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000
FXUS66 KPQR 172141
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
240 PM PDT FRI MAY 17 2013

.SYNOPSIS...SCATTERED SHOWERS WILL GRADUALLY DECREASE THIS EVENING AS
WEAK SURFACE HIGH PRESSURE BUILDS INTO OREGON AND SW WASHINGTON. THE
NEXT PACIFIC SYSTEM WILL MOVE IN FOR SATURDAY...PROBABLY BRINGING A
PERIOD OF STEADY LIGHT RAIN SATURDAY FOLLOWED BY DECREASING SHOWERS
SATURDAY NIGHT AND SUNDAY. DRIER WEATHER IS EXPECTED SUN NIGHT/MON...
BUT IT IS LOOKING MORE LIKELY THAT A COOL AND UNSETTLED PATTERN WILL
SET UP OVER THE PACIFIC NORTHWEST FOR THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...TONIGHT THROUGH MONDAY...A WEAK UPPER LEVEL TROUGH
CONTINUES TO GENERATE SCATTERED SHOWERS ACROSS THE FORECAST AREA THIS
AFTERNOON. THIS INSTABILITY IS PRETTY MUCH ALL SURFACE BASED BUT VERY
SHALLOW...WITH A CAPPING INVERSION IN PLACE AROUND 10KFT. WHILE THE
SHOWERS ARE NOT DEEP ENOUGH TO PRODUCE LIGHTNING...THE MIXED LAYER IS
STILL MOISTURE RICH. SO THERE STILL COULD BE SOME BRIEF HIT AND MISS
DOWNPOURS THROUGH THE RUSH HOUR COMMUTE.

SUBSIDENCE WILL INCREASE THIS EVENING AS SURFACE HIGH PRESSURE BUILDS
INTO OREGON. THIS SHOULD BRING A GRADUAL END TO SHOWER ACTIVITY BUT
IT WILL PROBABLY REMAIN CLOUDY DUE TO THE MOIST LOW LEVEL AIR MASS.
NAM CROSS SECTIONS THROUGH THE WILLAMETTE VALLEY SEEM TO SUPPORT THIS
THINKING. EITHER WAY...IT WILL NOT BE LONG BEFORE HIGHER CLOUDS BEGIN
TO MOVE IN AHEAD OF OUR NEXT SYSTEM NOW SHOWN APPROACHING 130W ON
IR/WV SATELLITE IMAGERY.

STILL LOOKS LIKE A DECENT CHANCE FOR RAIN THROUGHOUT THE DISTRICT
SATURDAY AS THAT MODEST FRONTAL SYSTEM MOVES ONSHORE. THERE WILL BE
SOME WEAK ISENTROPIC LIFT AHEAD OF THIS SYSTEM...SO JUST ABOUT
EVERYONE SHOULD GET SOME LIGHT RAIN. ONLY MODEST OROGRAPHIC
ENHANCEMENT WITH 15-25 KT SW 850 MB WINDS...SO EXPECT RAIN TOTALS TO
RANGE FROM 0.10-0.25 INCH IN THE VALLEYS AND 0.50 TO LOCALLY 1 INCH
IN THE HIGHER TERRAIN. RAIN WILL TAPER TO SHOWERS SATURDAY NIGHT WITH
A FEW LINGERING INTO SUNDAY...MAINLY OVER THE HIGHER TERRAIN.

TEMPERATURES WILL HOVER NEAR OR A LITTLE BELOW NORMAL THROUGH THE
WEEKEND. SNOW LEVELS SHOULD REMAIN ABOVE THE PASSES THROUGHOUT THE
WEEKEND...BUT MAY GET AS LOW AS 4500-5000 FT AT TIMES. MONDAY APPEARS
TO BE A DRIER DAY WITH MILD TEMPS AS A SHORTWAVE RIDGE MOVES ACROSS
THE PACIFIC NORTHWEST...BUT THIS WILL BE BRIEF AS THE NEXT SYSTEM
LOOMS FOR TUESDAY AND MIDWEEK. WEAGLE

