Small Craft Advisory 740, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
336 PM AKST MON DEC 3 2012

.SHORT TERM...EARLY AFTERNOON SATELLITE LOOP SHOWS PERSISTING HIGH
PRESSURE AREAS OVER THE CANADIAN YUKON AND ALASKAN INTERIOR WITH A
LOW PRESSURE SYSTEM ROTATING ACROSS THE GULF OF ALASKA. SEVERAL
SURFACE TROUGHS ARE PUSHING PRECIPITATION BAND ACROSS THE EASTERN
GULF AND THE PANHANDLE FROM THE SOUTH. SNOW CONTINUES NEAR HYDER
AND OVER THE NORTHERN AND CENTRAL PANHANDLE WITH RAIN ACROSS THE
SOUTHERN MOST AREAS. TIGHTENED NORTHERLY PRESSURE GRADIENT
MAINTAINS STRONG NORTH WIND ACROSS THE NORTHERN INNER CHANNELS AND
STRONG OUTFLOW WINDS NEAR INTERIOR PASSES.

 MODELS ARE IN FAIR AGREEMENT WITH A COMPLEX LOW PRESSURE SYSTEM
REMAINING CROSS THE ALASKAN GULF THROUGH TONIGHT. A 985 MB LOW
MOVING INTO THE SOUTHEAST GULF TONIGHT WILL DEEPEN A LITTLE OVER
THE EASTERN GULF AND SOUTHERN PANHANDLE BY TUESDAY MORNING...THEN
WEAKEN AS IT DRIFTS TO THE NORTHERN GULF THROUGH LATE TUESDAY
NIGHT. THE HIGH PRESSURE AREA IN THE CANADIAN YUKON AND ALASKAN
INTERIOR WILL PERSIST AND MAINTAIN THE STRONG NORTHERLY PRESSURE
GRADIENT.

 AS THE LOW MOVES INTO THE SOUTHEASTERN GULF TONIGHT...AN
ASSOCIATED OCCLUDED FRONTAL PASSAGE WILL BEGIN AFFECTING THE
SOUTHERN AREAS WITH RAIN AND SNOW...BECOMING HEAVY AT TIMES BY
EARLY EVENING. MIXED PRECIPITATION WILL BECOME ALL SNOW OVER
KETCHIKAN AREA TO THE NORTH AND 2 TO 4 INCHES OF SNOW ACCUMULATION
WILL BE POSSIBLE WITH ADDITIONAL ACCUMULATION UP TO AN INCH BY
TUESDAY MORNING. WILL ISSUE A WINTER WEATHER ADVISORY FOR
KETCHIKAN ZONE WITH THE AFTERNOON PACKAGE.

 STRONG WIND HEADLINES WILL STAY FOR THE NORTHERN MOST ZONES AND
STORM FORCE WINDS ACROSS THE NORTHERN INNER CHANNELS WITH HEAVY
FREEZING SPRAY. GALE FORCE WINDS WILL LIKELY TO PREVAIL OVER THE
CENTRAL INNER CHANNELS WITH FREEZING SPRAY THROUGH TUESDAY
MORNING.

 &&

 .LONG TERM...BROAD AREA OF LOW PRESSURE REMAINS OVER THE AK GULF
THROUGH THE WEEK WITH HIGH PRESSURE OVER THE YUKON. THE MAIN
CENTER WILL ROTATE AROUND THE GULF PUSHING WAVES OF PRECIPITATION
OVER THE PANHANDLE. NEXT MAIN BAND OF PRECIP FROM THIS LOW LOOKS
TO MOVES OVER THE REGION WEDNESDAY NIGHT. THE BLOCKING RIDGE THAT
HAD BEEN KEEPING A STABLE PATTEN OVER THE AREA LOOKS TO BREAK DOWN
EARLY IN THE WEEK ALLOWING A WAVE TO MOVE DOWN FROM THE KAMCHATKA
PENINSULA. THIS NEW LOW WILL BECOME VERTICALLY STACKED AS IT
BECOMES NEARLY STATIONARY NEAR THE TIP OF THE ALEUTIAN CHAIN. THE
BROAD LOW PRESSURE SYSTEM CURRENTLY OVER THE GULF WILL BE PUSHED
TO THE SOUTHEAST WITH AN ADVANCING RIDGE AHEAD OF THE ALEUTIAN
LOW. A STRONG FRONT AND TRIPLE POINT LOW LOOK TO DEVELOP FROM THIS
PARENT LOW AND WILL MOVE ACROSS THE AK GULF AND OVER THE PANHANDLE
SATURDAY INTO SUNDAY. THERE ARE SOME ISSUE WITH THE EXACT TIMING
OF THIS FRONT. PRECIPITATION MOVING IN WITH THIS FRONTAL BAND WILL
BE THE BIG QUESTION. THE ORIENTATION IS NOT CONDUCIVE FOR
SNOW...HOWEVER WITH THE COLD AIR THAT HAS BEEN ENTRENCHED OVER THE
PANHANDLE THIS COULD TURN INTO A SIGNIFICANT OVER RUNNING EVENT.
THERE IS PLENTY OF MOISTURE MOVING IN WITH THE FRONT AS THERE IS
GOOD TROPICAL CONNECTION INDICATED.

