Heavy Snow in Washington, January 16 to 18, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
945 AM PST MON JAN 16 2012

.SYNOPSIS...SNOW SHOWERS WILL INCREASE TODAY AND CONTINUE INTO
TUESDAY AS AN UPPER LEVEL DISTURBANCE AND ARCTIC FRONT MOVE INTO
CENTRAL PORTIONS OF WESTERN WASHINGTON. ANOTHER LOW AND ASSOCIATED
FRONTAL SYSTEM WILL MOVE INTO THE AREA LATE TUESDAY NIGHT THROUGH
WEDNESDAY OR WEDNESDAY NIGHT BRINGING THE POTENTIAL FOR VERY
SIGNIFICANT SNOWFALL AMOUNTS. PRECIPITATION WILL LIKELY TURN TO RAIN
FROM THE SOUTH LATER WEDNESDAY THROUGH THURSDAY MORNING. A VERY
ACTIVE WEATHER PATTERN IS EXPECTED THURSDAY THROUGH NEXT WEEKEND.

&&

.SHORT TERM...VERY HIGH IMPACT WINTER WEATHER IS EXPECTED THROUGH
WEDNESDAY NIGHT OR THURSDAY. SNOWFALL AMOUNTS AT SEATAC COULD EXCEED
ANYTHING SEEN SINCE NOVEMBER 1985...A TOP 5 RECORD 24 HOUR SNOWFALL
AMOUNT.

FOR TODAY...ARCTIC AIR OVER NORTHERN BC AND THE YUKON IS HEADED
SOUTH WITH THE ARCTIC FRONT MAKING ITS WAY DOWN THROUGH WILLIAMS
LAKE. COLD AIR IS SPILLING OUT THROUGH GAPS IN THE CANADIAN COASTAL
TERRAIN AND SPINNING UP LOW PRESSURE OFF VANCOUVER ISLAND. IT
APPEARS THAT FRONTOGENESIS IS TAKING SHAPE FROM THE SAN JUANS TO
BELLINGHAM THIS MORNING AND WILL ONLY INTENSIFY AS THE DAY GOES ON.
HEAVY SNOW SHOWERS DROPPING SOUTHEAST FROM OFF VANCOUVER ISLAND
APPEAR TO BE ENHANCING AND IS GIVING HEAVY SNOW SHOWERS TO THE
COAST. WILL ISSUE A WINTER STORM WARNING FOR THE COASTAL ZONES AND
FOR THE NORTH INLAND ZONES FROM SKAGIT COUNTY AND THE SAN JUANS INTO
WESTERN WHATCOM COUNTY FOR TODAY THROUGH TONIGHT. SHOWERS AND
WESTERLY FLOW WILL ALSO LIKELY GIVE ADVISORY AMOUNTS OF SNOW TO THE
MOUNTAINS...THE SOUTHWEST INTERIOR...THE EVERETT AREA WITH SOME
CONVERGENCE...AND THE EAST PUGET SOUND LOWLANDS.

FOR TONIGHT AND TUESDAY MORNING...A QUICK LOOK AT INCOMING 12Z
GUIDANCE SHOWS THE ARCTIC FRONT MOVING SOUTH THROUGH THE NORTH
INTERIOR TONIGHT AND INTO THE SEATTLE TACOMA AND EVERETT AREA IN
TIME FOR THE MORNING COMMUTE. THIS IS SHOWN BEST BY THE GFS AND IS
HINTED AT BY THE NAM AND THE WRFGFS SOLUTION. WITH FRASIER OUTFLOW
GETTING STRONG AND LOW PRES MOVING JUST S OF THE OLYMPICS INTO SW
WA...OVERRUNNING OF THE ARCTIC FRONT MAY GIVE A SHOT OF HEAVY SNOW
ALONG THE ARCTIC FRONT LATER TONIGHT OR TUE MORNING. BRIEF BLIZZARD
LIKE CONDITIONS OVER WESTERN WHATCOM COUNTY ARE POSSIBLE AS THE
ARCTIC FRONT MOVES THROUGH. ALONG THE STRAIT AND FROM EVERETT
SOUTHWARD SNOW WILL ACCOMPANY THE ARCTIC FRONT AS IT GETS OVERRUN BY
MOISTURE WRAPPING AROUND THE OFFSHORE LOW. WILL ISSUE A WINTER STORM
WATCH FOR THE AREA FROM EVERETT DOWN TO THE TACOMA AREA FOR THE
POSSIBILITY OF 3 TO 6 INCHES OF SNOW WITH THE ARCTIC FRONT.

CONDITIONS IMPROVE A BIT TUESDAY AFTERNOON AND TUESDAY NIGHT BUT IT
LOOKS LIKE IT IS GOING TO BE COLD WITH TEMPERATURES POSSIBLY HOLDING
30 OR BELOW.

THE BIG OVERRUNNING SNOW EVENT STARTS LATE TUE NIGHT AND CONTINUES
THROUGH WED. THE NAM AND ECMWF KEEP EVERYONE FROM SEATTLE NORTHWARD
AS ALL SNOW THROUGH WED NIGHT. THE GFS STILL SCOURS OUT COLD AIR
SOUTH OF DOWNTOWN SEATTLE OR SO WED AFTERNOON. THE ECMWF IS MORE
LIKE THE 12Z NAM. ALL MODELS SHOW 6 TO 12 INCHES OF SNOW OVER THE
LOWLANDS...AND WITH COLD AIR NORTH OF SEATTLE RATIOS COULD BE HIGHER
EVERETT NORTHWARD. ALBRECHT

.LONG TERM...THE GENERAL TREND OF THE MODELS IS FOR A WARMER AND
MORE ACTIVE PATTERN SETTING UP THROUGH THE WEEKEND...BUT THE MODELS
SHOW LITTLE CONTINUITY OR RUN TO RUN CONSISTENCY. THE 00Z ECMWF DOES
SHOW A WIND STORM FOR SATURDAY TO ADD TO THE MIX. FOR NOW THE
GENERAL BROADBRUSH OF RAIN AT TIMES AND WARMER WITH MOUNTAIN SNOW
WILL STAY IN THE FORECAST.

