Small Craft Advisory 671, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT WED SEP 4 2013

.ANALYSIS AND UPPER LEVELS...
THERE IS A LARGE UPPER LOW CENTERED JUST WEST OF BETHEL. CYCLONIC
FLOW COVERS MOST OF SOUTHERN ALASKA AND THE BERING SEA. A STRONG JET
(150+ KTS) IS OVER THE NORTH PACIFIC FROM KAMCHATKA SOUTHEAST TO
AROUND 40 DEGREES NORTH LATITUDE AND 155 DEGREES WEST LONGITUDE.
ANOTHER JET STRETCHES NORTHEAST FROM 40 NORTH TO NEAR YAKUTAT. A
SURFACE LOW IS JUST BEGINNING TO SPIN UP AT THE "INTERSECTION" (LEFT
EXIT/RIGHT ENTRANCE) OF THESE TWO JETS...FAIRLY OBVIOUS ON THE WATER
VAPOR SATELLITE IMAGERY AS A BAROCLINIC LEAF.

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE BASICALLY IN GOOD AGREEMENT THROUGH 84
HOURS. THE EXCEPTION IS THE NAM...WHICH BECOMES ANOMALOUS WITH A
DEVELOPING NORTH PACIFIC LOW AFTER 36 HOURS INTO THE FORECAST
(THURSDAY AFTERNOON). OTHERWISE THE MODELS ARE FAIRLY CLOSE WITH
JUST SOME MINOR TIMING/SPEED DIFFERENCES.

.SHORT TERM FORECAST...
FOR SOUTH CENTRAL AND SOUTHWEST ALASKA...THE ALASKAN UPPER LOW WILL
WEAKEN AND SPLIT OVER THE NEXT FEW DAYS AS MOST OF THE "ENERGY"
DIVES SOUTH INTO THE DEVELOPING NORTH PACIFIC LOW BETWEEN THE TWO
JETS. THIS LOW WILL MOVE INTO THE NORTHERN GULF THURSDAY NIGHT AND
INTO SOUTH CENTRAL ALASKA AND THE EASTERN PORTION OF SOUTHWEST
ALASKA ON FRIDAY. THIS LOW WILL THEN MOVE WELL INLAND ON SATURDAY
AND DISSIPATE AFTER LOOSING ITS UPPER LEVEL SUPPORT.

IN PRACTICAL WEATHER TERMS...SHOWERS WILL DIMINISH OVER SOUTH
CENTRAL ALASKA TONIGHT AND THURSDAY AND OVER SOUTHWEST ALASKA
THURSDAY AND THURSDAY NIGHT AS THE ALASKAN UPPER LOW DISSIPATES AND
HIGH PRESSURE BUILDS AHEAD OF THE NORTH PACIFIC LOW. WINDS AND RAIN
WILL INCREASE ON FRIDAY AS THE LOW MOVES INTO SOUTHERN ALASKA...THEN
CHANGE TO SHOWERS AND DECREASE ON SATURDAY AS THE LOW WEAKENS.

FOR THE BERING SEA AND ALEUTIANS...HIGH PRESSURE WILL BUILD OVER
THE BERING SEA ON FRIDAY AND SATURDAY FILLING THE VOID LEFT BY THE
FORMER ALASKA UPPER LOW. THE UPPER LEVEL STORM TRACK WILL REMAIN
OVER THE NORTHERN PACIFIC AND A WEATHER SYSTEM WILL MOVE INTO THE
WESTERN ALEUTIANS ON FRIDAY AND INTO THE CENTRAL ALEUTIANS ON
SATURDAY UNDERNEATH THE BERING SEA RIDGE...WITH THE SURFACE LOW
SLIDING EASTWARD JUST SOUTH OF THE ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 120 130 132 138 150.
FIRE WEATHER...NONE.

LUDWIG SEP 13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1240 AM AKDT THU SEP 5 2013

AKZ181-051500-

...MINOR ASH FALL POSSIBLE NEAR PORT HEIDEN...

OBSERVED SEISMIC ACTIVITY INDICATES THAT VENIAMINOF VOLCANO CONTINUES
TO ERUPT WITH MINOR ASH EMISSIONS. WINDS ARE EXPECTED TO TRANSPORT
THE ASH TO THE NORTHEAST...WHICH COULD RESULT IN SOME VERY
LIGHT ASHFALL NORTHEAST OF THE VOLCANO ALONG THE ALEUTIAN RANGE TO
PORT HEIDEN OVERNIGHT.

THIS STATEMENT WILL BE UPDATED AT 700 AM AKDT THURSDAY OR SOONER IF
CONDITIONS WARRANT.