Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 011022
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
221 AM PST SUN FEB  1 2015

.SYNOPSIS...HIGH PRES ALOFT WILL CONTINUE TO SHIFT EAST TODAY AS A
WEAK WEATHER SYSTEM APPROACHES THE COAST. THE OFFSHORE LOW-LEVEL FLOW
WILL GRADUALLY WEAKEN DURING THE DAY...LIKELY SHIFTING TO WEAK
ONSHORE BY LATE AFTERNOON. THE FRONTAL SYSTEM IS EXPECTED TO REACH
THE COAST THIS MORNING THEN REACH THE CASCADES BY THE AFTERNOON.
OVERALL PRECIPITATION AMOUNTS WILL BE RATHER LIGHT. A MUCH WETTER
SYSTEM IMPACTS THE AREA LATE SUNDAY NIGHT AND MONDAY. COMPUTER MODEL
SOLUTIONS SHOW HIGH VARIABILITY TUESDAY THROUGH THURSDAY...BUT THE
MOST LIKELY SCENARIO IS A BRIEF DRYING TREND WEDNESDAY AND WEDNESDAY
NIGHT...FOLLOWED BY A RETURN TO A MUCH WETTER PATTERN LATE IN THE
WEEK.

&&

.SHORT TERM...TODAY THROUGH TUESDAY...MAIN STORY EARLY THIS MORNING
IS THE LOW-LEVEL OFFSHORE FLOW. AT 0930Z THE KTTD-KDLS GRADIENT WAS
AT -6.4 MB...SLIGHTLY HIGHER THAN THE 03-HR FORECAST FROM THE 06Z NAM
RUN. THIS GRADIENT IS PRODUCING WIND GUSTS OF 40-50 MPH AT THE WEST
END OF THE COLUMBIA GORGE...BUT UP TO 65 MPH AT CROWN POINT. THESE
GUSTS ARE DOWN ABOUT 10 MPH FROM LATE SAT EVENING. THE COOL POOL
APPEARS TO BE A BIT DEEPER THAN MODELS SUGGEST...AS EVIDENCED BY THE
26F DEGREE READING AT A RAWS SITE AT 3450 FT MSL IN THE S WA
CASCADES. THE OFFSHORE GRADIENT IS BEING SUPPLEMENTED BY AN
APPROACHING WEAK FRONTAL SYSTEM...ALLOWING LOWERING PRESSURE
OFFSHORE FOR INCREASING GRADIENTS. THE 06Z NAM ELIMINATES THE
OFFSHORE GRADIENT BY 21Z TODAY...BUT IT TENDS TO WEAKEN THE OFFSHORE
FLOW TOO SOON. WOULD EXPECT THE EAST WIND TO DIE OFF MORE TOWARD 00Z
OR EVEN EARLY THIS EVENING.

KRTX DUAL-POL DOPPLER RADAR SHOWING SOME PRECIP ECHOES NEARING THE
COAST AS OF 0930Z. THE MID AND HIGH CLOUD COVER HAS LIMITED FOG
FORMATION. KEUG HAD DROPPED TO ONE-QUARTER MILE EARLIER BUT HAS COME
UP TO JUST OVER 2 MILES VISIBILITY SHORTLY BEFORE 10Z. NOT MUCH
CHANGE TO THE SUNDAY FORECAST. MODELS AGREE THAT PRECIP ALONG THE
COAST SHOULD COMMENCE AROUND 12-14Z AND THEN SPREAD INLAND.
INITIALLY...THE LOW-LEVEL OFFSHORE FLOW WILL SLOW THE MOISTENING
PROCESS OF THE COLUMN...THUS NOT EXPECTING PRECIP TO BEGIN AT KPDX
UNTIL AROUND 16-18Z. THE 08Z HRRR SHOWS PRECIP BY 16Z...BUT BELIEVE
THIS MAY BE A BIT TOO SOON. IN ANY EVENT...PRECIP WITH THIS FRONTAL
SYSTEM WILL BE RATHER LIGHT...MAYBE ONE-QUARTER TO ONE-HALF INCH
TOTAL FOR THE COAST RANGE...WILLAPA HILLS AND CASCADES. PRECIP LIKELY
TO BEGIN AS SNOW IN EASTERN SKAMANIA COUNTY OF SW WA AND THE EAST
SIDE OF MT. HOOD DUE TO THE RELATIVELY DEEP COOL POOL. THIS SYSTEM
MAY NOT BE STRONG ENOUGH TO TOTALLY MIX OUT THE COLDER AIR IN THOSE
AREAS. ANY PRECIP IN THE UPPER HOOD RIVER VALLEY SHOULD STAY AS
LIQUID.

