Lightning Strike in Washington, November 4, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 AM PST TUE NOV 4 2008

.SYNOPSIS...A LOW PRESSURE SYSTEM OVER SOUTHEAST WASHINGTON THIS
MORNING WILL MOVE AWAY FROM THE AREA. STRONG ONSHORE FLOW
INTERACTING WITH THE TERRAIN BEHIND THIS LOW WILL BRING SHOWERS AND
A CONVERGENCE ZONE TO THE CENTRAL PUGET SOUND AREA THROUGH THIS
EVENING. WEAK HIGH PRES WILL BUILD INTO THE AREA TONIGHT AND SHIFT
EAST WED. A WARM FRONT WILL ARRIVE WEDNESDAY NIGHT AND THURSDAY.
ANOTHER FRONTAL SYSTEM IS EXPECTED FRIDAY. A COLD FRONT WILL MOVE
THROUGH THE AREA SATURDAY MORNING.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS THE DEEP LOW THAT MOVED INTO
SW OREGON LATE MON NOW AROUND LEWISTON ID AND MOVING ENE. THE BACK
EDGE OF THE PRECIPITATION SHIELD ASSOCIATED WITH THIS LOW IS NOW
MOVING INTO THE CASCADES AND A CONVERGENCE ZONE APPEARS TO BE
FORMING AROUND SEATTLE...THOUGH PRES GRADIENTS ARE STRONG ENOUGH
THAT IT IS BEING SHUNTED INTO THE CASCADES. THE CONVERGENCE ZONE
WILL BUILD BACK TO THE WEST THIS AFTERNOON AND EVENING AS ONSHORE
FLOW GRADUALLY RELAXES. A SECOND CONVERGENCE ZONE ALSO APPEARS TO BE
FORMING AROUND WESTERN SKAGIT COUNTY AND IT SHOULD ALSO BUILD BACK
TO THE WNW TOWARD SE VANCOUVER ISLAND AS GRADIENTS RELAX TODAY.
MESOSCALE MODELS SHOW THESE TRENDS WELL.

PRECIPITATION HAS TURNED TO SNOW AT SNOQUALMIE PASS. WHILE MOST
MOUNTAIN SITES HAVE NOT YET STARTED GIVING PRECIPITATION
DATA...TRAFFIC CAMERAS SHOW SNOW FALLING AT ALL OF THE PASSES. WILL
MAINTAIN THE SNOW ADVISORY THROUGH 3 PM THIS AFTERNOON AS
SHOWERS...FOLLOWED BY CONVERGENCE ZONE ACTIVITY...KEEP THINGS GOING.
A CLUSTER OF SHOWERS IN THE OFFSHORE WATERS APPEARS TO BE HEADED
TOWARD THE S WA COAST AND NW OREGON WITH CONVECTIVE ACTIVITY
SUPPRESSED OVER THE W WA WATERS IN THE WAKE OF THE LOW. THE 12Z
NAM12 CONFIRMS SATELLITE TRENDS THAT TAKE THIS ACTIVITY IN JUST TO
THE SOUTH OF THE FORECAST AREA. CONVECTIVE AVAILABLE POTENTIAL
ENERGY REACHES NEAR 400 J/KG AROUND HOQUIAM THIS AFTERNOON...BUT
EXCEEDS 175 J/KG WITH THE CONVERGENCE ZONE ACTIVITY IN THE NORTH
INTERIOR. BEST SHOT OF A ONE-CLAP TSTM AT THIS POINT APPEARS TO BE
THIS AFTERNOON JUST SOUTH OF THE FORECAST AREA.

WEAK HIGH PRES WILL BUILD INTO THE AREA OVERNIGHT THEN SHIFT E OF
THE CASCADES WED. SCATTERED SHOWER ACTIVITY WILL END THIS EVENING AS
THE HIGH BUILDS IN AND THE AIR MASS STABILIZES. A WARM FRONT
EXTENDING E AND SE OF A LOW NEAR 45N/160W WILL MOVE NE TOWARD THE
AREA LATE WED. WHILE MODEL QPF WITH THIS WARM FRONT ARE LIGHTER THAN
PREVIOUS SOLUTIONS...THEY CONTINUE TO SHOW RAIN DEVELOPING FROM THE
W WED NIGHT AND CONTINUING THRU THU MORNING. ONCE SW WIND ALOFT
REACHES ABOUT 45 KT AROUND 850 MB MIDDAY THU...THE S FACING SLOPES
OF THE OLYMPICS...THE COAST...AND POTENTIALLY THE NORTH CASCADES
WILL SEE A 18-24 HOUR PERIOD OF HEAVY PRECIPITATION. AFTER
CONSULTING WITH THE RIVER FORECAST CENTER IN PORTLAND TODAY...WILL
POSSIBLY ISSUE A FLOOD POTENTIAL OUTLOOK FOR PORTIONS OF THE
FORECAST AREA LATER THU INTO FRI. ALBRECHT

