Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 220411
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
906 PM PDT SUN SEP 21 2014

.SYNOPSIS..A DYING FRONT MAY HOLD TOGETHER ENOUGH TO BRING A FEW
SHOWERS TO THE COAST MONDAY NIGHT...THEN FURTHER INLAND TUESDAY. A
MORE ORGANIZED SYSTEM WILL BRING MORE WIDESPREAD RAIN MIDWEEK...WITH
COOL AND SHOWERY WEATHER AFTERWARDS. AFTER A LONG HOT SUMMER...AUTUMN
WEATHER WILL BE ARRIVING RIGHT ON TIME.

&&

.EVENING UPDATE...A CLUSTER OF SHOWERS AND THUNDERSTORMS DEVELOPED
OVER KLAMATH AND DESCHUTES COUNTIES THIS AFTERNOON...AND HAVE SLOWLY
PROGRESSED NORTHWESTWARD INTO EASTERN LANE COUNTY THIS EVENING. IT
SEEMS STORMS ARE BEGINNING TO FINALLY TREND WEAKER...BUT
ADMITTEDLY...IT SEEMS JUST WHEN WE BEGIN THINKING THIS...A NEW
UPDRAFT GOES UP AND TEMPORARILY INVIGORATES AN EXISTING OR NEW STORM.
THE PRIMARY THREAT WITH THESE STORMS WILL BE BRIEF HEAVY RAIN AND AN
OCCASIONAL CLOUD TO GROUND LIGHTNING STRIKE. THE LATTER HAS
DEFINITELY BEEN TRENDING LESS OVER THE LAST HOUR. SUSPECT THESE
STORMS WILL WEAKEN FURTHER AS THEY ENTER EASTERN LINN COUNTY.

GLOBAL TO HIGH RESOLUTION SHORT TERM MODELS HAVE NOT BEEN
PARTICULARLY HELPFUL THIS EVENING. TO VARYING DEGREES THOUGH...LOWER
RESOLUTION MODELS DO PRODUCE SOME LIGHT QPF OVER THE CASCADES TONIGHT
INTO WEDNESDAY MORNING. THE RAP ALSO INDICATES THE STORMS ACROSS
EASTERN LANE COUNTY ARE FORMING IN A LOCALIZED REGION OF NEGATIVE 700
TO 500MB THETA LAPSE RATES. THE RAP SUGGESTS THIS REGION OF NEGATIVE
THETA LAPSE RATES WILL GRADUALLY WEAKEN AS IT SHIFTS NORTHWARD ACROSS
THE CASCADES TONIGHT AND EVENTUALLY EAST OF THE CREST TOWARDS
MORNING. NONETHELESS...BANDS OF ALTOCUMULUS HAVE DEVELOPED OVER THE
COAST AND WILLAMETTE VALLEY THIS EVENING. WITH NO DISTINCT INCOMING
VORT MAX ON WATER VAPOR THIS EVENING...SUSPECT THIS ALTOCUMULUS WILL
STAY RELATIVELY SHALLOW...BUT I AM STILL NERVOUS THAT SOMETHING
MIGHT FIRE FURTHER WEST OVER THE FOOTHILLS OR EVEN THE WILLAMETTE
VALLEY TONIGHT. WILL CONTINUE TO KEEP PRECIP/THUNDER CHANCES OVER
THE CASCADES...AND LEAVE A MENTION OUT OF THE FORECAST FOR THE
WILLAMETTE VALLEY...BUT WILL BE MONITORING THE SITUATION CLOSELY.

NO CHANGES TO THE REST OF THE FORECAST. WEDNESDAY STILL LOOKS TO BE
THE WETTEST DAY OF THE WEEK. /NEUMAN

PREVIOUS DISCUSSION BELOW...

