Heavy Snow in Washington, March 14 to 15, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
345 PM PDT SAT MAR 14 2009

.SYNOPSIS...ANOTHER FRONT WILL PASS THROUGH WESTERN WASHINGTON THIS
EVENING WITH RAIN TURNING TO SHOWERS AFTER MIDNIGHT. WINDS WILL
INCREASE ACROSS THE AREA ON SUN AS A DEEP SURFACE LOW DEVELOPS OFF
THE COAST. COOL AND SHOWERY WEATHER WILL CONTINUE THROUGH EARLY NEXT
WEEK AS A BROAD UPPER LEVEL TROUGH REMAINS PARKED ACROSS THE PACIFIC
NORTHWEST.

&&

.SHORT TERM...VERY ACTIVE WEATHER PATTERN EXPECTED OVER THE NEXT 24
HOURS.

WE HAD A BRIEF BREAK IN THE SHOWERS THIS AFTERNOON BUT THE RADAR IS
FILLING BACK IN AS THE NEXT FRONT HEADS INLAND. THE FRONT SHOULD
PASS THROUGH THE INTERIOR AROUND 03Z WITH BREEZY SOUTHERLY WINDS
DECREASING AFTER MIDNIGHT. VISIBLE SATELLITE DOES SHOW SOME BREAKS
BEHIND THE FRONT SO WILL DECREASE POPS A BIT OVERNIGHT WITH MOST OF
THE ACTIVITY IN THE MOUNTAINS. WITH STRONG WESTERLY UPSLOPE
FLOW...AND PASSING UPPER LEVEL TROUGH WILL CONTINUE TO SEE SNOW
SHOWERS ACROSS THE OLYMPICS AND CASCADES. SNOW LEVELS WILL REMAIN
BELOW PASS LEVELS WITH 850 MB TEMPS AROUND -6 TO -7 C. SO FAR SNOW
AMOUNTS ARE RUNNING BEHIND...BUT STILL EXPECT TO HIT WINTER WEATHER
ADVISORY CRITERIA WITH STORM TOTALS OF 8 TO 16 INCHES BY EARLY SUN.

NO RELIEF IN SIGHT AS SUNDAY LOOKS RATHER ACTIVE. MESOSCALE MODELS
DEVELOP A STRONG SURFACE LOW OVER THE OFFSHORE WATERS LATE SUN
MORNING THAT WILL WHIP NE INTO SOUTHERN B.C. BY THE AFTERNOON. AS
FOR THE TRACKING OF THE LOW...LATEST MODEL RUNS SHOWING A DEEPER 975
MB LOW...BUT IT IS ALSO TRACKING FARTHER NORTH. THE 18Z NAM12
SHOWS THE LOW MOVING INLAND AROUND CENTRAL VANCOUVER ISLAND AS
OPPOSED TO THE WA NORTH COAST ON THE 12Z RUN. THE POTENTIAL IS STILL
THERE FOR STRONG WINDS ACROSS THE REGION SO WILL CONTINUE WITH A
HIGH WIND WATCH FOR THE WA COAST. STRONG WINDS MAY ALSO DEVELOP
ACROSS THE INTERIOR DURING THE AFTERNOON WITH POSSIBLE WIND ADVISORY
CONDITIONS WITH GUSTS NEAR 50 MPH. WINDS SHOULD EASE LATE SUN
EVENING WITH THE LOW FILLS AND HEADS FARTHER INLAND INTO SOUTHERN
B.C. UPPER TROUGH REMAINS OVER THE REGION SO WILL CONTINUE TO SEE
SHOWERS.

COOL AND SHOWERY WEATHER CONTINUES INTO MON AS THE 140 KT POLAR JET
LIES OVER THE WA/ORE BORDER. EXPECT ABOVE NORMAL POPS AND TEMPS
BELOW THE CLIMO NORMS.

