Tornado in Oregon, April 14, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
210 PM PDT TUE APR 14 2015

.SYNOPSIS...A COOL UPPER TROUGH WAS MOVING EAST OF SOUTHWEST
WASHINGTON AND NORTHWEST OREGON THIS AFTERNOON...BUT ONE LAST SHORT
WAVE THIS AFTERNOON WILL BRING MORE SHOWERS...SNOW LEVELS NEAR 2000
FEET...AND A CHANCE OF THUNDERSTORMS. SHOWERS WILL DECREASE TONIGHT
BEHIND THIS LAST SHORT WAVE AND AS AN UPPER RIDGE BEGINS TO MOVE IN
FROM THE WEST. THE UPPER RIDGE WILL CONTINUE TO BUILD WEDNESDAY FOR
CONTINUED DRY WEATHER...WHICH COULD LAST INTO NEXT WEEK EXCEPT FOR
THE TAIL END OF A WEAK SYSTEM THAT MAY BRING AT LEAST SOME CLOUDS TO
THE AREA FRIDAY NIGHT INTO SATURDAY. THE NEXT SYSTEM MAY ARRIVE THE
MIDDLE OF NEXT WEEK.

.SHORT TERM...TONIGHT THROUGH FRIDAY...A COLD UNSTABLE UPPER TROUGH
WAS MOVING EAST OF THE FORECAST AREA THIS AFTERNOON. THE SNOW LEVEL
APPEARS TO BE AROUND 2000 FEET THIS AFTERNOON. THERE IS STILL ONE
LAST SHORT WAVE ON THE BACK SIDE OF THE UPPER TROUGH WITH ONE MORE
BATCH OF COOLER TOPPED ENHANCED SHOWERS MOVING ONSHORE AND THROUGH
OUR FORECAST AREA THIS AFTERNOON. THUS EXPECT MORE SHOWERS AND
POSSIBLY A FEW THUNDERSTORMS THIS AFTERNOON. MODEL SOUNDINGS ARE
SHOWING A SUBSIDENCE INVERSION DEVELOPING AND LOWERING THIS AFTERNOON
AS THE UPPER TROUGH MOVES EAST...AND THIS MIGHT REDUCE OR POSSIBLY
CAP THE THREAT OF THUNDERSTORMS THIS AFTERNOON...BUT WITH SOME
AFTERNOON SUNSHINE AND THE SHORT WAVE MOVING THROUGH MIGHT BE JUST
ENOUGH TO GET A LOW TOPPED THUNDERSTORM OR TWO TO POP.

THIS WILL ALL MOVE THROUGH BY EARLY EVENING WITH DRAMATICALLY
DECREASING SHOWERS. AN UPPER RIDGE WILL CONTINUE TO MOVE IN FROM THE
WEST AND BE OVER THE AREA WEDNESDAY FOR DRY WEATHER. SOME CLOUDS FROM
A WARM FRONT ASSOCIATED WITH THE SYSTEM CURRENTLY OUT 50N/140W WILL
BRUSH THE NORTHWEST PART OF THE FORECAST AREA WEDNESDAY...BUT THE
MODELS ARE KEEPING ANY PRECIPITATION NORTH OF OUR FORECAST AREA ON
WEDNESDAY. SUSPECT THERE WILL BE SOME LOCAL FOG AND LOW CLOUDS
DEVELOPING AS WELL LATE TONIGHT AND WEDNESDAY MORNING UNDER THE
STABILIZING AIR MASS. LOW TEMPS TONIGHT WILL BE COOL WITH A LOT OF
30S AS WE CONTINUE IN THE COOL AIR MASS LEFT OVER FROM THE DEPARTING
SYSTEM.

