Gale Warning 81, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1045 AM PST MON DEC 29 2008

UPDATED MARINE WARNING LIST.

.SYNOPSIS...AN ENERGETIC JET STREAM WILL STEER SUCCESSIVELY STRONGER
PACIFIC STORMS ACROSS THE REGION THROUGH THURSDAY. THE FIRST SYSTEM
WILL MOVE ACROSS THE AREA TODAY...AND WILL BE FOLLOWED BY A STRONGER
ONE TUESDAY NIGHT. THIS STORM WILL BRING SIGNIFICANT SNOWFALL TO THE
MOUNTAINS. THE SYSTEM THAT IS ANTICIPATED TO AFFECT THE REGION ON
THURSDAY MAY BRING SIGNIFICANT RAINFALL TO THE REGION AS WELL AS
WIDESPREAD STRONG WINDS.

&&

.SHORT TERM...LATEST IR SATELLITE IMAGERY INDICATES CLOUD TOP
BRIGHTENING AS A DEVELOPING DEFORMATION BAND LIFTS ACROSS THE AREA
THIS MORNING. A COUPLE LIGHTNING STRIKES WERE ALSO NOTED EARLIER
ALONG THE COAST INDICATING UNSTABLE CONDITIONS. THE SURFACE LOW
TRACKING INTO THE N WA COAST SHOULD DEEPEN TO ABOUT 998 MB AS IT
CROSSES THE N INLAND WATERS THIS AFTERNOON. SLY WINDS SHOULD REALLY
PICK UP THIS AFTERNOON BUT THE MM5NAM/MM5GFS DIFFER ON THE STRENGTH
OF WINDS. GIVEN THE LATEST SATELLITE TRENDS POINTING TOWARD A
DEEPENING SYSTEM...THE NAM SOLUTION IS PREFERRED. THIS MODEL SHOWS A
SOLID WLY SURGE DOWN THE STRAIT THIS AFTERNOON WITH 35 KT EXTENDING
ALONG THE ERN STRAIT INTO WHIDBEY ISLAND. THE SAN JUANS ARE ON THE
EDGE BUT WILL LIKELY ADD THEM IN TO A WIND ADVISORY FOR THIS
AFTERNOON.

MM5 QPF AMOUNTS ARE RUNNING AROUND .5 TO 1 INCH LIQUID OVER THE
MOUNTAINS THROUGH TONIGHT. THIS SUPPORTS THE 7 TO 14 INCH AMOUNTS
INDICATED IN THE FORECAST THROUGH 4 AM. WILL LEAVE THE WINTER
WEATHER ADVISORY AS IS. SNOW LEVELS WILL FALL OFF AS COLDER AIR
ALOFT FILTERS IN. 850 MB TEMPS GET DOWN TO -7C WHICH COULD RESULT IN
SOME MIXED RAIN/SNOW IN HEAVIER SHOWERS. I DONT SEE A CLEAR PSCZ
SIGNATURE ON THE MODELS BUT CANT RULE IT OUT IN POST FRONTAL FLOW.
IF WE DO SEE ONE...SOME WET SNOW COULD FALL ON THE HILL TOPS IN
SNOHOMISH COUNTY.

THE NEXT STRONGER SYSTEM ARRIVES TUE NIGHT AND WED WITH RAIN AND
VERY WINDY CONDITIONS. MODELS TRACK A 985 MB SURFACE LOW INTO N
VANCOUVER ISLAND WITH A STRONG TRAILING COLD FRONT TO MOVE ACROSS
WRN WA TUE NIGHT. THIS SYSTEM COULD ALSO BE WORTHY OF A WIND
ADVISORY...FIRST FOR SE WINDS FROM WHIDBEY ISLAND TO THE N
INTERIOR...AND SECOND FOR THE WLY SURGE DOWN THE STRAIT TO FOLLOW
THE LOW. WILL NEED TO KEEP ANY EYE ON THIS. OROGRAPHIC FLOW INTO THE
MOUNTAINS WILL BE IMPRESSIVE FOR A 12-18 HOUR PERIOD WED WHICH MAY
WARRANT A WINTER STORM WATCH. WILL EVALUATE THIS AGAIN DURING THE
AFTERNOON AND POSSIBILITY ISSUE A WATCH WITH THE AFTERNOON FORECAST
PACKAGE.

JUST A QUICK LOOK AT THE NEW 12Z GFS SHOWS A 969MB LOW MAKING
LANDFALL ON S VANCOUVER ISLAND FRI MORNING. THIS IS A DANGEROUS
TRACK AND COULD RESULT IN HIGH WINDS ACROSS MUCH OF THE AREA.
HOWEVER..THIS IS FAR ENOUGH OUT IN TIME TO SIMPLY MONITOR AT THIS
POINT.

