Small Craft Advisory 796, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
132 PM AKDT MON OCT 13 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE GULF OF ALASKA WITH A TROUGH
EXTENDING TO THE NORTHWEST THROUGH NORTHWEST ALASKA. THERE IS A
RIDGE OVER THE BERING SEA. FURTHER WEST THERE IS AN UPPER LOW NEAR
THE KAMCHATKA PENINSULA AND A WEAKER LOW SOUTH OF THE WESTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT...WITH A COUPLE
OF EXCEPTIONS. THE FIRST IS WITH A LOW OFF THE COAST OF SOUTHEAST
ALASKA WEDNESDAY THROUGH THURSDAY. THE ECMWF AND GEM AGREE ON A
LOCATION THAT IS A BIT FURTHER WEST THAN THE GFS AND NAM. DUE TO
THE SUPERIOR RECENT PERFORMANCE OF THE ECMWF...THE FURTHER WEST
SOLUTION IS PREFERRED. ALSO IN THE WEDNESDAY THROUGH THURSDAY TIME
FRAME THE MODELS HAVE SOME DIFFERENCES IN HOW THEY HANDLE A LOW
SLIDING EAST ACROSS THE ALEUTIANS. THIS LOW CONTAINS THE EXTRA-
TROPICAL REMNANTS OF FORMER TYPHOON VONGFONG. FOR THIS SYSTEM THE
GFS AND ECMWF ARE IN VERY GOOD AGREEMENT...WITH THE CANADIAN NH
GEM SLOWER WITH THE SURFACE LOW. THIS MAKES THE GFS A GOOD CHOICE
FOR THIS SYSTEM FOR THE SAME REASONS MENTIONED EARLY ABOUT THE
ECMWF.

&&

.SHORT TERM FORECAST...

FOR SOUTH CENTRAL ALASKA...THE LOW IN THE GULF WILL SLIDE EAST AND
SETTLE OFF THE COAST OF THE PANHANDLE BY TUESDAY. SOUTH CENTRAL
ALASKA WILL REMAIN WITHIN THE UPPER LEVEL TROUGH THROUGH THURSDAY.
BUT WITH WEAK DYNAMICS AND LOW LEVEL OFFSHORE FLOW CONDITIONS
WILL REMAIN BASICALLY DRY...ESPECIALLY INLAND. THE EXCEPTIONS WILL
BE SOME SHOWERS THROUGH AND NEAR PRINCE WILLIAM SOUND...AS WELL
AS SOME ISOLATED/SCATTERED SHOWERS OVER THE HIGHER TERRAIN OF THE
COPPER RIVER BASIN. SOME GAP WINDS ARE EXPECTED INTO
WEDNESDAY...BUT WITH LACK OF STRONG COLD ADVECTION THESE ARE NOT
EXPECTED TO BE PARTICULARLY STRONG.

FOR SOUTHWEST ALASKA...THE BERING RIDGE WILL SLOWLY SLIDE EAST FOR
THE NEXT COUPLE OF DAYS PUSHING THE UPPER TROUGH OVER ALASKA EAST
AS WELL. THIS WILL RESULT IN DIMINISHING SHOWERS THROUGH TUESDAY
NIGHT THEN...THEN DRY WEDNESDAY. A SLIGHT CHANCE OF PRECIPITATION
AGAIN ON THURSDAY WITH AN APPROACHING LOW. BREEZY (BUT NOT
STRONG) NORTH TO NORTHWEST WINDS WILL CONTINUE INTO EARLY
WEDNESDAY WITH THE SURFACE GRADIENT ASSOCIATED WITH THE LOW LEVEL
FEATURES OF THE RIDGE AND TROUGH. WINDS WILL THEN DIMINISH ON
WEDNESDAY AS THE GRADIENT RELAXES.

FOR THE BERING SEA/ALEUTIANS...THE RIDGE OVER THE AREA WILL SLIDE
EASTWARD INTO WEDNESDAY THEN SETTLE ALONG THE SOUTHWEST COAST OF
ALASKA AND THEN WEAKEN THROUGH THURSDAY. TWO FRONTS...ONE
ASSOCIATED WITH THE KAMCHATKA LOW AND THE OTHER WITH THE LOW SOUTH
OF THE ALEUTIANS...WILL MERGE TONIGHT AND MOVE INTO THE
WESTERN/CENTRAL ALEUTIANS AND WESTERN BERING SEA. THIS MERGED
FRONT WILL SLIDE EAST ACROSS THE CENTRAL ALEUTIANS/BERING ON
TUESDAY THEN WEAKEN/DISSIPATE ON WEDNESDAY AS IT REACHES THE
EASTERN BERING/ALEUTIANS. THE EXTRA-TROPICAL REMNANTS OF FORMER
TYPHOON VONGFONG WILL REACH THE WESTERN ALEUTIANS WEDNESDAY
MORNING...THE CENTRAL ALEUTAINS LATER IN THE DAY AND THEN THE
EASTERN ALEUTIANS LATE WEDNESDAY NIGHT INTO THURSDAY. THIS SYSTEM
WILL BE FAIRLY VIGOROUS...BUT NOTHING OUT OF THE ORDINARY FOR THIS
TIME OF YEAR.

&&

.LONG TERM FORECAST...
DETERMINISTIC AND ENSEMBLE FORECAST MEMBERS CONTINUE TO BE IN
DECENT AGREEMENT THROUGH THE MAJORITY OF THE LONG TERM FORECAST.
THE OVERALL PATTERN WILL CONSIST OF A LONGWAVE TROUGH EXTENDING
FROM THE KAMCHATKA PENINSULA TO THE PACIFIC NORTHWEST COAST OF THE
CONTINENTAL UNITED STATES. THIS TROUGH WILL AMPLIFY SIGNIFICANTLY
THROUGH THE FIRST HALF OF THE WEEKEND AS THE RESIDUAL UPPER LEVEL
ENERGY ASSOCIATED WITH POST-TROPICAL VONGFONG PHASES WITH THE MEAN
LONGWAVE TROUGH AND A STRONG MID-LEVEL AND UPPER-LEVEL JET DIGS
THE TROUGH FURTHER SOUTH. SHORT LIVED LONGWAVE RIDGING WILL
DEVELOP OVER THE WESTERN BERING SEA ON FRIDAY IN THE WAKE OF THE
AMPLIFYING LONGWAVE TROUGH. A VERTICALLY STACKED LOW WILL PUSH OFF
THE KAMCHATKA PENINSULA AND INTO THE WESTERN BERING SEA ON
SATURDAY AND DRIFT EASTWARD THROUGH MONDAY AND DISPLACE THE RIDGE
OVER THE WESTERN BERING SEA. ALL IN ALL...THE BERING SEA AND
ALEUTIANS ISLANDS WILL SEE AN ACTIVE WEATHER PATTERN WITH GENERAL
COLD AIR ADVECTION SHOWERS AND STRATIFORM PRECIPITATION IN
RESPONSE TO THE LOW AND ASSOCIATED FRONT PUSHING OFF OF KAMCHATKA.

THE ALASKA MAINLAND WILL REMAIN MOSTLY DRY THROUGH THE UPCOMING
WEEKEND AS THE AMPLIFIED LONGWAVE PATTERN KEEPS THE MAJORITY OF
THE SHORTWAVE ENERGY AND UPPER LEVEL DISTURBANCES WELL SOUTH IN
THE NORTH PACIFIC. HOWEVER...RAIN SHOWERS WILL POSSIBLE ALONG THE
NORTHERN GULF COAST AS A LOW WEST OF THE ALASKA PANHANDLE ON
THURSDAY MOVES INTO THE NORTHERN GULF ON FRIDAY. BY SATURDAY...THE
REMNANTS OF VONGFONG WILL MOVE INTO THE SOUTHERN GULF OF ALASKA
AND THE AFOREMENTIONED LOW WILL DISSIPATE OVER THE NORTHERN GULF.
THIS WILL PROVIDE EVEN GREATER CHANCES FOR PRECIPITATION ALONG THE
GULF COAST ON SATURDAY AS VONGFONG MOVES INTO THE CENTRAL/NORTHERN
GULF AND WILL PERSIST THROUGH THE BEGINNING OF NEXT WEEK. MODEL
GUIDANCE VARIES QUITE A BIT AS VONGFONG ENTERS THE GULF OF
ALASKA...SO IT IS QUITE DIFFICULT TO PINPOINT EXACTLY HOW FAR
INLAND PRECIPITATION WILL SPREAD. HOWEVER...MODELS ARE DEPICTING
SOME WARM AIR ADVECTION FROM THE NORTH PACIFIC IN RESPONSE TO
VONGFONG...WHICH WOULD LIKELY LEAD TO A SPELL OF SLIGHTLY WARMER
THAN NORMAL TEMPERATURES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 130 131 150 155 176 177.
FIRE WEATHER...NONE.

&&

LUDWIG/MCLAY OCT 14