Flood Watch 16, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST MON DEC 3 2012

.SYNOPSIS...SHOWERS WILL DECREASE THIS AFTERNOON IN THE WAKE OF
SUNDAYS FRONTAL SYSTEM. MORE WIDESPREAD RAIN AND WINDY CONDITIONS
WILL RESUME TONIGHT AND TUESDAY AS ANOTHER STRONG PACIFIC FRONTAL
SYSTEM MOVES ONSHORE. COOLER MORE UNSTABLE AIR WILL FOLLOW FOR A
SHOWERY WEATHER PATTERN STARTING TUESDAY AFTERNOON THROUGH SUNDAY
WITH MOUNTAIN SNOW LEVELS FALLING BELOW THE PASSES WEDNESDAY.

&&

.SHORT TERM...MOIST WESTERLY FLOW WILL CONTINUE THIS MORNING OVER
WESTERN WASHINGTON. AN EMBEDDED SHORTWAVE WITH LOTS OF SHOWERS WILL
MOVE INLAND THIS MORNING. SO EXPECT SHOWERS TO EASE BY THIS
AFTERNOON. WILL KEEP THE WINTER WEATHER ADVISORY IN THE CASCADES
GOING UNTIL 10 AM.

OUR PERSISTENT UPPER LEVEL TROUGH REMAINS OVER THE NE PACIFIC.
SATELLITE IMAGERY SHOWS ONE MORE GOOD SHORTWAVE OFF CALIFORNIA NEAR
150W. PROGS HAVE A DECENT HANDLE ON THIS ONE. NOTE THE SUBTROPICAL
TAP AS SHOWN IN THE CIRA BLENDED TOTAL PRECIPITABLE WATER IMAGERY
LOOP. THE JETSTREAM THAT SPENT QUITE A BIT OF TIME NEAR THE OREGON/
CAL BORDER LAST WEEK WILL LIFT NORTH THROUGH US. BY TUE...THE JET
LIFTS NORTH OF US PUTTING US IN THE WARM SECTOR WITH SNOW LEVELS
RISING WELL ABOVE THE PASSES.

THIS SYSTEM WILL BRING ANOTHER ROUND OF SIGNIFICANT PRECIPITATION
AND WINDY CONDITIONS. PRECIPITATION AMOUNTS OF 1 TO 3 INCHES ARE
LIKELY IN THE MOUNTAINS WITH THE SNOW LEVEL RISING TO AROUND 5500 TO
6500 FEET. THE LOWLANDS WILL GET MAINLY 0.25 TO 1 INCH. SUSTAINED
WINDS SHOULD PEAK IN THE 20 TO 35 MPH RANGE...WITH THE HIGHEST WINDS
GENERALLY AT THE COAST AND IN THE NORTH INTERIOR. MOST LIKELY THIS
WILL BE A WIND ADVISORY EVENT IN THOSE AREAS. WILL ISSUE A SPECIAL
WEATHER STATEMENT LATER THIS MORNING TO PROVIDE SOME ADDITIONAL LEAD
TIME.

THE COLD FRONT SHOULD MOVE ONSHORE TUE MORNING WITH COLD AIR
ADVECTION BEGINNING IN THE AFTERNOON AS WESTERLY FLOW ALOFT RESUMES.
EXPECT SNOW LEVELS TO DROP BACK DOWN BELOW THE PASSES BY WED AS THE
JETSTREAM DROPS BACK SOUTH OF OUR AREA AND WE GET BACK INTO A COOLER
SHOWERY WEATHER PATTERN. BUEHNER

.LONG TERM...THE MODELS ARE COMING TOGETHER REGARDING THE PATTERN
FOR THE REST OF THE WEEK. WESTERLY OR EVEN NORTHWESTERLY FLOW ALOFT
SHOULD MAINTAIN A COOLER SHOWERY PATTERN...GOOD FOR UPSLOPE MOUNTAIN
CONDITIONS AND SNOW SHOWERS THERE. EMBEDDED SHORTWAVES SHOULD
ENHANCE SHOWERS AT TIMES. TEMPERATURES SHOULD BE AT OR A BIT BELOW
EARLY DEC AVERAGES. BUEHNER

&&

.HYDROLOGY...RAINFALL AMOUNTS HAVE TAPERED OFF IN THE WAKE OF
SUNDAYS SYSTEM. THE SKOKOMISH RIVER SHOULD SLOWLY RECEDE TODAY BUT
NOT ENOUGH TO FALL BELOW FLOOD STAGE. KEEPING AN EYE ON SEVERAL
OTHER RIVERS AS WELL.

