Flash Flood and High Wind in Washington, December 14 to 15, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PST THU DEC 14 2006

.SYNOPSIS...A STRONG FRONT WILL MOVE OVER WESTERN WASHINGTON TODAY.
A DEEP LOW PRESSURE SYSTEM WILL REACH VANCOUVER ISLAND THIS EVENING.
EXPECT DAMAGING WINDS ACROSS WESTERN WASHINGTON TONIGHT....STRONG
WESTERLY WINDS WILL REACH THE COAST AROUND 9PM AND SPREAD DOWN THE
STRAIT OF JUAN DE FUCA AROUND MIDNIGHT. A SURGE OF SOUTHWESTERLY
WINDS WILL MOVE THROUGH THE INLAND PORTION OF WESTERN WASHINGTON
AROUND MIDNIGHT.

&&

.SHORT TERM...FOR THE STRONGEST WINDS I HAVE ADDED SOME TIMING
DETAILS TO THE SYNOPSIS ABOVE AND WILL INCORPORATE THOSE INTO THE
THE MORNING RETRANSMISSION OF THE HIGH WIND WARNING. IT WILL BE
WINDY WITH THE FRONT ITSELF LATER TODAY...BUT THE STRONGEST WINDS
ARRIVE WITH THE BENT BACK OCCLUSION AND RAPID PRESSURE RISES
TONIGHT. THE NAM IS A LITTLE WEAKER AND WOULD ONLY SUPPORT A WIND
ADVISORY TYPE EVENT FOR SOME ZONES...BUT STILL THE RIGHT IDEA WITH
THE HIGHEST WINDS ON THE COAST AND SOUTHWEST/CHEHALIS GAP. THE GFS
IS JUST LIKE PREVIOUS RUNS AND SHOWS A VERY STRONG GRADIENT SETTING
UP TONIGHT AS THE LOW AND BENT BACK TROF PLOW INTO THE AREA. THE
WESTERLY SURGE IN THE BENT BACK OCCLUSION IS ESPECIALLY IMPRESSIVE
ON THE MORNING RUN OF THE MM5GFS AND IS SIMILAR TO MANY OF THE MM5
SOLUTIONS OVER THE PAST COUPLE DAYS: PEOPLE ON THE COAST AND
ESPECIALLY MARINE INTERESTS SHOULD RUSH TO COMPLETION PREPARATIONS
FOR THESE WINDS AS THEY ARE EXPECTED TO BE THE STRONGEST WESTERLY
WINDS SO FAR THIS FALL/WINTER. I WOULD EXPECT THAT SURGE TO ARRIVE
GRAYS HARBOR AROUND 06Z PLUS OR MINUS A COUPLE HOURS. THE SLY WINDS
WITH THE FRONT ARE QUITE STRONG TOO...BUT NOT REALLY MUCH DIFFERENT
THAN WINDS WE HAVE SEEN ALREADY SEVERAL TIMES THIS SEASON. IT IS THE
SURGE IN THE BENT BACK TROF THAT IS IMPRESSIVE.

