Small Craft Advisory 865, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST MON NOV 4 2013

.ANALYSIS AND UPPER LEVELS...

STACKED LOW PRESSURE SYSTEMS IN THE WESTERN GULF AND THE SOUTHEASTERN
BERING WILL MERGE TODAY OVER THE GULF...THEN BEGIN TO MOVE INTO THE
EASTERN GULF TUESDAY. BEHIND THIS SYSTEM A SHARP MID-LEVEL TROUGH
WILL PUSH A COLD FRONT EAST ACROSS SOUTHWEST ALASKA THROUGH THE DAY
TODAY AND ACROSS SOUTHCENTRAL AS WELL AS THE GULF OF ALASKA BY LATE
TUESDAY EVENING. THIS WILL REPRESENT THE LEADING EDGE OF A SEASONABLY
COLDER AIR MASS AND WILL BRING INCREASED DRYING AND OFFSHORE
FLOW...AND WILL ESPECIALLY HELP TO INCREASE WINDS THROUGH CHANNELED
TERRAIN BETWEEN THE INLAND AREAS AND THE GULF TUESDAY AND TUESDAY
NIGHT.

MEANWHILE...THE MAIN EVENT FOR THE NEXT FEW DAYS WILL BEGIN TO
RAPIDLY STRENGTHEN AND EXPAND TODAY OVER THE NORTHWEST
PACIFIC...CROSS THE WESTERN ALEUTIANS INTO THE WESTERN BERING
TUESDAY...AND THEN REACH PEAK INTENSITY TUESDAY NIGHT IN THE FAR
WEST-CENTRAL BERING. AT ITS PEAK THE CIRCULATION AND RESULTING FRONT
WILL LIKELY ENVELOP MOST OF THE BERING SEA WITH STORM TO HURRICANE
FORCE WINDS...MODERATE TO HEAVY PRECIPITATION...AND/OR A LARGE SEA
SWELL CONTRIBUTING TO POTENTIALLY DANGEROUS WAVE HEIGHTS.

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT SYNOPTICALLY. THE NAM AND GFS WERE
PREFERRED THROUGH MIDWEEK...THEN THE EUROPEAN (EC) MODEL IS PREFERRED
THEREAFTER THROUGH MOST OF THE REST OF THE WEEK THROUGH NEXT WEEKEND.

.SHORT TERM FORECAST...

SOUTHCENTRAL...

WITH UPPER LEVEL FORCING FOR ASCENT REMAINING LARGELY OFFSHORE
TODAY...PRECIPITATION WILL HAVE A HARD TIME MOVING INLAND FROM THE
GULF COAST. BY TONIGHT...THE LEADING EDGE OF COLD AIR MOVES EAST
ACROSS THE AREA AND CONTINUE TO FILTER ACROSS THE AREA THROUGH
TUESDAY INTO TUESDAY NIGHT. ABOUT HALF OF ANCHORAGE'S SNOW EVENTS
OCCUR WITH HEALTHY COLD ADVECTION IN THE LOWER LEVELS OF THE
ATMOSPHERE...BUT WE'D ALSO LIKE TO SEE THE COLD ADVECTION MOVING FROM
THE SOUTH AND WEST UP THE INLET WHERE IT CAN TAP INTO THE MOISTURE
SOURCE FROM THE SOUTH. UNFORTUNATELY FOR SNOW LOVERS...THE COLD AIR
IN THIS CASE WILL BE COMING FROM THE NORTH AND WEST...RESULTING IN
MORE LOW LEVEL DRY AIR AND A QUICKER CUT-OFF TO THE PRECIPITATION.
THEREFORE...WE ARE ADVERTISING A CHANCE OF SEEING LIGHT SNOW DURING
THE DAY ON TUESDAY...BUT ACCUMULATIONS ARE LIKELY TO BE MINIMAL AND
WILL FAVOR HIGHER ELEVATIONS. HOWEVER...IT IS WITHIN REASON THAT THE
ANCHORAGE FORECAST OFFICE RECORDS THEIR FIRST OFFICIAL SNOWFALL OF
THE SEASON BY MIDNIGHT TUESDAY NIGHT.

OFFSHORE FLOW DEVELOPS LATE TUESDAY INTO WEDNESDAY ACROSS THE
REGION...BUT WILL NOT BE UNUSUALLY HAZARDOUS AND WILL BE FAIRLY
SHORT-LIVED BEFORE A WARM FRONT FROM THE SOUTH AND WEST MOVES INTO
THE REGION THURSDAY INTO THURSDAY NIGHT.

SOUTHWEST...

RAIN AND RAIN SHOWERS WILL CONTINUE THROUGH TODAY...ENDING FROM WEST
TO EAST OVER THE NEXT 18 TO 36 HOURS BRINGING A DISTINCT DRYING TREND
ALONG WITH SEASONABLY STRONGER NORTHWEST WINDS THAN WHAT HAS BEEN
SEEN RECENTLY. HIGH PRESSURE BUILDS OVER THE STATE TUESDAY INTO THE
FIRST HALF OF WEDNESDAY BEFORE THE WEAKENING FRONT ASSOCIATED WITH
THE POWERFUL LOW IN THE WEST-CENTRAL BERING SEA MOVES INLAND ACROSS
THE REGION BRINGING A WINTRY MIX TO MOST OF THE SOUTHWEST MAINLAND
WEDNESDAY NIGHT INTO EARLY THURSDAY.

BERING SEA/ALEUTIANS/AKPEN...

NORTHWEST FLOW WITH RAIN AND SNOW SHOWERS WILL GRADUALLY
DIMINISH...THEN ATTENTION TURNS TO THE RAPIDLY INTENSIFYING LOW WHICH
WILL BEGIN TO IMPACT THE WESTERN ALEUTIANS AND NEARBY WATERS LATE
TONIGHT BEFORE PUSHING TO THE CENTRAL ALEUTIANS DURING THE DAY ON
TUESDAY. HIGH WIND WARNINGS HAVE BEEN ISSUED TO COVER THE STRONG
FRONTAL PASSAGE AHEAD OF THE LOW AS WELL AS WITH THE CIRCULATION OF
THE LOW ITSELF. OF PARTICULAR CONCERN IS THE IMMEDIATE BACK SIDE OF
THE LOW...WHERE A SWATH OF HURRICANE FORCE WINDS WILL BE POSSIBLE
ESPECIALLY NEAR SHEMYA AT THE SAME TIME THAT THE LOW WILL BE REACHING
PEAK INTENSITY. THE IMPRESSIVE STORM WILL ALSO IMPACT MOST OF THE
REGION WITH AN UNUSUALLY LARGE SEA SWELL...THUS CONTRIBUTING TO AN
INCREASED DANGER TO MARINERS AS WELL THROUGH MIDWEEK.

.LONG TERM FORECAST...

STRONG WESTERLY FLOW WILL ENVELOP THE BERING SEA BY THURSDAY AND WILL
PUSH A WEAKENING FRONT EAST INTO THE SOUTHERN MAINLAND. THIS FRONT
WILL GENERATE PRECIPITATION ACROSS THE REGION AND RESULT IN THE NEXT
GOOD CHANCE OF RAIN AND/OR SNOW FOR PARTS OF SOUTHCENTRAL MAINLY FROM
THE MATANUSKA VALLEY SOUTH LATE THURSDAY. HIGH PRESSURE ALOFT MOVES
OVER THE REGION FROM THE WEST THIS WEEKEND...THEN IS FOLLOWED BY A
LARGE AMPLITUDE TROUGH THAT WILL MOVE QUICKLY WEST TO EAST ACROSS THE
STATE SUNDAY INTO MONDAY OF NEXT WEEK AND BRING ANOTHER SHOT OF
PRECIPITATION FOLLOWED BY A RETURN TO A COLDER AIR MASS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...187 191
MARINE...GALES...120 130-132 136-138 150 155 160 165 172-174 179 180
                 185
         STORMS...119 175-178
FIRE WEATHER...NONE.

CC NOV 13