 TEMPERATURES WILL REMAIN CONSISTENT FOR THE FIRST PART OVER THE
LONG RANGE. THE SOUTHERN PANHANDLE WILL SEE A BIT OF WARMING
EARLIER AS GULF LOW MOVES UP SOME HIGHER 850 MB TEMPS FROM THE
SOUTH. COLD AIR SHOULD REMAIN IN PLACE NORTH OF FREDERICK SOUND
THROUGH THE WEEK. BY THE END OF THE WEEK THE ADVANCING RIDGE AND
THEN FRONT WILL MOVE IN SOME SIGNIFICANTLY WARMER TEMPERATURES.
THIS WARM AIR LOOKS TO MOVE AS FAR NORTH AS ICY STRAIT...SO
SATURDAY INTO SUNDAY EVENT COULD START AS SNOW THEN TRANSITION
INTO RAIN FOR THE CENTRAL PANHANDLE AS FLOW SHIFTS FROM THE NORTH
TO SOUTHEAST.

 THE STRONGER WINDS OVER THE NORTHERN INNER CHANNELS WILL FINALLY
BEGIN TO SUBSIDE THROUGH THE WEEK AS THE YUKON HIGH BEGINS TO
SHIFT TO THE EAST THEN THE GULF LOW MOVES TO THE SOUTHEAST. AS THE
PRESSURE GRADIENT WEAKENS WILL STILL SEE SOME LINGER GALES FOR
NORTHERN LYNN BUT ALL INSIDE CHANNELS SHOULD DROP TO SMALL CRAFT
OR BELOW BY THE WEEKEND. WINDS OVER THE AK GULF ON THE OTHER HAND
WILL PICK UP THROUGH THE WEEKEND...WITH UPPER GALE FORCE WINDS
POSSIBLE DUE TO THE INCOMING FRONT.

 NEW FORECAST HAD A SHIFT FROM PREVIOUS DAYS MODEL OF CHOICE. THE
ECMWF WHILE PREVIOUSLY MORE CONSISTENT SHOWED SIGNIFICANT CHANGES
RUN TO RUN FROM SUNDAYS 00Z OUTPUT. THE 12Z ECMWF IS NOW MORE IN
LINE WITH THE GFS...WHICH AS BEEN FAIRLY CONSISTENT SINCE SUNDAY.
FOR THE START OF THE LONG TERM ALL MODELS ARE HAVING ISSUES THE
NAM BECOMES AN EARLY OUTLIER WITH THE LOW CENTER FURTHER TO THE
NORTH AND EAST. HOWEVER NON OF THE MODELS IS REALLY HAVING A GREAT
TIME DEALING WITH THE POSITION OF THE LOW CENTER AS IT ROTATES
AROUND THE GULF. AS STATED ABOVE NEW GFS AND ECMWF WERE IN FAIR
AGREEMENT THOUGH THE FIST HALF OF THE LONG RANGE. FOR THE FRONT
MOVING ACROSS THE GULF TOWARD THE PANHANDLE SAT NIGHT INTO SUNDAY
THE ECMWF IS MORE PROGRESSIVE THAN THE GFS. USED A BLEND OF
GFS/ECMWF AND INHERITED GRIDS THROUGH DAY 3 THEN TRANSITIONED TO A
GFS/HPC BLEND FOR THE REMAINDER OF THE LONG RANGE. HAVE NOT RAISED
POPS OR WINDS QUITE UP TO THE MODELS FOR THE WEEKEND DUE TO THE
UNCERTAINTY RESOLVING THE FRONT. FORECAST CONFIDENCE IS AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH TUESDAY
     AFTERNOON FOR AKZ019.
         STRONG WIND THROUGH TUESDAY AFTERNOON FOR AKZ018.
         WIND CHILL ADVISORY UNTIL 9 AM AKST TUESDAY FOR AKZ018.
         WINTER WEATHER ADVISORY UNTIL 6 AM AKST TUESDAY FOR AKZ028.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011.
         HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-032.
         SMALL CRAFT ADVISORY FOR PKZ033>036-041>043-051-052.

&&

AHN/PRB