.SHORT TERM...TONIGHT THROUGH WEDNESDAY...TEMPERATURES ARE GENERALLY
DOWN A COUPLE DEGREES VERSUS THIS TIME SATURDAY...AS LIGHT ONSHORE
FLOW HAS REPLACED THE OFFSHORE FLOW OF YESTERDAY. THE MOST DRAMATIC
TEMPERATURE DROPS HAVE BEEN ALONG THE COAST...WHERE ONSHORE FLOW AND
LOW CLOUDS ARE RESULTING IN TEMPS 10-15 DEGREES F COOLER THAN THIS
TIME YESTERDAY.

THE MARINE LAYER IS IN THE PROCESS OF DEEPENING...AND WILL LIKELY
MAKE A SUBSTANTIAL INLAND PUSH OVERNIGHT TONIGHT. BY SUNRISE MONDAY
IT IS LIKELY MUCH OF THE FORECAST AREA WILL BE UNDER A BLANKET OF
STRATUS. THE LOW CLOUDS WILL TAKE A LITTLE WHILE TO RETREAT TO THE
COAST...PROBABLY SOMETIME AROUND MIDDAY OR SHORTLY THEREAFTER. THE
INCREASED CLOUD COVER COMBINED WITH 850 MB TEMPS 3-5 DEG C COOLER
THAN TODAY SHOULD LEAD TO MAX TEMPS IN THE MID TO UPPER 70S MONDAY
AND EVEN THAT MAY BE A LITTLE OPTIMISTIC.

THIS WILL BE THE BEGINNING OF A TREND AWAY FROM THE PERSISTENT VERY
WARM AND DRY WEATHER THIS SUMMER HAS BROUGHT. AFTER 21 DAYS OF TEMPS
90 DEGREES OR WARMER AT PDX...AND A RECORD 36 DAYS AT OR ABOVE 90
DEGREES IN EUGENE...IT MAY BE SOMEWHAT SAFE TO SAY WE HAVE SEEN THE
LAST SUCH HEAT OF THE SEASON. AS WE NEAR THE END OF SEPTEMBER...THE
DAYS ARE GETTING SHORTER...AND THE SUN IS GETTING LOWER IN THE SKY.
IT BECOMES RAPIDLY MORE DIFFICULT CLIMATOLOGICALLY TO ACHIEVE 90
DEGREES AS WE MOVE TOWARD OCTOBER.

AND THIS TRANSITION IS HAPPENING RIGHT ON CUE...AS THE AUTUMNAL
EQUINOX IS FAST APPROACHING - 723 PM PDT ON MON SEP 22. MONDAY
EVENING A LARGE UPPER LOW AND TROUGH WILL BE APPROACHING THE PAC NW
COAST...LIKELY TO BRING A SIGNIFICANT AMOUNT OF RAIN TO OUR DISTRICT
AS ITS ASSOCIATED FRONTAL SYSTEM SLOWLY MOVES SLOWLY ONSHORE TUE-WED.
18Z NAM CONTINUES TO SHOW SOME POTENTIAL FOR A DECENT COASTAL JET
SETUP ALONG THE COAST TUE EVENING...PERHAPS BRINGING SOME SOUTH WIND
GUSTS 40-50 MPH TO THE BEACHES AND HEADLANDS. THIS WOULD BE THE FIRST
SUCH EVENT OF THE SEASON. CURRENT FORECAST DOES NOT REFLECT THIS JUST
YET...AS THERE IS SOME POTENTIAL FOR ENERGY TO BE SPLITTING AS THE
FRONT MOVES ONSHORE. LOWER PRESSURE TO THE NORTH AND LOWER PRESSURE
TO THE SOUTH WOULD CUT DOWN ON THE POTENTIAL OF SOUTH TO NORTH
GRADIENTS TO DRIVE SUCH WIND GUSTS.

