Debris Flows in Washington, January 8 to 9, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST TUE JAN 8 2013

.SYNOPSIS...A VIGOROUS FRONTAL SYSTEM WILL BRING RAIN AND WINDY
CONDITIONS TO WESTERN WASHINGTON TONIGHT AND WEDNESDAY MORNING. A
COLD UPPER TROUGH WILL MOVE OVER THE REGION WEDNESDAY AND THURSDAY
AS SHOWERS DECREASE. A WEAK SYSTEM WILL MOVE THROUGH THE PACIFIC
NORTHWEST SATURDAY WITH A CHANCE OF LIGHT RAIN AND SNOW. DRIER
NORTHERLY FLOW ALOFT WILL PREVAIL SUNDAY AND EARLY NEXT WEEK.

&&

.SHORT TERM...SLY WINDS HAVE STARTING PICKING UP THE PAST COUPLE
HOURS ACROSS MOST THE LOWLAND ZONES. GRADIENTS ARE ON THE RISE WITH
KPDX-KBLI ALREADY UP TO +7 MB. THE FLOW SHOULD CONTINUE TO INCREASE
THROUGH THE EVENING HOURS AS A 988-990 MB SURFACE LOW TRACKS INTO
FAR N VANCOUVER ISLAND. WILL KEEP THE WIND ADVISORY IN EFFECT FOR
THE LOWLANDS FOR GUSTS OF 45-50 MPH AND EXTEND IT A BIT LATER
THROUGH 4 AM GIVEN THAT WINDS ARE LATE TO PICK UP. THE COAST AND N
PUGET SOUND/ADMIRALTY INLET WILL LIKELY HAVE THE HIGHEST WIND GUSTS
BUT IT WILL BE LOCALLY WINDY ELSEWHERE.

THE WARM FRONT HAS BEEN DIFFICULT TO TRACK TODAY AND SURFACE
ANALYSIS APPEARS IT INDICATE IS HAS BECOME MORE N/S ORIENTED ALONG
THE COAST AND VERY SLOW TO LIFT ACROSS THE INTERIOR. IN
ADDITION...ELY FLOW CONTINUES LATE THIS AFTERNOON IN THE PASSES
INCLUDING SNOQUALMIE AND STEVENS PASS...BOTH STILL IN THE MID/UPPER
20S. THESE CASES ARE ALWAYS DIFFICULT WHEN COLD AIR GETS TRAPPED IN
THE PASSES EVEN WAS WARMER AIR MOVES IN ALOFT. IT HAS BEEN SNOWING
HEAVILY THE PAST FEW HOURS AT SNOQUALMIE AND STEVENS PASSES. A
CHANGE OVER TO RAIN SHOULD OCCUR OVER THE NEXT FEW HOURS AT
SNOQUALMIE BUT AREAS NORTH TOWARD STEVENS WILL SEE SNOW OR FREEZING
RAIN LAST LONGER THROUGH THE EVENING. DECIDED TO ISSUE A WINTER
WEATHER ADVISORY FOR THE CENTRAL CASCADES TO COVER POSSIBLE
ACCUMULATIONS OF 5 TO 10 INCHES AND UP TO A QUARTER INCH OF FREEZING
RAIN...ESPECIALLY IMPACTING STEVENS PASS. THE NORTH CASCADES WILL
STAY MOSTLY SNOW THROUGH THE EVENT BUT A PERIOD OF RISING SNOW
LEVELS COULD STILL OCCUR LATER TONIGHT. SNOWFALL RATES LOOK QUITE
HEAVY SO 1 TO 2 FEET OF SNOW OVERNIGHT APPEAR REASONABLE.