MERCER

.LONG TERM...
PREVIOUS DISCUSSION FOLLOWS...THE THU SYSTEM APPEARED QUITE
STRONG...AND IF THE GFS SOLUTION PREVAILS THEN WE MAY NEED TO
CONSIDER THE POTENTIAL FOR FLOODING ON THE SKOKOMISH RIVER. THE SNOW
LEVEL IS ANTICIPATED TO RISE TO NEAR 5K FT AND WITH STRONG UPSLOPE
FLOW...RAINFALL RATES COULD END UP QUITE INTENSE AS THIS SYSTEM
APPEARED QUITE WET. THE GFS SOLUTION WAS INDICATING UP TO 1.5 INCHES
LIQUID ON THE OLYMPICS THU AND UP TO 2.5 INCHES THU NIGHT. WINDS
WILL ALSO BECOME QUITE STRONG AGAIN ACROSS THE CWA WITH HIGH WINDS
POSSIBLE ON THE COAST AND AT LEAST WIND ADVISORY CRITERIA SPEEDS
ELSEWHERE.

BEYOND THU...THE OVERALL PATTERN APPEARED UNSETTLED...HOWEVER THE
UNCERTAINTY IN THE MODELS INCREASES DURING THIS PERIOD. THUS IT
WOULD BE PRUDENT TO GO WITH PERSISTENCE...THAT IS WET AND
UNSETTLED...FOR THE TIME BEING.

&&

.AVIATION...SOUTHWEST FLOW ALOFT WILL BECOME NORTHWEST BY LATE THIS
EVENING AS AN UPPER LEVEL TROUGH APPROACHING THE COAST THIS MORNING
MOVES EAST OF THE CASCADES. SHORTWAVE TROUGH IS UNDERGOING RAPID
INTENSIFICATION THIS MORNING AS SEEN ON SATELLITE WITH THE TROUGH
AXIS STILL OFFSHORE. RAIN WILL TURN TO SHOWERS THIS AFTERNOON AS THE
LOW PASSES TO THE EAST. WITH COLDER AIR ALOFT MOVING IN THE AIRMASS
WILL FURTHER DESTABILIZE THIS AFTERNOON. AN ISOLATED THUNDERSTORM
CAN NOT BE RULED OUT THIS AFTERNOON AS 500 MB TEMPS PLUNGE TO -36C
BY 00Z. CEILINGS IN THE CENTRAL SOUND THAT HAVE MANAGED TO STAY
RELATIVELY HIGH THIS MORNING...WILL COME DOWN TO MVFR LEVELS THIS
AROUND 18Z. AS THE SURFACE LOW PASSES AROUND THE SAN JUANS THIS
AFTERNOON...GUSTY SW WINDS WILL AFFECT SEA-TAC AREA AND SOUTHWARD
UNTIL EASING OFF AFTER 3Z.

KSEA...CIGS HAVE LOWERED TO NEAR 030 WITH STEADY RAIN THIS MORNING.
CEILING RANGE OF 015-030 SEEMS REASONABLE WITH RAIN THROUGH EARLY
AFTERNOON AS SURFACE LOW PASSES NORTH AND EAST OF THE AREA. LATEST
MESO MODELS ARE STILL SHOW AN EXPECTED CONVERGENCE ZONE AROUND THE
PAE AREA NEAR 00Z THIS AFTERNOON. SOUTH TO SOUTHEAST WINDS SHOULD
PICK UP TO AROUND 10 KNOTS LATER THIS MORNING...THEN BECOME
SOUTHWEST 10 TO 20 KNOTS...GUSTING TO 25 PLUS KNOTS AFTER 19Z.
DAMICO

&&

.MARINE...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR ALL WATERS.
SURFACE LOW PRES OFF QUILLAYUTE WILL PASS OVER THE EAST ENTRANCE
AFTER 18Z. RAPID PRESSURE RISES ON THE COAST WILL GIVE A BRIEF BURST
OF WESTERLIES EARLY THIS AFTERNOON. MM5 NAM SHOWS GALES FOR EAST
ENTRANCE/ADMIRALTY INLET...WILL CONSIDER WHETHER TO ISSUE GALE
WARNING FOR THESE AREAS WITHIN THE NEXT HOUR. AS UPPER TROUGH PASSES
OVER THE AREA EARLY THIS AFTERNOON DESTABILIZING THE ATMOSPHERE
...EXPECT GUSTY WINDS FOR ALL AREAS. DAMICO

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE OLYMPICS
     AND CASCADES UNTIL 4 AM PST TUE.
     WIND ADVISORY EASTERN STRAIT OF JUAN DE FUCA...ADMIRALTY
     INLET...WESTERN SKAGIT COUNTY...SAN JUAN COUNTY UNTIL 7 PM THIS
     EVENING.

PZ...GALE WARNING COASTAL WATERS...CENTRAL AND EASTERN
     STRAIT...AND ADMIRATELY INLET.
     SMALL CRAFT ADVISORY ALL OTHER WATERS.
     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS.

WEATHER.GOV/SEATTLE