Lightning Strike in Oregon, May 17, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
834 PM PDT SAT MAY 17 2014

.SYNOPSIS...AN UPPER LEVEL LOW WILL SLOWLY DRIFT CLOSER TO THE COAST
THIS WEEKEND FOR CONTINUED COOLER AND UNSETTLED WEATHER. THE CHANCE
OF SHOWERS WILL SLOWLY RISE THROUGH THE WEEKEND...WITH THE BEST
CHANCE OF SHOWERS FROM TONIGHT INTO MONDAY AS THE LOW MOVES CLOSER
AND THEN MOVES THROUGH THE FORECAST AREA. ISOLATED THUNDER IS
POSSIBLE DURING THIS PERIOD...ESPECIALLY SUNDAY AND MONDAY
AFTERNOONS. DRY AND MILDER WEATHER RETURNS IN THE MIDDLE OF NEXT WEEK
AS AN UPPER RIDGE MOVES INTO THE PACIFIC NORTHWEST.
&&

.EVENING UPDATE...SKIES HAVE BECOMING PARTLY CLOUDY THIS EVENING
ALTHOUGH LOW CLOUDS HAVE STARTED FILLING ALONG THE COAST. BIT OF
EXCITEMENT INLAND. HAVE SEEN WHAT APPEARS TO BE A MORE DEFINED MARINE
SURGE OVER CENTRAL AND SOUTH VALLEY...AS DEW POINT TEMPERATURES MUCH
HIGHER. THIS DENSE AIR IS PUSHING DOWN THE WILLAMETTE VALLEY. ALONG
THE LEADING EDGE...THERE IS JUST ENOUGH INSTABILITY TO POP SCATTERED
SHOWERS AND EVEN A FEW THUNDERSTORMS. THESE WILL CONTINUE TO PUSH
NORTHEASTWARD ACROSS THE EASTERN WILLAMETTE VALLEY AND INTO THE
CASCADES. DO HAVE OTHER SHOWERS/ISOLATED THUNDERSTORMS POPPING UP
OVER THE CASCADES...AGAIN ALONG THE LEADING EDGE OF MARINE LAYER. ALL
THUNDERSTORMS WILL LIKELY END BY 1030 PM. AFTERWARDS...WILL SEE
CLOUDS INCREASE WITH SHOWERS THAT ARE OFFSHORE PUSHING INLAND.

REST OF FORECAST/TRENDS REMAINS UNCHANGED.

.SHORT TERM...AN UPPER LEVEL LOW IS LOCATED OVER THE NORTHEAST
PACIFIC THIS AFTERNOON...WITH A ITS CENTER WEST OF 130W. ONE WEAK
SHORT WAVE DISTURBANCE MOVED THROUGH THE PACIFIC NORTHWEST THIS
MORNING WITH SOME SPOTTY LIGHT PRECIPITATION. WE ARE IN BETWEEN
DISTURBANCES THIS AFTERNOON WITH PLENTY OF ONSHORE FLOW
CONTINUING...MAINTAINING A FAIR AMOUNT OF CLOUD COVER. THERE ARE SOME
BREAKS IN THE CLOUDS WITH A BIT OF SUNSHINE PEAKING THROUGH THAT MAY
ALLOW TEMPS TO REACH THE 65 TO 70 RANGE TODAY INLAND. CANNOT RULE OUT
A FEW SHOWERS DEVELOPING IN THE AFTERNOON FROM THE DAYTIME
HEATING...BUT RIGHT NOW THE MOST ARE IN THE NORTHWEST CORNER OF OUR
FORECAST AREA. WILL MONITOR ANY CHANCES OF SEEING THUNDER LATER TODAY
OR THIS EVENING BUT WILL CONTINUE TO LEAVE OUT FOR NOW.

THE NEXT DECENT SHORT WAVE DISTURBANCE HAS CROSSED INSIDE OF 130W
THIS AFTERNOON. THIS DISTURBANCE WILL SPREAD ONSHORE THIS EVENING AND
MOVE ACROSS OUR FORECAST AREA TONIGHT INTO EARLY SUNDAY. THIS FEATURE
WILL MORE SIGNIFICANTLY INCREASE THE SHOWERS OVER SOUTHWEST
WASHINGTON AND NORTHWEST OREGON OVERNIGHT TONIGHT WITH A DECENT SLUG
OF QPF. THIS FEATURE WILL MOVE EAST EARLY SUNDAY. HOWEVER...THE
COMMA CLOUD BAND AROUND THE LOW CENTER ITSELF THAT IS NOW BETWEEN
130W AND 135W IS FORECAST TO SWING ONSHORE INTO SOUTHWEST WASHINGTON
AND NORTHWEST OREGON DURING THE DAY SUNDAY AS THE LOW CENTER DRIFTS
INSIDE 130W AND CLOSER TO THE COAST. WE SHOULD SEE TEMPS ALOFT AT
500 MB FALL TO MINUS 22 TO MINUS 23 DEG C ON SUNDAY...AND THUS
EXPECT MORE SHOWERS FROM THIS FEATURE...WITH EVEN A SMALL CHANCE OF
THUNDER OVER OUR AREA SUNDAY AFTERNOON AND EVENING. THE CHANCE OF
ANY THUNDER WILL DEPEND ON HOW WARM IT GETS SUNDAY AND HOW SOLID THE
CLOUDS ARE. RIGHT NOW IT MAY BE PRETTY CLOUDY AND IT WILL PROBABLY
BE THE COOLEST DAY OF THIS STRETCH...BUT WILL STAY WITH A SLIGHT
CHANCE OF THUNDER.

