Small Craft Advisory 675, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 PM AKDT SUN SEP 18 2011

.ANALYSIS AND UPPER LEVELS...THE MAJOR WEATHER FEATURE TODAY IS THE
STRONG LOW SOUTH OF THE ALASKA PENINSULA. IT SHOULD BE NEAR ITS
LOWEST PRESSURE THIS AFTERNOON AND EVENING AND THEN SLOWLY WEAKEN AS
IT MOVES INTO THE WESTERN GULF OF ALASKA TUESDAY.
A STRONG JET AT 250 MB WITH WINDS APPROACHING 200 MPH IS FEEDING INTO
THIS LOW. THE JET STREAM WILL REMAIN ALONG THE SAME TRACK THE NEXT
FEW DAYS AS IT FLOWS ACROSS THE SOUTHERN PART OF THE KAMCHATKA
PENINSULA EAST SOUTHEAST TO NEAR 45N 160W BEFORE TURNING
NORTHEASTWARD AND INTO THE GULF OF ALASKA. HOWEVER WINDS OVER THE
GULF OF ALASKA ARE MUCH LOWER...ONLY AROUND 100 MPH IN THE JET STREAM
THERE.

ASSOCIATED WITH THE SURFACE LOW IS A WEATHER FRONT THAT WILL MOVE
INTO THE GULF OF ALASKA OVERNIGHT AHEAD OF THE MAIN LOW. THIS FRONT
WILL BE A SIGNIFICANT WEATHER FOR THE MARINE AREAS IN AND AROUND THE
GULF. STORM WARNINGS WILL BE IN EFFECT AROUND KODIAK ISLAND WITH THIS
FRONT AND A BARRIER JET WILL DEVELOP ALONG THE NORTH GULF COAST
MONDAY AFTERNOON INTO MONDAY EVENING. THIS BARRIER JET IS EXPECTED TO
PRODUCE HURRICANE FORCE WINDS ALONG THE NORTH GULF COAST AT THAT
TIME.

.MODEL DISCUSSION...MODELS INITIALIZE VERY GOOD ON BOTH THE STRONG
LOW IN THE SOUTHEASTERN GULF OF ALASKA AND THE ONE ALONG THE ALEUTIAN
ISLANDS. THEY ARE LOCKED IN ON THE SAME SOLUTION INTO TUESDAY NIGHT
AND THEN A DEVELOPING LOW MOVING INTO THE EASTERN GULF BEGINS TO
AFFECT THE GULF OF ALASKA OFFSHORE AREA. HUGH DIFFERENCE IN BOTH
STRENGTH AND POSITION OF THIS FEATURE BETWEEN THE GFS ECMWF NAM AND
UKMET. FOR EXAMPLE ON TUESDAY NIGHT...THE GFS IS 18 MB STRONGER AND
350 MILES FARTHER NORTH THAN THE NAM. WHILE THE SHORT TERM IS GOOD
THERE ARE SIGNIFICANT DIFFERENCES IN MODELS THAT WILL IMPACT THE
EASTERN PORTION OF THE FORECAST AREA. AREAS FROM THE ALASKA RANGE
WEST WILL NOT BE IMPACTED TOO MUCH BY THE MODEL DIFFERENCES AS THE
PARENT LOW WHICH WILL BE THE MAIN WEATHER FEATURE IN THOSE AREAS IS
HANDLED WELL BY ALL MODELS. IT IS THE DEVELOPING TRIPLE POINT LOW
THAT IS CAUSING THE MODELS PROBLEMS.

.SHORT TERM FORECAST...STRONG WINDS AND RAIN WILL CONTINUE TO EFFECT
THE ALASKA PENINSULA AND MOVE INTO KODIAK BY LATE THIS AFTERNOON.
SUBSIDENCE WELL AHEAD OF THE FRONT WILL ALLOW SIGNIFICANT CLEARING
OVER MAINLAND ALASKA SOUTH OF THE ALASKA RANGE UNTIL AFTER MIDNIGHT.
DUE TO THIS CLEARING THERE IS A CHANCE FOR AREAS THAT ARE NORMALLY
COLDER...SUCH AS EAST ANCHORAGE AND AREAS AROUND KENAI...TO SEE
TEMPERATURES DROP TO NEAR FREEZING FOR THE FIRST TIME THIS SEASON
BEFORE CLOUD COVER MOVES IN.

STRONG WINDS WILL MOVE INTO THE BRISTOL BAY REGION BY TOMORROW
MORNING AS THE FRONT MOVES NORTHWARD. THE EASTERN PART OF THE BRISTOL
BAY ZONE WILL SEE A LARGE AMOUNT OF DOWNSLOPE WHICH SHOULD MITIGATE
THE RAINFALL...BUT AREAS WEST AND SOUTH OF KING SALMON WILL LIKELY
SEE PRECIPITATION.

.LONG TERM FORECAST...FROM MIDWEEK ON MOST OF THE WEATHER ACROSS THE
REGION WILL BE DOMINATED BY THE LARGE AND SLOWLY WEAKENING LOW THAT
WILL BECOME NEARLY STATIONARY OVER SOUTHWEST ALASKA. THIS WILL KEEP
THE MAINLAND IN A GENERALLY COOL AND SHOWERY PATTERN THROUGH THE END
OF THE WEEK. MEANWHILE THE BERING SEA REGION WILL SEE CONTINUED
NORTHERLY FLOW WITH COOL AND RELATIVELY BENIGN WEATHER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 141 160 165 170 171 172.
         STORM 125 132 138 140 150 155.
         HURRICANE FORCE 120 130.
FIRE WEATHER...NONE

SEP 11