Gale Warning 7, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST WED JAN 9 2013

.SYNOPSIS...RAIN AND SNOW SHOWERS ALONG WITH A PUGET SOUND
CONVERGENCE ZONE WILL DOMINATE THE WEATHER PATTERN TONIGHT AND
THURSDAY. COLDER AIR WILL FILTER INTO THE AREA WHICH MAY ALLOW FOR
SPOTTY SNOW LOWLAND SNOW ACCUMULATIONS. DRIER BUT COLDER AIR MOVES
INT THURSDAY NIGHT AND FRIDAY. A WEAK SYSTEM ON SATURDAY WILL BRING
ANOTHER POSSIBILITY OF SOME LOWLAND SNOW. DRIER NORTHERLY FLOW ALOFT
WILL PREVAIL SUNDAY AND EARLY NEXT WEEK.

&&

.SHORT TERM...A COLDER AND UNSTABLE AIR MASS IS MOVING INTO WRN WA
BEHIND THE FRONT THAT PUSHED EAST OF THE AREA THIS MORNING. IR
IMAGERY SHOWS A LOT OF COLD TOP CU STREAMING INTO WRN WA THIS
AFTERNOON. THESE SHOWERS WILL CONTINUE THROUGH THURSDAY ACROSS MOST
THE AREA WITH THE EXCEPTION OF SOME SHADOWING OVER THE CENTRAL PUGET
SOUND WHICH WILL MINIMIZE PRECIPITATION AMOUNTS THERE. MODELS
INDICATE 850 MB TEMPS AND 1000-850 MB THICKNESS VALUES FALL THROUGH
THE NIGHT AND SUPPORT MIXED PRECIPITATION OR POSSIBLY JUST SNOW DOWN
TO NEAR SEA-LEVEL. LOCAL SNOW ACCUMULATIONS OF A DUSTING TO A HALF
INCH COULD FALL LATER TONIGHT AND THURSDAY UNDER HEAVIER SHOWERS.

OF GREATER CONCERN IS THE POSSIBILITY OF CONVERGENCE ZONE SNOW
MAINLY FROM NORTH SEATTLE ALONG THE I-5 CORRIDOR TO BELLINGHAM. MESO
MODELS ALL SHOW SOME CONVERGENCE ZONE ACTIVITY ALBEIT IN DIFFERENT
PLACES AT DIFFERENT TIMES. THE NAM-12 AND WRFGFS/WRFNAM BOTH SHOW A
COUPLE OF CONVERGENCE BANDS DEVELOPING TONIGHT. ONE OF THESE BANDS
IS ALREADY IN PROGRESS EXTENDING FROM ADMIRALTY INLET INTO WRN
SNOHOMISH AND FAR N SEATTLE. IF THE SECONDARY BAND FORMS IT WILL
OCCUR FURTHER NORTH OVER WHATCOM/SKAGIT COUNTIES ASSOCIATED WITH NW
FLOW OUT OF THE STRAIT OF GEORGIA. THIS SEEMS REASONABLE GIVEN THE
SHORT WAVE AND WEAK SURFACE TROUGH OVER VANCOUVER ISLAND THAT WILL
DIVE SE ALONG THE WA COAST LATER TONIGHT. THIS FEATURE SHOULD INDUCE
SOME NW FLOW DOWN THE STRAITS. QPF AMOUNTS ARE TOUGH WITH
CONVERGENCE ZONES BUT MODELS SUGGEST UP TO A QUARTER INCH LIQUID IN
SPOTS WHICH EQUATES TO A COUPLE INCHES OF SNOW. DECIDED TO ISSUE A
SPECIAL WEATHER STATEMENT TO EMPHASIZE THE POTENTIAL OF 1-2 INCHES
OF SNOW FROM NORTH SEATTLE UP TO BELLINGHAM LATE TONIGHT THROUGH
THURSDAY.

