Small Craft Advisory 65, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1140 AM AKST SUN JAN 20 2013

.ANALYSIS AND UPPER LEVELS...A VERY LARGE CLOSED LOW ENCOMPASSES
THE BERING SEA AND ALEUTIANS WHILE TO THE EAST A HIGH AMPLITUDE
RIDGE CENTERED ALONG THE U.S. WEST COAST EXTENDS NORTH-NORTHWEST
ACROSS BRITISH COLUMBIA AND THE YUKON INTO NORTHERN ALASKA. IN
BETWEEN THE TWO A LONG SOUTHERLY FETCH ORIGINATING AROUND 20N
LATITUDE IS TRANSPORTING ABUNDANT MOISTURE NORTHWARD TO THE PRINCE
WILLIAM SOUND AREA. INTERESTINGLY NONE OF THE POPULATION CENTERS
SURROUNDING PRINCE WILLIAM SOUND ARE OBSERVING HEAVY PRECIP THIS
MORNING - ALTHOUGH THE MOUNTAINS AND ICE FIELDS CERTAINLY ARE.
THIS IS DUE IN PART TO UNFAVORABLE LOW LEVEL FLOW OUT OF THE NORTH
TO EAST. A WEAK TRIPLE POINT LOW OVER THE GULF WAS INITIALLY
RESPONSIBLE FOR THIS...ALTHOUGH A SURFACE WAVE MOVING UP THE FRONT
ACROSS THE GULF THIS MORNING IS REINFORCING THIS FLOW. MEANWHILE
STRONG DOWNSLOPING WINDS ACROSS THE KENAI AND CHUGACH MOUNTAINS
KEPT MOST INLAND AREAS DRY OVERNIGHT. THESE WINDS ARE WEAKENING
THIS MORNING AS THE FRONT MAKES SLOWLY EASTWARD PROGRESSION AND
LIGHT SNOW OR FLURRIES HAVE BEGUN TO FALL FROM THE WESTERN KENAI
PENINSULA TO ANCHORAGE AND THE MAT-SU.

OUT WEST THE MAIN FOCUS IS THE EASTERN ALEUTIANS AND SOUTHERN ALASKA
PENINSULA UP INTO THE EASTERN BERING. ONE LOW WHICH MOVED THROUGH
YESTERDAY IS WEAKENING WEST OF THE PRIBILOF ISLANDS. AN OCCLUDED
FRONT FROM ANOTHER LOW OVER THE NORTH-CENTRAL PACIFIC IS SPREADING
RAIN NORTHWARD TOWARD THE EASTERN BERING. SOUTHWEST ALASKA IS MOSTLY
DRY ON THE EAST SIDE OF THIS SYSTEM.

.MODEL DISCUSSION...MODELS GENERALLY SHOW THE SAME PATTERN EVOLUTION
OVER THE NEXT FEW DAYS. THERE ARE SOME DIFFERENCES IN LOW POSITIONS
AS WE HEAD INTO MONDAY AND TUESDAY. PREFER AN AVERAGE POSITION OF
THE GFS AND ECMWF WHICH ARE FAIRLY CLOSE THROUGH DAY 3.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A STRONG UPPER JET CROSSING THE NORTH PACIFIC
WILL HELP PUSH THE LOW/SHORT-WAVE SOUTH OF THE EASTERN ALEUTIANS AND
ALASKA PENINSULA INTO THE DOWNSTREAM RIDGE. THIS IN TURN WILL HELP
PUSH THE EXISTING FRONTAL BOUNDARY OVER THE GULF EASTWARD THIS
AFTERNOON THROUGH TONIGHT GRADUALLY BRINGING RAIN AND SNOW TO AN
END FROM WEST TO EAST. THE UPPER RIDGE WILL BE FURTHER EAST...BUT A
LONG FETCH OF SOUTHERLY FLOW WILL PERSIST...WITH A WARM FRONT COMING
BACK NORTHWARD ACROSS THE GULF ON MONDAY. MEANWHILE...THE LOW SOUTH
OF THE ALASKA PENINSULA WILL MOVE TOWARD THE SOUTHERN GULF CAUSING
FLOW TO BACK TOWARD THE EAST ON MONDAY. THE END RESULT WILL BE
WIDESPREAD RAIN ALONG THE GULF COAST. INLAND AREAS WILL REMAIN
MOSTLY DRY UNDER THE INFLUENCE OF OFFSHORE FLOW. THE RAIN WON'T
BE LONG LIVED AS THE LOW EXITS TO THE EASTERN GULF ON WEDNESDAY.

SOUTHWEST ALASKA...SOUTHWEST ALASKA WILL STAY MOSTLY DRY ON THE
PERIPHERY OF MOISTURE STREAMING NORTHWARD INTO THE EASTERN BERING.
AS THE LOW SOUTH OF THE ALASKA PENINSULA MAKES EASTWARD PROGRESS
TOWARD THE GULF ON MONDAY SOME PRECIP WILL ROTATE BACK INTO BRISTOL
BAY...BUT WILL BE ON THE LIGHT SIDE. OTHERWISE...THINGS ARE LOOKING
PRETTY BENIGN AS WE HEAD THROUGH THE NEXT FEW DAYS.

BERING SEA/ALEUTIANS...THE LOW OVER THE CENTRAL BERING WILL CONTINUE
TO VERY SLOWLY WEAKEN AS IT BACKS ALL THE WAY TO THE KAMCHATKA
PENINSULA ON TUESDAY. MEANWHILE...THE OCCLUDED FRONT CROSSING THE
EASTERN ALEUTIANS AND SOUTHERN ALASKA PENINSULA THIS MORNING WILL
DISSIPATE AS IT MOVES TOWARD THE CENTRAL BERING TONIGHT WHILE THE
PARENT LOW HEADS EASTWARD TOWARD THE GULF. PRECIP WILL HANG ON INTO
MONDAY AS AN UPPER TROUGH LIFTS NORTHEASTWARD THROUGH THE REGION.
THE NEXT MAJOR LOW WILL DEVELOP ALONG THE JET OVER THE NORTH-CENTRAL
PACIFIC TONIGHT THROUGH MONDAY. HOWEVER...THE UPPER JET WILL CONTINUE
OFF TO THE EAST LEAVING THE LOW SITTING IN WEAKER FLOW. BY THE TIME
IT NEARS THE CENTRAL AND EASTERN ALEUTIANS LATE TUESDAY IT WILL
ALREADY HAVE BEGUN THE PROCESS OF FILLING.

.LONG TERM FORECAST...ALL INDICATIONS ARE THAT A FAIRLY QUIET
PATTERN WILL SET UP FOR THE DAY 4 THROUGH 7 TIME PERIOD. THE LOW
SOUTH OF THE CENTRAL ALEUTIANS MID WEEK WILL MAINTAIN A SOUTHERLY
TRACK AS IT HEADS EASTWARD LATE IN THE WEEK...REMAINING WELL SOUTH
OF SOUTHCENTRAL. MODELS INDICATE ANOTHER LOW DEVELOPING OVER THE
NORTHWEST PACIFIC AND TRACKING TO THE WESTERN ALEUTIANS LATE IN
THE WEEK WITH STRONG RIDGING OUT AHEAD OF IT. THIS WILL ONCE AGAIN
KEEP AN IMPACTS AWAY FROM MAINLAND ALASKA. THE AIR MASS OVER THE
SOUTHERN MAINLAND LOOKS LIKE IT WILL GRADUALLY COOL MID THROUGH
LATE WEEK SO EXPECT TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL BY
NEXT WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 150 155 160 165 185.
FIRE WEATHER...NONE.

SEB JAN 13