FXUS66 KSEW 151636
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 AM PST TUE DEC 15 2009
.SYNOPSIS...LOWLAND RAIN SHOWERS AND MOUNTAIN SNOW WILL PERSIST
TODAY BEHIND A COLD FRONT. ANOTHER FRONT WILL BRING MORE RAIN
AND MOUNTAIN SNOW TO WESTERN WASHINGTON LATER TODAY AND TONIGHT. A
SERIES OF FRONTAL SYSTEMS WILL CONTINUE TO AFFECT THE REGION THROUGH
THE WEEKEND.
&&
.SHORT TERM...RADAR SHOWS SCATTERED SHOWERS AROUND THE AREA TODAY...
AND LIGHT SNOW AT TIMES IN THE MOUNTAINS. WILL END THE WINTER STORM
WARNING FOR THE MOUNTAINS AS AMOUNTS TODAY WILL NOT ADD UP TO MUCH.
ANOTHER SYSTEM WILL ARRIVE FROM THE SOUTHWEST THIS AFTERNOON...
SPREADING RAIN OVER THE LOWLANDS AND BRINGING SNOW BACK TO THE
MOUNTAINS. THIS WILL TAPER LATE TONIGHT. THERE IS A WINTER WEATHER
ADVISORY FOR THE MOUNTAINS TONIGHT...WILL START THAT EARLIER AT 1 PM
AND CALL IT GOOD.
AFTER A RELATIVELY DRY PERIOD EARLY WEDNESDAY...ANOTHER SYSTEM
SWEEPS THROUGH WESTERN WASHINGTON WEDNESDAY AFTERNOON AND EVENING.
MODELS ARE THEN FAIRLY DRY LATE WEDNESDAY NIGHT AND THURSDAY
MORNING. THE NEXT SYSTEM IN THE SERIES CLIPS THE NORTHWEST ON
THURSDAY AFTERNOON AND EVENING. THIS ONE SHOULD SOAK THE COAST AND
OLYMPICS BUT MAY NOT BRING MUCH RAIN TO THE INLAND LOWLANDS.
TEMPERATURES ALL THREE DAYS WILL BE RIGHT AROUND NORMAL...HIGHS IN
THE 40S...LOWS 35-40. BURKE
.LONG TERM...PREVIOUS DISCUSSION...A FLAT RIDGE BUILDS OVER THE WRN
U.S. FRIDAY INTO THE WEEKEND. THE GFS/ECMWF BOTH AGREE THAT SYSTEMS
BREAKING OVER THE TOP WILL BE STRONG ENOUGH TO DRAG WEAK SYSTEMS
THROUGH THE AREA. EXPECT A CHANCE OF SOME RAIN EACH DAY BUT RAINFALL
AMOUNTS DURING THE PERIOD ARE LIKELY TO BE ON THE LIGHT SIDE. TEMPS
WILL ALSO WARM SLIGHTLY WITH SNOW LEVELS POSSIBLY RISING ABOVE SOME
OR MOST OF THE PASSES.
&&
.HYDROLOGY...PREVIOUS DISCUSSION...A SERIES OF PROGRESSIVE SYSTEMS
WILL BRING PERIODS OF RAIN TO THE MOUNTAINS BELOW 4-5K FEET OVER THE
NEXT FEW DAYS. SNOW IS EXPECTED ABOVE THIS LEVEL WHICH WILL HELP
MITIGATE RIVER RISES. MOST BASINS ARE CURRENTLY RUNNING LOW AND THE
DURATION OF PRECIP EVENTS SHOULD NOT BE LONG ENOUGH FOR FLOOD
CONCERNS.
HIGHER PRESSURE BUILDS LATE IN THE WEEK AND THE WEEKEND. SYSTEMS
WILL STILL BRUSH WESTERN WASHINGTON AT TIMES BUT RAINFALL AMOUNTS
SHOULD BE ON THE LIGHT SIDE. FLOODING IS NOT ANTICIPATED IN THE
EXTENDED.
NO FLOODING IS EXPECTED ON THE GREEN RIVER OVER THE NEXT WEEK. MERCER
&&
.AVIATION...WESTERN WASHINGTON IS BETWEEN WEATHER SYSTEMS THIS
MORNING. A WARM OCCLUSION NOT SITTING IN THE OFFSHORE WATERS WILL
LIFT NE THROUGH THE AREA THIS EVENING. AT THIS TIME IT APPEARS THAT
THE FRONT WILL REACH THE WASHINGTON COAST AROUND 01Z THEN PULL NE OF
THE AREA BY 06Z. LOW LEVEL PRES GRADIENTS AHEAD OF THIS FRONTAL
SYSTEM ARE OFFSHORE. HENCE EXPECT CEILINGS TO REMAIN 020-030 IN THE
INTERIOR THROUGH MID AFTERNOON. RAIN WILL INCREASE ON THE COAST
EARLY THIS AFTERNOON AND WILL SPREAD INTO THE INTERIOR MID
AFTERNOON. EXPECT MAINLY MVFR VIS AND CIG WITH THE LIGHT
PRECIPITATION AHEAD OF AND WITH THE FRONT.