SNOW LEVELS ARE HIGHER OVER THE OLYMPICS WITH HEAVY RAIN CONTINUING
THROUGH THE NIGHT. THE FLOOD POTENTIAL CONTINUES FOR THE OLYMPIC
PENINSULA. THE CHANCE OF FLOODING IN THE CASCADES APPEARS RATHER LOW
DUE TO VARIABLE SNOW LEVELS WHICH HAVE BEEN SLOW TO RISE. SEE THE
LATEST HYDRO DISCUSSION BELOW FOR FURTHER DETAILS. THE FLOOD WATCH
REMAIN IN EFFECT FOR PORTIONS OF WRN WA.

RAIN WILL CHANGE TO SHOWERS AS THE COLD FRONT PUSHES ACROSS THE AREA
WEDNESDAY MORNING. THE FRONT WILL USHER IN COLDER AIR ALOFT AND A
SOMEWHAT DRIER AIR MASS. THERE WILL STILL BE RESIDUAL LOW LEVEL
MOISTURE AND A MODIFIED CANADIAN FRONT MOST LIKELY STAYING HUNG UP
OVER THE N INTERIOR. THIS FEATURE MAY PROVIDE AREAS OF CONVERGENCE
WEDNESDAY NIGHT AND THURSDAY MORNING. SNOW LEVELS WILL FALL TO NEAR
SEA-LEVEL SO ANY PERSISTENT SNOW BANDS COULD PUT DOWN A COUPLE
INCHES. THE BEST CHANCE OF THIS OCCURING WILL BE FROM FAR N KING
COUNTY INTO WRN SNOHOMISH COUNTY. THERE IS AN OUTSIDE CHANCE AT SOME
LIGHT SNOW SHOWERS DRIFTING FURTHER S INTO THE SEATTLE/TACOMA AREAS
BUT NOT MUCH IN THE WAY OF ACCUMULATION IS EXPECTED AT THIS POINT.
SOME MODELS SUCH AS THE WRFGFS HOLD ONTO A CONVERGENCE ZONE INTO
THURSDAY NIGHT AND FRIDAY. THE NAM AND OTHER MODELS ARE MUCH DRIER.
KEPT SOME CHANCE POPS FOR SNOW SHOWERS AROUND...MAINLY TOWARD THE
COAST AND MOUNTAINS. MODELS HAVE NOT BEEN IN GOOD AGREEMENT EVEN IN
THE SHORT TERM SO CONFIDENCE IS NOT VERY GOOD TOWARD THE END OF THE
WEEK. IT DOES APPEAR COLDER AIR WILL TRICKLE IN AS NLY FLOW ALOFT
AND IN THE LOW LEVELS PERSISTS. HIGHS WILL PROBABLY REMAIN IN THE
30S WITH LOWS IN THE 20S TO AROUND 30. POSSIBLY THE COLDEST
TEMPERATURES SO FAR THIS SEASON.

.LONG TERM...LONG RANGE MODELS CONTINUE TO BE IN POOR AGREEMENT
WITH EACH OTHER AND WITH LITTLE RUN TO RUN CONSISTENCY. THE TREND
TODAY HAS BEEN TO SPLIT THE NRN STREAM ON SATURDAY WHICH WOULD TAKE
SHORT WAVE ENERGY AND LOW PRESSURE FURTHER OFF THE COAST. 00Z
CANADIAN/ECMWF MODELS WERE QUITE STRONG AND CONSOLIDATED WITH THIS
SYSTEM...DIGGING THE LOW DOWN RIGHT OVER US WITH IMPRESSIVE QPF. THE
LATEST RUNS WOULD IMPLY ONLY LIGHT PRECIPITATION AND MORE FOCUSED
TOWARD THE COAST. MODELS ARE CLEARLY UNSTABLE WITH ANY OF THE
SOLUTIONS THE PAST COUPLE DAYS STILL PLAUSIBLE. IT DOES APPEAR COLD
ENOUGH OVER THE AREA SO THAT ANY PRECIPITATION THAT DOES FALL SHOULD
BE MOSTLY AS SNOW.

