Small Craft Advisory 908, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
115 PM AKST WED NOV 19 2008

.ANALYSIS AND UPPER LEVELS...LARGE LOW COMPLEX EMBEDDED WITHIN HIGH
AMPLITUDE LOW WAVELENGTH THROUGH IS CENTERED SOUTH OF THE GULF. THIS
POSITION IS FARTHER NORTH THAN ON TUESDAY AND SYSTEMS ARE NOW
AFFECTING SOUTHCENTRAL. THERE ARE CURRENTLY FOUR SURFACE LOWS
EMBEDDED WITHIN THE LARGE SCALE UPPER LEVEL CIRCULATION. OF MOST
CONCERN TODAY IS A 995 MB LOW SOUTHEAST OF KODIAK ISLAND AND THE
OCCLUDED FRONT WHICH EXTENDS NORTHEAST FROM THE LOW CENTER. THERE
IS A BAND OF STORM FORCE WINDS AHEAD OF THE FRONT ALONG THE GULF
COAST AS SEEN IN QUICKSCAT WINDS. GAP WINDS HAVE INCREASED ACROSS
SOUTHCENTRAL OVERNIGHT THROUGH THIS MORNING WHILE NEARBY AREAS
REMAIN UNDER THE INFLUENCE OF A TEMPERATURE INVERSION WITH LIGHT
WINDS. THIS HAS CREATED LARGE TEMPERATURE DIFFERENCES BETWEEN WINDY
AREAS AND NON-WINDY AREAS ACROSS VERY SMALL DISTANCES. RADAR RETURNS
IN THE PRINCE WILLIAM SOUND REGION HAVE LOOKED IMPRESSIVE...BUT
STRONG OFFSHORE FLOW IS HELPING TO MAINTAIN LOW LEVEL DRY AIR SO
VERY LITTLE PRECIPITATION REACHING THE GROUND. SNOW IS FALLING OVER
KODIAK ISLAND UNDER STRONG NORTHWEST SURFACE FLOW...WHICH IS HELPING
MAINTAIN TEMPERATURES COLD ENOUGH FOR SNOW AND REDUCING VISIBILITIES
TO AROUND ONE HALF MILE. A TIGHT PRESSURE GRADIENT COMBINED WITH
COLD ADVECTION IS ALSO PRODUCING GUSTY NORTHERLIES ACROSS SOUTHWEST
ALASKA AND THROUGH THE ALASKA PENINSULA...ALTHOUGH MUCH OF THE
KUSKOKWIM DELTA AND VALLEY REMAIN UNDER AN INVERSION WITH
TEMPERATURES WELL BELOW ZERO.

ANOTHER LARGE UPPER LOW IS MOVING OUT OF EASTERN ASIA WITH UPPER JET
DRIING NORTHEASTWARD TOWARD THE WESTERN BERING SEA. THIS IS HELPING
TO PUSH ON AND AMPLIFY THE RIDGE SITTING OVER THE BERING. WINDS ARE
GENERALLY LIGHT ACROSS THE CENTRAL BERING WHILE WINDS ARE RAPIDLY
INCREASING ACROSS THE WESTERN BERING WITH THE APPROACHING SYSTEM.

.MODEL DISCUSSION...MODELS INITIALIZED WELL WITH SYNOPTIC FEATURES
AND SHOW FAIR TO POOR RUN-TO-RUN CONSISTENCY THROUGH THE FIRST THREE
DAYS OF THE FORECAST. THE GENERAL EVOLUTION OF THE PATTERN IS THE
SAME...BUT THE DETAILS OF INDIVIDUAL LOW TRACKS AND STRENGTH ARE NOT
VERY CONSISTENT. THERE IS A LITTLE MORE CONFIDENCE IN THE
GULF/SOUTHCENTRAL FORECAST WHERE THE MODELS ARE IN BETTER AGREEMENT.

THE MODEL PREFERENCE IN THE EAST IS TOWARD THE 12Z GFS WHILE OUT
WEST WILL TREND SLIGHTLY TOWARD THIS SOLUTION. ALSO OF NOTE...ALL
MODELS ARE OVERDOING PRECIPITATION ACROSS PRINCE WILLIAM SOUND...AND
THIS WILL BE REFLECTED IN THE NEW FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...OCCLUDED FRONT WILL DISSIPATE OFFSHORE TONIGHT
AS THE LOW OVER THE SOUTHWEST GULF ROTATES SOUTHWARD. THERE IS AN
UPPER LEVEL VORTICITY-MAXIMUM THAT WILL ROTATE A LITTLE FARTHER
WESTWARD ACROSS THE KENAI PENINSULA AND KODIAK ISLAND BEFORE
WEAKENING AND ROTATING SOUTHWESTWARD. THIS WILL HELP PUSH SNOW
ONSHORE OVER WESTERN PRINCE WILLIAM SOUND AND MAINTAIN SNOW OVER
KODIAK ISLAND THROUGH MUCH OF TONIGHT. DUE TO CONTINUES STRONG
OFFSHORE FLOW...AMOUNTS WILL BE LIGHT OVER PRINCE WILLIAM SOUND.
MODELS HINT AT A LITTLE BIT OF SNOW MAKING ACROSS THE COASTAL RANGE
TO ANCHORAGE AND THE WESTERN KENAI PENINSULA...BUT THINK IT WILL
BE VERY DIFFICULT FOR SNOW TO REACH THE GROUND DUE TO STEADY SUPPLY
OF DRY AIR UNDER NORTHERLY SURFACE FLOW. A DEVELOPING LOW ON THE
EAST SIDE OF THE UPPER CIRCULATION WILL ROTATE INTO THE SOUTHERN
GULF LATER TONIGHT AND BECOME THE NEW PRIMARY CENTER OF THE UPPER
CIRCULATION. THE LOW WILL THEN TRACK EASTWARD THURSDAY THROUGH
FRIDAY AS THE SYSTEMS OUT WEST GRADUALLY FORCE THE PATTERN TO
PROGRESS. THUS THE FRONT ASSOCIATED WITH THIS SECOND LOW WILL NOT
MAKE IT VERY FAR NORTH AND WEST ACROSS THE GULF SO THERE WILL BE
JUST A CHANCE OF LIGHT PRECIPITATION ALONG THE IMMEDIATE GULF COAST.

