Small Craft Advisory 355, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT MON APR 22 2013

.MODEL DISCUSSION...
NUMERICAL GUIDANCE IN GOOD AGREEMENT THROUGH 84 HOURS. FORECASTS
GENERALLY FOLLOW THE NAM DUE TO ITS BETTER DEPICTION OF SMALL SCALE
FEATURES.

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL RIDGE SITUATED ROUGHLY NORTH/SOUTH ACROSS
CENTRAL ALASKA. THERE IS ANOTHER AND MUCH STRONGER RIDGE OVER THE
BERING SEA. THERE IS A LOW SOUTH OF THE ALASKA PENINSULA WITH A LONG
SOUTHERLY FETCH OF MOISTURE STREAMING TOWARDS SOUTHERN ALASKA. WEAK
"TROUGHINESS" ALONG THE WEST COAST OF ALASKA WEAKLY ATTACHES THIS
LOW TO A SHORT WAVE LOW MOVING EAST OVER THE BERING STRAIT.

.SHORT TERM FORECAST...
FOR SOUTH CENTRAL AND SOUTHWEST ALASKA...MOISTURE FROM THE LOW SOUTH
OF THE ALASKA PENINSULA WILL PUSH INTO SOUTHERN ALASKA TONIGHT.
PRECIPITATION WILL SPREAD INTO SOUTHWEST ALASKA TONIGHT (EXCEPT THE
KUSKOKWIM DELTA REGION AND THE WESTERN PORTION OF THE THE LOWER
KUSKOKWIM VALLEY...WHICH WILL REMAIN DRY) AND INTO SOUTH CENTRAL ON
TUESDAY. PRECIPITATION MAY START AS SNOW...BUT WILL CHANGE TO RAIN
FOR MOST AREAS TUESDAY AFTERNOON AS WARM AIR SURGES NORTH INTO
SOUTHERN ALASKA. ONLY HIGHER ELEVATIONS AND AREAS FAR INLAND WILL
STAY SNOW THROUGH THE EVENT. THE BERING STRAIT SYSTEM WILL CONTINUE
TO MOVE EAST AND WILL BEGIN TO PUSH THE PRECIPITATION EAST AS
WELL...ENDING FROM THE WEST TUESDAY EVENING INTO WEDNESDAY. FLOW
ALOFT WILL BECOME MORE CYCLONIC AND NORTHWESTERLY LATE WEDNESDAY
THROUGH THURSDAY. THIS WILL KEEP A CHANCE OF PRECIPITATION FOR
PORTIONS OF SOUTH CENTRAL (MAINLY INLAND). IT WILL ALSO BRING IN
COLDER AIR ALOFT.

FOR THE ALEUTIANS AND BERING SEA...HIGH PRESSURE WILL REMAIN OVER
THE BERING SEA THROUGH THURSDAY BUT WILL CHANGE IN ORIENTATION AND
CHARACTER. CURRENTLY THE RIDGE EXTENDS SOUTHWARD INTO THE TROPICS
BLOCKING ALL WESTERLY FLOW ACROSS THE DATELINE FROM THE BERING SEA
SOUTH. AS A TROUGH TO THE WEST PUSHES INTO THE RIDGE IT WILL BEGIN
TO UNDERCUT THE RIDGE TUESDAY AFTERNOON AND COMPLETELY PUSH UNDER
IT BY WEDNESDAY AFTERNOON. THE RIDGE WILL THEN BECOME EAST/WEST
ORIENTED AND FORM A REX BLOCK (CLOSED HIGH NORTH OF A CLOSED LOW)
WHICH IS VERY STABLE...AND WILL HELP PUSH NORTHWESTERLY FLOW INTO
MAINLAND ALASKA AS MENTIONED ABOVE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 120 130 138 150 155 170 176.
FIRE WEATHER...NONE.

LUDWIG APR 13