.LONG TERM...PREVIOUS LONG TERM DISCUSSION FOLLOWS...RAIN JUST
STARTS TO TAPER OFF THU NIGHT BUT THEN INCREASES FRIDAY WITH ANOTHER
WAVE ON THE BAROCLINIC ZONE. NAM HAS ARND A 1011MB LOW...BUT NOT
DEEPENING...AND THEN RIDING UP THE BAROCLINIC ZONE TO THE WA WATERS.
GFS SHOWS ONLY A TRIPLE POINT FRIDAY BUT NO CLOSED LOW ASSOCIATED
WITH THE FNTL SYS. FINALLY A COLD FROPA COMES SAT MORNING. NO
ADJUSTMENTS WERE MADE TO THE EXTENDED FCSTS WITH THE EXCEPTION OF
THE SNOW LEVELS WHICH WERE KNOCKED DOWN A BIT. LOOKS LIKE A COOLER
PATTERN WITH SNOW LEVEL PROBABLY AVERAGING 4000FT STARTING SAT. 19

&&

.AVIATION...NEGATIVE TILT UPPER LEVEL TROUGH AXIS LIES ACROSS WA
THIS MORNING. DISTINCT BACK EDGE OF THE DEFORMATION ZONE SEEN ON
SATELLITE AND RADAR WITH THE BULK OF THE PRECIP LOCATED ALONG AND
E/NE OF THE I-5 CORRIDOR. RAIN WILL CONTINUE TO MOVE EASTWARD INTO
THE CASCADES THIS MORNING WITH SNOW DOWN TO AT LEAST 3000 FT.
SCATTERED SHOWERS EXPECTED ACROSS THE AREA THIS AFTERNOON AS CUMULUS
FIELD DRIFTS IN ALONG THE W/NW FLOW. AIRMASS WILL REMAIN COOL AND
UNSTABLE WITH POSSIBLE ISOLATED THUNDERSTORM NEAR THE CENTRAL COAST.

KSEA...A BREAK FROM THE STEADY RAIN EXPECTED THIS MORNING AS
DEFORMATION BANDS SHIFTS TOWARD THE E. CEILINGS WILL GRADUALLY
IMPROVE TO VFR THIS AFTERNOON. VICINITY SHOWERS WILL REMAIN IN THE
FORECAST THROUGH THIS EVENING AS MODELS SHOW A CONVERGENCE ZONE
DEVELOPING. WINDS WILL REMAIN SOUTHERLY AT 10-15KT...THEN EASING TO
10KT OR LESS THIS EVENING. 33

&&

.MARINE...BROAD 999 MB SFC LOW PRES REMAINS EAST OF THE CASCADES
THIS MORNING AND WILL CONTINUE TO TRACK NE. PRES GRADIENT REMAIN
STRONG THROUGH THE STRAIT OF JUAN DE FUCA WITH WINDS 20 TO 30 KT
EXPECTED THROUGH THIS EVENING. WEAK SFC HI PRES RIDGE WILL BUILD
ALONG THE COAST WED MORNING...WITH A FLOW REVERSAL DURING THE
AFTERNOON AS OFFSHORE SOUTHEASTERLIES DEVELOP AHEAD ON INCOMING WARM
FRONT. THIS SYSTEM MAY PRODUCE GALE FORCE WINDS OVER THE COASTAL
WATERS ON THU. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY FOR THE WEST SLOPES OF THE CASCADES
      THROUGH 3 PM THIS AFTERNOON.
PZ...SMALL CRAFT ADVISORY COAST ALL WATERS EXCEPT PUGET SOUND.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

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