Small Craft Advisory 698, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKDT SAT SEP 13 2008

.MODEL DISCUSSION...MODELS ARE DOING WELL FOR THE FIRST TWO DAYS OF
THE FORECAST PERIOD. AFTER THAT THEY BEGIN TO DIVERGE IN TWO AREAS.
THE FIRST IS WITH A WAVE MOVING INTO THE GULF OF ALASKA MONDAY NIGHT
AND TUESDAY. ALL MODELS WANT TO BRING IT THROUGH THE GULF FRONT HE
SOUTH BUT THE TIMING IS THE MAJOR FACTOR. PRESSURE DIFFERENCES
BETWEEN MODELS RANGE AROUND 7 MB SO WHILE THE STRENGTH IS STILL
UNCERTAIN THERE ARE NOT EXTREME DIFFERENCES.
THE SECOND AREA OF UNCERTAINTY IS IN THE NORTHERN BERING SEA WHERE A
LOW WILL BE MOVING OUT OF EASTERN RUSSIA INTO THE BERING SEA. THIS
SHOULD OCCUR MONDAY NIGHT OR TUESDAY WITH THE GFS SOLUTION OF A
DEEPER LOW ENTERING THE NORTHERN BERING SEA TUESDAY.
MID TO LONG TERM PROJECTIONS ARE A CONCERN SINCE THERE IS GREAT
DISAGREEMENT BETWEEN THE GFS AND ECMWF MODELS. NEITHER MODEL HAS BEEN
VERY STABLE FROM RUN TO RUN AND IT IS LIKELY WE WILL BE STRUGGLING
WITH THE SOLUTIONS FOR THE MAJORITY OF NEXT WEEK.

.ANALYSIS AND UPPER LEVELS...THE ACTIVE FALL WEATHER PATTERN REMAINS
OVER THE FORECAST AREA AS ATTESTED TO BY THE DIFFICULTIES THE MODELS
ARE HAVING. IN THE UPPER LEVELS A LONG WAVE TROUGH DIGS WELL SOUTH OF
THE AREA TO NEAR 30N SITUATED BETWEEN THE 150W AND 170W MERIDIANS.
THE UPPER LEVEL LOW CENTER ASSOCIATED WITH THIS TROUGH IS OVER
BRISTOL BAY AND WILL SLOWLY WEAKEN AND IT MOVES INLAND THROUGH
MONDAY. THE JET STREAM FOLLOWS THIS PATTERN AND IS VISIBLE ON THE IR
SATELLITE OVER THE WEST AND CENTRAL ALEUTIANS AND THEN AGAIN OVER THE
GULF OF ALASKA. THIS JET WILL BECOME MORE ZONAL AS WE MOVE INTO THE
MIDDLE OF THE WEEK NEXT WEEK.
A SURFACE LOW IS OVER BRISTOL BAY THIS AFTERNOON AND IT WILL REMAIN
QUASI-STATIONARY THROUGH MONDAY WHEN IT DISSIPATES. ANOTHER LOW SOUTH
OF SHEMYA WILL ELONGATE SOUTH OF THE ALEUTIAN ISLANDS OVERNIGHT AND
THEN KEEP MOVING SOUTHEAST AND OUT OF THE FORECAST AREA.

.SHORT TERM FORECAST...RAIN AND RAIN SHOWERS OVER MOST OF THE
MAINLAND AREAS AND THE ALASKA PENINSULA. FLOW HAS TURNED MORE
SOUTHEAST OVER SOUTH CENTRAL ALASKA WHICH IS CREATING MORE
DOWNSLOPING CONDITIONS THAN EARLIER IN THE DAY BUT WILL LIKELY GIVE
WAY TO MORE RAIN OVERNIGHT AND INTO SUNDAY AS THIS FLOW WEAKENS AND
TURNS MORE SOUTHERLY. A STIFF PRE-FRONTAL RIDGE IS ALONG THE NORTH
GULF COAST THIS AFTERNOON. THIS FEATURE WILL CONTINUE TO BRING
TURNAGAIN ARM WINDS THROUGH THE EVENING AND THEN WEAKEN OVERNIGHT AS
THE GRADIENT RELAXES.

.LONG TERM FORECAST...GREAT UNCERTAINTY IN THE LONG TERM FORECASTS
DUE TO POOR MODEL PERFORMANCE. WHAT IS MORE CERTAIN IS THAT THE UPPER
LEVEL TROUGH WILL MAINLY STAY OVER THE EASTERN BERING SEA AND
SOUTHWEST ALASKA BRINGING COOL MOIST WEATHER INTO THE AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 120.
FIRE WEATHER...NONE.

SEP 08