Funny Area Forecast Discussion

[senorpepr]

270
FXUS66 KSEW 161202
AFDSEW

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

SYNOPSIS
SHOWERS WILL INCREASE THIS AFTERNOON AND CONTINUE INTO
TUESDAY AS A DISTURBANCE EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT
MOVES OVER WESTERN WASHINGTON. A STRONG WARM FRONT WILL APPROACH THE
AREA FROM THE SOUTH TUESDAY NIGHT THEN MOVE THROUGH MOST OF WESTERN
WASHINGTON WEDNESDAY AND WEDNESDAY NIGHT. THIS SYSTEM MAY GIVE HEAVY
SNOW TO PORTIONS OF THE LOWLANDS BEFORE PRECIPITATION TURNS TO RAIN.
AN ACTIVE WEATHER PATTERN IS EXPECTED THURSDAY THROUGH NEXT WEEKEND.



SHORT TERM
"LOOKS LIKE I PICKED THE WRONG WEEK TO QUIT DRINKING"
STEVE MCCROSKEY

PRETTY CHALLENGING NEXT FEW DAYS FOR THE FORECAST OFFICE. RIGHT NOW
WSR-88D'S PICKING UP A BAND OF SNOW SHOWERS REACHING THE COAST ALONG
WITH SOME ISOLATED SNOW SHOWERS OVER THE INTERIOR. SATELLITE IMAGERY
SHOWS NEXT SHORTWAVE EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT NEAR
130W. THIS FEATURE WILL MOVE OVER WESTERN WASHINGTON LATER THIS
MORNING INTO THIS AFTERNOON ENHANCING THE SHOWER ACTIVITY OVER THE
REGION. FOR THIS MORNING...OUTSIDE OF THE COAST JUST SOME ISOLATED
SHOWERS WITH THE UNSTABLE AIR MASS OVER THE AREA. 1000-850 MB
THICKNESS VALUES REMAINING IN THE 1280 METER RANGE ALL DAY...COLD
ENOUGH FOR ALL OF THE SHOWERS TO BE IN THE FORM OF SNOW. HEAVIEST
PRECIPITATION AMOUNTS ALONG THE COAST TODAY SO WILL ISSUE A WINTER
WEATHER ADVISORY FOR 1 TO 2 INCHES OF SNOW TODAY. FOR THE REMAINDER
OF THE AREA AMOUNTS OF AN INCH OR LESS LOOK TO BE THE NORM.
INITIALLY WITH THE NORTHWESTERLY FLOW ALOFT THE CENTRAL SOUND WILL
GET SNOW SHADOWED. THERE IS THE POSSIBILITY OF SOME WEAK CONVERGENCE
DEVELOPING OVER THE CENTRAL SOUND LATER THIS AFTERNOON INTO THIS
EVENING. THIS WILL BE THE BEST CHANCE FOR ACCUMULATING SNOW IN THE
CENTRAL SOUND.

COOL UPPER LEVEL TROUGH HANGING OVER WESTERN WASHINGTON TONIGHT INTO
TUESDAY WITH PLENTY OF SHOWER ACTIVITY OVER THE AREA. 1000-850
THICKNESS VALUES WILL REMAIN BELOW 1300 METERS MEANING ALL OF THE
SHOWER ACTIVITY WILL BE IN THE FORM OF SNOW. CURRENT QPF GUIDANCE
HAS A GENERAL 1 TO 3 INCHES OF SNOW ACROSS THE REGION TONIGHT INTO
TUESDAY. THE FLOW ALOFT WILL BECOME MORE WESTERLY WHICH WILL SHIFT
THE SNOW SHADOW IN THE CENTRAL SOUND A BIT BUT AT THIS POINT IT
LOOKS LIKE THE LOWER SNOW AMOUNTS WILL BE OVER THE CENTRAL SOUND.
PLENTY OF SHOWER ACTIVITY FOR THE CASCADES AS WELL WITH THE 850 MB
WINDS RUNNING IN THE 25-35 KNOT RANGE. THIS IS GOOD BUT NOT GREAT
OROGRAPHIC FLOW BUT WITH NO LET UP TONIGHT THROUGH TUESDAY BY THE
TIME TUESDAY NIGHT ROLLS AROUND 1 TO 2 FEET OF SNOW IS EXPECTED.
WILL ISSUE A WINTER STORM WARNING FOR THE NORTH AND CENTRAL
CASCADES.