MODELS ALSO IN GENERAL AGREEMENT REGARDING THE SUN NIGHT/MON SYSTEM.
MAIN MODEL DISCREPANCIES LIE IN THE TIMING AND FOCUS OF THE HEAVIEST
QPF. THE ECMWF SEEMS TO BE A BIT FASTER AND KEEPS THE HEAVIEST QPF
OVER SWRN OREGON MON MORNING. GFS HAS THE QPF BULLS-EYE A LITTLE
FURTHER NORTH WHILE THE NAM IS JUST A TOUCH MORE N THAN THE GFS. NAM
ALSO ALSO DEVELOPS A SLIGHTLY STRONGER SURFACE LOW NEAR BUOY 029 18Z
MON WHILE THE GFS HAS IT A BIT WEAKER AND FURTHER N. BREEZY TO WINDY
SOUTH WIND WOULD DEVELOP IF THE NAM VERIFIES...ESPECIALLY ALONG THE
COAST. NAM ALSO SHOWS A SHARPER AND MORE DYNAMIC COLD FRONT. THIS
WOULD ALSO BREAK THROUGH VALLEY INVERSIONS AND WARM UP THE LOWLANDS
CONSIDERABLY...JUST BEFORE COLD FRONTAL PASSAGE. IN ADDITION...00Z
NAM BUFR SOUNDINGS SHOW THE POTENTIAL FOR SOME INSTABILITY...WITH
CAPE OF 400-800 J/KG JUST ABOVE LOW-LEVEL INVERSION. THERE IS THE
SLIM POTENTIAL MONDAY AFTERNOON FOR SOME SURFACE-BASED CONVECTION
WITH THE COLD FRONT. THE SOUNDINGS ALSO SHOW DECENT DIRECTIONAL
SHEAR WITHIN THE UNSTABLE LAYER. HAVE MAINTAINED THE SLIGHT CHANCE
OF THUNDER MONDAY AFTERNOON AND EARLY EVENING.

TOTAL QPF FOR THIS SYSTEM EXPECTED TO BE ON THE ORDER OF 1 TO 1.5
INCHES FOR THE MOUNTAINS AND 0.25 TO 0.75 FOR THE LOWLANDS. MODELS
THEN START TO DIVERGE MON NIGHT AND BEYOND. THE ECMWF BRINGS A WARM
FRONT INTO SWRN OREGON TUE MORNING....AS DOES THE NAM BUT IT HAS IT A
LITTLE MORE TO THE S...CLOSER TO THE CALIFORNIA BORDER. THE GFS IS
MORE IN BETWEEN THE TWO. THIS WARM FRONTAL FEATURE GRADUALLY DRIFTS N
TUE AFTERNOON...BUT STAYS S OF THE COLUMBIA RIVER BY 00Z WED.
THUS...SNOW LEVELS WILL BE MUCH LOWER IN THE S WA AND FAR N OREGON
CASCADES TUE...COMPARED TO AREAS S OF MT. JEFFERSON. WEISHAAR

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...MODELS SOLUTIONS VARY IN
THE MID-WEEK PERIOD. THE GFS INDICATES AN UPPER RIDGE RETURNING TO
THE PACIFIC NW WED WHILE THE ECMWF KEEPS A REMNANT WARM-FRONTAL
BAROCLINIC BOUNDARY OVER THE REGION. THERE IS A THE GEM IS MORE IN
LINE WITH THE GFS COMPARED TO THE ECMWF. MADE SOME SMALL ADJUSTEMENTS
TO THE WED AND WED NIGHT PERIODS...MAINLY TO TRIM POPS A BIT. SHOULD
THE GFS PAN OUT...FURTHER REDUCTION WOULD BE NECESSARY AND WOULD ALSO
NEED TO CONSIDER THE INCLUSION OF NIGHT NIGHT AND MORNING FOG FOR THE
INTERIOR VALLEYS. MODELS ARE IN SURPRISING AGREEMENT FOR THE END OF
THE EXTENDED PERIOD. IT LOOKS LIKE A PERIOD OF MUCH WETTER WEATHER
WILL IMPACT THE REGION LATE IN THE WEEK...AND POSSIBLY INTO NEXT
WEEKEND AS A SWATH OF SUBTROPICAL MOISTURE COMBINED WITH A SERIES OF
ATMOSPHERIC WAVES SETS UP OVER THE NE PACIFIC. THIS WEATHER PATTERN
WILL LIKELY BRING A SUBSTANTIAL AMOUNT OF RAIN TO PARTS OF THE
PACIFIC NORTHWEST. HOWEVER...CONFIDENCE IN TIMING AND AREAS OF
PRIMARY QPF FOCUS REMAIN RATHER LOW AT THIS TIME. WEISHAAR