THE AIR MASS WILL REMAIN RATHER MOIST BEHIND THE FRONT LATE TONIGHT
AND EARLY WED. EXPECT AREAS OF CIGS AROUND 015 AND A MAIN LAYER
AROUND 030.
MOISTURE INCREASES WITH YET ANOTHER FRONTAL SYSTEM LATE WED MORNING.
PER 06Z GFS AND 12Z NAM GUIDANCE THIS FRONT APPEARS ON TRACK TO MOVE
ACROSS THE AREA WED EVENING.
KSEA...EXPECT LOW LEVEL OFFSHORE GRADIENTS TO KEEP CIGS ABOVE 020
TODAY. RAIN WITH THE NEXT SYSTEM SHOULD REACH THE TERMINAL AROUND
22Z AND CONTINUE UNTIL FROPA AROUND 03Z. EXPECT 3-5SM -RA BR OVC012
FOR 3-4 HRS AHEAD OF THE FRONT LATER THIS AFTERNOON AND EVENING.
WINDS AT 050 WILL BRIEFLY RISE TO 22050KT 00Z - 06Z. EXPECT P6SM
BKN018 OVC035 TO DOMINATE BEHIND THE FRONT TONIGHT THROUGH WED
MORNING WITH CONDITIONS AGAIN DETERIORATING TO 4SM -RA BR OVC012 18Z
WED. SURFACE WIND SE 07 KT TODAY TURNING SLY 10 KT WITH THE FRONT
THIS EVENING THEN BACK TO SE 07 KT LATER TONIGHT THRU WED MORNING.
ALBRECHT
&&
.MARINE...AN OCCLUDED FRONT...ASSOCIATED WITH A DEVELOPING 989 MB
LOW IN THE OFFSHORE WATERS THAT IS MOVING TOWARD THE QUEEN CHARLOTTE
SOUND...WILL MOVE NE THROUGH THE WATERS LATER THIS AFTERNOON THROUGH
THIS EVENING. SMALL CRAFT ADVISORY SE WINDS PERSIST AT THE EAST
ENTRANCE TO THE STRAIT...ALONG THE COAST...AND IN THE NORTHERN
INLAND WATERS THIS MORNING. EXPECT WINDS ALONG THE COAST TO INCREASE
TO MARGINAL GALE RIGHT WITH THE FRONT LATE THIS AFTERNOON AND EARLY
THIS EVENING IN THE COASTAL WATERS. SMALL CRAFT ADVISORY SELY WINDS
WILL PERSIST AT THE EAST ENTRANCE AND IN THE NORTH INLAND WATERS AND
WILL DEVELOP IN ADMIRALTY INLET AND AT THE WEST ENTRANCE.
ANOTHER FRONTAL SYSTEM WILL APPROACH THE WATERS LATER WED AND MOVE
THROUGH THE WATERS WED EVENING. WINDS WITH THIS SECOND FRONT ARE
EXPECTED TO BE A FEW KNOTS LIGHTER THAN THIS EVENINGS FRONT...BUT
WILL STILL REACH SMALL CRAFT ADVISORY CRITERIA MOST WATERS.
FORECAST TIMING OF A NUMBER OF WEATHER SYSTEMS THAT WILL AFFECT THE
WATERS THU THROUGH THE WEEKEND IS UNCERTAIN AS MODELS HAVE
CONSISTENCY AND CONTINUITY PROBLEMS. BUT IT GENERALLY APPEARS ACTIVE
WITH SYSTEMS MOVING THROUGH THE WATERS EVERY 24 HOURS OR SO. AT THIS
POINT NONE OF THE SYSTEMS LOOK STRONG.
A VERY LARGE 30 FOOT SWELL TRAIN HAS DEVELOPED TO THE SOUTH OF A LOW
PRESSURE SYSTEM OVER THE CENTRAL NORTH PACIFIC. THIS SWELL TRAIN
WILL REACH THE WASHINGTON COAST LATER WED THROUGH EARLY THU AT
AROUND 20 FT AT 15 SECONDS. ALBRECHT
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA....A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE OLYMPICS
AND CASCADES FROM 1 PM TODAY THROUGH 6 AM WEDNESDAY MORNING.
.AVALANCHE WARNING IN EFFECT TODAY.
PZ...GALE WARNING COAST.
.SMALL CRAFT ADVISORY ENTRANCES TO THE STRAIT...CAMANO ISLAND TO
POINT ROBERTS AND ADMIRALTY INLET.
.SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR CONDITIONS.
$$