MOVING ON TO THE MAIN EVENT...TUESDAY NIGHT INTO WEDNESDAY. WHILE
LAST NIGHT THERE WAS AT LEAST SOME CONSISTENCY IN THE MODELS ON THE
SCENARIO THAT WOULD DEVELOP JUST SOME TIMING DIFFERENCES...THE 00Z
RUNS HAVE MULTIPLE SOLUTIONS FOR WHAT IS GOING TO HAPPEN. THIS DOES
NOT LEAD TO MUCH CONFIDENCE IN THE FORECAST AT THIS POINT IN TIME.
FIRST UP...THE GFS SOLUTION. THE GFS SWINGS A WARM FRONT UP THROUGH
WESTERN WASHINGTON ON WEDNESDAY FOR A CLASSIC OVERRUNNING EVENT. THE
TIMING OF THE TRANSITION OF THE PRECIPITATION TYPE FROM SNOW TO RAIN
IS ALONG THE SOUTH COAST IN THE MORNING AND FROM ABOUT SEATTLE SOUTH
IN THE AFTERNOON WITH THE POSSIBILITY THAT THE COLD AIR HANGS TOUGH
OVER THE NORTHWEST INTERIOR INTO EARLY THURSDAY MORNING. THIS IS THE
FASTEST OF THE MODELS WITH THE TRANSITION TO THE WARMER AIR MASS.
EVEN WITH THIS "FASTER" TRANSITION...THERE IS POTENTIAL FOR
SIGNIFICANT SNOWFALL OVER THE LOWLANDS...4 TO 8 INCHES...WITH
LOCALLY HIGHER AMOUNTS ESPECIALLY OVER THE NORTHWEST INTERIOR. THE
ECMWF 00Z RUN SHOWS A WARM FRONT ALSO MOVING UP INTO THE AREA ON
WEDNESDAY BUT IS SLOWER THAN THE GFS WITH THE TRANSITION TO A WARMER
AIR MASS...AT LEAST SIX HOURS. THE ECMWF ALSO TRACKS THE SURFACE LOW
INLAND A LITTLE FURTHER SOUTH WHICH KEEPS THE COOL AIR SPILLING OUT
OF SOUTHERN BRITISH COLUMBIA OVER THE NORTHWEST INTERIOR
LONGER...INTO THURSDAY MORNING. WITH THE SLOWER TRANSITION TO THE
WARMER AIR MASS THE ECMWF HAS THE POTENTIAL FOR EVEN MORE SNOW OVER
THE INTERIOR OF WESTERN WASHINGTON ESPECIALLY OVER THE NORTHWEST
INTERIOR. THE NAM AND THE CANADIAN MODEL ARE FURTHER SOUTH WITH THE
PARENT LOW ASSOCIATED WITH THE WARM FRONT. IN THIS SCENARIO WESTERN
WASHINGTON NEVER TRANSITIONS OUT OF THE COLD AIR MASS ON WEDNESDAY
WITH SNOW ALL DAY. THE FURTHER SOUTH SOLUTION ALSO RESULTS IN LESS
PRECIPITATION OVER WESTERN WASHINGTON WITH THE 00Z RUN NOT BRINGING
ANY PRECIPITATION TO SEATTLE NORTHWARD BY 00Z THURSDAY. AT THIS
POINT THE ONLY MODEL SHOWING MUCH RUN TO RUN CONSISTENCY IS THE GFS
BUT THE ECMWF HAS BEEN VERIFYING BETTER LATELY. AT THIS POINT THE
NAM CANADIAN SOLUTION LOOKS TO BE AN OUTLIER. NORMALLY I WOULD BE
RELUCTANT TO PUT OUT A WINTER STORM WATCH THIS FAR AHEAD OF TIME
GIVEN THE LARGE UNCERTAINTY IN THE SOLUTIONS BUT BECAUSE OF THE
POTENTIAL FOR A SIGNIFICANT SNOW EVENT FOR THE LOWLANDS WILL GO
AHEAD AND ISSUE A WATCH FOR WEDNESDAY INTO WEDNESDAY EVENING FOR
MOST OF WESTERN WASHINGTON. FELTON