THE NEXT SYSTEM WILL PROBABLY BRING 2 TO 4 INCHES TO THE SOUTHERN
OLYMPICS. THIS SHOULD KEEP THE SKOKOMISH RIVER AT OR ABOVE FLOOD
STAGE INTO WEDNESDAY THOUGH ONLY MINOR FLOODING IS FORECAST.
FLOODING IS UNLIKELY ON ANY OTHER RIVERS.

AFTER TUESDAY...NO MAJOR SYSTEMS ARE FORECAST THE REST OF THE WEEK.
THE SKOKOMISH SHOULD FALL BELOW FLOOD STAGE MID WEEK AND FLOODING IS
UNLIKELY ON ANY RIVERS. BUEHNER

&&

.AVIATION...WESTERLY FLOW ALOFT BECOMING SOUTHWESTERLY LATE. AIR
MASS MOIST AND SLIGHTLY UNSTABLE STABILIZING LATE. MODERATE ONSHORE
SURFACE PRESSURE GRADIENTS WILL EASE LATE THIS MORNING WITH THE
GRADIENTS GOING WEAK OFFSHORE LATE IN THE DAY. SHOWERS WILL DECREASE
LATER THIS MORNING INTO THE AFTERNOON HOURS. RAIN OUT AHEAD OF THE
NEXT FRONTAL SYSTEM WILL BEGIN THIS EVENING.

A WIDE RANGE OF CEILINGS WILL CONTINUE THROUGH THIS MORNING. IN AND
AROUND THE SHOWERS CEILINGS ARE IN THE 1500 TO 2500 FOOT RANGE. AWAY
FROM THE SHOWERS CEILINGS IN THE 3500 TO 5000 FOOT RANGE. CEILINGS
WILL IMPROVE LATE THIS MORNING INTO THE AFTERNOON AS THE SURFACE
GRADIENTS TURN OFFSHORE IN RESPONSE TO THE NEXT APPROACHING SYSTEM.
EXPECT VFR CEILINGS WITH THE ONSET OF PRECIPITATION WITH THE NEXT
FRONT THIS EVENING.

KSEA...ABOVE DISCUSSION APPLIES FOR KSEA. SOUTHERLY WINDS 10 TO 15
KNOTS BECOMING SOUTHEASTERLY 6 TO 10 KNOTS THIS AFTERNOON INTO THE
EVENING HOURS. FELTON

&&

.MARINE...SMALL CRAFT ADVISORY WINDS ARE OCCURRING OVER ALL WATERS
EXCEPT THE CENTRAL STRAIT. ONSHORE FLOW WILL EASE THIS MORNING WITH
THE WINDS OVER ALL OF THE WATERS DIMINISHING.

A STRONG FRONTAL SYSTEM WILL APPROACH THE AREA TONIGHT AND MOVE
THROUGH THE WATERS ON TUESDAY. GALE WARNING HAVE BEEN ISSUED FOR THE
COAST...ENTRANCES TO THE STRAIT AND NORTHERN INLAND WATERS FOR LATER
TONIGHT INTO TUESDAY. STRONG ONSHORE FLOW WILL FOLLOW THE FRONT
LATER TUESDAY INTO TUESDAY NIGHT. GRADIENTS EASE WEDNESDAY WITH
WEAKER SYSTEMS ARRIVING LATER IN THE WEEK. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY NORTH AND CENTRAL CASCADES ABOVE 3000
     FEET UNTIL 10 AM TODAY.

PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT CENTRAL STRAIT TODAY.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WARNING COAST...ENTRANCES TO THE STRAIT AMD NORTHERN
     INLAND WATERS FOR TONIGHT AND TUESDAY.

&&

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML

WEATHER.GOV/SEATTLE

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