THE LOW WILL STILL LINGER JUST OFF THE COAST THROUGH EARLY MONDAY
THEN DRIFT SOUTH TOWARD CALIFORNIA. THIS MAY ALLOW MORE SUN BREAKS TO
DEVELOP MONDAY AFTERNOON AND EVENING...WHILE STILL BEING UNDER THE
CYCLONIC CIRCULATION TO THE NORTH OF THE LOW. THIS COULD LEAD TO THE
BEST CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS FROM THIS
LOW.

THE LOW IS WELL SOUTH OF OUR AREA ON TUESDAY...WITH NORTHWEST
ONSHORE FLOW CONTINUING. THE THREAT OF SHOWERS SHOULD BE
WANING...THOUGH WE MIGHT SEE A FEW POP UP OVER THE HIGHER TERRAIN IN
THE AFTERNOON AND EVENING. TEMPS INLAND MAY PUSH UP INTO THE LOWER
70S AGAIN.

SNOW LEVELS WILL REMAIN ABOVE THE CASCADE PASSES DURING THE ENTIRE
SHORT TERM PERIOD...BUT THE HIGHER MOUNTAINS IN THE CASCADES WILL SEE
SOME SNOW ESPECIALLY THROUGH MONDAY. TOLLESON

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...THE CLOSED UPPER LEVEL
LOW MOVING THROUGH THE PAC NW THIS WEEKEND AND EARLY NEXT WEEK IS
EXPECTED TO PUSH SOUTH INTO CALIFORNIA ON TUE...AND WILL LIKELY BE IN
THE U.S. SOUTHWEST BY TUE NIGHT. MODEL AGREEMENT IS GOOD THAT AN
UPPER LEVEL RIDGE WILL THEN BUILD OVER THE PAC NW FROM TUE NIGHT INTO
THU. THIS SHOULD BRING A COUPLE OF DAYS OF WARMER AND DRIER WEATHER
ON WED AND THU. IT APPEARS THAT AN UPPER LEVEL TROF OVER THE GULF OF
ALASKA WILL TRY TO SWING A COUPLE OF SHORTWAVES TOWARD THE REGION FRI
AND SAT. THERE IS SOME UNCERTAINTY IN HOW MUCH IMPACT THERE WILL BE
FROM THESE WAVES. THE 12Z ECMWF RUN MOVES THE UPPER RIDGE OFF TO THE
EAST AND BRINGS ORGANIZED PRECIPITATION INTO THE REGION...WHILE THE
12Z GFS KEEPS THE RIDGE MORE OR LESS IN PLACE AND KEEPS THINGS MAINLY
DRY. FOR NOW...WILL CONTINUE TO KEEP LOW CHANCE POPS IN THE FCST FOR
FRI AND SAT. PYLE
&&

.AVIATION...ISOLATED THUNDERSTORMS WILL WEAKEN IN THE CENTRAL
WILLAMETTE VALLEY BETWEEN KCVO AND KUAO AFTER SUNSET. OTHERWISE
INCREASING MVFR STRATUS AND RAIN IS DEVELOPING ALONG THE COAST AS
FRONTAL SYSTEM APPROACHES...WHILE MVFR CIGS BECOME LIKELY AFTER
08Z TONIGHT ACROSS THE INTERIOR AS FRONT PROGRESSES. A MIX OF
HIGH- END IFR AND MVFR CONDITIONS POSSIBLE AT THE COAST OVERNIGHT
SUN...WHILE MVFR/VFR ACROSS THE INTERIOR THROUGH SUN WITH RAIN
CONTINUING AND A SLIGHT CHANCE OF THUNDERSTORMS SUN AFTERNOON.

KPDX AND APPROACHES...VFR CONDITIONS THROUGH AT LEAST 06Z SUN.
MVFR CIGS AROUND 2500 FT LIKELY ARRIVE AROUND 08Z SUN AS FRONT
ARRIVES. RAIN CONTINUES THROUGH SUN BUT WITH SOME IMPROVEMENT TO
HIGH-END MVFR TO LOWER VFR CONDITIONS LIKELY. SLIGHT CHANCE OF
THUNDERSTORMS SUN AFTERNOON. CULLEN/27

&&

.MARINE...THE LOW PRES SYSTEM OFFSHORE OF VANCOUVER ISLAND WILL
MOVE S AND PASS THROUGH THE COASTAL WATERS TONIGHT AND SUN...AND
BE LOCATED OFFSHORE NEAR THE CALIFORNIA/OREGON BORDER BY LATE SUN
NIGHT. A WEAK FRONT ASSOCIATED WITH THE LOW WILL MOVE ACROSS THE
COASTAL WATERS TONIGHT. GUSTY S WINDS TO 20 KT POSSIBLE OFF THE
CENTRAL OREGON COAST SUN EVENING AS THE LOW PRES MOVES
THROUGH...ALONG WITH A SLIGHT POSSIBILITY OF THUNDERSTORMS OVER
THE WATERS. HIGH PRES REBUILDS OFFSHORE LATER MON...AND N WINDS
WILL INCREASE BY MIDWEEK WITH GUSTY 25 KT WINDS POSSIBLE. SEAS
WILL REMAIN 3 TO 6 FT THROUGH MOST OF NEXT WEEK...BUT WIND-
DOMINATED AND CHOPPY AT TIMES. CULLEN
&&

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