FXUS66 KSEW 261723
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
925 AM PST THU NOV 26 2009
.SYNOPSIS...A COLD FRONT WILL CONTINUE TO MOVE SOUTHEAST OUT OF THE
AREA LATER TODAY. THUS EXPECT THE RAIN TO DECREASE FROM THE
NORTHWEST THROUGH THIS EVENING. THERE WILL BE A LINGERING THREAT OF
SHOWERS FRIDAY MORNING AS THE LOW PRESSURE SYSTEM ALOFT MOVES ACROSS
THE REGION. LOOK FOR DRY WEATHER FRIDAY AFTERNOON UNDER HIGH
PRESSURE ALOFT. EXPECT A CHANCE OF RAIN FRIDAY NIGHT THROUGH
SATURDAY AS A WEAK SYSTEM MOVES ACROSS THE AREA.
&&
.SHORT TERM...THE MAIN BAND OF RAIN IS ALREADY SOUTH OF HERE WITH
MODERATE TO HEAVIER RAINS FALLING OVER AN AREA THAT HAS NOT SEEN
MUCH OF ANYTHING YET SO THIS IS GOOD. THE SYSTEM ROLLING ONSHORE IS
WEAKER THAN EARLIER ANTICIPATED WHICH IS A GOOD THING FOR AREA
RIVERS AS THERE HAS BEEN AND WILL BE A SHORTER PERIOD OF TIME FOR
THE HEAVIER RAIN OVER THE REGION. THE WEAK SURFACE LOW IS SITTING
OFF THE CENTRAL COAST OF OREGON THIS MORNING AND WILL CONTINUE TO
MOVE NE AND CROSS THE COAST NEAR OR JUST SOUTH OF ASTORIA. THIS
FEATURE AND THE UPPER LEVEL SYSTEM ARE NOT WRAPPING UP ENOUGH TO
STALL THE BAROCLINIC BAND SO IT WILL CONTINUE TO GRADUALLY
TRANSITION SE OUT OF THE AREA THROUGH THE EVENING HOURS. THERE WILL
LIKELY BE A SECONDARY BAND OF LIGHT RAIN MOVING ACROSS THE AREA
TONIGHT ALONG AND JUST AHEAD OF THE UPPER TROUGH AXIS BUT THIS WILL
HAVE LITTLE AFFECT ON THE AREA OTHER THAN KEEPING THINGS WET.
THIS ENTIRE SYSTEM TRANSLATES QUICKLY TO THE EAST WHICH SHOULD ONLY
LEAVE A FEW LINGERING SHOWERS FRIDAY MORNING OVER THE EASTERN PUGET
SOUND AND THE CASCADES...OTHERWISE IT WILL BE DRY. THERE WILL BE
PLENTY OF LOW LEVEL MOISTURE AROUND BUT WOULDNT BE SURPRISED TO SEE
A COUPLE OF BREAKS IN THE CLOUD COVER DURING THE AFTERNOON.
BEYOND THAT...AS A UPPER RIDGE BEGINS TO BUILD OFFSHORE...WARM
ADVECTION WILL DEVELOP FROM WESTERN WASHINGTON NORTHWARD FRIDAY
NIGHT...PEAKING DURING THE DAY SATURDAY. WESTERN WASHINGTON
CONTINUES TO BE ON THE SOUTHERN EDGE OF THE SIGNIFICANT LIFT AND
THUS WILL BE IN THE TRANSITION AREA BETWEEN RAIN AND CLOUDS WITH NO
RAIN. IT STILL LOOKS AS THOUGH WE WILL GET PRECIPITATION...JUST HOW
MUCH IS THE QUESTION. MORE AND MORE IT LOOKS LIKE WE NEED TO LEAN
TOWARD LIGHTER AMOUNTS. THIS IS MORE OF A QUESTION OF HOW MUCH SNOW
TO FORECAST IN THE MOUNTAINS AS THE SNOW LEVELS WILL BE LOW.
EARLIER IT WAS LOOKING LIKE SIGNIFICANT SNOWS...NOW WE MAY NOT EVEN
REACH ADVISORY LEVELS. CERNIGLIA
.LONG TERM...DEPENDING ON HOW PRONOUNCED THE RIDGE BECOMES ON THE
WEST COAST SUNDAY WILL DETERMINE HOW MUCH IF ANY PRECIPITATION WE
WILL GET SUNDAY. RIGHT NOW OUR AREA IS RIGHT ON THE EDGE OF THE
AREA OF VERY LIGHT RAIN BUT THE TREND HAS BEEN TOWARD DRIER. IT WILL
NOT TAKE MUCH MORE BUILDING OF THE RIDGE TO SHOVE THE MOISTURE NORTH
OF THE AREA FOR A DRY AND PARTLY SUNNY DAY.