NLY FLOW WILL INCREASE THURSDAY AFTERNOON AND ANY CONVERGENCE ZONE
ACTIVITY SHOULD START TO BREAK UP AND SHIFT FURTHER SOUTH. THIS
MEANS THE REST OF PUGET SOUND COULD SEE SOME SNOW SHOWERS OR
RAIN/SNOW MIXED INTO THURSDAY EVENING BEFORE THE AREA DRIES OUT.
ACCUMULATIONS FROM SEATTLE SOUTHWARD LOOK TO BE LESS THAN AN INCH
AND SPOTTY AT BEST. THE ENTIRE AREA SHOULD DRY OUT FRIDAY WITH A
BREAK IN SHOWERS. NW FLOW WILL DRIVE MOISTURE SWD OFFSHORE BUT I DID
MAINTAIN SOME LOW POPS NEAR THE COAST JUST IN CASE SOME LIGHT
RAIN/SHOW SHOWERS BRUSH COASTAL AREAS. HIGH TEMPERATURES WILL BE
EVEN COLDER WITH HIGHS STUCK IN THE 30S. LOW TEMPERATURES WILL BE
WELL DOWN IN THE 20S ACROSS THE AREA AND EVEN SOME LOWER TEENS
POSSIBLE OVER WRN WHATCOM/SKAGIT COUNTIES.

THE PATTERN ON SATURDAY REMAINS INTERESTING BUT ALSO HIGHLY
UNCERTAIN. ABOUT HALF THE MODELS CONTINUE TO DIG A SHORT WAVE
THROUGH THE AREA IN NLY FLOW WHICH COULD POTENTIALLY PRODUCE
WIDESPREAD 1-3 INCH AMOUNTS. THERE ARE OTHER MODELS THAT TAKE MOST
THE ENERGY OFFSHORE AND WOULD RESULT IN NO SNOW AT ALL OR PERHAPS
JUST NEAR THE COAST. HOPEFULLY MODELS WILL START TO COME INTO BETTER
AGREEMENT AS WE APPROACH THAT TIME PERIOD. KEPT A CHANCE OF SNOW IN
THE FORECAST WITH SOME LIKELY POPS TOWARD THE COAST.

.LONG TERM...LONG RANGE MODELS ARE IN BETTER AGREEMENT OF SLOWLY
NUDGING THE UPPER RIDGE OFFSHORE CLOSER TO THE AREA SUNDAY. NLY
FLOW WILL KEEP TEMPERATURES BELOW AVERAGE WITH DRY WEATHER. HIGH
PRESSURE IS EXPECTED TO BUILD CLOSER TO THE AREA EARLY TO THE MIDDLE
PART OF NEXT WEEK. THIS WILL RESULT IN WEAKER FLOW WITH SOME GRADUAL
WARMING. SHELTERED COLD POCKETS COULD GET RATHER STRONG INVERSIONS
IN THIS PATTERN SO IT IS POSSIBLE THAT STAGNATION ISSUES MAY ARISE.
NO PRECIPITATION IS EXPECTED THROUGH THE EXTENDED PERIOD. MERCER

&&

.HYDROLOGY...SHOWERS AND CONVERGENCE ZONE BANDS WILL PERSIST THROUGH
THURSDAY. SNOW LEVELS WILL BE CLOSE TO SEA LEVELS SO ANY ADDITIONAL
PRECIPITATION WILL NOT CAUSE HYDROLOGY CONCERNS. THERE IS STILL
RESIDUAL RUN OFF WITH RIVER RUNNING HIGH. FLOOD WARNINGS ARE STILL
IN EFFECT FOR SOME RIVERS ON THE OLYMPIC PENINSULA AND ALSO FOR THE
STILLAGUAMISH IN SNOHOMISH COUNTY. SEE THE LATEST FLOOD STATEMENT
FOR FURTHER DETAILS.