THE UPPER RIDGE WILL CONTINUE TO BE OVER THE PACIFIC NORTHWEST
THURSDAY INTO FRIDAY FOR MORE DRY AND MILD WEATHER EXCEPT FOR A FEW
FOG MORNING PATCHES. AS THE AIR MASS WARMS THURSDAY AND CONTINUES TO
BE MILD FRIDAY...TEMPS IN THE VALLEYS WILL LIKELY APPROACH 70
THURSDAY AFTERNOON AND LIKELY EXCEED 70 ON FRIDAY. TOLLESON

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...12Z MODELS HAVE NOW
PUSHED A WEAK SHORTWAVE FURTHER NORTH OF THE REGION...CLOSER TO THE
CANADA/U.S. BORDER LATE FRIDAY. SO WITH IT FURTHER NORTH...HAVE
ELIMINATED THE THREAT FOR PRECIP FRIDAY NIGHT INTO SATURDAY WITH JUST
ONSHORE FLOW AND INCREASED CLOUD COVER EXPECTED. LATEST DEVELOPMENT
HAS BEEN WITH THE GFS TRYING TO CUT OFF A PIECE OF ENERGY ASSOCIATED
WITH THE SHORTWAVE TROUGH PUSHING EASTWARD...AND ATTEMPTING TO FORM A
SORT OF REX BLOCK PATTERN OVER THE PACIFIC NORTHWEST SUNDAY. THIS
COULD BRING SOME CONVECTIVE PRECIP OVER THE AREA BY MONDAY. OVERALL
EXPECT WARM AND DRY CONDITIONS THROUGH EARLY MONDAY AS HIGH PRESSURE
PREVAILS OVER THE EASTERN PACIFIC...UNTIL THE NEXT INCOMING FRONTAL
SYSTEM ARRIVES MONDAY NIGHT INTO TUESDAY BRINGING INCREASING SHOWERS
AND CLOUDS. /27
&&

.MARINE...W-NW WINDS WILL DECREASE TONIGHT AS A SURFACE TROUGH MOVES
INLAND AND WEAK HIGH PRESSURE BUILDS OVER THE WATERS. SEAS ARE
CURRENTLY 12 TO 13 FT AT 12 SECONDS AND WILL SLOWLY SUBSIDE TO 9 FT
LATE TONIGHT. SEAS HAVE BEEN RUNNING 1 TO 2 FT ABOVE MODEL GUIDANCE
AND HAVE ADJUSTED THE SHORT TERM FORECAST TO ACCOUNT FOR THIS
DISCREPANCY. AS A RESULT THE SEAS MY TAKE A LITTLE LONGER TO DROP
BELOW 10 FEET AND HAVE EXTENDED THE SMALL CRAFT ADVISORY THROUGH
MIDNIGHT TONIGHT.

NORTHERLY WINDS WILL DOMINATE THE WATERS THROUGH AT LEAST THE WEEKEND
AS THERE WILL BE GENERALLY HIGH PRESSURE OVER THE OREGON AND
WASHINGTON WATERS AND LOWER PRESSURE TO THE SOUTH. A THERMAL LOW OVER
NORTHERN CA WILL EXTEND NORTHWARD OVER THE SOUTH OREGON COAST
THURSDAY. THIS WILL RESULT IN GUSTY N WINDS...MAINLY SOUTH OF CASCADE
HEAD THAT WILL FLIRT WITH ADVISORY CRITERIA...21 KT...AT TIMES.

A LONG PERIOD NW SWELL APPROACHES THE WATERS ON THURSDAY. AN ASCAT
PASS NEAR THE GENERATING LOW SHOWED A DECENT FETCH TOWARDS THE OREGON
WATERS. THE ASCAT WINDS COMPARED FAIRLY WELL WITH THE GFS FORECAST
WINDS SO HAVE NO REASON TO DEVIATE FROM THE WAVE MODEL GUIDANCE AT
THIS POINT AND STILL EXPECT A 12 TO 14 FT SWELL AT 17-19 SECONDS TO
MOVE THROUGH THE WATERS THU AND THU NIGHT. TJ
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 6 PM PDT THIS EVENING FOR
     CASCADES IN LANE COUNTY-NORTHERN OREGON CASCADES.

WA...WINTER WEATHER ADVISORY UNTIL 6 PM PDT THIS EVENING FOR SOUTH
     WASHINGTON CASCADES.

PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL MIDNIGHT PDT
     TONIGHT FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL
     5 AM PDT WEDNESDAY.
&&

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.