.LONG TERM...MONDAY EVENING THROUGH FRIDAY...COLD CLOSED LOW
PRESSURE SYSTEM WILL PUSH ONSHORE MONDAY NIGHT...BRINGING RAIN AND
MUCH COOLER TEMPERATURES TO THE AREA. THIS LOW WILL LINGER OVER THE
PAC NW TUESDAY AND MUCH OF THE DAY WEDNESDAY...WITH RECORD LOW
MAXIMUM TEMPERATURES POSSIBLE ON WEDNESDAY. BY THURSDAY MODELS
DISAGREE ON WHERE THE LOW WILL PROPAGATE...BUT THE OVERALL TREND IS
FOR SHOWERY AND COOL CONDITIONS TO PERSIST THROUGH THE END OF THE
WEEK. BURGESS

&&

.AVIATION...SHOWER ACTIVITY HAS PICKED UP THIS AFTERNOON DUE TO
AFTERNOON HEATING AND INCREASING ONSHORE FLOW INTO THE COAST RANGE
THIS IS TRIGGERING SHOWERS IN THE ELEVATED MOUNTAIN TERRAIN THAT ARE
DRIFTING INTO THE INTERIOR LOWLANDS. EXPECT THIS SHOWER ACTIVITY
TO CONTINUE THROUGH THE AFTERNOON...ALTHOUGH VFR CONDITIONS ARE
EXPECTED TO CONTINUE. SHOWERS WILL DIMINISH THIS EVENING AS TEMPS
COOL AND THE UPPER LEVEL TROUGH AXIS PUSHES FURTHER EAST OF THE
AREA. MVFR CIGS WILL BEGIN TO SPREAD INTO THE COAST OVERNIGHT...
POTENTIALLY PUSHING INTO SOME INLAND SITES TOWARDS DAYBREAK AS WELL.
A FRONTAL PASSAGE WILL BRING LIGHT RAIN TO THE REGION DURING THE DAY
TOMORROW. EXPECT CONDITIONS WILL BE IN AND OUT OF MVFR THROUGH THE
DAY.

KPDX AND APPROACHES...VFR CIGS THROUGH TONIGHT. SCATTERED SHOWER
ACTIVITY IS EXPECTED THROUGH THE AFTERNOON...BEFORE DIMINISHING THIS
EVENING. THERE IS A CHANCE OF MVFR CIGS BY SUNRISE SATURDAY. A
FRONT WILL PUSH INLAND LATER IN THE MORNING...WITH A MIX OF VFR AND
MVFR EXPECTED THROUGH THE DAY IN LIGHT RAIN. PYLE

&&

.MARINE...WINDS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS
THROUGH TONIGHT. A FRONTAL BOUNDARY WILL PASS THROUGH THE WATERS
TOMORROW...BRINGING SOME STRONGER PREFRONTAL SW WINDS. THE FCST
MODELS ARE INDICATING THAT GUSTY WINDS WILL NOT BE QUITE WIDESPREAD
OR FREQUENT ENOUGH FOR A SMALL CRAFT ADVISORY. HOWEVER...THERE IS THE
POTENTIAL FOR A BIT OF A COASTAL JET FORMING IN THE NEARSHORE WATERS
DURING THE LATE MORNING/EARLY AFTERNOON HRS. SO A FEW GUSTS UP INTO
THE MID 20 KT RANGE ARE POSSIBLE. NORTHWEST WINDS WILL THEN
PREDOMINATE THE REMAINDER OF THE WEEKEND AND MUCH OF NEXT WEEK. A
SMALL CRAFT ADVISORY MAY BE REQUIRED FOR MONDAY AFTERNOON OR EVENING
TIME FRAME.

SEAS ARE FORECAST TO REMAIN AROUND 5 OR 6 FT FOR SEVERAL DAYS. WE
MAY SEE SEAS REACH 10 FT NEXT WEEK DUE TO THE BRISK NORTHWEST
WINDS. PYLE

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

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

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.