Winter Storm Warning 16, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
212 PM AKST SUN MAR 1 2009

.SHORT TERM...MORNING SATELLITE LOOP SHOWS A WEAKENING LOW IN
THE NORTHERN GULF WITH ITS ASSOCIATED TRAILING TROUGH MOVING
NORTH JUST WEST OF YAKUTAT BAY. PERSISTING HIGH PRESSURE OVER
WESTERN YUKON CONTINUES GENERATE TIGHT PRESSURE GRADIENT OVER THE
NORTHERN PANHANDLE WITH GUSTY WINDS ACROSS THE SKAGWAY AND HAINES
AREAS. WILL NEED TO BRING THE CURRENT WIND ADVISORY FOR
SKAGWAY...BEGINS AT 9 PM THIS EVENING...EARLIER TO AROUND 3 PM
THIS AFTERNOON. A DEVELOPING LOW IN THE NORTHEAST PACIFIC PUSHES
AN OCCLUSION TOWARDS THE QUEEN CHARLOTTES WITH ITS TRIPLE POINT
HEADING TO WEST OF DIXON ENTRANCE. SNOW BEGAN OVER
KETCHIKAN...ANNETTE AND HYDER AREAS BY MID MORNING. THIS SNOW
EVENT WILL TURN TO RAIN AS WARMER AIR MOVES INTO THE AREA THIS
AFTERNOON WITHOUT ANY SIGNIFICANT ACCUMULATION. MODELS ARE IN
FAIR AGREEMENT WITH THE LOW IN THE NORTHEAST PACIFIC TRACKING
SLOWLY NORTH INTO THE SOUTHEAST GULF THROUGH LATE MONDAY NIGHT.
WILL USE THE NAM12 SOLUTIONS TO MAKE FINE TUNES OVER THE
INHERITED GRIDS.

 THE NORTHEAST PACIFIC LOW WILL PLAY A MAJOR ROLE FOR SOUTHEAST
ALASKA WEATHER TONIGHT AND MONDAY. AN INVERTED TROUGH AHEAD OF
THE INCOMING OCCLUSION WILL MOVE NORTH ACROSS THE PANHANDLE COAST
THROUGH LATE TONIGHT. THE OCCLUDED FRONT WILL KEEP ITS TRIPLE
POINT MARCHING NORTH ACROSS THE DIXON ENTRANCE THIS EVENING AND
FARTHER NORTH ACROSS THE CENTRAL PANHANDLE THROUGH MONDAY
MORNING. MODERATE ISENTROPIC LIFTING IS EXPECTED WHILE THE TRIPLE
POINT TRAVELS NORTH ACROSS THE CENTRAL PANHANDLE. EXPECT 3 TO
6 INCHES OF SNOW ALONG THE SNOW CORRIDOR FROM SITKA TO JUNEAU.
WILL ISSUE SNOW ADVISORY FOR TONIGHT THROUGH MONDAY MORNING.
JUNEAU AND VICINITY MAY RECEIVE A BIT HIGHER SNOW AMOUNT MONDAY
MORNING.

 AS THE LEADING EDGE OF THE FRONT MOVES FROM SOUTH ACROSS DIXON
ENTRANCE...WIND WILL PICK UP ALONG THE OUTER COAST OF HYDER ZONE
THIS EVENING. WILL ISSUE WIND ADVISORY FOR HYDER ZONE FOR THIS
EVENING.HIGH PRESSURE OVER WESTERN YUKON WILL WEAKEN AND MOVE
EAST BUT ANOTHER HIGH PRESSURE OVER ALASKA INTERIOR WILL TRACK
EAST INTO THE WESTERN YUKON. THIS WILL MAINTAIN TIGHT NORTHEAST
PRESSURE GRADIENT ACROSS THE NORTHERN PANHANDLE...INCLUDING
YAKUTAT...THROUGH MONDAY MORNING. WILL ISSUE WIND ADVISORY FOR
NORTHERN ZONES. GALE WILL CONTINUE ACROSS GLACIER BAY AND
NORTHERN LYNN CANAL TONIGHT.

.LONG TERM...THE REMNANTS OF INVERTED TROF OVER THE PANHANDLE
WILL CONTINUE TO WEAKEN AND MOVE OFF SHORE AS THE PARENT LOW
SOUTHWEST OF QUEEN CHARLOTTE ISLAND CONTINUES TO WEAKEN AND MOVE
TO THE SOUTHEAST. THE SNOW IN THE CENTRAL AND NORTHERN PANHANDLE
AND RAIN IN THE SOUTHERN PANHANDLE WILL TAPER OFF ON TUESDAY AS
MIDDLE AND UPPER LEVEL NORTH PACIFIC RIDGE BUILDS BACK TOWARDS THE
NORTHEAST GULF OF ALASKA. IN THE LOW LEVELS A HIGH MOVING THROUGH
THE YUKON AND INTO NORTHERN BC WILL BRING WEAK OFF SHORE FLOW.
WINDS REMAIN THROUGH LATE THURSDAY AND INTO FRIDAY AS THE NEXT
SYSTEM DEVELOPS IN THE NORTHERN GULF OR SOUTHERN ALASKA AND PULLS
A STRONG SHORTWAVE TROF OVER THE PANHANDLE.

CONSIDERABLE SPREAD EXISTS IN THE MODELS BY FRIDAY FOR POSITION
AND STRENGTH OF THE NORTH PACIFIC HIGH AND CONSEQUENTLY FOR
SYSTEMS DEVELOPING UPSTREAM. OPTED TO NOT INTRODUCE LARGE CHANGES
INTO THE GRIDS FOR DAY 6 AND BEYOND BY UPDATING INHERITED GRIDS
WITH LATEST HPC GUIDANCE. FOR THE TOMORROW NIGHT PERIOD THROUGH
DAY 4 I OPTED TO BLEND INHERITED GRIDS WITH 12Z NAM12 AS THIS
PROVIDED NICE CONTINUITY WITH MONDAYS SYSTEM AND BLENDED WELL WITH
SHORT TERM HAND OFF. 12Z NAM INITIALIZED WELL AND IS HANDLING THE
DEVELOPING GRADIENT IN THE NORTHERN ZONES WELL. A NUDGE FROM
INHERITED GRIDS TO HPC GUIDANCE WAS MADE FOR DAY 4 TO DAY 6 GRIDS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 12 PM AKST
     MONDAY FOR AKZ021-023>025.
         WIND ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM AKST MONDAY FOR
     AKZ020-022.
         WIND ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT AKST TONIGHT
     FOR AKZ029.
         WIND ADVISORY FROM 6 PM THIS EVENING TO 9 AM AKST MONDAY FOR
     AKZ019.
         WIND ADVISORY UNTIL 12 PM AKST MONDAY FOR AKZ018.
         WIND ADVISORY FROM 9 PM THIS EVENING TO 12 PM AKST MONDAY FOR
     AKZ017.
MARINE...GALE WARNING FOR PKZ011-012-051.
         SMALL CRAFT ADVISORY FOR PKZ013-021-022-031-032-035-036-041>043-
     052.

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SJA/CCC