FOR THE INLAND AREAS...STRONGEST WINDS WILL START AROUND MIDNIGHT
WITH THE PDX-BLI GRADIENT INCREASING TO ARND 20MB BY 12Z ON GFS. I
AM COMFORTABLE WITH A HIGH WIND WARNING FOR ALL OF WRN WA...IT WOULD
NOT BREAK MY HEART TO SEE THE NAMS WEAKER GRADIENTS VERIFY...BUT WE
OUGHT TO BE PREPARED FOR THE GFS SOLUTION WHICH GIVES US THE
STRONGEST GRADIENT OF THE YEAR SO FAR. THIS IS LIKELY TO BE A
STRONGER BUT MUCH SHORTER BURST OF WINDS FOR THE SEATTLE AREA...THE
SUSTAINED VERY BLUSTER WINDS OF YESTERDAY ESSENTIALLY LASTED ALL
DAY...I THINK TONIGHT WE ARE LOOKING AT A MUCH SHORTER BURST OF
WINDS THAT HAVE A GOOD CHANCE OF BEING MORE DAMAGING IN TERMS OF
NUMBER OF TREES DOWN A SUCH. THEN...AROUND DAYBREAK ON FRIDAY THE
STRONG CONVERGENCE OF SWLY WINDS COMING AROUND THE OLYMPICS TO THE
SOUTH...AND THE STRONG WESTERLY SURGE THROUGH THE STRAIT...WILL MEET
UP AND CAUSE THE WIND TO DROP OFF DRAMATICALLY IN THE
AREA...ESPECIALLY JUST NORTH OF SEATTLE IN THE PSCZ AREA. FARTHER
NORTH...STRONG WEST WINDS ARE LIKELY TO CONTINUE TO CROSS WHIDBEY
ISLAND AND IT WILL TAKE A WHILE FOR THE WESTERLIES TO DIE BACK
FRIDAY. MM

&&

.LONG TERM...THE LONGER RANGE MODELS ARE IN GENERAL AGREEMENT THAT
SUN THROUGH WED WILL BE A RELATIVELY QUIET PERIOD. AN UPPER RIDGE
OVER THE AREA SUN AND MON WILL PROBABLY GIVE WAY TO A FRONTAL SYSTEM
AROUND TUE AND THEN REBOUND ON WED. MCDONNAL

&&

.AVIATION...WARM FRONT JUST OFF THE COAST THE COAST GIVING N/NE
OFFSHORE WINDS. WINDS WILL SHIFT AROUND TO THE SOUTH MOST AREAS AFT
20Z AS THE SFC WARM FRONT LIFTS THROUGH.  WINDS WILL INCREASE
STEADILY THEREAFTER.  STRONGEST WINDS WILL SPREAD INTO INLAND ROUTES
00Z-03Z...WITH SFC WIND GUSTS TO 70 KT POSSIBLE TIL 10Z...HIGHEST
NEAR THE COAST AND ROUTE PORTION NEAR THE EAST ENTRANCE OF THE
STRAIT.

AT KSEA...RAIN WILL CONTINUE TO INCREASE WITH LOW MVFR CIGS DVLPG BY
20Z. N/NE WINDS 8-12 KT WILL CONTINUE THROUGH ARND 20Z AHEAD OF A
WARM FRONT.  WINDS WILL SHIFT SLY AFTER 20Z AND INCREASE SLOWLY
THROUGH THE AFTERNOON. THIS WILL POSE THE POTENTIAL FOR LOW LEVEL
WIND SHEAR AS WINDS WILL BE INCREASING FROM THE S JUST ABOVE THE
SURFACE. AROUND 03Z...AHEAD OF THE OCCLUDED FRONT...WINDS WILL
BECOME SLY 15-25 KT. FROPA IS EXPECTED AROUND 04-05Z...WITH S TO SW
WINDS RAPIDLY INCREASING TO 30-40 KT...WITH GUSTS AS HIGH AS 55 KT.
WINDS WILL SLOWLY SLACK OFF AFT 10Z. DTM
&&

.MARINE...ALONG WITH STORM WARNINGS...SEAS ON THE COAST WILL BUILD
VERY HIGH...A HIGH SURF WARNING WILL REPLACE THE ADVISORY AND
COASTAL FLOOD WATCH THIS MORNING.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
1. HIGH WIND WARNING FOR MOST OF WESTERN WASHINGTON (INCLUDES THE
OLYMPICS BUT NOT THE CASCADES) THIS AFTERNOON THROUGH FRI MORNING.
2. WINTER STORM WARNING FOR THE CASCADES NOON TODAY THROUGH NOON
FRI.
3. STORM WARNING ALL WATERS.
4. HIGH SURF WARNING FOR THE WASHINGTON COAST.

WEATHER.GOV/SEATTLE