Small Craft Advisory 657, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT THU AUG 29 2013

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW IN THE GULF OF ALASKA WITH A DEFORMATION
ZONE STRETCHING ACROSS SOUTH CENTRAL ALASKA. A DEEP LOW (520 DM AT
500 MB) IS CENTERED JUST OFF THE NORTHWEST COAST OF ALASKA. THERE IS
AND UPPER LEVEL RIDGE OVER THE EASTERN BERING SEA AND SOUTHWEST
ALASKA. A FRONTAL SYSTEM MOVING INTO THE CENTRAL BERING SEA AND
CENTRAL ALEUTIANS IS ASSOCIATED WITH AN UPPER LOW JUST EAST OF THE
KAMCHATKA PENINSULA.

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN VERY GOOD AGREEMENT ON THE GENERAL
PATTERN AND SURFACE DETAILS. THIS LEADS TO HIGHER THAN NORMAL
CONFIDENCE IN THE WIND FORECASTS. HOWEVER...WITH THE FAST WESTERLY
FLOW ALOFT AND THE SLIGHT TIMING DIFFERENCES IN DYNAMICS/MOISTURE
FIELDS...THE CONFIDENCE IN PRECIPITATION FORECASTS IS NOT AS
HIGH...BUT NOT BAD FOR THIS TIME OF YEAR.

.SHORT TERM FORECAST...
FOR SOUTH CENTRAL AND SOUTHWEST ALASKA...THE GULF LOW WILL MOVE
RAPIDLY SOUTH TONIGHT. THE DEFORMATION ZONE OVER SOUTH CENTRAL
ALASKA WILL WEAKEN TONIGHT AND DISSIPATE FRIDAY MORNING. WESTERLY
FLOW ALOFT WILL INCREASE ON FRIDAY INTO SATURDAY AS THE UPPER LOW
OFF THE NORTHWEST COAST OF ALASKA MOVES EAST ACROSS NORTHERN ALASKA.
AT THE SAME TIME THE RIDGE OVER SOUTHWEST ALASKA WILL FLATTEN. THIS
WILL ALLOW MOISTURE AND SOME JET ENERGY TO ENTER SOUTHERN ALASKA.
THE RESULT WILL BE PERIODIC CHANCES OF SHOWERS...MAINLY IN AREAS
WITH UP-SLOPE COMPONENTS FROM WESTERLY FLOW.

ON SUNDAY THE KAMCHATKA LOW WILL MOVE EAST INTO THE ALEUTIANS AND
BERING SEA. THIS WILL INDUCE SOME RIDGING OVER SOUTHWEST
ALASKA...THOUGH THE RIDGE IS LIKELY TO BE FAIRLY "DIRTY" (FAIRLY
CLOUDY AND MOIST)...ESPECIALLY OVER SOUTHWEST ALASKA.

FOR THE BERING SEA AND ALEUTIANS...THE SYSTEM CURRENTLY MOVING INTO
THE CENTRAL ALEUTIANS WILL REACH THE PRIBILOFS LATE TONIGHT AND THE
EASTERN ALEUTIANS FRIDAY MORNING THEN SPLIT APART LATER FRIDAY INTO
SATURDAY. THE NEXT LARGE SYSTEM WILL MOVE INTO THE WESTERN ALEUTIANS
ON SATURDAY AS THE KAMCHATKA LOW MOVES EAST. THIS SYSTEM WILL WORK
ITS WAY INTO THE EASTERN BERING SEA SATURDAY NIGHT AND THE EASTERN
ALEUTIANS SUNDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 132 138 150 155 176.
FIRE WEATHER...NONE.

LUDWIG AUG 13