Small Craft Advisory 294, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT WED APR 3 2013

.MODEL DISCUSSION...
FORECAST MODELS ARE VERY GOOD AGREEMENT THROUGH 60 HOURS...THEN
BEGIN TO DIVERGE A BIT FROM 60 TO 84 HOURS. THE MAIN DIFFERENCES
INVOLVE THE LOCATIONS AND STRENGTHS OF VARIOUS LOWS. THESE ARE
SUBTLE DIFFERENCES...BUT ONE OF THEM (AN UPPER LOW MOVING INTO
ALASKA) PROVIDES THE MAIN UNCERTAINTY IN THE FORECAST...WHICH IS
CHANCES OF SNOW IN SOUTHERN ALASKA ON SATURDAY.

.ANALYSIS AND UPPER LEVELS...
THERE IS A LARGE UPPER LEVEL LOW CENTERED SOUTH OF THE CENTRAL
ALEUTIANS. ANOTHER UPPER LOW IS OVER NORTHWEST CANADA. IN BETWEEN
THESE LOWS ACROSS SOUTHERN ALASKA IS A NEGATIVELY TILTED UPPER
HIGH. A FRONTAL BAND ASSOCIATED WITH THE ALEUTIAN LOW STRETCHES FROM
JUST NORTH OF THE PRIBILOFS SOUTHEAST ACROSS THE ALASKA PENINSULA
INTO THE NORTH PACIFIC.

.SHORT TERM FORECAST...
A PATTERN CHANGE IS GETTING STARTED OVER ALASKA. THE MAIN CATALYST
OF THIS CHANGE IS THE UPPER LOW OVER NORTHWEST CANADA. THIS LOW WILL
WORK ITS WAY WESTWARD OVER THE NEXT SEVERAL DAYS AND END UP PARKED
OVER SOUTHWEST ALASKA BY THE WEEKEND. THIS WILL PUSH THE SOUTHERN
ALASKA UPPER RIDGE WESTWARD INTO NORTHEAST RUSSIA.

FOR SOUTH CENTRAL ALASKA...NORTHWESTERLY FLOW ALOFT WILL INCREASE
OVER THE AREA AS THE CANADIAN LOW WORKS WESTWARD. GAP WINDS WILL
DEVELOP TONIGHT AS COLDER AIR ALOFT MOVES IN. CONDITIONS ARE EXPECTED
TO BE QUITED DRY THROUGH FRIDAY. THE EXCEPTION WILL BE KODIAK ISLAND
WHICH WILL SEE CONTINUED SHOWERS TONIGHT THEN BECOMING ISOLATED ON
THURSDAY AND FRIDAY. ON FRIDAY NIGHT AND SATURDAY THE UPPER LOW WILL
HAVE WORKED FAR ENOUGH WEST TO BRING SOUTHWESTERLY FLOW TO THE AREA.
THIS WILL BRING IN CHANCES OF PRECIPITATION. THE GFS IS A LITTLE
FASTER THAN THE NAM AND ECMWF IN BRINGING IN THE PRECIPITATION.

FOR SOUTHWEST ALASKA...HIGH PRESSURE WILL REMAIN OVER SOUTHWEST
ALASKA INTO FRIDAY. AS THE LOW MOVES INTO WESTERN ALASKA ON SATURDAY
THE FLOW WILL BE STRONGLY CYCLONIC. THERE IS A SLIGHT CHANCE OF
PRECIPITATION WITH THIS BUT IT SHOULD BE LIMITED BY THE DRY SOURCE
REGION FOR THE AIR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 130 138 150 160 165 170 179.
         STORM WARNING 155.
FIRE WEATHER...NONE.

LUDWIG APR 13