FXUS66 KSEW 160450
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
850 PM PST TUE DEC 15 2009
.SYNOPSIS...A WARM FRONT MOVED THROUGH WESTERN WASHINGTON THIS
EVENING. ADDITIONAL WEATHER SYSTEMS WILL MOVE THROUGH THE REGION
WEDNESDAY THROUGH THURSDAY NIGHT. THERE IS A GOOD CHANCE THAT FRIDAY
AND SATURDAY WILL BE RELATIVELY DRY. ANOTHER WEATHER SYSTEM MIGHT
ARRIVE LATER SUNDAY.
&&
.SHORT TERM...SE PRESSURE GRADIENTS AND WINDS PEAKED WITH THE WARM
FRONT THIS EVENING...NEARLY REACHING GALE AT SMITH ISLAND...BUT HAVE
SINCE BACKED OFF TO ARND 25KT THERE. BREEZY ARND ADMIRALTY INLET
THRU WHIDBEY AND THE SAN JUANS TONIGHT...AND MORE OF THE SAME ON
WEDNESDAY AS THE NEXT SYSTEM MOVES THRU WITH SW 850MB WINDS
40-50KT...WHICH TENDS TO KEEP THAT AREA RATHER BREEZY. THIS NEXT
FNTL SYS IS NOT VERY ORGANIZED ON SATIMG YET...BUT WITH SFC LOW PRES
AND AN UPPER TROF...AND THAT STRONG SW FLOW...WED AND WED NITE
PROMISE TO BE WET FOR MOST OF WRN WA. THE SYS MAY NOT ORGANIZE INTO
SOMETHING THAT LOOKS LIKE A GENUINE FRONT BUT BANDS OF SHOWERS WILL
ESSENTIALLY MERGE INTO RAIN BANDS...SIMILAR TO THE ONE THAT MOVED
THRU WRN WA THIS EVENING. A MORE ORGANIZED SYSTEM...WHICH IS
CURRENTLY OUT ARND 35N/155W...WILL ARRIVE BY MIDDAY THURSDAY SO THU
AFTERNOON AND NITE ARE WET AGAIN...AND THEN FRIDAY SHUD BE
POSTFRONTAL WITH JUST SCT SHOWERS. LOOKING TO THE MTNS...THE TEMP UP
AT PARADISE AND HURRICANE RIDGE IS NEAR OR JUST ABV FREEZING SO THE
SNOW LEVEL IS PROBABLY PEAKING THIS EVENING...BUT THE AIR MASS IS
SLIGHTLY COOLER OFFSHORE AND BY WED AFTERNOON AND NITE THE SNOW
LEVEL SHUD RETURN TO ARND 4500FT...FCSTS IS JUST A NOTCH TOO
LOW...EXCEPT OF COURSE FOR THE CASCADE PASSES WHERE COLD AIR TRAPPED
ALONG THE EAST SLOPES OF THE CASCADES WILL MAINTAIN A SNOW LEVEL AT
THE SFC ALONG THE CASCADE CREST...PROBABLY INTO WED NITE. 19
.LONG TERM...THE GFS AND EURO ARE IN AGREEMENT FOR SATURDAY...
KEEPING THE WEATHER DRY...PARTING THE CLOUDS BRIEFLY...AND ALLOWING
TEMPERATURES TO FALL SOMEWHAT. HAVE KEPT A CHANCE OF SHOWERS IN THE
FORECAST BUT HAVE ALSO MENTIONED SUN ON SATURDAY. BOTH MODELS
DEVELOP A LOW OFFSHORE AND MOVE IT TOWARD WASHINGTON ON SUNDAY.
BEYOND THAT THE DETAILS DIFFER SIGNIFICANTLY...WITH THE EURO WETTER
ON SUNDAY AND THE GFS HOLDING OFF MOST OF THE PRECIPITATION UNTIL
MONDAY. HAVE OPTED FOR THE GFS WITH A BUMP UPWARD IN POPS ON MONDAY
AND CHANCE POPS ON SUNDAY AND TUESDAY. CONFIDENCE IS LACKING IN
TIMING DETAILS. BURKE
&&
.HYDROLOGY...NO UPDATES TO THE HYDRO DISCUSSION THIS EVENING...THE
SKOKOMISH WILL RISE THRU THE END OF THE WEEK AND THERE IS A CHANCE
OF THAT REACHING FLOOD STATE FRI...HOWEVER PRECIP AMOUNTS AND SNOW
LEVELS ARE A NOTCH TOO LOW TO THREATEN ANYTHING BUT THE SKOKOMISH.
19 HERE IS THE PREV DISCUSSION: AROUND TWO INCHES OF RAIN FELL OVER
THE SOUTHERN OLYMPICS LAST NIGHT...AND RAIN IS FALLING AGAIN THERE.
