Lightning Strike in Washington, December 9, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PST THU DEC 9 2010

.SYNOPSIS...MOIST WESTERLY FLOW ASSOCIATED WITH A DEEP UPPER LOW IN
THE GULF OF ALASKA WILL KEEP WESTERN WASHINGTON SHOWERY THROUGH
FRIDAY. HEAVY SNOW WILL CONTINUE TO FALL IN THE MOUNTAINS. AFTER A
RELATIVE BREAK LATE FRIDAY AND FRIDAY NIGHT...RAINY AND MILDER
WEATHER WILL DEVELOP OVER THE WEEKEND AND CONTINUE INTO EARLY NEXT
WEEK.

&&

.SHORT TERM...REGARDING THE WINTER STORM WARNING IN THE CASCADES...
OVERNIGHT MT BAKER HAD 14 INCHES OF NEW SNOW...PARADISE HAD 10
INCHES...AND THE PASSES HAD 4-6 INCHES. RADAR SHOWS PLENTY OF
SHOWERS AND BOTH THE NAM AND GFS SHOW SHOWERS CONTINUING INTO
FRIDAY. THE WINTER STORM WARNING WILL REMAIN IN EFFECT.

FRIDAY WILL HAVE A RELATIVE LULL IN THE WEATHER. THERE WILL STILL BE
SNOW SHOWERS IN THE MOUNTAINS AND SCATTERED RAIN SHOWERS OVER THE
LOWLANDS BUT THE TREND WILL BE TOWARD DRYING. FRIDAY NIGHT AND
SATURDAY MORNING LOOK PRETTY DRY. HIGHS TODAY AND FRIDAY WILL BE
AROUND 50 WITH OVERNIGHT LOWS AROUND 40.

MODELS CONTINUE TO SHOW A WARM AND WET EVENT DEVELOPING LATER
SATURDAY. RAIN WILL BEGIN OVER FAR SOUTHERN AREAS SATURDAY AFTERNOON
AND SPREAD OVER ALL OF WESTERN WASHINGTON SATURDAY NIGHT. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE STRONG WARM FRONT WILL
CONTINUE TO LIFT NORTHWARD SUNDAY AND SUNDAY NIGHT...WITH THE SNOW
LEVEL CLIMBING TO AROUND 7000 FT ACROSS THE ENTIRE FORECAST AREA.
THE COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL MOVE SOUTHEAST
ACROSS WESTERN WASHINGTON MONDAY. IT WILL BRING MORE RAIN BUT THE
COOLER AIR MASS BEHIND THE FRONT WILL BRING THE SNOW LEVEL DOWN TO
2500 FT OR SO ON TUESDAY. THE COOLER SHOWERY REGIME SHOULD CONTINUE
THROUGH THURSDAY. THE LONGER RANGE MODELS AGREE BROADLY ON THIS
SCENARIO. MCDONNAL

&&

.HYDROLOGY...IN THE SHORT TERM...A FLOOD WARNING REMAINS IN EFFECT
FOR THE SKOKOMISH RIVER. DUE TO A GAUGE MALFUNCTION...DATA HAVE BEEN
AVAILABLE ONLY SPORADICALLY. IT WAS A COUPLE TENTHS OF A FOOT ABOVE
FLOOD STAGE AT 7 AM AND REMAINING STEADY. IT WILL FALL BELOW FLOOD
STAGE LATER TODAY OR TONIGHT.

IN THE LONGER RANGE...MODELS CONTINUE TO SUPPORT THE IDEA THAT AN
EPISODE OF WARM AND WET WEATHER WILL START SATURDAY AND CONTINUE
THROUGH MONDAY. THE 00Z RUN OF THE GFS INTRODUCED EXTRA UNCERTAINTY
BY SHOWING THE HEAVIEST RAIN OVER THE CENTRAL AND SOUTH CASCADES.
THE SUBSEQUENT 06Z AND 12Z RUNS RETURNED TO THE MAIN NARRATIVE...
WHICH MOVES A WARM FRONT FROM SOUTH TO NORTH SATURDAY NIGHT AND
SUNDAY...AND A COLD FRONT FROM NORTHWEST TO SOUTHEAST MONDAY. IN
THIS SCENARIO THE HEAVIEST RAINFALL WOULD BE OVER THE OLYMPICS AND
NORTH CASCADES.

