000
FXUS66 KSEW 220354
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT 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 AT LEAST
FRIDAY. THE UPPER LOW WILL GIVE COOL AND SHOWERY WEATHER TO THE AREA.

&&

.SHORT TERM...AN UPPER LEVEL LOW WILL MAINTAIN A COOL SHOWERY
WEATHER PATTERN FOR THE NEXT SEVERAL DAYS. THE COOLEST AIR ALOFT
THIS EVENING IS BEING DIRECTED INTO WESTERN OREGON AND THE MAIN
CENTER OF THE LOW WILL SHIFT FROM THERE TO EASTERN OREGON BY
DAYBREAK WED. THAT AREA WILL THEN ROTATE NORTH INTO EASTERN
WASHINGTON WED AFTERNOON AND EVENING...AND THEN TO NEAR KBLI BY
DAYBREAK THU WHILE ANOTHER CENTER ROTATES ABOUT THE LOW INTO WESTERN
OREGON. SHOWERS ARE LIKELY TO BE MORE ORGANIZED IN THESE VORTICITY
CENTERS. THE AIR MASS WILL REMAIN RATHER COOL AND THE MOUNTAINS WILL
PICK UP SOME SNOW SHOWERS AT TIMES...ALTHOUGH THE HEAVIER SNOW
SHOWERS THIS EVENING ARE DOWN SOUTH IN THE OREGON CASCADES.

.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 TROUGH WILL REMAIN STALLED OVER THE PAC NW
THROUGH WEDNESDAY. LOWER PRESSURE E OF THE CASCADES WILL MAINTAIN
ONSHORE FLOW OVER WRN WA. LIGHT TO MODERATE W TO SW FLOW ALOFT.
MOIST AT ALL LEVELS AND SOMEWHAT UNSTABLE...ESPECIALLY WEDNESDAY.
ISOLATED THUNDERSTORMS ARE POSSIBLE WEDNESDAY AFTERNOON BUT
CONFIDENCE IS LOW. SCATTERED SHOWERS TONIGHT...THEN MORE NUMEROUS
SHOWERS WEDNESDAY AFTERNOON AND NIGHT.

LOW-END VFR TO MVFR CONDITIONS WILL CONTINUE THIS EVENING...THEN
DETERIORATE SOMEWHAT LATER TONIGHT AS LESS MIXING OCCURS.

KSEA...SW WIND 10-15 KT W/ GUSTS 22 KT...BECOMING S 5-8 KT LATER
TONIGHT AND VEERING TO SOUTHWEST AGAIN WEDNESDAY AFTERNOON. DTM

&&

.MARINE...W TO NW WINDS TO 25 KT OVER THE COASTAL WATERS WILL EASE
BELOW 20 KT AFTER MIDNIGHT AS A 1006 MB LOW FORMS OFF THE N TIP OF
VANCOUVER ISLAND. THE LOW IS EXPECTED TO WEAKEN AS IT MOVES SLOWLY S
ACROSS THE WA OFFSHORE WATERS WED AND WED NIGHT AND INTO THE OREGON
OFFSHORE WATERS THU AND THU NIGHT.

A LITTLE STRONGER ONSHORE FLOW WILL DEVELOP FRIDAY AND CONTINUE
SATURDAY AND SUNDAY. SMALL CRAFT WINDS CAN BE EXPECTED IN THE
CENTRAL AND EAST STRAIT DURING THE AFTERNOON AND NIGHT-TIME HOURS.
DTM

&&

.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