WINDS WILL DIMINISH ACROSS THE REGION FRIDAY AS THE GRADIENT WEAKENS.
THE LATEST MODELS INDICATE THE BERING LOW TRACKING TO SOUTHCENTRAL
SATURDAY BRINING A SHOT OF SNOW...BUT THERE IS LOW CONFIDENCE IN
THIS SOLUTION.

SOUTHWEST ALASKA/ALASKA PENINSULA...AS THE BERING RIDGE CONTINUES
TO AMPLIFY AN UPPER TROUGH CURRENTLY OVER THE NORTH SLOPE OF ALASKA
WILL BE FORCED SOUTHWARD TO SOUTHWEST ALASKA ON THURSDAY. THIS WILL
ADVECT ARCTIC AIR SOUTHWARD WHICH WILL COMBINE WITH AN ALREEADY
TIGHT PRESSURE GRADIENT TO PRODUCE STRONG AND GUSTY NORTHERLIES
ACROSS SOUTHWEST ALASKA AND THE ALASKA PENINSULA. IT APPEARS THAT
THERE IS ENOUGH COLD ADVECTION ALOFT TO ELIMINATE THE SURFACE-BASED
INVERSION AND ALLOW WINDS TO MIX DOWN TO THE SURFACE ACROSS THE
ENTIRE REGION. THE STRONGEST ADVECTION AND WINDS LOOK TO EXTEND
DOWN THE HEART OF THE KUSKOKWIM VALLEY TO BRISTOL BAY AND ACROSS
THE ALASKA PENINSULA SOUTH OF KING SALMON. THE COLD ADVECTION WILL
END LATE THURSDAY NIGHT AND THE SURFACE GRADIENT WILL WEAKEN AS THE
GULF LOW TRACKS EASTWARD...SO WINDS WILL DIMINISH QUICKLY. BERING
LOW LOOKS LIKE IT WILL TRACK ALONG THE ALASKA PENINSULA FRIDAY NIGHT
AND SATURDAY AND BRING A CHANCE OF PRECIPITATION TO THESE AREAS...BUT
THERE IS LOW CONFIDENCE IN THIS TRACK.

BERING SEA/ALEUTIANS...A STRONG LOW CURRENTLY OVER THE SOUTH END
OF KAMCHATKA WILL TRACK NORTHEASTWARD TODAY PUSHING A STRONG FRONT
EASTWARD ACROSS THE WESTERN BERING AND ALEUTIANS. A STRONG JET OVER
THE NORTHWEST PACIFIC WILL AID DEVELOPMENT OF A LOW ALONG THE FRONT
WHICH WILL INTENSIFY AS IT CROSSES THE WESTERN ALEUTIANS INTO THE
BERING SEA ON THURSDAY. THERE IS STILL QUITE A BIT OF MODEL
DISAGREEMENT ON THE STRENGTH AND TRACK OF THIS LOW...SO HAVE STUCK
FAIRLY CLOSE TO CURRENT FORECAST WHICH MAXES WINDS OUT AT 45KT. ALL
MODELS DO INDICATE BERING SEA RIDGE WILL BREAK DOWN COMPLETELY
FRIDAY...SO EXPECT STORM SYSTEM TO MAKE EASTWARD PROGRESS FRIDAY
AND SATURDAY AS ANOTHER STORM MOVES TO THE WESTERN ALEUTIANS.

.LONG TERM FORECAST...MEAN TROUGH WILL ENCOMPASS THE FORECAST
AREAS THROUGH THE EXTENDED PERIOD WITH A STRONG JET JUST SOUTH
OF THE ALEUTIANS. THUS...EXPECT A VERY ACTIVE PATTERN WITH FAST
MOVING STORM SYSTEMS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 132 138 140 150 155 160 165 170 172
                        175 176 185 179.
         HEAVY FREEZING SPRAY WARNING...160 180.
FIRE WEATHER...NONE.

SEB NOV 08