THE 12Z RUN OF THE NAM WAS SOMEWHAT WETTER OVER THE CENTRAL CASCADES
THAN MOST PREVIOUS RUNS...AND THE 00Z EURO MOVED THE FOCUS OF HEAVY
RAINFALL SOUTH OUT OF BRITISH COLUMBIA BUT STILL KEPT IT OVER THE
OLYMPICS AND NORTH CASCADES. MEANWHILE THE ENSEMBLE MEMBERS OF THE
GFS AND THE SREF DO NOT SHOW ANY REAL CHANGES FROM THIS MAIN IDEA.
THE ENSEMBLE BASED PROBABILISTIC QPF FROM HPC...BASED ON THE 00Z
GFS...SHOWS LESS THAN A 5 PERCENT CHANCE OF 4 INCHES IN ANY 24 HOUR
PERIOD.

IN GENERAL THE HIGH RESOLUTION OPERATIONAL RUNS OF THE MAIN FORECAST
MODELS ARE PROBABLY MORE RELIABLE THAN IN THE RELATIVELY LOW
RESOLUTION RUNS OF THE ENSEMBLE MEMBERS. THE UPSHOT IS THERE IS
SOMEWHAT MORE UNCERTAINTY IN WHERE THE AREAS OF HEAVY RAIN WILL BE.
THE OLYMPICS AND NORTH CASCADES SEEM LIKE THE LIKELIEST AREAS BY
FAR...BUT THERE IS SOME CHANCE HEAVY RAIN WILL ALSO FALL ON THE
CENTRAL CASCADES.

NOT PLANNING ANY CHANGES TO THE FLOOD POTENTIAL OUTLOOK THIS
MORNING. IT ALREADY HIGHLIGHTS ALL AREAS OF WESTERN WASHINGTON.

BASED ON THE DISCUSSION ABOVE...THERE IS STILL ONLY A VERY LOW RISK
OF FLOODING ON THE GREEN RIVER...BUT THE RISK IS NOT ZERO. BURKE

&&

.AVIATION...AREAS OF MVFR CIGS AND VSBY IN SHOWERS...MOIST SW FLOW
AND UNSTABLE AIR. THE SHOWERS ARE PROBABLY GOING TO BE MORE
WIDESPREAD THIS MORNING...THEN SOME MORE SUNBREAKS EARLY THIS
AFTERNOON...THEN I THINK CLOSING IN AGAIN LATE THIS AFTERNOON OR
EVENING. ISOLATED THUNDERSTORMS POSSIBLE...MAINLY ALONG THE COAST.
MTNS AND FOOTHILLS REMAIN MOSTLY OBSCURED. THE NAM HAS A MORE
ORGANIZED DISTURBANCE MOVING THRU WRN WA THIS EVENING WHICH COMES
FROM THE PATCH OF COLD TOWERING CU JUST OUTSIDE OF 130W AT 8AM THIS
MORNING. 19

KSEA...BANDS OF SHOWERS AND BREEZY AT TIMES...THE PATCH OF COLD
TOWERING CU JUST OUTSIDE OF 130W AT 8AM THIS MORNING WILL BE COMING
THRU WRN WA THIS EVENING SO I WROTE THE TAF WITH TEMPO 4SM SHRA
BKN020 02Z-06Z AND DEPENDING ON WHAT THE SATELLITE IMAGERY AND RADAR
SHOW THIS AFTERNOON THAT COULD CHANGE TO VCTS BKN020CB THIS
EVENING...SOMETHING I MIGHT DO IN THE 21Z TAF. 19

&&

.MARINE...BLUSTERY ONSHORE FLOW...SHOWERS GIVE GUSTY WINDS...CHANCE
OF A THUNDERSTORM AGAIN...ESPECIALLY COAST LATE AFTERNOON OR
EVENING. THE UW WRFGFS CLEARLY SHOWS A TROUGH REACHING THE COASTAL
WATERS THIS EVENING...SO THE WINDS MAY DIMINISHING AND BACK TO MORE
SE LATE THIS AFTERNOON...AND THEN SURGE TO WSW 20-30KT THIS EVENING
BEHIND THE TROF. THE STRONG ONSHORE FLOW OVERNIGHT SHOULD RELAX
FRIDAY.

A STRONG WARM FRONT WILL LIFT THROUGH THE WATERS SAT NIGHT AND WILL
BE FOLLOWED BY A COLD FRONT LATER SUN OR MONDAY...EXPECT GALES TO
DEVELOP IN THE COASTAL WATERS AND PERHAPS INLAND WATERS LATER SAT
NIGHT OR SUN INTO MON. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNING FOR THE SKOKOMISH RIVER.
    .WINTER STORM WARNING FOR THE NORTH AND CENTRAL WASHINGTON
     CASCADES UNTIL NOON FRIDAY.
    .WINTER WEATHER ADVISORY FOR THE OLYMPIC MOUNTAINS UNTIL
     NOON FRIDAY.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT CENTRAL STRAIT.
    .SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.