Small Craft Advisory 576, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
230 PM AKDT MON SEP 26 2011

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS A 975MB LOW SW
OF HAIDA GWAII DRIFTING NE. THIS LOW WILL CONTINUE ON THIS TRACK
AND MOVE OVER THE FAR SOUTHERN AREAS THROUGH TONIGHT AND INTO
CANADA TUESDAY. A RIDGE OF HIGH PRESSURE WILL BUILD OVER THE
FORECAST AREA LATE TUE AFTERNOON. RAIN IS BEING REPORTED OVER THE
FAR SOUTHERN ZONES ATTM AND WILL SLOWLY SPREAD NORTHWARD THROUGH
TONIGHT BUT WITH STRONG OFFSHORE FLOW THE NORTHERN AREAS WILL
REMAIN ON THE DRY SIDE. THE RAIN WILL SLOWLY TAPPER OFF TO
SCATTERED SHOWERS OVER THE SOUTHERN HALF THROUGH TUESDAY WITH A
CHANCE OVER THE CENTRAL AREAS NEAR THE COAST RANGE.

 GALE FORCE WINDS ARE BEING REPORTED OVER THE SE GULF ALONG OVER
THE SOUTHERN INNER CHANNELS WITH STRONG GUST OVERLAND. THE
NORTHERN HALF OF THE PANHANDLE ARE SEEING NORTHERLY SMALL CRAFTS
WITH A TIGHT PRESSURE GRADIENT AS THE LOW LIFTS NORTH. THESE
WINDS WILL SLOWLY DIMINISH TONIGHT AS THE LOW WEAKENS AND THE
PRESSURE GRADIENT RELAXES. AS THE LOW LIFTS INTO CANADA AND THE
RIDGE BUILDS OVER THE AREA THE WINDS WILL SLOWLY BACK AROUND TO
THE SOUTH AND INCREASE TO RANGE FROM 15 TO 25 KT FROM SOUTH TO
NORTH BY THE LATE AFTERNOON.

 USED MAINLY THE 12Z EC FOR THE UPDATES TO THE FORECAST FOR THE
NEXT 24HRS WITH ABOVE AVERAGE FORECASTER CONFIDENCE.

&&

.LONG TERM...MODELS ARE IN GENERAL AGREEMENT THROUGH THURSDAY
NIGHT WITH A WEAK RIDGE OF HIGH PRESSURE BUILDS ACROSS THE EASTERN
GULF AND SOUTHEAST ALASKA TUESDAY NIGHT...AND THE RIDGE WILL BEGIN
ERODING BY WEDNESDAY NIGHT AS A DEVELOPING LOW IN THE WESTERN GULF
MOVES INTO THE NORTH CENTRAL GULF...THEN ANOTHER DEVELOPING STORM
IN THE NORTHEAST PACIFIC MOVES IN THE FAR SOUTHEAST GULF THURSDAY
MORNING.

 THE GFS AND NAM HANDLE THE SYNOPTIC FEATURES TOO QUICKLY AND
PREFER THE SLOWER ECMWF SOLUTIONS FOR THE AFTERNOON FORECAST
PACKAGE. REFRESHED THE INHERITED GRIDS WITH THE ECMWF THROUGH
THURSDAY NIGHT. THE LOW MOVING INTO THE NORTH CENTRAL GULF WILL BE
ABSORBED BY THE INCOMING STORM IN THE FAR SOUTHEAST GULF BY MIDDAY
THURSDAY. THE STORM WILL CONTINUE TO DRIFT NORTHWARD ACROSS HAIDA
GWAII AND DIXON ENTRANCE THROUGH LATE THURSDAY NIGHT THEN ONSHORE
OVER THE SOUTHERN PANHANDLE BY FRIDAY MORNING BEFORE DISSIPATING
NORTHEAST OF THE AREA ON FRIDAY AFTERNOON.

 A RIDGE WILL REBUILD BEHIND THE DISSIPATING LOW ACROSS THE
FORECAST DOMAIN. BY THE TIME...HOWEVER...MODEL DIVERGENCE GROWS
SOMEWHAT BIGGER AND MODEL SOLUTIONS ARE STRUGGLING FOR THE REST OF
THE LONG TERM PERIODS. PREFERRED THE HPC OUTPUT OF ECMWF AND ECMWF
ENSEMBLE APPROACHES FOR THE PRESSURE FIELDS. ANOTHER DEVELOPING
STORM IN BERING SEA ON FRIDAY MORNING WILL MOVE INTO THE WESTERN
GULF EARLY SATURDAY MORNING...PUSHING THE RIDGE EASTWARD INTO
CANADA AND BRINGING A FRONTAL PASSAGE INTO THE EASTERN GULF
THROUGH SATURDAY AND SUNDAY.

 GALE FORCE WINDS ARE EXPECTED AGAIN WITH THE FROPA ACROSS THE
OUTSIDE COASTAL WATERS OVER THE WEEKEND. THE ECMWF HAS SHOWN A
PRETTY GOOD CONSISTENCY OVER THE PAST SEVERAL RUNS AND BLENDED TO
POPULATE THE POP FIELDS FOR THE ENTIRE LONG TERM PERIODS. EXCEPT
YAKUTAT AREA AND NORTHERN MOST PANHANDLE...LIKELY TO CATEGORICAL
POPS WILL PREVAIL ACROSS THE PANHANDLE MUCH OF THE WEEK...AND INTO
THE WEEKEND THROUGH EARLY NEXT WEEK.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 4 PM AKDT THIS AFTERNOON FOR AKZ027>029.
MARINE...GALE WARNING FOR PKZ036-041-042.
         SMALL CRAFT ADVISORY FOR PKZ012-013-022-031>035-043.

&&

ABJ/AHN