HAS KEPT THE
MARINE LAYER SHALLOW...WITH ALL BUT IMMEDIATE COASTAL AREAS WARMING
UP A FEW DEGREES ABOVE NORMAL EACH DAY.

THE PACIFIC NORTHWEST IS PRESENTLY BETWEEN UPPER DISTURBANCES... WITH
WEAK SHORTWAVE RIDGING TRANSITING THE REGION. THE ASSOCIATED
SUBSIDENCE AND SLIGHTLY WARMER TEMPERATURES ALOFT ARE LIKELY WHY
CONVECTION HAS BEEN LIMITED THIS AFTERNOON...EVEN IN THE CASCADES.
THURSDAY SHOULD BE A DIFFERENT STORY...AS A WELL DEFINED VORTMAX IS
GAINING STRENGTH OFF THE CA COAST NEAR 35N/135W. MEANWHILE REMNANT
MOISTURE FROM EX-HURRICANE HERNAN IS LIFTING NORTH INTO CALIFORNIA.
THESE TWO FEATURES SHOULD COMBINE FOR FAIRLY WIDESPREAD CONVECTION
FOR THE CASCADES EAST THURSDAY AND FRIDAY...STARTING IN NORTHERN CA
THEN LIFTING THROUGH OREGON THU...THEN INTO WA FRI.

PATTERN RECOGNITION-WISE IT APPEARS LIKELY AT LEAST A COUPLE
THUNDERSTORMS WILL FORM IN OUR CASCADES ZONES THURSDAY. HOWEVER
LOOKING AT MODEL SOUNDINGS...BOTH MOISTURE AND INSTABILITY ARE RATHER
MARGINAL. THAT SAID...MODIFYING NAM OR GFS BUFR SOUNDINGS TO REFLECT
THE FORECASTED TEMPS IN THE CASCADE CREST YIELDS QUITE A BIT OF
SURFACE BASED INSTABILITY...UP TO 1000 J/KG OF CAPE OR MORE. OVERALL
CHANCE OF THUNDERSTORMS APPEARS TO BE THE BEST FORECAST SOUTH OF MT
JEFFERSON...WITH A SLIGHT CHANCE EXTENDING INTO THE FOOTHILLS OF LANE
COUNTY. SLIGHT CHANCE OF THUNDER EXTENDS NORTH INTO THE WA CASCADES
FRI. WITH FLOW ALOFT MAINLY S-SW...IT APPEARS UNLIKELY THUNDER WILL
DRIFT WEST OF THE CASCADES. A BAGGY UPPER LEVEL TROUGH LINGERS OVER
THE PAC NW INTO THE WEEKEND AS THE UPPER RIDGE ERODES TO OUR EAST.
THIS COULD PROVIDE ENOUGH INSTABILITY FOR ISOLATED TO SCATTERED
CASCADE THUNDERSTORMS TO CONTINUE INTO SATURDAY.

ELSEWHERE...EXPECT LITTLE SENSIBLE CHANGE THE NEXT FEW DAYS. HIGH
TEMPS WILL REMAIN SOMEWHERE NEAR 90 DEGREES FOR THE INLAND VALLEYS
WHILE COASTAL AREAS ARE SEASONABLY COOLER WITH HIGHS IN THE 60S AND
LOWER 70S. SLIGHTLY DRIER NORTHERLY FLOW TEMPORARILY CLEARED THE
STRATUS FROM THE COASTAL WATERS TODAY...BUT SUSPECT IT WILL COME BACK
BEHIND THE DISTURBANCE THU NIGHT. NO SIGNIFICANT DEEPENING NOR INLAND
INTRUSION OF THE MARINE LAYER IS EXPECTED THROUGH THIS WEEKEND.
WEAGLE

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...FAIRLY GOOD CONSENSUS
BETWEEN THE MEDIUM RANGE MODELS THAT THE UPPER RIDGE TO OUR EAST WILL
GRADUALLY ERODE THROUGH EARLY NEXT WEEK. THIS MAY ALLOW A GREATER
WESTERLY/ONSHORE COMPONENT TO THE FLOW...PERHAPS COOLING INLAND AREAS
BY A FEW DEGREES AND DOWN CLOSER TO NORMAL. AS ONSHORE FLOW BECOMES A
BIT STRONGER...EXPECT THE THUNDER RISK TO DECREASE ON OUR SIDE OF THE
CASCADES. ALSO THE MARINE LAYER SHOULD DEEPEN A LITTLE...PUSHING A
BIT FURTHER INLAND AS THE THERMAL LOW OVER THE MID-COLUMBIA BECOMES
MORE DOMINANT AND INCREASES THE ONSHORE PRESSURE GRADIENT/FLOW. NO
SIGNIFICANT WIDESPREAD RAIN EVENTS ON THE HORIZON GOING WELL INTO
NEXT WEEK.  WEAGLE

&&

.AVIATION...HIGH PRESSURE AND WEAK ONSHORE FLOW WILL GENERALLY KEEP
INLAND CONDITIONS VFR THROUGH 00Z FRIDAY. IT IS LIKELY THAT AREAS OF
IFR CONDITIONS IN A LOW STRATUS WILL DEVELOP ALONG THE COAST FROM
09Z TO 12Z...AND RETURN BACK TO VFR CONDITIONS BETWEEN 17Z AND 19Z.

KPDX AND APPROACHES...HIGH PRESSURE AND NORTHWESTERLY FLOW WILL
PRODUCE VFR CONDITIONS THROUGH 00Z FRIDAY. THERE IS A 20 PERCENT
CHANCE HIGH END IFR CONDITIONS WILL IMPACT THE TERMINAL BETWEEN
13Z AND 16Z THURSDAY.

&&

.MARINE...LITTLE CHANGE EXPECTED TO THE WEATHER PATTERN THROUGH THE
WEEKEND AS HIGH PRESSURE LINGERS OFFSHORE. THIS WILL KEEP A FAIRLY
TYPICAL SUMMERTIME PATTERN OF NORTH WINDS...GENERALLY STRONGEST EACH
DAY FROM THE LATE AFTERNOON THROUGH MIDNIGHT. STEEP LOCALLY DRIVEN
WIND WAVES WILL TEND TO DOMINATE THE SEAS FOR THE NEXT FEW DAYS...
BUT TOTAL WAVE HEIGHTS WILL GENERALLY REMAIN UNDER 6 FT.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THIS EVENING FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
     OUT 10 NM-COASTAL WATERS FROM CASCADE HEAD TO FLORENCE OR
     OUT 10 NM-WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
     FROM 10 TO 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 3 AM PDT THURSDAY FOR
     WATERS FROM CASCADE HEAD TO FLORENCE OR FROM 10 TO 60 NM.

&&

$$

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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