WOULD NOT BE SURPRISED TO SEE SOME LOCATIONS SEE 1-3 INCHES OF RAIN
OUT OF THIS EVENT TUE THROUGH WED...PARTICULARLY COAST AND COAST
RANGE. INLAND AREAS COULD SEE UPWARDS OF 0.50-1.00 INCH DEPENDING ON
HOW WAVES TRACK ALONG THE FRONTAL ZONE AS IT LUMBERS ONSHORE. IF RAIN
GETS HEAVY...IT COULD BE A CONCERN FOR DEBRIS FLOWS IN SOME OF OUR
HARDER HIT FIRE AREAS THESE PAST FEW WEEKS. WILL CONTINUE TO MONITOR
THIS POSSIBILITY AND OF COURSE PASS ALONG MORE INFORMATION AS WE
LEARN THE SEVERITY OF THESE BURN SCARS.  WEAGLE

.LONG TERM...AFTER OUR SLOW-MOVING FRONT CLEARS THE REGION WEDNESDAY
EVENING...MODELS SHOW DECENT AGREEMENT THAT AN UPPER LEVEL TROUGH
WILL SETTLE OVER THE PACIFIC NORTHWEST. THIS WILL MEAN COOL AND
UNSETTLED WEATHER WITH PLENTY OF SHOWERS AROUND FOR THE REST OF THE
WEEK. IT MAY TAKE UNTIL NEXT WEEKEND FOR TEMPS TO REBOUND BACK TO
NORMAL...THOUGH BEYOND FRIDAY MODELS HAVE ALL SORTS OF DIFFERENT
IDEAS OF HOW TO HANDLE OUR PATTERN. BEST GUESS IS THAT SOME FLAT
RIDGING WILL ATTEMPT TO RETURN BY THE WEEKEND...FOLLOWED BY SOME
FRONTAL SYSTEMS ATTEMPTING TO CLIP THE PAC NW BY EARLY NEXT WEEK.
THIS BASED MORE ON PATTERN RECOGNITION THAN ANYTHING ELSE...SO
CONFIDENCE IN ANY PARTICULAR SOLUTION IS RATHER LOW STARTING NEXT
WEEKEND.  WEAGLE

&&

.AVIATION...VFR CONDITIONS CONTINUE ACROSS THE INTERIOR UNDER SCT
TO BKN CIRRUS AND SOME SMOKE FROM NEARBY WILDLAND FIRES FORMING A
SCATTERED LAYER AROUND 5000 FT. STORMS IN EASTERN LANE COUNTY
WILL NOT AFFECT EUGENE TERMINAL. A DEEPENING MARINE LAYER WILL
PUSH LOW MVFR STRATUS INTO MUCH OF THE VALLEY BY AROUND 12Z MON.
AT THE COAST...IFR CIGS HAVE PUSHED BACK ONSHORE AND WILL REMAIN
THROUGH LATE MONDAY MORNING BEFORE RISING TO MVFR.

KPDX AND APPROACHES...VFR CONDITIONS THROUGH 11Z MON THEN
INCREASING CHANCES FOR MVFR CIGS AROUND 1500 FT AS MARINE LAYER
DEEPENS AND PUSHES INLAND. MVFR CIGS LIKELY BY 13Z MON...LASTING
THROUGH 17Z MON WITH IMPROVEMENT TO VFR CONDITIONS THEREAFTER.
BOWEN/CULLEN

&&

.MARINE...SOUTHERLY WINDS CONTINUE ACROSS THE WATERS AND HAVE
WEAKENED THIS EVENING AS ANTICIPATED WITH CURRENT GUSTS AROUND 15
KT. UPDATES THIS EVENING INCLUDED SLIGHT ADJUSTMENT OF WINDS
BASED ON BEGINNINGS OF THE 00Z NAM. STILL LOOKS LIKE CONDITIONS
WILL REMAIN BENIGN THROUGH MONDAY WITH WINDS PICKING UP A BIT
MONDAY NIGHT AS A WEAK FRONT MOVES ACROSS THE WATERS. BOTH WINDS
AND SEAS INCREASE TUESDAY WITH THE APPROACH OF A STRONGER SYSTEM
WITH SEAS BUILDING TO 10-15 FT AND AT LEAST SMALL CRAFT ADVISORY
WINDS.

&&

.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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