FXUS66 KSEW 262231
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 PM PST SAT DEC 26 2009
.SYNOPSIS...UPPER LEVEL HIGH PRESSURE WILL CONTINUE TO SLOWLY LOOSEN
ITS GRIP ON THE AREA AS A WEAK FRONT APPROACHES FROM THE SOUTH
SUNDAY. THIS FRONT WILL BRING CLOUDS AND A THREAT OF RAIN LATER
SUNDAY NIGHT INTO MONDAY. ANOTHER WEAK SYSTEM IS EXPECTED LATE
TUESDAY FOLLOWED BY A POTENTIAL BRIEF BREAK. A STRONGER SYSTEM IS
ON THE HORIZON FOR NEW YEARS EVE INTO NEW YEARS DAY.
&&
.SHORT TERM...CROSS CASCADE PRESSURE GRADIENT IS STILL HIGH...BUT IT
IS SLOWLY DROPPING OFF. TALKING WITH A SPOTTER WITH THE STRONGEST
WINDS HE MENTIONED THAT THE WIND WAS VERY SLOWLY EASING UP BUT STILL
NEAR WARNING LEVELS. WITH THE CONTINUED DOWNWARD TREND WILL LET THE
WARNING EXPIRE AT 4 PM AND HAVE A WIND ADVISORY FOR 4 PM UNTIL
MIDNIGHT AS THE WIND CONTINUES TO RAMP DOWN. TONIGHT SHOULD BE THE
FINAL CLEAR NIGHT OF THE SERIES AND TEMPERATURES WILL BE SIMILAR TO
WHAT WE HAD LAST NIGHT AND WILL VARY SIGNIFICANTLY FROM SHELTERED TO
WIND EXPOSED AREAS.
SUNDAY...A WEAK SYSTEM WILL BEGIN ROTATING UP FROM THE SOUTH DURING
THE DAY AND SPREAD CLOUDS SLOWLY UP FROM THE SOUTH. THE INITIAL
CLOUDS WILL BE HIGH AND NOT AMOUNT TO MUCH AND THE LOWER AND MID
CLOUDS WILL FOLLOW SUNDAY NIGHT. SUNDAY WILL BE ANOTHER TRICKY DAY
FOR HIGH TEMPS AS THERE WILL AGAIN BE A RATHER LARGE RANGE FROM
AREAS THAT MIX OUT THE LOW LEVEL INVERSION TO THOSE THAT STAY LOCKED
IN. THE OVERALL LOW LEVEL AIR MASS WILL BE COOLER THAN TODAY WITH
LESS DOWNSLOPE OFF THE CASCADES SO WENT WITH LOW 40S INVERSION AREAS
AND MID TO UPPER 40S BREAKOUT AREAS.
SUNDAY NIGHT THE WEAKENING FRONT MOVES OVER THE SOUTHERN HALF OF
WESTERN WA WITH A CHANCE OF SOME LIGHT RAIN WITH CLOUDS INCREASING
OVER NORTHERN AREAS. WITH THE CLOUD COVER COMES WARMER OVERNIGHT
LOW TEMPERATURES.
MONDAY...WHATS LEFT OF THE FRONT CONTINUES TO MOVE NORTH AND THE
ASSOCIATED WEAK UPPER LOW MOVES INTO OREGON...THE THREAT OF LIGHT
PRECIPITATION WILL SPREAD THROUGHOUT WESTERN WA WITH PLENTY OF CLOUD
COVER. WITH THE LACK OF SUN AND MUCH WIND...HIGH TEMPERATURES WILL
BE HELD TO WITHIN A COUPLE OF DEGREES OF 40.
THAT SYSTEM FALLS APART MONDAY NIGHT AND A WEAK RIDGE IS EXPECTED TO
MOVE OVERHEAD TUESDAY FOR DRIER WEATHER. BUT NOT NECESSARILY DRY AS
THERE WILL BE LINGERING MOISTURE FROM THE DEPARTING SYSTEM AND THE
NEXT FRONT IS JUST OFFSHORE NEAR THE END OF THE DAY IF THE CURRENT
TIMING IS CORRECT. SO CAN/T REMOVE THE THREAT OF RAIN FROM THE
FORECAST JUST YET...BUT ITS CLOSE. CERNIGLIA
.LONG TERM...THE SYSTEM APPROACHING LATE TUESDAY WILL OOZE THROUGH
TUESDAY NIGHT AND WEDNESDAY WITH PERIODS OF WET DOWN LOW AND WHITE
IN THE MOUNTAINS. TEMPERATURES WILL BE NEAR SEASONAL NORMS. THIS
WILL BE FOLLOWED BY A BREAK IN THE WEATHER THEN ANOTHER FRONT IS
EXPECTED TO APPROACH THE AREA LATE NEW YEARS EVE...WITH RAIN
DEVELOPING AND LIKELY CONTINUING INTO NEW YEARS DAY. ALTHOUGH
STRONGER THAN THE PREVIOUS FRONTS THAT WILL AFFECT THE AREA...IT IS
NOT STRONG OVERALL. SO PERIODS OF RAIN AND NORMAL WINTER BREEZES.
THEN THERE WILL BE ANOTHER BREAK WITH A SYSTEM POSSIBLY AFFECTING
THE REGION NEXT WEEKEND. CERNIGLIA
&&
.AIR QUALITY...AREAS OF THE CENTRAL SOUND...STRAIT AND COAST HAVE
CLEARED OUT THE AIR NICELY THANKS TO THE WINDS OUT OF THE
CASCADES...WHILE OTHER AREAS REMAIN LOCKED IN UNDER AN INVERSION
WITH ELEVATED POLLUTION LEVELS. TONIGHT WITH CLEAR SKIES AND
PRESSURE GRADIENTS EASING...I AM EXPECTING THE LOW LEVEL INVERSION
TO RE-DEVELOP AND BECOME ESTABLISHED ACROSS MOST OF THE INTERIOR.
