FXUS66 KSEW 261207 CCA
AFDSEW
AREA FORECAST DISCUSSION...CORRECTION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
406 AM PST THU NOV 26 2009
CORRECTED TYPOS IN THE WATCH/WARNING/ADVISORY SECTION.
.SYNOPSIS...A COLD FRONT WILL MOVE ACROSS 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. ALAS...EXPECT A
CHANCE OF RAIN FRIDAY NIGHT THROUGH SATURDAY AS A WEAK SYSTEM MOVES
ACROSS THE AREA.
&&
.SHORT TERM...
RAIN CONTINUED OVER THE AREA EARLY THIS MORNING...ALTHOUGH MUCH OF
IT WAS OCCURRING OVER THE NW THREE-QUARTERS OF THE FORECAST AREA.
ANOTHER WAVE DEVELOPED ON THE SRN END OF THE BAROCLINIC ZONE...AND
RESULTED IN SOME SLOWING OF THE SE PROGRESSION OF THE FRONT. THUS
HAVE INDICATED A SOMEWHAT SLOWER TIMING OF THE FRONTAL PASSAGE THAN
THE GFS PREDICTED. SATELLITE IMAGERY SHOWED A PRONOUNCED BACK EDGE
OR DRY SLOT BEHIND THE NRN END OF THE FRONTAL BOUNDARY...BUT THIS
SHOULD BE TEMPORARY AS CLOUDS ARE LIKELY TO FILL IN OVER THIS AREA
DURING THE NEXT SEVERAL HOURS.
ANTICIPATE RAIN TO GRADUALLY DECREASE FROM THE NW DURING THE DAY
TODAY. BY MIDNIGHT TONIGHT...THE FRONT WILL BE SE OF THE AREA...WITH
ONLY SHOWERS EXPECTED IN ITS WAKE. THE UPPER TROF WILL MOVE ACROSS
WRN WA FRI MORNING...WITH THE RISK OF SHOWERS COMING TO AN END BY
NOON. FRI AFTERNOON WILL BE DRY UNDER A WEAK...UPPER RIDGE.
ANOTHER...BUT WEAKER...SYSTEM WILL BRING A THREAT OF RAIN TO THE
AREA FRI NIGHT AND SATURDAY.
.LONG TERM FROM THE PREV DISCUSSION...
DEPENDING ON HOW PRONOUNCED THE RIDGE BECOMES ON THE WEST COAST
SUNDAY WILL DETERMINE HOW MUCH IF ANY PRECIPITATION WE WILL GET
SUNDAY. WITH THE WAY THINGS HAVE BEEN OF LATE WOULD BET ON A LEAST
MOSTLY CLOUDY AND SOME LIGHT RAIN SUNDAY. HOWEVER...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 SO STAY TUNED.
WHAT HAS BEEN FAIRLY CONSISTENT IN THE LONG RANGE MODELS IS A
PATTERN CHANGE TAKING PLACE BEGINNING LATER 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 MOVED SOUTHEAST DURING THE
NIGHT AND NOW THE HEAVIEST PRECIPITATION IS IN A BAND RUNNING KHQM
TO KBLI...WITH SIGNIFICANT RAIN IN THE OLYMPICS AND NORTH CASCADES.
SO FAR ABOUT 1.5 INCHES HAVE FALLEN IN THE OLYMPICS WITH OVER 2
INCHES AT KUIL AND THE HOH RANGER STATION. THE NORTH CASCADES HAVE
HAD UP TO 2 INCHES. ON THE OTHER HAND RAIN HAS NOT YET BEGUN IN THE
WILLAPA HILLS AND CENTRAL CASCADES.
ONE PIECE OF GOOD NEWS IS THAT RAIN HAS TAPERED ON THE FAR NORTHWEST
CORNER OF THE OLYMPIC PENINSULA. THAT HAS ALLOWED THE FAST
RESPONDING BOGACHIEL TO CREST...A FULL 3 FEET BELOW FLOOD STAGE. THE
DUNGENESS AND ELWHA ARE STILL RISING AND WILL BE WATCHED. THE RAIN
FORECAST CALLS FOR THE SLOW-MOVING BAND TO CONTINUE SOUTHEAST TODAY.