THE SHORT WAVES DIVES SWD SATURDAY NIGHT AND SUNDAY. THE 12Z/18Z
MODEL TREND IS TO MIGRATE THE RIDGE EWD AND KEEP THE AREA DRY BUT
STILL COOL. SOME 00Z MODEL RUNS FROM LAST NIGHT SHOWED ADDITIONAL
SHORT WAVE ENERGY DRIVING SWD POSSIBLY BRINGING MORE SHOWERS/ OR
MIXED PRECIPITATION TO THE AREA SUNDAY INTO EARLY NEXT WEEK. KEPT
SOME CHANCE POPS JUST IN CASE BUT THE LATEST TREND IS CLEARLY TOWARD
DRIER. MERCER

&&

.HYDROLOGY...FLOODING IS STILL POSSIBLE ON RIVERS RUNNING OFF THE
OLYMPICS. SNOW LEVELS ARE HIGHER HERE THAN THE CASCADES WITH UP TO 5
INCHES STILL POSSIBLE BY WEDNESDAY MORNING. THE SKOKOMISH RIVER
REMAINS AT HIGHEST RISK OF FLOODING. ELSEWHERE...SNOW LEVELS HAVE
BEEN SLOW TO RISE OVER THE CASCADES. THIS SIGNIFICANTLY REDUCES THE
ODDS OF FLOODING. HOWEVER...HEAVY PRECIPITATION WILL OCCUR OVERNIGHT
AND THERE IS STILL SOME RISK OF FLOODING MAINLY ON THE STILLAGUAMISH
IN SNOHOMISH COUNTY.

SNOW LEVELS FALL BEHIND THE FRONT WEDNESDAY MORNING AND
PRECIPITATION WILL TAPER OFF. A FAIRLY DRY AND COLDER PATTERN WILL
DOMINATE THROUGH EARLY NEXT WEEK. ADDITIONAL FLOODING IS NOT
EXPECTED. MERCER

&&

.AVIATION...WESTERLY FLOW ALOFT WILL GRADUALLY TURN SOUTHWESTERLY
TONIGHT AS UPPER LEVEL TROUGH DIGS SOUTH OFF THE COAST. A WARM FRONT
WILL CONTINUE TO LIFT NORTH THROUGH THE AREA THIS AFTERNOON FOLLOWED
BY A STRONG COLD FRONT TONIGHT. AIR MASS MOIST AND STABLE.

SOME VARIATIONS CONTINUE IN THE CIGS THIS AFTERNOON. NORTHERNMOST
TAF SITES...CLM AND BLI HAVE THE HIGHEST...RANGING BETWEEN 2000-6000
FT...WHILE REMAINDER OF WESTERN WA TAF SITES ARE AT OR BELOW 1000
FT. FRONTAL PASSAGE LATE THIS AFTERNOON AND TONIGHT SHOULD HELP CIGS
IN MOST LOCATIONS TO RISE BETWEEN 1000-2000 FT. SIMILAR STORY WITH
VISIBILITIES...AS CONTINUING RAINFALL AHEAD OF THE WARM FRONT HAS
BROUGHT VISIBILITIES DOWN TO THE 1-2SM RANGE...EXPECTING FRONTAL
PASSAGE TO HELP THOSE CLIMB MORE INTO THE 4-6SM RANGE THIS EVENING
AND CONTINUING THROUGH THE OVERNIGHT. THE TRAILING COLD FRONT WILL
MOVE INTO THE AREA THIS EVENING AND STALL OVERNIGHT BEFORE DROPPING
SOUTH WEDNESDAY MORNING KEEPING MVFR CEILINGS INTO WEDNESDAY
MORNING.

WINDS ALOFT WILL CONTINUE TO INCREASE THIS AFTERNOON AND CONTINUE
THROUGH THIS EVENING WITH 5000 FT WINDS SWLY 60-75 KT.