THIS WILL DIFFICULT TO BREAK AND THERE WON/T BE MUCH WIN TO MIX
THINGS UP. THE LOW LEVEL INVERSION...WHILE WEAKER...REMAINS INTO
MONDAY WITH LITTLE TO NO HORIZONTAL MIXING. AS A RESULT THE
STAGNATION ADVISORY WILL REMAIN IN EFFECT FOR NOW. CERNIGLIA
&&
.HYDROLOGY...THERE IS NO THREAT OF FLOOD-PRODUCING RAINFALL THROUGH
NEXT WEDNESDAY. THE THREAT OF WIDESPREAD FLOODING FROM NEXT
THURSDAY THROUGH THE FIRST WEEKEND OF 2010 IS LOW. A WEATHER SYSTEM
AROUND NEW YEARS EVE OR NEW YEARS DAY COULD BE ACCOMPANIED BY
MODERATE RAINFALL AMOUNTS. THIS COULD BRING RISES ON AREA
RIVERS...BUT FLOOD-PRODUCING RAINFALL AMOUNTS ARE NOT EXPECTED.
RIVER LEVELS WILL ALSO START OUT LOW AFTER AN EXTENDED PERIOD OF DRY
WEATHER.
FLOODING ON THE GREEN RIVER IS NOT EXPECTED FOR THE NEXT 10 DAYS.
&&
.AVIATION...AN UPPER RIDGE IS CENTERED OVER SOUTHERN BRITISH
COLUMBIA WITH A TROUGH WELL OFF THE COAST. THIS IS GIVING LIGHT
SOUTHEAST FLOW ALOFT. AT THE SURFACE STRONG HIGH PRESSURE EXTENDING
FROM SOUTHEAST BRITISH COLUMBIA INTO NORTHERN IDAHO WILL GIVE
CONTINUING OFFSHORE FLOW THROUGH SUNDAY. DOWNSLOPE EASTERLY WINDS
HAVE DRIED THE LOWER LAYERS OF THE AIR MASS.
SKIES ARE CLEAR EXCEPT FOR SOME STRATUS IN THE STRAIT OF GEORGIA AND
A PATCH OF FOG BETWEEN KSHN AND KOLM. OFFSHORE GRADIENTS HAVE EASED
TODAY WHICH SHOULD ALLOW FOR A BIT MORE FOG AND STRATUS TO FORM
TONIGHT. THIS WILL PROBABLY BE CONFINED TO THE SOUTHWEST INTERIOR
AND THE SOUTH PUGET SOUND AREA.
KSEA...STRATUS NEARLY MADE IT TO KSEA THIS MORNING BEFORE THE EAST
WINDS DISSIPATED IT. THE WINDS WILL NOT BE AS STRONG TONIGHT AND SO
THERE COULD BE A LITTLE STRATUS OR FOG IN THE MORNING. WILL PROBABLY
HAVE A TEMPO IFR GROUP 12Z-16Z. CHB
&&
.MARINE...HIGH PRESSURE EXTENDING FROM SOUTHEAST BRITISH COLUMBIA
INTO NORTHERN IDAHO WILL KEEP THE STRONG OFFSHORE FLOW PATTERN
INTACT THROUGH SUNDAY. HOWEVER GRADIENTS HAVE EASED AND THE GALES AT
THE WEST ENTRANCE APPEAR TO BE OVER. WILL CONVERT THAT TO A SMALL
CRAFT ADVISORY. ALSO SOME GUSTY EAST WINDS AT THE EAST ENTRANCE AND
CENTRAL STRAIT AND WILL HAVE SMALL CRAFT ADVISORIES THERE. THESE
ADVISORIES ALONG WITH THE ONES ON THE COAST SHOULD KEEP GOING
THROUGH AT LEAST SUNDAY.
A DISSIPATING FRONT WILL MOVE THROUGH THE AREA SUNDAY NIGHT AND
MONDAY AND WINDS WILL DIMINISH...ESPECIALLY INLAND. ANOTHER SYSTEM
ARRIVES ABOUT WEDNESDAY AND THAT COULD AGAIN INCREASE GRADIENTS TO
THE POINT THAT SMALL CRAFT ADVISORIES ARE NEEDED. A STRONGER SYSTEM
IS IN THE MODELS ABOUT THURSDAY NIGHT.
WESTERLY SWELLS OF 10-12 FEET OVER THE COASTAL WATERS WILL GRADUALLY
BUILD TO AROUND 14 FT TONIGHT AND REMAIN AROUND 14 FEET ON SUNDAY.
THE SWELL WILL GRADUALLY SUBSIDE SUNDAY NIGHT INTO TUESDAY. EXPECT
SMALL CRAFT ADVISORY LEVEL ROUGH BAR CONDITIONS AT GRAYS HARBOR FOR
THE NEXT SEVERAL DAYS. CHB
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WARNING EAST PUGET SOUND LOWLANDS UNTIL 4 PM.
WIND ADVISORY EAST PUGET SOUND LOWLANDS 4 PM UNTIL MIDNIGHT.
PZ...SMALL CRAFT ADVISORY COAST AND STRAIT.
.SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
$$
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