Small Craft Advisory 757, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
214 PM AKST WED NOV 23 2011

.SHORT TERM...COMPLEX LOW OVER THE GULF WILL GRADUALLY MOVE EWD
TO THE FAR ERN GULF BY LATE TONIGHT...THEN INLAND AND WEAKEN OVER
THE N-CENTRAL PANHANDLE THU. A SMALL BUT STRONG POLAR LOW OVER
THE S-CNTRL GULF WILL MOVE NE TO NEAR CAPE EDGECUMBE BY LATE
EVENING...THEN INLAND TO NEAR HOONAH BY DAYBREAK THU. THIS LOW
WILL RAPIDLY WEAKEN AS IT MOVES INLAND AND LIKELY DISSIPATE BY
LATE THU MORNING OVER THE NRN PANHANDLE. ANOTHER LOW WILL TRACK
NE ACROSS SRN HAIDA GWAII THEN TO THE CENTRAL BC COAST THU. USED
THE 12Z ECMWF AS IT HAD BEST FIT TO OBS AND SATELLITE DATA
ESPECIALLY WITH THE POLAR LOW.

 MAIN FORECAST CONCERNS WILL BE SNOWFALL AND WINDS. THE 2 MAIN
AREAS OF CONCERN FOR SNOWFALL ARE THE N-CENTRAL AREA...AND THE
FAR SERN CORNER. THE NRN AREA WILL SEE SNOW SHOWERS INCREASE LATE
THIS EVENING AS THE POLAR LOW MOVES ONSHORE. THERE WILL BE A WELL
DEFINED COMMA HEAD/DEFORMATION ZONE THAT REMAINS OVER THE
PAGS/PAOH/PAEL AREAS TONIGHT ALONG AND JUST NW OF THE POLAR
LOW... WHILE AREAS JUST E OF THERE ON SE SIDE OF THE POLAR LOW
WILL GET MORE SHOWERY PRECIP. WILL GO WITH WS WARNING FOR THE
ENTIRE N-CENTRAL AREA THRU 18Z THU 6 TO 12 INCHES OF SNOW. WILL
EXTEND CURRENT WW ADVY FOR ZONE 19 S OF PAHN AREA...WITH 4 TO
8 INCHES OF SNOW EXPECTED BY 18Z THU S OF PAHN.

 OVER THE SRN AREA...INVERTED TROF WILL DEVELOP TO THE NNE OF THE
LOW MOVING PAST THEM TO THE S...AND PRECIP WILL INCREASE OVER THE
SRN AREA TONIGHT. THERE WILL BE A FAIRLY SHARP NWRN EDGE TO THE
STEADIER PRECIP...WITH THE AXIS OF HEAVIEST PRECIP IN SERN ZONE
29. PTYPE MAY BE AN ISSUE ALONG DIXON ENTRANCE AREA AS SOME
WARMER MARINE AIR MOVES IN ON SE WINDS. WILL ISSUE WS WARNING FOR
ZONE 29 FOR MAINLY THE NE CORNER OF THAT AREA...WITH 18 TO
24 INCHES OF SNOW EXPECTED IN HYDER THRU THU AFTERNOON. WILL ALSO
ISSUE WW ADVY  FOR PAKT ZONE FOR 3 TO 8 INCHES MAINLY AROUND THE
PAKT AREA THRU THU AFTERNOON.

 AS FOR WINDS...MOST IMPORTANT AREA WIND WISE WILL BE AROUND THE
POLAR LOW MOVING IN TONIGHT. ON ITS S AND E SIDE EXPECT 40-45 KT
SLY WINDS ALONG THE FAR E-CNTRL GULF AND ADJACENT COASTAL AREA
LATE TONIGHT. WILL HAVE A PERIOD OF GALES IN THE N-CENTRAL
CHANNELS LATE TONIGHT AND EARLY THU MORNING AS POLAR LOW MOVES NE
TO HEAR HOONAH AROUND DAYBREAK THU. MAY SEE BRIEF PERIOD OF NLY
GALES IN LYNN CANAL EARLY THU MORNING AHEAD OF THE POLAR
LOW...WITH SCA WINDS EXPECTED IN THE ICY STRAIT/CROSS
SOUND/GLACIER BAY AREAS LATER TONIGHT AND THU MORNING.

