FXUS66 KSEW 152303
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST TUE DEC 15 2009
.SYNOPSIS...RAIN WILL CHANGE TO SHOWERS TONIGHT AS A WARM FRONT
MOVES FROM SOUTH TO NORTH. MORE RAIN WILL COME ON WEDNESDAY AS
ANOTHER FRONT ARRIVES. ANOTHER SYSTEM WILL MOVE IN THURSDAY. AFTER
SHOWERS ON FRIDAY...A RELATIVELY DRY PERIOD IS POSSIBLE SATURDAY.
&&
.SHORT TERM...RAIN DEVELOPED QUICKLY OVER THE WHOLE AREA LATE THIS
MORNING AND IS STILL FALLING. A WARM FRONT IS OVER NORTHERN OREGON
AND WILL MOVE NORTH THROUGH WASHINGTON TONIGHT. TEMPERATURES ARE
MAINLY IN THE MID 40S THIS AFTERNOON. AFTER THE WARM FRONT GOES
THROUGH TONIGHT TEMPERATURES WILL RISE SOMEWHAT...PROBABLY INTO THE
45-50 RANGE...AND STAY THERE THROUGH THE NIGHT AND INTO WEDNESDAY.
ANOTHER FRONTAL FEATURE ARRIVES WEDNESDAY AFTERNOON. THERE WILL BE
RAIN AT TIMES WEDNESDAY...WITH SOME RAIN SHADOWING POSSIBLE OVER THE
SEATTLE AREA. HOWEVER EVERYWHERE WILL SEE SOME RAIN. SHOWERS AGAIN
WEDNESDAY NIGHT. YET ANOTHER SYSTEM WILL ARRIVE THURSDAY...WITH
SHOWERS AGAIN THURSDAY NIGHT. THE GFS IS FASTER WITH THESE SYSTEMS
THAN THE NAM. GIVEN THE GENERALLY PROGRESSIVE FLOW...AND THE FACT
THE SYSTEM TODAY ARRIVED FASTER THAN FORECAST...HAVE FAVORED THE GFS.
SHOWERS TAPER FRIDAY AND FOR ONCE THERE IS NO NEXT SYSTEM POISED TO
ARRIVE IMMEDIATELY. THE SUN MIGHT EVEN PEEK OUT IN THE AFTERNOON.
HIGH TEMPERATURES FOR ALL THREE DAYS WILL BE 45-50 WITH LOWS AROUND
40...WHICH IS SLIGHTLY ABOVE NORMAL FOR THIS TIME OF YEAR. BURKE
.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...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...AN OCCLUDED FRONT FROM NORTHWEST OREGON WNW INTO A LOW
NEAR 49N/132W WILL LIFT NE ACROSS THE AREA THIS EVENING. THE FRONT
SHOULD REACH KHQM BY 02Z...THEN LIFT N INTO CANADA BY 06Z. CIGS
AHEAD OF THIS FRONT WILL GENERALLY FALL TO AROUND 015 WITH VIS 3-5SM
-RA AND LOCALLY TO 1SM COAST AND NEAR THE OLYMPICS. RAIN WILL END
FROM THE SW OVERNIGHT BEHIND THE FRONT AND WITH POST FRONTAL SLY
FLOW...CIGS WILL IMPROVE TO 025-030 LATER THIS EVENING BEFORE
FALLING AGAIN TO 015 LATER TONIGHT.
A TROUGH OF LOW PRES SITTING S OF A MATURE LOW NEAR 46N/141W WILL
MOVE E ACROSS THE AREA WED EVENING. EXPECT MORE SHOWERS AND LOCALLY
BREEZY CONDITIONS LATE WED MORNING THROUGH WED EVENING AHEAD OF THIS
TROUGH WITH GENERALLY MVFR CONDITIONS.
KSEA...RAIN HAS BEGUN. OFFSHORE PRES GRADIENTS HAVE KEPT CIGS HIGH
ACROSS MUCH OF THE INTERIOR BUT WILL COME DOWN TO OVC012-015 WITH
AND BEHIND THE FRONT...THAT WILL PASS THE TERMINAL ABOUT 03Z. WIND
WILL TURN FROM ELY 8 TO 10 KT TO SLY 10-15 KT WITH THE FRONT...THEN
WILL FALL BACK BELOW 10 KT OVERNIGHT. SOME IMPROVEMENT IN CIGS TO
ABOUT 025 WILL OCCUR 2 HRS AFTER FROPA THEN FALL BACK TO 015
OVERNIGHT AS PRES GRADIENTS RELAX. SHOWERS WITH 3-5 SM WILL RETURN
AROUND 18Z AND CONTINUE THROUGH 03Z-06Z WED. SW WIND WILL BRIEFLY
RISE TO 55 KT AT 050 00Z-06Z THIS EVENING...THEN DECREASE TO 30-35
KT AFTER 06Z. ALBRECHT
&&
.MARINE...AN OCCLUDED FRONT FROM NORTHWEST OREGON WNW INTO A LOW
NEAR 49N/132W WILL LIFT NE ACROSS THE WATERS THIS EVENING.
GALES ARE EXPECTED WITH THE FRONT UNTIL SHORTLY AFTER MIDNIGHT IN
THE COASTAL WATERS...AND SMALL CRAFT ADVISORY CONDITIONS ARE
EXPECTED IN THE REMAINING WATERS.
A TROUGH OF LOW PRES EXTENDING SOUTH OF A MATURE LOW NEAR 46N/141W
WILL MOVE E ACROSS THE AREA WED EVENING. SMALL CRAFT ADVISORY
CONDITIONS ARE EXPECTED OVER MOST OF THE WATERS IN ADVANCE OF AND
WITH THIS FEATURE WED AND WED NIGHT.
AFTER THE PASSAGE OF ANOTHER SYSTEM LATE THU...FORECAST GUIDANCE
APPEARS TO BE SUFFERING SOME CONSISTENCY AND CONTINUITY PROBLEMS.
NEWEST MODEL SOLUTIONS ARE TENDING TO BUILD HIGH PRES OVER B.C. FRI
NIGHT THROUGH SUN.
A VERY 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 WED
AND CONTINUE THROUGH THROUGH EARLY THU. THE NEXT SHIFT MAY NEED TO
CONSIDER A HIGH SURF ADVISORY FOR THE COAST LATER WED OR WED NIGHT.
BAR CONDITIONS ALONG THE COAST WILL BECOME SEVERE WED THRU THU.
ALBRECHT
&&
.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.
$$
