Small Craft Advisory 50, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST TUE JAN 15 2013

.ANALYSIS AND UPPER LEVELS...THE LARGEST FEATURE ON THE WEATHER MAP
IS A LARGE 937 MB LOW SOUTHWEST OF THE ALEUTIAN ISLANDS. THIS LOW IS
TRACKING SLOWLY NORTHEAST AND WILL BECOME THE MAIN WEATHER MAKER FOR
THE BERING SEA AND ALEUTIAN ISLANDS IN SHORT ORDER. THE SURFACE
FEATURES OVER MAINLAND ALASKA AS WELL AS THE GULF OF ALASKA AND
EASTERN BERING SEA ARE WEAK TODAY WITH A RIDGE OVER THE GULF THAT
PUSHES INTO SOUTH CENTRAL AND PART OF SOUTHWEST ALASKA AND A WEAK LOW
IN BRISTOL BAY. THERE IS ALSO A SURFACE LOW IN THE CHUKCHI SEA THAT
HAS A WEAK UPPER LEVEL WAVE ASSOCIATED WITH IT THAT IS MOVING OVER
SOUTHWEST ALASKA THROUGH TONIGHT.
THE JET STREAM COMES WEST TO EAST OFF OF JAPAN AND IS FEEDING THE
LARGE STORM SOUTHWEST OF THE ALEUTIANS. THE JET THEN WEAKENS SOME AS
IT TURNS MORE TO THE NORTHEAST AND THEN INCREASES OVER THE GULF OF
ALASKA THROUGH THE NORTHERN PANHANDLE OF THE STATE. THIS JET IS THE
REASON FOR THE CLOUDS OVER SOUTH CENTRAL ALASKA IN SPITE OF THE
SURFACE RIDGE.

.MODEL DISCUSSION...MODELS HAVE ALL LOCKED ON VERY WELL TO THE LARGE
STORM SOUTHWEST OF THE ALEUTIAN ISLANDS. MODEL-TO-MODEL AND
RUN-TO-RUN CONSISTENCY WITH THIS STORM IS VERY GOOD. THE MODELS ARE
IMPROVING IN THE GULF OF ALASKA REGION BUT THERE ARE STILL SOME
ISSUES TO RESOLVE. THE NAM AND ECMWF ARE CLOSING IN ON A COMMON
STRUCTURE AND TRACK OF THE LOWS MOVING OUT OF THE NORTH PACIFIC TO
THE NORTH GULF COAST. THE GFS IS STILL OUT ON ITS OWN WITH VARYING
SOLUTIONS FROM RUN TO RUN. THE CENTRAL PRESSURES OF THE NAM AND ECMWF
HAVE BEEN SIGNIFICANT BUT WITH THE NEWEST NAM RUN DEEPENING TO NEAR
THE ECMWF STRENGTH ON WEDNESDAY NIGHT IT FURTHER CONFIRMS THAT THE
NAM/ECMWF GUIDANCE SHOULD BE THE BEST.

.SHORT TERM FORECAST...A HIGH WIND WARNING IS IN EFFECT FROM ADAK
WESTWARD FOR OVERNIGHT INTO TOMORROW DUE TO A FRONT ASSOCIATED WITH
THE APPROACHING LOW. PRECIPITATION IN THE WESTERN ALEUTIANS WILL
START OFF AS SNOW AS THE FRONT APPROACHES AND THEN TURN TO RAIN WITH
THE STRONG WARMING. THERE MAY BE SOME REDUCED VISIBILITIES FOR A
SHORT TIME DUE TO BLOWING SNOW BUT IT DOES NOT APPEAR THAT THIS WILL
LAST VERY LONG IF IT DOES OCCUR.

THE UPPER LEVEL WAVE IN SOUTHWEST ALASKA AND THE WEAK LOW IN BRISTOL
BAY IS PRODUCING ENOUGH LIFTING TO BRING A LITTLE SNOWFALL INTO THE
AREA. THIS WILL END FROM WEST TO EAST OVERNIGHT WITH JUST SOME SNOW
REMAINING ALONG THE ALASKA RANGE AND ALEUTIAN RANGE BY MORNING.
AS THIS WAVE PROGRESSES EASTWARD INTO TOMORROW IT WILL RUN INTO SOME
MOISTURE MOVING INTO SOUTH CENTRAL ALASKA AND THIS WILL BE ENOUGH TO
CAUSE SOME LIGHT SNOWFALL IN FROM THE KENAI PENINSULA THROUGH THE
SUSITNA VALLEY INCLUDING THE ANCHORAGE AREA AND MATANUSKA VALLEY.
THE DEVELOPMENT OF A WEAK LOW NEAR THE NORTH GULF COAST WILL ENHANCE
THE SNOWFALL OVER THE PRINCE WILLIAM SOUND AREA AND NORTHWARD INTO
THE COPPER RIVER BASIN TOMORROW.

.LONG TERM FORECAST...FOR THIS WEEKEND MODELS STILL SHOW A BROAD
TROUGH OVER THE WESTERN PART OF THE AREA HIGHLIGHTED BY THE COMPLEX
UPPER LOW MEANDERING AROUND THE BERING SEA/ALEUTIAN CHAIN WITH UPPER
LEVEL RIDGING BUILDING INTO THE EASTERN GULF. AS ENERGY ROTATES
AROUND THE BASE OF THE TROUGH IN THE NORTH PACIFIC AND RUNS UP
AGAINST THE RIDGE...STORM TRACK WILL BE DIRECTED NORTHWARD TOWARDS
THE AKPEN/EASTERN BERING SEA. OVERALL...EXPECTING A FAIRLY WARM AND
ACTIVE PATTERN FOR THE BULK OF THE AREA FROM THIS WEEKEND INTO EARLY
NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 187 191.
MARINE...GALE
FIRE WEATHER...NONE.

JAN 13