Small Craft Advisory 748, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
631 AM AKST MON NOV 21 2011

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS A LOW PRESSURE
SYSTEM OVER THE EASTERN GULF PRODUCING WINTER WEATHER OVER THE
NORTHERN TWO THIRDS OF THE INNER CHANNELS. ALONG WITH THE WINTER
WEATHER THE LOW IS ALSO PRODUCING LOCALLY STRONG WINDS WITH GUSTS
TO 45 MPH. STATIONS FROM THE CENTRAL COASTAL AREAS TO THE
SOUTHERN INNER CHANNELS HAVE CHANGED OVER TO RAIN WITH WARM AIR
LIFTS NORTH. THIS WARMER AIR WILL PUSH ITS WAY THROUGH THE INNER
CHANNELS THROUGH THE DAY AS THE PRESSURE GRADIENT STRENGTHENS
FROM THE SOUTH. THE WINDS WILL DIMINISH THROUGH THIS AFTERNOON AS
THE LOW WEAKENS AND LIFTS INTO THE NORTHEAST GULF THIS EVENING
AND INTO THE NORTHERN GULF LATE TONIGHT.

 MODERATE TO HEAVY SNOW WILL CONTINUE OVER THE INNER CHANNELS
THROUGH THIS EVENING. AS THE LOW TRACKS NE THE WARMER AIR WILL
DRIFT NORTH THROUGH THE DAY TO ABOUT THE ICY STRAIT AREA WITH
SNOW PERSIST FROM THERE NORTHWARD. THE SNOW WILL MIX AND CHANGE
TO RAIN THROUGH THE EARLY AFTERNOON OVER THE CENTRAL INNER
CHANNELS AND OVER THE NORTH CENTRAL AREAS BY THE LATE AFTERNOON.
SNOW AMOUNTS WILL RANGE FROM 6 TO 10 INCHES OVER THE CENTRAL
AREAS WITH 8 TO 15 INCHES FROM PAOH NORTHWARD. THE JUNEAU AREA
WILL SEE 3 TO 5 INCHES BY THIS AFTERNOON BEFORE MIXING WITH RAIN
IN THE AFTERNOON. DID ISSUES A WINTER STORM WARNING FOR ZONES
20 AND 19 THROUGH LATE TONIGHT AS MOISTURE WILL CONTINUE TO
OVERRUN THE COLD ARCTIC AIR IN PLACE AND A DEFORMATION BAND WILL
SET UP FROM PAGS TO PAHN THIS EVENING. THE PRECIP WILL TAPPER OFF
LATE TONIGHT AS THE UPPER LEVEL DYNAMICS WEAKENS BUT MOST PLACE
WILL SWITCH BACK TO SNOW OVER THE NORTHERN HALF THE LOW LEVEL
FLOW BACKS AROUND TO THE EAST. SNOW WILL DEVELOP OVER THE
NORTHERN COAST COAST LATE THIS AFTERNOON INTO THIS EVENING WITH
ABOUT 2 INCHES EXPECTED.

 THE LOW IS PRODUCING STRONG WINDS OVER THE MARINE WATERS OF THE
EASTERN GULF AND INNER CHANNELS THIS MORNING. MOST MARINE
STATIONS OVER THE SOUTHERN HALF ARE REPORTING SE WINDS FROM 25 TO
40 KT WITH HIGHER GUST FROM INTERIOR PASSES. THERE IS GALE FORCE
WINDS OVER E/W CHANNELS AND STORM FORCE TO GALES OVER LYNN CANAL.
THESE WINDS WILL DECREASE THROUGH THIS AFTERNOON AS THE PRESSURE
GRADIENT WEAKENS. OVER LAND THE IS LOCALLY WINDY CONDITIONS WITH
GUSTS TO 40 MPH IN EXPOSED AREAS AND NEAR INTERIOR PASSES. THESE
WINDS WILL ALSO DIMINISH BY THIS AFTERNOON. THE ONLY PLACE THAT
WILL CONTINUE TO SEE STRONG WINDS FROM THE NORTH INTO TONIGHT
WILL BE OVER LYNN CANAL AND NEAR PAGY. MOST OTHER PLACES WILL SEE
MIN SMALL CRAFT FROM THE EAST TO SOUTHEAST.

.LONG TERM /TUESDAY THROUGH SUNDAY/...MID LEVELS: A 500 MB LONG
WAVE TROUGH OVER THE AK GULF WILL BE THE MAIN FEATURE THROUGH THE
LONG RANGE FORECAST. A 500 MB RIDGE TO THE WEST WILL BEGIN TO
FLATTEN THROUGH TUE THEN BY THURSDAY ANOTHER RIDGE WILL BUILD IN
THE BERING SEA THEN FLATTEN AS IT MOVES EAST INTO THE AK GULF
THROUGH THE WEEKEND. A CLOSED MID LEVEL LOW ORIGINATING IN THE
ARCTIC WILL DROP SOUTH DOWN THE AK INTERIOR AND INTO THE NORTHERN
AK GULF TUE THEN SIT THERE THROUGH THURSDAY. SOME MIGHTY COLD AIR
WILL MOVE SOUTH WITH THIS LOW.

