Small Craft Advisory 4, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
919 AM PST SAT JAN 5 2013

.SYNOPSIS...PRECIPITATION WILL INCREASE LATER TODAY AHEAD OF A
WEAK LOW PRESSURE SYSTEM THAT WILL MOVE ACROSS THE REGION
TONIGHT. HIGH PRESSURE ALOFT MAY PROVIDE MUCH OF THE AREA WITH A
BRIEF DRY SPELL SUNDAY MORNING BEFORE PRECIPITATION INCREASES
AHEAD OF A WARM FRONT. THIS FRONT WILL SWEEP ACROSS THE REGION
LATE SUNDAY NIGHT AND WILL BE FOLLOWED BY A WEAKENING COLD FRONT
ON MONDAY. LOCALLY HEAVY PRECIPITATION IS POSSIBLE ON MONDAY ALONG
WITH GUSTY WINDS.

&&

.SHORT TERM...
THERE WERE AREAS OF LIGHT PRECIPITATION ACROSS THE AREA THIS
MORNING. THE PRECIP APPEARED TO BE ASSOCIATED WITH THE TRAILING
END OF A RELATIVELY MOISTURE STARVED...DISSIPATING WARM FRONT
THAT WAS PRIMARILY ALOFT. IN GENERAL...ANTICIPATE A CLOUDY DAY
TODAY WITH OCCASIONAL DRIPS OR SPRINKLES...WITH FLURRIES OR LIGHT
SNOW IN THE MOUNTAINS.

THERE WILL BE AN UPSWING IN THE PRECIP LATE TODAY OR EARLY THIS
EVENING AHEAD OF AN UPPER TROF AND ASSOCIATED WEAKENING OCCLUDED
FRONT. BOTH WILL MOVE ACROSS THE FORECAST AREA OVERNIGHT. IT
APPEARED THAT THE BULK OF THE PRECIP WAS OCCURRING AHEAD OF THE
FRONT/UPPER TROF.

HIGH PRESSURE ALOFT WILL PREVAIL OVER THE REGION ON SUNDAY. THERE
MAY BE A BRIEF DRY SPELL ACROSS MUCH OF THE AREA SUNDAY MORNING...
HOWEVER INCREASING MOIST ONSHORE FLOW COMBINED WITH WARM AIR
ADVECTION DURING THE DAY WILL RESULT IN AN UPSWING IN THE PRECIP...
ESPECIALLY IN THE AFTERNOON.

LOOK FOR WET WEATHER SUNDAY NIGHT AND MON. A WARM FRONT IS EXPECTED
TO MOVE ACROSS THE REGION LATE SUNDAY NIGHT AND WILL BE FOLLOWED
BY A WEAKENING COLD FRONT LATE MON MORNING OR EARLY AFTERNOON.
LOCALLY HEAVY PRECIP IS ANTICIPATED ON MON...ESPECIALLY IN THE
MOUNTAINS WHERE STRENGTHENING OROGRAPHIC LIFT WILL LIKELY ENHANCE
PRECIP RATES. ANOTHER ITEM TO WATCH WILL BE THE POSSIBILITY OF
FREEZING RAIN OR A WINTRY MIX IN THE LOWER CASCADE PASSES /SUCH AS
SNOQUALMIE PASS/ ON MON BEFORE THE ONSHORE FLOW KICKS IN. IT WILL
ALSO BECOME BREEZY TO LOCALLY WINDY ON MON.

.LONG TERM FROM THE PREV DISCUSSION...
IT LOOKS LIKE WED WILL BE THE TRANSITION DAY FROM WARM/WET TO A
COOL/WET PATTERN AS A DEEP UPPER LEVEL LOW SWINGS IN. SNOW LEVELS
START TO PLUMMET AS THE FLOW ALOFT TURNS TOWARD THE NORTH OR
NORTHWEST. MODELS SHOW A FEW ISOLATED SHOWERS AND THE LOWLANDS
COULD SEE A FEW RAIN/SNOW SHOWERS AS WELL...ESPECIALLY WED NIGHT
AND THU. THE AIR MASS IS A BIT DRIER BY THU AND MAYBE FRI TOO BUT
OVERALL CONFIDENCE IS LOW THAT FAR IN THE FORECAST. 33

&&

.HYDROLOGY...
A SERIES OF WET PACIFIC STORMS WILL IMPACT THE REGION THE FIRST
HALF OF THE UPCOMING WEEK. THE MON AND TUE SYSTEMS WILL BE THE
ONES TO WATCH AS THEY HAVE THE POTENTIAL TO PRODUCE LOCALLY HEAVY
PRECIP. THIS COMBINED WITH RISING SNOW LEVELS ON MON COULD RESULT
IN SHARP RISES ON AREA RIVERS...ESPECIALLY THOSE DRAINING FROM
LOWER ELEVATIONS SUCH AS THE CHEHALIS AND SKOKOMISH.

A TRANSITION TO A COOLER PATTERN WILL REDUCE THE THREAT OF RIVER
FLOODING TOWARD THE END OF NEXT WEEK. 33

&&

.AVIATION...SOUTHWESTERLY FLOW ALOFT TODAY WILL BECOME WEST OR
NORTHWEST TONIGHT AS AN UPPER TROUGH AND ASSOCIATED FRONTAL SYSTEM
MOVE ONSHORE. AIR MASS MOIST AND STABLE WITH MID AND HIGH LEVEL
MOISTURE THIS MORNING. INCREASING LOW LEVEL MOISTURE THIS AFTERNOON
INTO THIS EVENING AS AN APPROACHING FRONT SPREADS RAIN ONSHORE.
FRONT REACHING THE COAST AROUND MIDNIGHT...CASCADES AROUND 12Z
SUNDAY.

KSEA...SOUTHEAST WIND 4-8 KNOTS. RAIN DEVELOPING IN THE AFTERNOON
WITH LOWERING CEILINGS. SCHNEIDER

&&

.MARINE...A FRONTAL SYSTEM WILL BRING SMALL CRAFT ADVISORY SOUTHERLY
WINDS TO MOST WATERS TODAY AND TONIGHT. THERE WILL ALSO BE SOME 10
TO 14 FOOT SWELL MOVING INTO THE COASTAL WATERS TONIGHT.

ANOTHER FRONT WILL MOVE THROUGH THE AREA LATER SUNDAY WITH
ADDITIONAL FRONTS AFFECTING THE WATERS MONDAY THROUGH WEDNESDAY.
SMALL CRAFT ADVISORY LEVEL WINDS ARE EXPECTED OVER MOST OF THE
WATERS WITH THE FRONTS. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS...
     ENTRANCES TO THE STRAIT OF JUAN DE FUCA...ADMIRALTY INLET...
     AND NORTHERN INLAND WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS FROM 7 PM THIS EVENING UNTIL 6 AM SUNDAY.

&&

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