THE RESPONSE OF THE SKOKOMISH RIVER HAS SO FAR BEEN MINIMAL...COLD
TEMPERATURES HAVE LOCKED UP SOME OF THAT RAIN AS SNOW. WHEN THE WARM
FRONT ARRIVES TONIGHT ANOTHER INCH OF RAIN WILL FALL...AND SOME SNOW
ON THE GROUND WILL MELT. ANOTHER BATCH OF RAIN IS DUE
WEDNESDAY...AND ANOTHER ONE WILL ARRIVE THURSDAY. THE SKOKOMISH
RIVER WILL RISE... POSSIBLY SIGNIFICANTLY BY THE TIME ALL THE RAIN
HAS COME. FLOODING IS NOT FORECAST THERE BUT THE POSSIBILITY OF SOME
MINOR FLOODING EXISTS. WILL AWAIT FURTHER DEVELOPMENTS BEFORE
THINKING ABOUT A FLOOD WATCH.
ALL OTHER RIVERS WILL ALSO RISE BUT NOT AS MUCH AS THE SKOKOMISH.
THE SOUTHERN OLYMPICS WILL BE GETTING THE BRUNT OF THE RAIN OVER THE
NEXT 60 HOURS. BEGINNING ABOUT FRIDAY THERE SHOULD BE A BREAK IN THE
RAIN AND RIVERS WILL RECEDE THROUGH ABOUT SUNDAY. MORE RAIN IS
LIKELY EARLY NEXT WEEK BUT SYSTEMS NEXT WEEK SHOULD BE SEPARATED BY
LONGER DRY PERIODS.
NO FLOODING IS EXPECTED ON THE GREEN RIVER. BURKE
&&
.AVIATION...A WARM FRONT EMBEDDED IN STRONG SOUTHWESTERLY FLOW ALOFT
LIFTED ACROSS WESTERN WASHINGTON EARLIER THIS EVENING. MUCH OF THE
FORECAST AREA IS EXPERIENCING SOMETHING OF A BREAK AT THIS TIME...AS
THE BAND OF PRECIPITATION HAS SHIFTED EAST INTO THE CASCADES.
HOWEVER THE AIR MASS WILL REMAIN MOIST AND WEAKLY UNSTABLE.
SHOWERY PRECIPITATION CAN BE EXPECTED AT TIMES FOR THE REMAINDER OF
TONIGHT AND WEDNESDAY MORNING...WITH MORE WIDESPREAD PRECIPITATION
DEVELOPING AGAIN WEDNESDAY MIDDAY AND AFTERNOON. CEILINGS TONIGHT
AND WEDNESDAY MORNING WILL BE SOMEWHAT VARIABLE...BUT GENERALLY BE
IN THE 2000-4500 FT RANGE FOR A MIX OF VFR AND MVFR CONDITIONS.
CONDITIONS SHOULD DETERIORATE DURING THE AFTERNOON WITH THE STEADIER
RAINFALL.
SOUTHWESTERLY FLOW WILL ALSO REMAIN STRONG. EXPECT 40-50 KT WINDS AT
5000 FT.
KSEA...SOUTH WIND 8-12 KT WITH OCCASIONAL GUSTS TO AROUND 20 KT
TONIGHT AND WEDNESDAY. MCDONNAL
&&
.MARINE...A 986 MB SURFACE LOW WEST OF NORTHERN VANCOUVER ISLAND
NEAR 50N/133W WILL MOVE NORTHEAST ACROSS THE QUEEN CHARLOTTES
WEDNESDAY MORNING AND INTO NORTHERN BRITISH COLUMBIA THURSDAY
EVENING. THE LOW WILL MAINTAIN SOUTHEAST PRESSURE GRADIENTS ACROSS
THE FORECAST AREA...WITH A MINOR SURFACE TROUGH SWINGING THROUGH THE
AREA WEDNESDAY.
A SMALL SURFACE RIDGE WILL BUILD INTO WESTERN WASHINGTON WEDNESDAY
EVENING...THEN QUICKLY SHIFT EAST OF THE CASCADES WEDNESDAY NIGHT
AHEAD OF THE NEXT APPROACHING PACIFIC FRONTAL SYSTEM. THE WARM FRONT
WITH THE NEXT SYSTEM WILL LIFT NORTHEAST ACROSS THE AREA THURSDAY
...FOLLOWED BY THE COLD FRONT THURSDAY NIGHT.
HIGH PRESSURE WILL BRING WEAK PRESSURE GRADIENTS TO THE REGION
FRIDAY AND FRIDAY NIGHT. ANOTHER WARM FRONT WILL LIFT ACROSS THE
FORECAST AREA SATURDAY AND SUNDAY.
A LARGE 30 FOOT SWELL TRAIN HAS DEVELOPED TO THE SOUTH OF A LOW
PRESSURE SYSTEM OVER THE EAST-CENTRAL NORTH PACIFIC. THIS SWELL
TRAIN WILL REACH THE WASHINGTON COAST AT 20 FT 15 SECONDS LATER
WEDNESDAY AND CONTINUE THROUGH THROUGH EARLY THURSDAY. A HIGH SURF
ADVISORY WILL LIKELY BE ISSUED WITH THE EARLY MORNING FORECAST
PACKAGE. MCDONNAL
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE OLYMPICS AND
CASCADES THROUGH 6 AM WEDNESDAY MORNING.
.AVALANCHE WARNING IN EFFECT TONIGHT.
PZ...GALE WARNING COAST.
.SMALL CRAFT ADVISORY REMAINING WATERS.
.SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH TO SEVERE BAR
CONDITIONS.
$$