 OTHERWISE...THE SNOW SHOWERS WILL DIMINISH LATER TONIGHT IN
ZONES 26 AND 27 AS THEY WILL BE IN BETWEEN SYSTEMS.

 &&

 .LONG TERM...EXTENDED RANGE PERIOD IS VERY ACTIVE WITH ONE SHORT
WAVE OR FRONT AFTER ANOTHER AFFECTING THE AREA THROUGH EARLY NEXT
WEEK. ALL OF THESE FOLLOWING THE SW FLOW ALOFT AROUND A LONG WAVE
TROUGH. SYSTEM ONE SHOWS UP EARLY FRIDAY AS A WEAK FRONT
ASSOCIATED WITH A 990 MB LOW IN THE CENTRAL GULF. TEMPERATURES
LOOK COLD ENOUGH FOR MORE SNOW FOR MOST AREAS OF THE PANHANDLE
WITH THE HIGHEST AMOUNTS, WITHIN ADVISORY CRITERIA, SHOWING UP IN
THE NORTHERN HALF OF THE PANHANDLE.

 SYSTEM NUMBER TWO FOLLOWS ON THE HEELS OF THE FIRST WITH A
980 MB LOW PLOWING INTO THE SOUTHERN PANHANDLE EARLY SAT BRINGING
PRECIP TO THE SOUTHERN HALF OF THE PANHANDLE. THE SOUTHERLY PUSH
AHEAD OF THE LOW WILL BRING GALES INTO CLARENCE STRAIT AS WELL AS
TURN THE SNOW INTO RAIN FROM SUMNER STRAIT SOUTHWARD. BEHIND IT,
THE COLD AIR RETURNS POSSIBLY CHANGING THE RAIN BACK TO SNOW JUST
BEFORE IT ENDS.

 BEHIND SYSTEM TWO IS A DAY LONG BREAK WITH ONLY A VERY WEAK
TROUGH TO BREAK IT EARLY SUNDAY. OTHERWISE SNOW SHOWERS CONTINUE
IN THE COLD AIR AND THE SW FLOW.

 LATE SUNDAY NIGHT IS WHEN SYSTEM NUMBER THREE MAKES ITS PRESENTS
KNOW AS A STRONG FRONT ASSOCIATED WITH ANOTHER 975 MB LOW IN THE
NW GULF MOVES INTO THE PANHANDLE. THIS SYSTEM WILL BRING WARMER
AIR IN BEHIND IT POSSIBILITY MIXING THE SNOW WITH RAIN OVER MOST
OF THE AREA BY MONDAY. MODEL AGREEMENT IS STARTING TO BREAK DOWN
WITH THIS SYSTEM AS THE CURRENT EC IS MUCH FASTER IN BRINGING THE
FRONT INTO THE AREA THAN THE GFS CURRENTLY IS.

 THEN BEHIND THAT ONE IS ONE OR TWO MORE SYSTEMS, DEPENDING ON
THE MODEL THAT YOU LOOK AT. DECIDED TO STICK WITH NAM WITH SOME
EC OR UK THROUGH THE MID RANGE PERIOD DUE TO GOOD AGREEMENT WITH
EACH OTHER IN SOME CASES. WENT TOWARD THE HPC DATA FOR EXTENDED
RANGE UPDATES DUE TO THE INCREASING DISAGREEMENTS IN THE LONGER
RANGE MODELS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY UNTIL 3 PM AKST THIS AFTERNOON FOR
     AKZ020>022-026.
         WINTER WEATHER ADVISORY UNTIL 4 PM AKST THIS AFTERNOON FOR
     AKZ017-018-023>025-027.
         WINTER STORM WARNING UNTIL 9 AM AKST THURSDAY FOR AKZ020>025.
         WINTER WEATHER ADVISORY UNTIL NOON AKST THURSDAY FOR AKZ028.
         WINTER STORM WARNING UNTIL 4 PM AKST THURSDAY FOR AKZ029.
         WINTER WEATHER ADVISORY UNTIL 9 AM AKST THURSDAY FOR AKZ019.
MARINE...GALE WARNING FOR PKZ012-031>033-041-042.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-034>036-043-051.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ052.

&&

RWT/EAL