 THIS MID LEVEL ARCTIC FEATURE WILL BE REFLECTED AT THE SURFACE
AS A 967 MB LOW DEVELOPING IN THE NORTHERN GULF ON TUESDAY. THE
LOW WILL BECOME QUASI STATIONARY WITH ITS CENTER ROTATING COUNTER
CLOCKWISE AROUND A POINT IN THE NORTH CENTRAL GULF. WHILE THIS
LOW IS WOBBLING AROUND THE GULF ON WED A SHORT WAVE TRACKING UP
FROM THE NORTH PACIFIC TOWARD HAIDA GWAII WILL BE ABSORBED AT A
TRIPLE POINT OF THE WOBBLING LOW BY WED. WHILE THIS SHORTWAVE MAY
PUSH UP SOME WARMER AIR THE ARCTIC AIR MASS LOOKS TO BE A BIT
STRONGER, AS SEEN WITH 850MB TEMPS OF -8C TO -14C. BY MID WEEK
THE WOBBLE IN THE LOW BECOMES A LITTLE MORE PRONOUNCED WITH THE
LOW CENTER PUSHING FURTHER SOUTH. BY THURSDAY A SECOND STRONGER
LOW MOVES UP FORM THE NORTH PACIFIC TRACKING TOWARD HAIDA GWAII.
SOME DIFFERENCES WITH THE STRENGTH OF THE LOW AND IT POSITION.
WITH THE ARCTIC JET MOVED FURTHER SOUTH EXPECTING THIS LOW TO
REMAIN SOUTH OF THE PANHANDLE. BY THE WEEKEND THE WOBBLING LOW
WILL HAVE WEAKENED AS HIGH PRESSURE BUILDS OVER BRITISH COLUMBIA.
YET ANOTHER LOW WILL MOVE UP FORM THE NORTH PACIFIC BUT MODELS
SPREAD IS FAIRLY HIGH WITH THIS LOWS TRACK.

 PRECIPITATION WILL CONTINUE THROUGH MID WEEK FOR MOST OF THE
REGION. BY THURSDAY WINDS WILL SHIFT OFFSHORE FOR THE NORTHERN
1/3 OF THE PANHANDLE AS THE LOW IN THE GULF TRACKS SOUTH SO
PRECIP WILL BEGIN TO DIMINISH. MEANWHILE THE SOUTHERN REGIONS
WILL SEE FEWER BREAKS IN PRECIP WITH ONSHORE FLOW AND FRONTAL
BANDS MOVING UP FROM THE SOUTH. WILL MAINLY SEE A RAIN SNOW MIX
FOR THE SOUTHERN THIRD TRANSITIONING TO SOLID SNOW AS ONE MOVES
NORTH.

 ONE ISSUE WITH THE LONG TERM FORECAST WAS DEALING WITH THE
INCOMING AIR MASS TEMPERATURE AND THE RESULTING PRECIPITATION
TYPE. GFS WAS MUCH COLDER THAN THE NAM WHICH WAS A BIT COLDER
THEN THE EC WHICH WAS A BIT COLDER THEN INHERITED GRIDS. NUDGED
TEMPS DOWN SLIGHTLY BUT WILL NEED TO WATCH THESE. MODELS START IN
FAIR AGREEMENT AT THE START OF THE LONG TERM, USED A EC/NAM BEND
WITH INHERITED GRIDS AS THEY WERE IN BEST AGREEMENT AND
TRANSITIONED WELL FROM SHORT TERM GRIDS. FROM THERE SWITCHED TO
HPC GUID FOR AN ENSEMBLE BLEND. FOR THE THURSDAY LOW GFS WAS
TRACKING FURTHER SOUTH AND WAS WEAKER THAN THE EC, WHILE THE FRI
LOW WAS FASTER WITH THE EC SOLUTION COMPARED TO THE GFS.
OPERATIONAL EC WAS FAIRLY CONSISTENT RUN TO RUN THROUGH THE
WEEKEND THEN BEGAN TO SEE A GREATER SPREAD. WITH THE FAIR AMOUNT
OF MODEL SPREAD FORECAST CONFIDENCE IS A BIT BELOW AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL NOON AKST TODAY FOR AKZ024-026-029.
         WINTER WEATHER ADVISORY UNTIL 4 PM AKST THIS AFTERNOON FOR
     AKZ025.
         WINTER STORM WARNING UNTIL 4 PM AKST THIS AFTERNOON FOR AKZ021-
     022.
         WINTER STORM WARNING UNTIL 1 AM AKST TUESDAY FOR AKZ019-020.
         WIND CHILL ADVISORY UNTIL 4 PM AKST THIS AFTERNOON FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ013-021-022-031-034>036-042-043.
         SMALL CRAFT ADVISORY FOR PKZ011-032-033-041-051>053.

&&

ABJ/PRB

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
724 AM AKST MON NOV 21 2011

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

0613 AM     HEAVY SNOW       PETERSBURG              56.81N 132.96W
11/21/2011  M5.0 INCH                           AK   CO-OP OBSERVER

            PETERSBURG AIRPORT

0613 AM     HEAVY SNOW       12 S PETERSBURG         56.64N 132.96W
11/21/2011  M7.0 INCH                           AK   CO-OP OBSERVER

            MITKOF ISLAND

0722 AM     HEAVY SNOW       9 S PETERSBURG          56.68N 132.96W
11/21/2011  M4.0 INCH                           AK   CO-OP OBSERVER

0722 AM     HEAVY SNOW       PETERSBURG              56.81N 132.96W
11/21/2011  M3.0 INCH                           AK   CO-OP OBSERVER

            IN TOWN

&&

GLS