LOW SNOW LEVELS WILL DOMINATE THE NEXT SEVERAL DAYS. ALSO...ANY
PRECIPITATION WILL BE LIGHT AND NOT HYDROLOGICALLY SIGNIFICANT.
FLOODING IS NOT EXPECTED BEYOND THE CURRENT ISSUES.

&&

.AVIATION...THERE WILL BE LIGHT FLOW ALOFT TONIGHT AS AN UPPER LEVEL
TROUGH MOVES OVER WESTERN WASHINGTON. UPPER FLOW WILL BECOME
NORTHERLY THURSDAY. MODERATE ONSHORE FLOW AT THE SURFACE WILL
CONTINUE INTO THE EVENING...THEN BECOME LIGHT OVERNIGHT. SURFACE
FLOW WILL TURN MORE NORTHERLY AND OFFSHORE LATE THURSDAY. AIR MASS
IS MOIST AND SOMEWHAT UNSTABLE.

RADAR SHOWS A PUGET SOUND CONVERGENCE ZONE IN SNOHOMISH COUNTY WITH
SCATTERED SHOWERS ELSEWHERE. SATELLITE IMAGERY SHOWS A CLEARING
TREND FROM THE WEST. IN THE CONVERGENCE ZONE CEILINGS WILL BE LOW
MVFR TO IFR WITH VISIBILITY OCCASIONALLY RESTRICTED BY RAIN...AND
LATE TONIGHT BY SNOW. AWAY FROM THE CONVERGENCE ZONE CONDITIONS WILL
BE GOOD VFR WITH OCCASIONAL DIPS TO MVFR IN SHOWERS.

KSEA...LOW MVFR CEILING AT KSEA LIKELY TO RISE TO VFR THIS EVENING.
THE CONVERGENCE ZONE IS FORECAST TO STAY NORTH OF THE TERMINAL
TONIGHT AND THURSDAY WITH ONLY A CHANCE OF SHOWERS AT KSEA. ANY
PRECIPITATION WILL LIKELY BE RAIN OR PERHAPS A MIX AT TIMES. GUSTY
SOUTHWEST WIND 8-12 KT WILL DIMINISH OVERNIGHT...THEN BECOME
NORTHERLY THURSDAY AFTERNOON. CHB

&&

.MARINE...MODERATE ONSHORE GRADIENTS WILL DIMINISH TONIGHT AS A WEAK
LOW CENTER MOVES SOUTH OFF THE COAST. SMALL CRAFT ADVISORY WINDS
WILL CONTINUE THIS EVENING OVER ALL THE WATERS EXCEPT ADMIRALTY
INLET WHERE A PUGET SOUND CONVERGENCE ZONE SHOULD KEEP WINDS
LIGHTER. WINDS WILL EASE TONIGHT INTO THURSDAY MORNING WITH SMALL
CRAFT ADVISORIES CONFINED TO THE COASTAL WATERS ON THURSDAY.

SURFACE HIGH PRES WILL BUILD OVER SOUTHERN BRITISH COLUMBIA THURSDAY
NIGHT AND REMAIN IN PLACE THROUGH SUNDAY. THIS WILL GIVE NORTHERLY
FLOW THROUGH PUGET SOUND WITH OFFSHORE FLOW IN THE STRAIT AND ALONG
THE COAST. A WEAK SYSTEM WILL MOVE THROUGH THE COASTAL WATERS
SATURDAY WITH POSSIBLE ADVISORY LEVEL WINDS ON THE COAST. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES AND WARNINGS FOR PORTIONS OF WESTERN WASHINGTON.
PZ...SMALL CRAFT ADVISORIES ALL WATERS EXCEPT ADMIRALTY INLET.