&&

.AVIATION...THE COAST AS WELL AS NORTH AND CENTRAL WILLAMETTE
VALLEY SITES REMAINS VFR AS COLD FRONT APPROACHES THE REGION.
INCREASING CLOUDS EARLY THIS MORNING WILL LIMIT FOG DEVELOPMENT IN
THESE AREAS...THOUGH THERE IS SOME PATCHY FOG AROUND KSLE
OCCASIONALLY REDUCING CIGS/VSBYS AT THIS SITE. CIGS WILL
GRADUALLY LOWER OVER NIGHT WITH RAIN DEVELOPING AROUND 14Z ALONG
THE COAST AND CLOSER TO 16Z AT SITES IN THE WILLAMETTE VALLEY.
FURTHER SOUTH...LIFR CIGS/VSBYS AT KEUG WILL CONTINUE UNTIL
SHOWERS START TO PUSH INTO THE REGION AROUND 16Z. CIGS/VSBYS WILL
GRADUALLY IMPROVE TO MVFR AFTER FRONTAL PASSAGE THIS
AFTERNOON/EVENING.

KPDX AND APPROACHES...VFR CONDITIONS WILL PREVAIL THIS MORNING WITH
GUSTY EAST WINDS. MID AND HIGH CLOUDS INCREASE OVERNIGHT WITH
CIGS FALLING FROM 100 TO 050 AROUND 16Z SUN ALONG WITH RAIN
DEVELOPING. MAY SEE IFR CIGS WORK SOUTH ALONG THE I-5 CORRIDOR
FROM THE KKLS AREA TOWARD KPDX BUT EASTERLY OUTFLOW FROM THE GORGE
SHOULD KEEP IT AS AN IFR STRATUS DECK IF IT ARRIVES AT ALL. RAIN
PICKS UP AROUND 16Z AND CIGS FALL TO 025. EXPECT FRONTAL PASSAGE
AND A TRANSITION TO SHOWERS NEAR 23Z. -MCCOY/JBONK

&&

.MARINE...AN APPROACHING COLD FRONT IS APPROACHING OUR WATERS THIS
MORNING AND WILL MOVE THROUGH THIS MORNING. WINDS WILL INCREASE
NEAR SMALL CRAFT ADVISORY ALONG AND AHEAD OF THE FRONT THIS
MORNING. CONFIDENCE IS STILL LOW THAT GUSTS ABOVE 20 KTS WILL BE
PREVALENT ENOUGH TO WARRANT A SMALL CRAFT ADVISORY...THOUGH A FEW
GUSTS OVER 20 KTS ARE POSSIBLE...ESPECIALLY AS THE FRONT NEARS
SHORE. SEAS START TO INCREASE WITH THIS SYSTEM BUT LOOK TO REMAIN
BELOW 10 FT TODAY. A SECOND...STRONGER SYSTEM MOVES THROUGH ON
MONDAY...BRINGING A VERY GOOD CHANCE FOR SMALL CRAFT WINDS WITH
GUSTS TO 30 KTS LIKELY. THIS SYSTEM WILL ALSO INCREASE SEAS TO 10
TO 12 FT. WINDS AND SEAS START TO SUBSIDE LATE MONDAY...BRINGING
SEAS BACK DOWN TO AROUND 7 TO 8 FT BY MIDWEEK AS SHORT-LIVED HIGH
PRESSURE BUILDS BACK OVER THE REGION. MODELS ARE IN AGREEMENT THAT
AN EVEN STRONGER SYSTEM WILL MOVE THROUGH LATE THIS WEEK...WHICH
COULD GENERATE SOUTHERLY GALES AND BRING SEAS UP TO NEAR 20 FT
THURSDAY OR FRIDAY. THERE IS UNCERTAINTY IN THE TIMING AND TRACK
OF THIS SYSTEM...WHICH SHOULD GET IRONED OUT AS THE WEEK
PROGRESSES. -MCCOY

&&

.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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