&&

.HYDROLOGY...NO WIDESPREAD RIVER FLOODING IS EXPECTED IN THE NEXT
SEVEN DAYS. SMALLER AND MORE FLOOD PRONE RIVERS MAY SEE SOME
FLOODING AFTER WEDNESDAY. THE TRANSITION OF PRECIPITATION TYPE FROM
SNOW TO RAIN COULD RESULT IN URBAN AND SMALL STREAM FLOODING
WEDNESDAY INTO THURSDAY DEPENDING ON HOW MUCH SNOW IS ON THE GROUND
BEFORE THE TRANSITION TO RAIN. ALBRECHT

&&

.AVIATION...A VERY COLD UPPER TROUGH WILL REMAIN IN PLACE OVER B.C.
AND THE PAC NW THROUGH AT LEAST TUESDAY. SURFACE LOW PRESSURE
CURRENTLY NEAR VANCOUVER ISLAND WILL DEEPEN TONIGHT AND SHIFT SWD
THROUGH WRN WA...DRAGGING AN ARCTIC BOUNDARY SWD LATE TONIGHT AND
TUESDAY MORNING. STRONG SW FLOW ALOFT BECOMING MODERATE NW FLOW ON
TUESDAY. SURFACE WINDS WILL SHIFT FROM SWLY TO NLY BEHIND THE ARCTIC
FRONT STARTING ACROSS THE N INTERIOR LATER TONIGHT AND THROUGH
THROUGH REST OF PUGET SOUND THROUGH TUESDAY MORNING. MOIST AT ALL
LEVELS AND SLIGHTLY UNSTABLE. SNOW WILL FALL ACROSS ALL OF WESTERN
WASHINGTON TODAY THROUGH TUESDAY...FOLLOWED BY A VERY HIGH IMPACT
SNOWFALL AFFECTING ALL TERMINALS TUESDAY NIGHT THROUGH WEDNESDAY
NIGHT.

KSEA...S/SW WIND 8-12 KT...SWITCHING TO NLY SOMETIME TUESDAY MORNING
BETWEEN 14-19Z. SNOW SHOWERS WILL BE HIT AND MISS WITH ACCUMULATION
LESS THAN 1 INCH TODAY AND THIS EVENING. SNOW WILL INCREASE LATE
TONIGHT AND TUESDAY WITH SNOWFALL AMOUNTS OF 2-6 INCHES DURING THAT
PERIOD. TEMPERATURES WILL ALSO STRUGGLE TO REACH ABOVE FREEZING ON
TUESDAY. A VERY HIGH IMPACT SNOWFALL WILL AFFECT THE TERMINAL
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. SNOWFALL IN THAT PERIOD COULD
EASILY 6+ INCHES...AND PERHAPS EXCEEDING 10 INCHES IF THE CHANGE
OVER TO RAIN IS LATER OR DOES NOT OCCUR BY LATE WEDNESDAY. DTM

&&

.MARINE...THERE WILL BE SOME SMALL CRAFT ADVISORY WEST WINDS LATER
TODAY THROUGH THIS EVENING FOR THE COASTAL WATERS AND OVER THE
STRAIT OF JUAN DE FUCA AS A TROUGH NEAR THE COAST SHIFTS INLAND.
THERE WILL ALSO BE SOME WEST SWELL AROUND 10 FEET OVER THE COASTAL
WATERS TODAY AND TONIGHT.

HIGH PRESSURE WILL BUILD OVER THE INTERIOR OF BRITISH COLUMBIA WITH
FRASER OUTFLOW DEVELOPING LATER TONIGHT AND TUESDAY. A VIGOROUS
WEATHER SYSTEM WILL MOVE THROUGH THE WATERS WEDNESDAY OR WEDNESDAY
NIGHT. DTM/SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING THROUGH TONIGHT COASTAL ZONES AND NORTH
INTERIOR       ZONES FROM SKAGIT AND ISLAND COUNTY NORTHWARD.
    .WINTER STORM WARNING MOUNTAINS TONIGHT AND TUESDAY/
    .WINTER STORM WATCH LATE TONIGHT AND TUESDAY STRAIT OF JUAN DE
      FUCA ZONES...AND INTERIOR LOWLANDS EVERETT SOUTH TO TACOMA AREA
      INCLUDING THE EAST PUGET SOUND LOWLANDS.
    .WINTER WEATHER ADVISORY TODAY...EVERETT AREA...EAST
      PUGET SOUND LOWLANDS...SOUTHWEST INTERIOR.
    .WINTER STORM WATCH ALL AREAS TUESDAY NIGHT THROUGH WEDNESDAY
      EVENING.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS THROUGH TONIGHT.
    .SMALL CRAFT ADVISORY WEST ENTRANCE THROUGH 6 PM THIS EVENING.
    .SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT THIS AFTERNOON
     THROUGH MIDNIGHT TONIGHT.
    .SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.

&&

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