THIS MEANS THE OLYMPICS AND NORTH CASCADES WILL STOP RECEIVING
SIGNIFICANT RAINFALL IN THE 18Z-21Z PERIOD...AND THE CENTRAL
CASCADES WILL GET ABOUT SIX HOURS OF RAIN BEFORE THE BAND EXITS THE
STATE.
IN THE SOUTHERN OLYMPICS ONLY THE SKOKOMISH RIVER IS RESPONDING SO
FAR TO THE RAIN. IT IS LESS THAN HALF A FOOT BELOW FLOOD STAGE AND
RISING...SO A WARNING IS POSSIBLE SOON. ONLY MINOR FLOODING IS
PREDICTED.
SEVERAL RIVERS IN THE NORTH CASCADES ARE FORECAST TO RISE AND CREST
ABOUT A FOOT BELOW FLOOD STAGE. PROBABLY A LOT MORE RAIN WOULD BE
NEEDED TO BRING THEM TO FLOOD. IF THE WEATHER SYSTEM BEHAVES AS
FORECAST THERE SHOULD BE NO FLOODING ON RIVERS FLOWING OFF THE NORTH
CASCADES.
FLOODING ON RIVERS IN THE CENTRAL CASCADES AND WILLAPA HILLS IS EVEN
LESS LIKELY. WILL MAINTAIN THE WATCH UNTIL THE MORNING AT LEAST IN
CASE SOMETHING GOES WRONG WITH THE FORECAST...LIKE MORE RAIN FALLING
THAN IS PREDICTED...OR A STALLING OF THE RAIN BAND.
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. BURKE
&&
.AVIATION...CEILINGS ARE GENERALLY MVFR WITH A FEW EXCURSIONS BOTH
ABOVE AND BELOW. MODERATE RAIN IS COMMON AT THE TERMINALS AND THIS
WILL CONTINUE...ALTERNATING WITH PERIODS OF LIGHT RAIN...UNTIL 18Z
OR SO. A BAROCLINIC BAND WILL MOVE SLOWLY SOUTHEAST DURING THE DAY
AND BY AFTERNOON THE RAIN WILL BE DIMINISHING CONSIDERABLY. HOWEVER
THE CEILINGS WILL STICK AROUND AND IN FACT WILL LOWER SOMEWHAT FROM
2-3K FT TO 1-2K FT...AND STAY THERE TONIGHT. THERE ARE ALSO
VISIBILITY RESTRICTIONS THIS MORNING...1-3SM IN RAIN...VISIBILITY
SHOULD IMPROVE IN THE AFTERNOON.
KSEA...FORECAST ABOVE HOLDS. WINDS SOUTHERLY 4-8 KT THIS MORNING
WILL SWITCH TO NORTHERLY 4-8 KT IN THE AFTERNOON.
&&
.MARINE...SOME ONSHORE FLOW HAS BEGUN ON THE COAST AND DOWN THE
STRAIT IN RESPONSE TO A FRONTAL BAND MOVING EAST. HAVE SMALL CRAFT
ADVISORIES IN EFFECT ON THE COAST AND IN THE CENTRAL STRAIT. ONSHORE
FLOW SHOULD DIMINISH BY AFTERNOON AS A LOW DEVELOPS SOUTHWEST OF
WASHINGTON. THIS LOW WILL MOVE INLAND OVERNIGHT AND ONSHORE FLOW
WILL RESUME FRIDAY.
NEW MODEL RUNS HAVE DOWNPLAYED THE DEPTH OF THE LOW AND THE STRENGTH
OF THE ONSHORE FLOW BEHIND IT. HAVE DROPPED THE GALE WATCH FOR
FRIDAY AND STUCK WITH SMALL CRAFT ADVISORY STRENGTH WINDS.
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. CHB
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES REMAIN IN EFFECT FOR MUCH OF THE CWA THROUGH
FRI MORNING.
PZ...A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE COASTAL WATERS
AND CENTRAL/EASTERN STRAIT OF JUAN DE FUCA THROUGH THIS
AFTERNOON.
A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS IS IN EFFECT FOR
THE WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA THROUGH
THIS AFTERNOON.
A SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS
REMAINS IN EFFECT THROUGH LATE TONIGHT.
$$
WWW.WEATHER.GOV/SEATTLE
FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.