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SEATTLE WA
146 PM PST WED JAN 9 2013

WAZ001-503>512-514>517-101230-
SAN JUAN COUNTY-WESTERN WHATCOM COUNTY-SOUTHWEST INTERIOR-
EAST PUGET SOUND LOWLANDS-WESTERN SKAGIT COUNTY-
EVERETT AND VICINITY-SEATTLE/BREMERTON AREA-TACOMA AREA-
ADMIRALTY INLET AREA-HOOD CANAL AREA-LOWER CHEHALIS VALLEY AREA-
EASTERN STRAIT OF JUAN DE FUCA-WESTERN STRAIT OF JUAN DE FUCA-
NORTH COAST-CENTRAL COAST-
146 PM PST WED JAN 9 2013

...MUCH COLDER TEMPERATURES AND A CHANCE OF SPOTTY LOWLAND SNOW AT
TIMES TONIGHT THROUGH THE WEEKEND...

LOW TEMPERATURES THURSDAY MORNING WILL GENERALLY BE IN THE LOW
30S BUT HIGHS WILL STRUGGLE TO REACH 40 DURING THE AFTERNOON
HOURS. WEAK FRASER OUTFLOW ALONG WITH A GRADUALLY DRYING AIR MASS
WILL ALLOW TEMPERATURES TO FALL EVEN FURTHER FRIDAY AND SATURDAY.
HIGHS WILL REMAIN IN THE 30S WITH LOW TEMPERATURES DOWN IN THE
20S. ALL OF WESTERN WHATCOM AND SKAGIT COUNTIES AND SOME OTHER
COLD POCKET LOCATIONS COULD SEE TEMPERATURES FALL INTO THE LOWER
TO MID TEENS OVERNIGHT. ONLY A SLIGHT MODERATION IS EXPECTED
SUNDAY. TEMPERATURES WILL SLOWLY RETURN TO NEAR AVERAGE EARLY NEXT
WEEK.

THERE IS STILL MOISTURE IN PLACE OVER WESTERN WASHINGTON WHICH
WILL RESULT IN SCATTERED SHOWERS THROUGH THURSDAY MORNING. THE AIR
MASS WILL BECOME COLD ENOUGH LATER TONIGHT SO THAT SOME SHOWERS
MAY FALL AS A MIX OF RAIN AND SNOW OR POSSIBLY JUST SNOW DOWN TO
SEA LEVEL. ISOLATED SNOW AMOUNTS ACROSS THE AREA WILL LIKELY
REMAIN BELOW ONE INCH IN THIS TYPE OF PATTERN. HOWEVER...THE PUGET
SOUND CONVERGENCE ZONE IS EXPECTED TO BE ACTIVE TONIGHT THROUGH AT
LEAST THURSDAY WHICH MAY PRODUCE LOCALLY HIGHER ACCUMULATIONS.
AREAS MOST LIKELY TO GET CONVERGENCE ZONE SNOW WILL BE FROM NORTH
SEATTLE ALONG THE I-5 CORRIDOR TO BELLINGHAM. SOME PLACES COULD
GET 1 TO 2 INCHES OF SNOW LATE TONIGHT THROUGH THURSDAY AFTERNOON.

DRIER AIR WILL FILTER INTO THE AREA THURSDAY NIGHT SO THE THREAT
OF PRECIPITATION WILL GREATLY DIMINISH THROUGH FRIDAY. ANOTHER
SYSTEM MAY ARRIVE SOMETIME SATURDAY AND SATURDAY NIGHT. CURRENT
COMPUTER MODELS SUGGEST THERE IS A CHANCE OF SOME LIGHT
ACCUMULATIONS ACROSS WESTERN WASHINGTON WITH THIS SYSTEM.

WEATHER.GOV/SEATTLE
MERCER/BURKE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PST WED JAN 09 2013

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1231 PM     HEAVY RAIN       1 E MARBLEMOUNT         48.53N 121.43W
01/09/2013  M2.85 INCH       SKAGIT             WA   TRAINED SPOTTER

            24 HOUR TOTAL AS OF NOON.

&&

GRUB