000
FXUS66 KSEW 190417
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT TUE JUN 18 2013

.SYNOPSIS...AN UPPER LOW JUST OFF THE COAST WILL CONTINUE TO BRING 
SCATTERED SHOWERS AND A FEW THUNDERSTORMS TO THE REGION THROUGH 
WEDNESDAY. AN ASSOCIATED TROUGH ROTATING WESTWARD TO THE NORTH OF 
THE LOW WILL LIKELY BRING A PERIOD OF RAIN TO MUCH OF WESTERN 
WASHINGTON WEDNESDAY NIGHT AND THURSDAY. THERE COULD BE LOCALLY 
HEAVY RAIN ACROSS THE NORTH CASCADES FROM THIS SYSTEM. WEAK HIGH 
PRESSURE WILL BUILD INTO THE AREA FRIDAY NIGHT AND SATURDAY. ANOTHER 
WET WEATHER PATTERN IS LIKELY TO DEVELOP EARLY NEXT WEEK WITH 
SEVERAL FRONTS MOVING ACROSS THE AREA.

&&

.SHORT TERM...THE UPPER LOW JUST OFF THE COAST IS GRADUALLY 
WEAKENING AND EVER SO SLOWLY BEGINNING ITS DRIFT SOUTHEASTWARD. OVER 
THE NEXT COUPLE OF DAYS THE LOW WILL TRACK EASTWARD ACROSS NORTHERN 
OREGON AND THEN NORTHEAST TO NORTHERN IDAHO BY THU. SHOWERS AND 
THUNDERSTORMS THIS EVENING WILL GRADUALLY DISSIPATE OVERNIGHT WITH 
ANOTHER ROUND OF SHOWERS AND ISOLATED THUNDERSTORMS TOMORROW WITH 
DAYTIME HEATING. 

THE MODELS... WHILE NOT AGREEING ON ALL OF THE DETAILS... CONTINUE 
TO INDICATE A VORT MAX WILL ROTATE WESTWARD ACROSS THE NORTH 
CASCADES AND POSSIBLY THE OLYMPICS BRINGING A PERIOD OF RAIN... 
POTENTIALLY HEAVY... TO THE NORTH CASCADES AND NORTHERN LOWLANDS. 
SOME MODELS ARE INDICATING OVER 4 INCHES OF RAIN IN THE VICINITY OF 
MT BAKER AND NORTH CASCADES IN A 36 HOUR PERIOD ENDING THURSDAY 
NIGHT.

FRIDAY INTO SATURDAY BRINGS A BIT OF A BREAK TO THE SHOWERY WEATHER 
WITH WARMER AND DRIER CONDITIONS AS THE CLOSED LOW MOVES EASTWARD. A 
NEW TROUGH EMBEDDED IN WESTERLY FLOW WILL BRING A CHANCE OF RAIN 
BACK TO THE AREA BY SATURDAY NIGHT. COLMAN

&&

.LONG TERM...FROM PREVIOUS DISCUSSION...TEMPORARY HIGH PRESSURE WILL 
BUILD INTO THE AREA FRIDAY NIGHT AND SATURDAY. A FRONT MAY REACH 
WESTERN WA SAT NIGHT AND SUNDAY MORNING. THERE IS A DIFFERENCE 
BETWEEN THE GFS AND THE ECMWF THIS WEEKEND...IF THE 12Z GFS IS 
CORRECT IT WILL NOT RAIN MUCH...MAINLY JUST ON THE COAST AND IN THE 
OLYMPICS AND THAT MODEL SHOWED NO RAIN AT ALL FOR A GOOD PORTION OF 
THE SEATTLE EVERETT AREA. THE EURO ON THE OTHER HAND GIVES MUCH OF 
WESTERN WA A GOOD SOAKING RAIN WITH MOST OF WESTERN WA GETTING AT 
LEAST AN INCH OF RAIN. AFTER THAT...RAIN IS LIKELY AT TIMES SUN NITE 
THRU NEXT TUE AS A NEW UPPER TROUGH MOVES INTO THE NE PACIFIC.

&&

.AVIATION...UPPER LEVEL LOW OFF THE COAST TUESDAY EVENING WILL MOVE 
SOUTHEAST INTO NORTHWEST OREGON WEDNESDAY MORNING. SOUTH 
SOUTHEASTERLY FLOW ALOFT BECOMING MORE SOUTHEASTERLY WEDNESDAY 
MORNING. AIR MASS STABILIZING SOMEWHAT AFTER 06Z. 

DOPPLER RADAR SHOWS SHOWER ACTIVITY PRETTY MUCH CONFINED TO THE 
MOUNTAINS AT 04Z. SCATTERED TO BROKEN DECK AOA 10000 FEET OVER THE 
AREA. THESE CONDITIONS WILL CONTINUE INTO WEDNESDAY AFTERNOON. 
SURFACE GRADIENTS ONSHORE OVERNIGHT INTO WEDNESDAY MORNING WHICH 
BRINGS UP THE POSSIBILITY OF A STRATUS DECK AROUND 2000 FEET FORMING 
AFTER SUNRISE. WHAT STRATUS THAT DOES FORM WILL NOT BE WIDESPREAD 
AND WILL ONLY LAST UNTIL LATE MORNING AT THE LATEST. AIR MASS 
BECOMING MORE UNSTABLE WEDNESDAY AFTERNOON FOR ANOTHER ROUND OF 
SCATTERED SHOWERS. 

KSEA...MOSTLY MID LEVEL CLOUD COVER OVERNIGHT INTO WEDNESDAY.
SOME STRATUS FORMING OVER THE SOUND WEDNESDAY MORNING COULD FLOAT 
OVER THE AIRPORT FOR A COUPLE OF HOURS IN THE MORNING. CONFIDENCE 
NOT REAL HIGH IN THIS SCENARIO. WILL GO WITH A TEMPO GROUP WITH 2000 
BROKEN FOR A FEW HOURS AFTER SUNRISE. FELTON

&&

.MARINE...A 1012 MB SURFACE LOW WILL SHIFT EAST AND DIMINISH OVER 
THE COASTAL WATERS TONIGHT. HIGH PRES OVER THE OFFSHORE WATERS AND 
LOW PRES OVER INTERIOR B.C. WILL MAINTAIN ONSHORE FLOW ACROSS 
WESTERN WASHINGTON WEDNESDAY THROUGH FRIDAY. THE CENTRAL AND EAST 
STRAIT OF JUAN DE FUCA MAY SEE GALE FORCE WESTERLY WINDS WEDNESDAY 
EVENING. WINDS WILL GRADUALLY EASE THROUGH THE STRAIT THURSDAY 
MORNING. A FRONT WILL APPROACH THE COASTAL WATERS ON 
SATURDAY...MOVING INLAND SAT NIGHT. 33/FELTON
  
&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML