Gale Warning 50, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 PM PDT THU OCT 22 2009

.SYNOPSIS...RAIN WILL SPREAD INLAND TONIGHT AS A WEAK WARM FRONT
BRUSHES THE THE AREA. A COLD FRONT WILL SWEEP THROUGH THE AREA
FRIDAY. AFTER ANOTHER PASSING RIDGE BRINGS DRY WEATHER ON
SATURDAY...A VIGOROUS FRONT WILL MOVE THROUGH THE AREA SUNDAY.
NORTHWEST FLOW ALOFT WILL GIVE COOL AND SHOWERY WEATHER NEXT WEEK...
WITH SNOW IN THE MOUNTAINS.

&&

.SHORT TERM...FRONT OFF THE COAST IS PROGRESSING EAST AND RAIN
SHOULD DEVELOP TONIGHT. FORECAST AND GRIDS HAVE CATEGORICAL POPS
STARTING ON THE COAST THIS EVENING AND INLAND AFTER MIDNIGHT. THE
GFS MODEL SHOWS THE FRONT INTO THE CASCADES IN THE AFTERNOON BUT THE
NAM HANGS IT UP A BIT WITH A FEW MORE IMPULSES IN THE AFTERNOON...SO
HAVE RAIN TAPERING IN THE AFTERNOON IN THE WESTERN ZONES. BY FRIDAY
EVENING THE RAIN SHOULD CHANGE TO SHOWERS AND DIMINISH CONSIDERABLY.
HAVE INDICATED A PUGET SOUND CONVERGENCE ZONE FRIDAY EVENING. WITH
STRONG ONSHORE FLOW DOWN THE STRAIT THE PSCZ SHOULD EVENTUALLY MOVE
SOUTH AND DISSIPATE...WHICH IS ALSO INDICATED IN THE GRIDS.

SATURDAY CONTINUES TO LOOK DRY WITH A SURFACE RIDGE BUILDING AND
HEIGHTS BRIEFLY RISING. NEXT SYSTEM...DUE SUNDAY...WILL NOW ARRIVE A
BIT LATER THAN EARLIER RUNS SHOWED. HAVE LOWERED POPS A LITTLE FOR
THE EARLY SUNDAY PERIOD. BY SUNDAY AFTERNOON IT SHOULD BE RAINING
EVERYWHERE. AFTER 06Z MONDAY THE RAIN WILL CHANGE TO SHOWERS...BUT
THE MOUNTAINS SHOULD STILL BE GETTING GOOD PRECIPITATION IN
NORTHWESTERLY FLOW. HIGH TEMPERATURES WILL BE IN THE 50S AND LOWS
WILL BE IN THE 40S ALL THREE DAYS. BURKE

.LONG TERM...SHOWERS PERSIST IN THE MOUNTAINS THROUGH MONDAY. THERE
WILL HAVE BEEN A TWO-STEP LOWERING OF THE SNOW LEVEL...AFTER THE
FIRST FRONT FRIDAY NIGHT AND AFTER THE SECOND FRONT SUNDAY NIGHT. BY
MONDAY MORNING WE WILL BE LOOKING AT A SNOW LEVEL AROUND 4000 FEET.
THIS IS MUCH LOWER THAN THE 9000 FEET OR SO WE HAVE BEEN SEEING
LATELY. ANYWAY MOST OF THE PRECIPITATION IN THE MOUNTAINS WILL BE IN
THE FORM OF SNOW MONDAY THROUGH ABOUT WEDNESDAY...WITH THE HIGHER
PASSES DEFINITELY SEEING SNOW.

ANOTHER WEATHER SYSTEM IS DUE AROUND WEDNESDAY. TIMING IS UNCERTAIN.
MODELS VARY QUITE A LOT ON THURSDAY AND HAVE A GENERIC FORECAST FOR
THAT DAY. BURKE

.HYDRO...TWO PERIODS OF HYDROLOGICALLY SIGNIFICANT RAINFALL ARE
COMING. THE FIRST IS FRIDAY...AND FOR THE 24-HOUR PERIOD FROM 06Z
FRIDAY THROUGH 06Z SATURDAY AMOUNTS ARE GENERALLY 1-2 INCHES IN THE
MOUNTAINS WITH SOME AREAS OF 3+ INCHES OVER THE SOUTHERN OLYMPICS
AND THE CASCADES FROM ABOUT THE SNOQUALMIE DRAINAGE NORTH. NOTE THAT
IT WILL ALSO RAIN IN THE LOWLANDS BUT AMOUNTS THERE DO NOT LOOK ALL
THAT IMPRESSIVE.

THE NEXT EVENT IS SUNDAY AND SUNDAY NIGHT. THIS ONE HAS SIMILAR
24-HOUR AMOUNTS IN THE MOUNTAINS...MOSTLY 1-2 INCHES WITH A COUPLE
OF 3+ INCH BULLSEYES IN THE NORTH CASCADES. AGAIN THERE WILL BE GOOD
RAINFALL IN THE LOWLANDS BUT THIS SHOULD NOT BE EXCESSIVE.

AS FAR AS RIVERS GO...THE AMOUNTS OF RAIN FROM THE TWO STORMS ARE
SIMILAR TO LAST WEEKEND...AND THE SNOW LEVEL WILL BE AS HIGH. ONE
DIFFERENCE IS THERE IS A DISTINCT GAP BETWEEN THE TWO STORMS...
PERHAPS AS LONG AS 36 HOURS. THIS WILL ALLOW RIVERS TO RECEDE
BETWEEN RAINFALL EVENTS AND WILL TEND TO KEEP RIVERS FROM RISING TOO
HIGH. ANOTHER DIFFERENCE IS THAT THE GROUND HAS BEEN WELL WETTED BY
NOW...AND RUNOFF SHOULD BE ENHANCED AS A RESULT. BEST GUESS IS
THAT...LIKE LAST WEEKEND...A FEW RIVERS MAY APPROACH FLOOD
STAGE...WITH THE SKOKOMISH BEING THE MOST LIKELY. NOTE THAT THE
GREEN RIVER...LIKE MOST RIVERS FLOWING OFF THE CENTRAL CASCADES...
WILL NOT BE SEEING THE LARGEST AMOUNTS OF RAINFALL IN ITS BASIN.
THEREFORE IT DOES NOT APPEAR THERE IS A THREAT OF FLOODING ON THE
GREEN RIVER. BURKE

&&

.AVIATION...JUST A FEW PATCHES OF LOW CLOUDS REMAIN THIS
AFTERNOON...THE LIGHT SE FLOW WILL PROBABLY KEEP THE STRATUS BANKED
UP ALONG THE EAST SLOPES OF THE OLYMPICS AND EXTENDING OUT OVER HOOD
CANAL...BUT ELSEWHERE SKIES ARE MID LEVEL CLOUDS AND VIRGA LOWERING.
WITH LIGHT RAIN DEVELOPING UNDER THE WARM FRONT TONIGHT CONDITIONS
WILL GRADUALLY DETERIORATE OVERNIGHT AND AREAS OF LOW CLOUDS WILL
REDEVELOP OVERNIGHT. AT 2PM THE HURRICANE RIDGE WEBCAM SHOWS THE MID
LEVEL DECK STILL ABOVE THE OLYMPICS BUT BY SUNSET PRECIP AND CLOUDS
SHOULD HAVE THE MTNS OBSCURED...AND THE CASCADES WILL BECOME
OBSCURED LATER THIS EVENING AS THE CIGS DROP. FRIDAY WILL HAVE MVFR
WITH LCL IFR COND IN THE MORNING WITH THIS RATHER MOIST FRONTAL SYS
OVER WRN WA...THEN RAIN TURNS TO SCATTERED SHOWERS MIDDAY WITH THE
COLD FRONTAL PASSAGE.

KSEA...CURRENT TAF LOOKS GOOD...ONLY TWEAKING IT AND FILLING IN THE
POSTFRONTAL CONDITIONS FOR THE LAST PART OF THE TAF. A PSCZ WILL
FORM FRIDAY EVENING AND THE WIND WILL BECOME VARIABLE FRIDAY NIGHT
WITH SHOWERS PERSISTING.

&&

.MARINE...THE GALE WATCHES BECOME GALE WARNINGS ON THIS AFTERNOON
PACKAGE FOR THE EAST ENTRANCE TO THE STRAIT AND COASTAL WATERS. THE
FORECAST IS ESSENTIALLY THE MESOSCALE WIND FORECAST. FOR NOW I HAVE
A GALE WATCH FOR THE CENTRAL STRAIT FOR THE POST FRONTAL WESTERLIES
FRI AFTERNOON AND NIGHT. THERE IS A CHANCE THAT THE PREFRONTAL SLY
WIND REACHES GALE FORCE IN THE WEST ENTRANCE TO THE STRAIT AND
ADMIRALTY INLET BY DAYBREAK...BUT THE LATEST 4KM GUIDANCE DIDNT
HAVE THAT SO SMALL CRAFT ADVISORIES ARE IN EFFECT THERE...AS WELL AS
THE REST OF THE INLAND WATERS. ANOTHER VIGOROUS FRONTAL SYSTEM
ARRIVES SUNDAY AFTERNOON.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE..
PZ...GALE WARNING COASTAL WATERS AND EAST ENTRANCE TO THE STRAIT OF
JUAN DE FUCA...GALE WATCH CENTRAL STRAIT FOR FRI AFTERNOON AND
EVENING...AND SMALL CRAFT ADVISORY REMAINING WATERS.

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