LONG TERM
DID NOT SPEND MUCH TIME ON THE EXTENDED SOLUTIONS THIS
MORNING WITH THE POSSIBLE BIG EVENT ON WEDNESDAY. THE GENERAL TREND
OF THE MODELS IS FOR A WARMER AND MORE ACTIVE PATTERN SETTING UP
THROUGH THE WEEKEND. THE ECMWF IS ALSO SHOWING 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.
FELTON



HYDROLOGY FROM THE PREV DISCUSSION

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 SOME URBAN AND SMALL STREAM FLOODING WEDNESDAY INTO
THURSDAY DEPENDING ON HOW MUCH SNOW IS ON THE GROUND BEFORE THE
TRANSITION TO RAIN. ALBRECHT



AVIATION
WESTERLY FLOW ALOFT WILL INCREASE TODAY AND TONIGHT. A
COUPLE OF UPPER LEVEL DISTURBANCES WILL MOVE ONSHORE...ONE THIS
AFTERNOON AND ANOTHER AFTER MIDNIGHT TONIGHT. AT THE SURFACE...A
TROUGH NEAR THE COAST AND OVER VANCOUVER ISLAND WILL MOVE INLAND
TODAY AND TONIGHT. AIR MASS MOIST AND SOMEWHAT UNSTABLE.

THERE IS ENOUGH INSTABILITY THAT SPOTTY SNOW SHOWERS HAVE
RE-DEVELOPED ACROSS THE AREA EARLY THIS MORNING. ASIDE FROM
THIS...THERE IS A MIX OF LOW CLOUDS AND PATCHY FREEZING FOG THIS
MORNING. LOW CLOUDS SHOULD INCREASE LATER TODAY AS AN UPPER LEVEL
DISTURBANCE ENHANCES THE SNOW SHOWER ACTIVITY OVER THE AREA.

KSEA...SPOTTY LIGHT SNOW SHOWERS WITH LOW CLOUDS AND OCCASIONAL
REDUCED VISIBILITIES CAN BE EXPECTED THIS MORNING BUT THEY SHOULD
NOT AMOUNT TO MUCH. SNOW SHOWERS SHOULD INCREASE THIS AFTERNOON AS
AN UPPER DISTURBANCE MOVES THROUGH WITH UP TO AN INCH OF
ACCUMULATION POSSIBLE AT THE TERMINAL. SOUTH WIND 4-8 KNOTS THIS
MORNING WILL INCREASE TO 8-12 KNOTS THIS AFTERNOON. SCHNEIDER



MARINE
THERE WILL BE SOME SMALL CRAFT ADVISORY WEST WINDS LATER
TODAY 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 TUESDAY AND TUESDAY NIGHT. A VIGOROUS
WEATHER SYSTEM WILL MOVE THROUGH THE WATERS WEDNESDAY OR WEDNESDAY
NIGHT. SCHNEIDER



SEW WATCHES/WARNINGS/ADVISORIES

WA...WINTER WEATHER ADVISORY COAST.
WINTER STORM WARNING NORTH AND CENTRAL CASCADES TONIGHT AND
TUESDAY.
WINTER STORM WATCH WEDNESDAY AND WEDNESDAY EVENING MOST AREAS.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND STRAIT OF JUAN DE FUCA.
.SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.





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