WHAT HAS BEEN FAIRLY CONSISTENT IN THE LONG RANGE MODELS IS A
PATTERN CHANGE TAKING PLACE BEGINNING LATE MONDAY. A COLD FRONT IS
EXPECTED TO SWEEP SOUTHEAST ACROSS THE AREA LATE MONDAY (GIVE OR
TAKE) WITH DRY NW FLOW TAKING OVER IN ITS WAKE. THIS SYSTEM WILL
HELP TO DIG A DEEP TROUGH OVER THE CENTRAL PART OF THE COUNTRY
LEAVING A RIDGE UP OVER THE EASTERN PACIFIC AND PACIFIC NORTHWEST
FOR A PERIOD OF PARTLY CLOUDY SKIES. THIS IS EXPECTED TO BE FOR AT
LEAST TUESDAY AND WEDNESDAY AND QUITE POSSIBLY SIGNIFICANTLY
LONGER. WITH THE CLEARING SKIES WILL COME COOLER TEMPERATURES WITH
LOWS AROUND FREEZING AND HIGHS GENERALLY IN THE 40S. CERNIGLIA
&&
.HYDROLOGY...MODERATE TO HEAVY RAIN HAS CONTINUED TO MOVE SOUTHEAST
DURING THE NIGHT AND NOW THE HEAVIEST PRECIPITATION IS IN A BAND
RUNNING ROUGHLY STEVENS PASS SOUTHWEST TO BETWEEN ASTORIA AND
PORTLAND OREGON. THE SKOKOMISH AND SEVERAL OTHER RIVERS ON THE
OLYMPIC PENINSULA HAVE ALREADY PEAKED BELOW FLOOD STAGE AND THE
REMAINING RIVERS IN THIS AREA THAT ARE STILL RISING ARE EXPECTED TO
PEAK BELOW FLOOD STAGE.
SEVERAL RIVERS IN THE NORTH CASCADES RISING AT A GOOD CLIP...BUT THE
RAIN HAS TAPERED OFF OVER A FEW HOURS AGO. THE NOOKSACK IS RISING
QUICKLY WHICH IS NOT UNCOMMON AND IS EXPECTED TO ROLL OVER UNDER
FLOOD. THE STILLAGUAMISH RIVER ALREADY HAS A FLOOD WARNING OUT ON
IT FOR CRESTING JUST ABOVE FLOOD STAGE LATER THIS MORNING.
FLOODING ON RIVERS IN THE CENTRAL CASCADES AND WILLAPA HILLS IS LESS
LIKELY AT THIS POINT AS HEAVY RAIN WILL BE LIMITED IN TIME OVER THIS
AREA...ALTHOUGH WE WILL CONTINUE TO MAINTAIN A WATCHFUL EYE ON THE
SITUATION.
ONCE WE GET BEYOND THIS SITUATION...THE SYSTEMS OVER THE WEEKEND ARE
TOO WEAK AND COLD TO CAUSE ANY ADDITIONAL RIVER FLOODING PROBLEMS
AND NEXT WEEK WILL SEE A TRANSITION INTO A DRY PATTERN WHICH WILL
ALLOW STREAMS TO FINALLY RETURN TO LOWER FLOWS.
NO FLOODING IS EXPECTED ON THE GREEN RIVER. CERNIGLIA
&&
.AVIATION...A BAROCLINIC BAND WILL MOVE SLOWLY SOUTHEAST THROUGH
THIS AFTERNOON WITH RAIN DECREASING FROM N TO S. LIGHT SW FLOW ALOFT
WILL BECOME MODERATE NW FLOW THIS EVENING AS THE UPPER TROUGH MOVES
ACROSS. THE CEILINGS WILL REMAIN IN THE 1-3 K FT RANGE THROUGH
TONIGHT WITH N/NW FLOW BEHIND LOW PRESSURE. THE AIR MASS WILL REMAIN
MOIST AND STABLE AT ALL LEVEL THROUGH TONIGHT.
KSEA...N WIND 3-6 KT...RISING TO 5 TO 9 KT THIS AFTERNOON. DTM
&&
.MARINE...WEAK SURFACE LOW PRES WILL TRACK INTO THE N OREGON COAST
TODAY RESULTING IN ONSHORE FLOW OVER THE COAST AND SMALL CRAFT
WINDS. WITH A WEAKER AND FURTHER S SURFACE LOW TRACK NOW
EXPECTED...WINDS ACROSS THE INLAND WATERS AND STRAIT ARE EXPECTED TO
REMAIN BELOW 20 KT THROUGH TONIGHT. WILL NEED TO WATCH FOR WLYS DOWN
THE STRAIT BUT WINDS HERE ALSO APPEAR TO STAY JUST BELOW SMALL CRAFT.
SWELL OF 12-14 FT WILL CONTINUE ACROSS THE COAST AND W ENTRANCE TO
THE STRAIT TODAY. THE SMALL CRAFT FOR WINDS COVERS THE HEADLINE FOR
THE COAST. THE SMALL CRAFT FOR HAZARDOUS SEAS REMAINS UP FOR THE W
ENTRANCE.
A WEAK RIDGE BUILDS FRIDAY NIGHT...THEN A WARM FRONT BRUSHES THE
AREA SATURDAY. THIS IS LIKELY TO BRING SMALL CRAFT ADVISORY
SOUTHEAST WINDS TO SOME MORE EXPOSED LOCATIONS. DTM
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES AND WARNINGS ARE IN EFFECT IN OUR CWA.
PZ...SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
SMALL CRAFT ADVISORY COAST.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS WEST ENTRANCE.
$$
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