.LONG TERM...BY MID WEEK THE POLAR JET STREAM WILL START TO MIGRATE
BACK NORTH INTO SOUTHERN B.C. AS A RESULT WILL START TO SEE RISING
HEIGHTS AND SLIGHTLY WARMER CONDITIONS ACROSS THE REGION.
HOWEVER...THE GFS DOES NOT SHOW MUCH AMPLIFICATION IN THE 500 MB
HEIGHTS WITH NEARLY ZONAL FLOW ALOFT. AS A RESULT MAY STILL SEE SOME
PRECIP ACROSS THE REGION AS UPPER LEVEL SHORT WAVE TROUGHS CLIP THE
STATE. WILL KEEP POPS IN THE FORECAST THROUGH THE END OF THE WEEK AS
BOTH THE GFS AND EURO SHOW AN UPPER LEVEL TROUGH DIGGING OFFSHORE. 33

&&

.AVIATION...AN UPPER TROF AND ASSOCIATED CDFNT WERE STILL POISED TO
MOVE ACROSS WRN WA LATE THIS AFTERNOON AND EVENING. THE FRONT WAS
CURRENTLY ABOUT 75 NM OFFSHORE...AND WAS MOVING RAPIDLY EWD. EXPECT
THIS FRONT TO BE E OF THE CASCADES BY 06Z.

MEANWHILE...STRONG WLY ALOFT ALOFT AND MODERATELY STRONG...LOW
LEVEL...ONSHORE FLOW WILL PERSIST. A STRONG FRONTAL SYSTEM IS
EXPECTED TO IMPACT THE AREA ON SUNDAY. CIGS WILL GENERALLY BE IN THE
1-3K FT RANGE BUT MAY IMPROVE SLIGHTLY LATE TONIGHT OR EARLY SUNDAY
AS THE LOW LEVEL FLOW BRIEFLY BECOMES OFFSHORE.

KSEA...CIGS WILL GENERALLY REMAIN IN THE 1500 TO 3K FT RANGE THROUGH
MUCH OF TONIGHT BUT MAY LIFT INTO THE 3-5K FT RANGE LATE TONIGHT OR
EARLY SUNDAY AS LOW LEVEL WINDS BACK AHEAD OF THE SUNDAY SYSTEM.
WINDS WILL REMAIN SLY 10 TO 15 KT WITH GUSTS NEAR 25 KT...
DIMINISHING OVERNIGHT. FROPA IS ANTICIPATED ABOUT 03Z. RAIN WILL
OCCASIONALLY REDUCE THE VISIBILITY DOWN TO 3 OR 4SM TIL ABOUT 06Z.

CONCERNED ABOUT THE POTENTIAL FOR LOW LEVEL WIND SHEAR AT KSEA
SUNDAY MORNING AS WINDS WILL BE LIGHT SE AT THE SURFACE BUT SLY
ABOUT 30 KT JUST ABOVE...THUS WILL MENTION LOW LEVEL WIND SHEAR
IN THE UPCOMING TAF PACKAGE.

&&

.MARINE...A COLD FRONT NOW ABOUT 75 NM W OF THE COAST WILL MOVE
ONSHORE LATE THIS AFTERNOON OR EARLY EVENING. THIS FRONT SHOULD BE
E OF THE CASCADES BY LATER THIS EVENING. EXPECT A STRONGER FRONTAL
SYSTEM TO MOVE ACROSS THE AREA ON SUNDAY FOR THE POTENTIAL OF GALE
FORCE WINDS ACROSS ALL WATERS...ALTHOUGH STORM FORCE WINDS ARE
POSSIBLE OVER THE COASTAL WATERS. AN ACTIVE WEATHER PATTERN WILL
THEN PERSIST MON AND TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE OLYMPICS
     AND CASCADES TIL 6 AM PDT SUNDAY.

     A HIGH WIND WATCH REMAINS IN EFFECT FOR THE COAST FOR SUNDAY
     AFTERNOON AND EVENING.

PZ...SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS.

     STORM WATCH IN EFFECT FOR THE COASTAL WATERS SUNDAY.

     GALE WATCH IN EFFECT FOR THE REMAINING WATERS SUNDAY.

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