428 FXUS66 KSEW 212216 AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 315 PM PDT TUE MAY 21 2013 .SYNOPSIS...A COLD UPPER LEVEL LOW WILL MOVE INTO OREGON THIS EVENING THEN SPIN AROUND OVER THE PACIFIC NORTHWEST THROUGH FRIDAY AT LEAST. THE UPPER LOW WILL GIVE COOL AND SHOWERY WEATHER TO THE AREA THROUGH THURSDAY. AFTER THAT TEMPERATURES WILL SLOWLY RISE AND SHOWERS WILL DECREASE. && .SHORT TERM...UPPER LEVEL LOW IS OFF THE NORTH OREGON COAST AND MOST OF WESTERN WASHINGTON IS IN A SHOWERY PATTERN. THERE HAVE BEEN SUN BREAKS THIS AFTERNOON AND THIS PATTERN WILL CONTINUE INTO THE EVENING. NO THUNDERSTORMS HAVE BROKEN OUT SO REMOVED THE MINOR MENTION OVER SOUTHERN AREAS THIS EVENING. MODELS SPIN THE UPPER LOW AROUND OVER OREGON AND WASHINGTON OVER THE NEXT THREE DAYS SO COOL AND SHOWERY CONDITIONS WILL REMAIN IN THE FORECAST. ON WEDNESDAY AND THURSDAY SKIES WILL STILL BE MOSTLY CLOUDY AND SHOWERS ARE LIKELY BUT SUN BREAKS WILL PROBABLY BE MORE NUMEROUS. THIS COULD ALLOW A FEW THUNDERSTORMS TO DEVELOP IN THE AFTERNOONS AND EVENINGS SO HAVE ADDED ISOLATED THUNDERSTORMS TO EACH DAY. AS IS SO OFTEN THE CASE IN SPRING...SOME THUNDERSTORMS MAY PRODUCE SMALL HAIL. IN FACT THERE COULD BE SOME HAIL WITHOUT THE THUNDERSTORMS. HIGH TEMPERATURES WILL REMAIN WELL BELOW NORMAL...RISING INTO ONLY THE LOW 60S ON THURSDAY. ON FRIDAY THE UPPER LOW IS RIGHT OVER THE AREA BUT IT IS FILLING AND BROADENING. THIS SHOULD DIMINISH THE SHOWERS SOMEWHAT SO POPS ARE MOSTLY IN THE CHANCE CATEGORY. A SLOW WARMING TREND WILL CONTINUE WITH HIGH TEMPERATURES CLIMBING A FEW DEGREES FROM THURSDAY. BURKE .LONG TERM...MODELS DIVERGE AFTER FRIDAY BUT THE HEIGHT RISES CONTINUE. WOULD EXPECT SLOW WARMING TO CONTINUE SATURDAY THROUGH MONDAY WITH SOME UPPER 60S IN THE FORECAST. THE GFS IS PRETTY DRY BY MONDAY BUT THE EURO SWINGS AN UPPER TROUGH THROUGH THE AREA SUNDAY NIGHT. HAVE KEPT THE BROAD BRUSH CHANCE POPS. ON TUESDAY A WEAK SYSTEM ARRIVES IN BOTH MODELS...KEEPING THE CHANCE POPS GOING BUT CHANGING THE WEATHER FROM CHANCE OF SHOWERS TO CHANCE OF RAIN. BURKE && .AVIATION...A DEEP UPPER LOW OVER THE OFFSHORE WATERS THIS AFTERNOON WILL CONTINUE TO AFFECT THE FORECAST AREA AS IT SHIFTS SLOWLY INLAND TONIGHT AND WEDNESDAY. THE AIR MASS WILL REMAIN MOIST AND SOMEWHAT UNSTABLE AND SHOWERY PRECIPITATION WILL CONTINUE. ISOLATED THUNDERSTORMS COULD DEVELOP OVER THE AREA WEDNESDAY AFTERNOON. THE CASCADES WILL REMAIN GENERALLY OBSCURED. LOW-END VFR TO MVFR CONDITIONS PREVAIL OVER THE FORECAST AREA THIS AFTERNOON WITH SCATTERED SHOWERS. CLOUD COVER IS ROUGHLY SCT010 SCT-BKN030 BKN-OVC050. THESE CONDITIONS SHOULD CONTINUE GENERALLY SPEAKING THROUGH THIS EVENING...THEN DETERIORATE SOMEWHAT TONIGHT AS MORE SHOWERS MOVE INTO THE REGION. KSEA...SOUTHWEST WIND 8-14 KT THIS AFTERNOON...BECOMING SOUTH 6-10 KT LATER TONIGHT AND VEERING TO SOUTHWEST AGAIN WEDNESDAY AFTERNOON. MCDONNAL && .MARINE...SMALL CRAFT ADVISORY WEST TO NORTHWEST WINDS OVER THE COASTAL WATERS WILL EASE TONIGHT AS A 1007 MB LOW FORMS NEAR THE NORTHWEST END OF VANCOUVER ISLAND. THERE IS STILL LOTS OF UNCERTAINTY...AND DIFFERENCES IN MODEL SOLUTIONS...WITH REGARD TO THE MOVEMENT OF THE LOW AND THE WINDS IT WILL PRODUCE. MOST LIKELY IT WILL WEAKEN AS IT MOVES SLOWLY SOUTH ACROSS THE WASHINGTON OFFSHORE WATERS WEDNESDAY AND WEDNESDAY NIGHT AND INTO THE OREGON OFFSHORE WATERS THURSDAY AND THURSDAY NIGHT. THE LOW COULD PRODUCE SMALL CRAFT ADVISORY WINDS OVER THE COASTAL WATERS AND IN SOME OF THE INLAND WATERS WEDNESDAY AND WEDNESDAY NIGHT...AN IDEA THAT IS SUPPORTED SOME OF THE UW WRF-GFS RUNS. THE FORECAST THAT WE ARE GOING WITH FOR NOW IS A BLEND OF THAT MODEL AND THE WEAKER NAM SOLUTION...AND THE RESULT KEEPS WINDS 20 KT OR LESS OVER THE MARINE ZONES. WEAK ONSHORE FLOW WILL DEVELOP FRIDAY AND CONTINUE SATURDAY AND SUNDAY. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...NONE. PZ...SMALL CRAFT ADVISORY COASTAL WATERS THROUGH MIDNIGHT...EXCEPT FOR THE NORTHERN INNER COASTAL WATERS ZONE. && $$ YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML