Small Craft Advisory 372, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SUN APR 28 2013

.MODEL DISCUSSION...
THE ECMWF AND GFS SEEM TO HAVE INITIALIZED THE ATMOSPHERE JUST FINE
THIS MORNING AT UPPER LEVELS AND THE SURFACE. THE NAM WAS A BIT OFF
WITH THE NORTH PACIFIC LOW IN STRUCTURE AND DEPTH. AT UPPER LEVELS
THE POLAR VORTEX IS OVER THE ARCHIPELAGO OF THE NORTHWEST TERRITORY
AND IT MOVES TO THE NORTH POLE BY LATE NEXT WEEK. THE HIGH PRESSURE
CENTER OVER THE BERING GETS PUSHED NORTH AND WEST OVER THE NEXT FEW
DAYS. THIS IS DUE TO A SHORT WAVE TROUGH DIVING SOUTH IN WESTERN
ALASKA AT THE SAME TIME A CLOSED LOW MOVES TOWARD THE ALEUTIAN CHAIN
OUT OF THE NORTH PACIFIC. A TROUGH BY WEDNESDAY EXTENDS FROM THE
ARCHIPELAGO INTO BRISTOL BAY AND CONNECTING WITH THE NORTH PACIFIC
NEAR 40N 180. THE TROUGH WILL REMAIN IN THE SAME GENERAL AREA THROUGH
THURSDAY. AT THE SURFACE...THE STRONG LOW IN THE NORTHERN GULF TO
MOVE INLAND OVER THE PANHANDLE AS AN AREA OF LOW PRESSURE REMAINS IN
THE NORTHERN GULF. THE NORTH PACIFIC LOW WRAPS UP NEAR 45N 170W
MONDAY WITH ANOTHER PIECE RUNNING UP TOWARD THE AKPEN TUESDAY. ALL
MODELS ARE IN AGREEMENT THROUGH THIS TIME OF THE FORECAST. WEDNESDAY
IS THE DAY WE SEE SOME DEVIATION AMONG THE GUIDANCE. RIGHT NOW...THE
FORECASTS ARE LEANING TO THE CANADIAN/ECMWF SOLUTIONS. THE GFS IS A
BIT FAST AND TOO FAR WEST WITH ITS LOW PLACEMENT IN THE GULF OF
ALASKA ON WEDNESDAY INTO THURSDAY.

FORECAST CONFIDENCE IS HIGH INTO MONDAY/TUESDAY WITH LOWER CONFIDENCE
MID TO LATE NEXT WEEK. THE GUIDANCE IS MOVING CLOSER INTO A SOLUTION
FOR THIS TIME FRAME.

.ANALYSIS
SURFACE AND UPPER LEVELS...
COLD AIR IS STILL FILTERING OVER THE MAINLAND WITH A CLOSED LOW OVER
THE ARCHIPELAGO OF CANADA AND HIGH CENTER OVER THE BERING. AN AREA OF
SURFACE LOW PRESSURE IS OVER THE NORTHERN GULF WITH A GOOD GRADIENT
FOR NORTHERLY GAP WINDS IN SOUTH CENTRAL ALASKA SUPPORTED BY MODERATE
TO STRONG NORTHERLY FLOW ALOFT. HIGH PRESSURE OVER THE BERING WITH
LOW STRATUS. A SHORT WAVE TROUGH IS MOVING OUT OF THE ARCTIC THIS
AFTERNOON OVER THE CHUKCHI SEA.

.SHORT TERM FORECAST...
SOUTH CENTRAL...
THE LOW IN THE GULF IS WEAKENING TODAY WITH NORTHERLY AND WESTERLY
GAP WINDS DIMINISHING THIS AFTERNOON. ENOUGH FAVORABLE COLD AIR AND
GRADIENT IN PLACE TO KEEP THE GAP WINDS GOING THROUGH TONIGHT. AN
UPPER LEVEL DISTURBANCE MOVING SOUTH THROUGH WESTERN ALASKA TOMORROW
WILL BRING AN INCREASE IN CLOUD COVER AND A CHANCE OF SNOW SHOWERS
TOMORROW NIGHT INTO TUESDAY. THIS WILL BE MAINLY OROGRAPHIC IN NATURE
DUE TO AFTERNOON AND EVENING INSTABILITY WITH UPPER LEVEL COLD AIR.
NOT MUCH WIND IN MID LEVELS TO DRIVE THE SHOWERS OFF THE TERRAIN. IN
THE MEANTIME...A LOW PRESSURE CENTER WRAPS TO NEAR THE AKPEN
INCREASING EASTERLY FLOW OVER THE GULF AND CHANCE OF SHOWERS OVER THE
COASTAL AREAS. RAIN WILL SPREAD INTO KODIAK LATE TUESDAY AFTERNOON
AND TO THE NORTHERN GULF COAST TUESDAY NIGHT. AFTER THAT...MODELS
DIFFER ON SPREAD OF PRECIP AND WIND PATTERNS.

SOUTHWEST ALASKA...
HIGH PRESSURE OVER THE BERING EXTENDS INTO WESTERN ALASKA. IN UPPER
LEVELS...NORTHWEST FLOW CONTINUES WITH A DISTURBANCE MOVING THROUGH
THE AREA TOMORROW. THIS WILL BRING AN INCREASE IN CLOUD COVER AND
SOME ISOLATED SNOW SHOWERS MAINLY OVER THE MOUNTAINS. THE SURFACE
FLOW INCREASES FROM THE NORTHEAST AS THE NORTH PACIFIC LOW GETS
CLOSER TO THE ALEUTIAN CHAIN. THE LOW STARTS TO MOVE TOWARD THE GULF
WEDNESDAY AND PRECIP WILL SPREAD INTO BRISTOL BAY.

FOR THE BERING SEA AND ALEUTIANS...
HIGH PRESSURE OVER THE BERING WILL RETREAT NORTH AND WEST STARTING
TOMORROW. STRATUS WILL LIKELY GET RIPPED UP A BIT AS A NORTH PACIFIC
LOW MOVES CLOSER TO THE CHAIN MONDAY NIGHT. THIS WILL INCREASE THE
FLOW ALONG THE CENTRAL AND EASTERN CHAIN TO NEAR GALE STRENGTH. WITH
THE LOW REMAINING TO THE SOUTH OF THE CHAIN THROUGH TUESDAY AND HIGH
PRESSURE IN THE NORTH BERING...NEAR GALE TO GALE STRENGTH WINDS TO
REMAIN OVER THE SOUTHERN BERING AND ALEUTIAN CHAIN. PRECIP WILL BE
SPOTTY. AS THE LOW STARTS TO MOVE TOWARD THE GULF TUESDAY NIGHT INTO
WEDNESDAY...PRECIP WILL PICK UP BRIEFLY OVER THE EASTERN ALEUTIANS
THEN RETREAT QUICKLY AS THE LOW MOVES FULLY INTO THE GULF WEDNESDAY.

.LONG TERM FORECAST...
ALL IN ALL THERE WILL BE LOW PRESSURE EAST OF THE ALEUTIAN RANGE WITH
HIGH PRESSURE OVER THE BERING WEDNESDAY THROUGH FRIDAY. THE LOW MOVES
INLAND SATURDAY WITH THE HIGH PRESSURE MOVING SOUTH AND EAST OVER THE
NORTH PACIFIC SOUTH OF THE ALEUTIAN CHAIN. MUCH UNCERTAINTY AFTER
SATURDAY WITH A GENERAL TREND OF THE TROUGH MOVING THROUGH THE STATE
AND THE RIDGE MOVING OUT OF THE BERING.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 170 172.
FIRE WEATHER...NONE.

NELSON APR 13