KSEA...CEILINGS AT OR JUST BELOW 1000 FT TONIGHT AND INTO EARLY
TOMORROW MORNING. MVFR TO IFR CONDITIONS EXPECTED THIS AFTERNOON AND
INTO TONIGHT...BECOMING MAINLY MVFR LATE AND INTO TOMORROW MORNING.
SOUTHERLY WIND UP TO 15 GUSTING 25 KNOTS EXPECTED BY LATE AFTERNOON.
WINDS AT 050 INCREASING TO SW 50-70KT BY 00Z. SMR

&&

.MARINE...A WARM FRONT WILL CONTINUE TO SLOWLY LIFT NORTHEAST ACROSS
THE COASTAL WATERS THIS AFTERNOON FOLLOWED BY A STRONG COLD FRONT
TONIGHT. THE PARENT LOW WILL MOVE INLAND AROUND THE NORTHERN TIP OF
VANCOUVER ISLAND THIS EVENING. WINDS CONTINUE TO RISE OVER COASTAL
LOCATIONS AND ARE EXPECTED TO REACH GALE STRENGTH BY LATE THIS
AFTERNOON OR EARLY THIS EVENING. EXPECTING WINDS OVER INLAND WATERS
AND THE STRAIT TO INCREASE THIS EVENING AND THROUGH THE NIGHT
TONIGHT. THIS POST FRONTAL ONSHORE FLOW WILL RAPIDLY DIMINISH ON WED
AFTERNOON AS A BROAD TROUGH OF LOW PRES DIGS DOWN OVER THE REGION.
BY THURSDAY THERE IS THE POTENTIAL FOR SMALL CRAFT ADVISORY WINDS ON
THE COASTAL WATERS...BUT CONDITIONS SEEM BORDERLINE AT THIS TIME.
SMALL CRAFT ADVISORY NORTHERLY FLOW IS POSSIBLE OVER THE NORTHERN
WATERS ON SAT AS HIGH PRES BUILDS OVER BRITISH COLUMBIA AND A LOW
DIGS DOWN OFF THE WASHINGTON COASTLINE. FELTON/SMR

&&

.AVALANCHE...A STRONG WARM FRONT HAS DEVELOPED FURTHER TUESDAY
HELPING TO SLOW THE EASTWARD MOVEMENT. THIS HAS ALLOWED SIGNIFICANT
SNOW TO BE DEPOSITED IN THE PASSES DUE TO COOLING EAST FLOW. HEAVY
SNOW AT WARMING TEMPERATURES ELSEWHERE AND THE IMPENDING CHANGE FROM
SNOW TO RAIN IN THE LOWER CASCADE PASSES IS LEADING TO A
SIGNIFICANTLY INCREASING AVALANCHE DANGER. INCREASING NATURAL
AVALANCHES ARE LIKELY LATER TUESDAY AND TUESDAY NIGHT. AS A RESULT
THE EXISTING AVALANCHE WARNING HAS BEEN EXTENDED TO ALL ZONES ALONG
THE WEST SLOPES OF THE WA CASCADES AND CONTINUES IN THE OLYMPICS.

KRAMER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY FOR ALL LOWLAND ZONES...EXCEPT THE
     STRAIT ZONES...THROUGH 4 AM PST WEDNESDAY MORNING.
    .WINTER STORM WARNING FOR THE NORTH CASCADES THROUGH NOON PST
     WEDNESDAY.
    .WINTER WEATHER ADVISORY FOR THE CENTRAL CASCADES THROUGH 10 PM
     THIS EVENING.
PZ...GALE WARNING COASTAL WATERS...ADMIRALTY INLET AND PUGET SOUND
     AND HOOD CANAL.
     GALE WARNING STRAIT OF JUAN DE FUCA AND NORTHERN INLAND WATERS
     FROM 4 PM PST THIS AFTERNOON UNTIL 4 AM PST WEDNESDAY.
    .SMALL CRAFT ADVISORY FOR STRAIT OF JUAN DE FUCA AND NORTHERN
     INLAND WATERS UNTIL 4 PM PST THIS AFTERNOON.
    .SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.