Small Craft Advisory 780, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT SUN OCT 6 2013

.MODEL DISCUSSION...
THE MODELS ARE IN DECENT AGREEMENT WITH THE LOW IN THE NORTHWEST
BERING SEA THROUGH THIS AFTERNOON BEFORE THE LOW DROPS SOUTHWARD AND
DISSIPATES. BY MONDAY AFTERNOON THE MODELS HAVE DIFFICULTY WITH THE
PLACEMENT AND STRENGTH OF A NORTH PACIFIC LOW THAT WILL TRACK ACROSS
THE EASTERN ALEUTIANS. THE GFS SEEMS TO BE THE OUTLIER WITH THE
NAM/ECMWF IN BETTER AGREEMENT AND POSITIONS THE NORTH PACIFIC LOW
JUST WEST OF UNALASKA. THE DIFFERENCE IN THE STORM TRACK WITH THE GFS
MODEL WILL BRING HIGH END GALE FORCE/STORM WINDS TO THE EASTERN
BERING SEA AND BRISTOL BAY REGION...WHERE THE NAM/ECMWF WILL POSSIBLY
BRING HIGH END STORM FORCE WINDS. THEREFORE...THE FORECAST CONFIDENCE
IS FAIR WITH THE PLACEMENT AND STRENGTH OF THE NORTH PACIFIC LOW THAT
WILL CROSS INTO THE EASTERN BERING SEA BY MONDAY AFTERNOON.

.ANALYSIS AND UPPER LEVELS...
THERE IS CLOSED LOW AT 500 MB LOCATED WEST OF SAINT MATTHEW ISLAND
WITH A SHORTWAVE TROUGH EXTENDING THROUGH THE NORTON SOUND INTO
BRISTOL BAY INTERIOR TOWARDS KODIAK ISLAND...WITH A POSITIVE TILTED
TROUGH EXTENDING FROM THE CLOSED LOW THROUGH THE WESTERN ALEUTIANS
JUST EAST OF SHEMYA. THE SATELLITE IMAGERY CORROBORATES THE POSITION
OF THE SURFACE LOW WEST OF SAINT MATTHEW ISLAND WITH AN ASSOCIATED
FRONTAL BOUNDARY THROUGH THE BRISTOL BAY INTERIOR. THE WATER VAPOR
IMAGERY REFLECTS THE STRONG 140 KNOT ZONAL JET STREAK OVER PRIBILOF
ISLANDS AND TRANSITIONS TO MERIDONAL OVER SOUTHWEST ALASKA.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE UPPER LEVEL SHORTWAVE WILL PUSH THROUGH THIS LATE MORNING INTO
THE AFTERNOON HOURS PRODUCING LIGHT RAIN AND SHOWERS WITH THE FRONTAL
PASSAGE. THERE WILL BE A SMALL RIDGE UPSTREAM THAT WILL HELP TO
STABILIZE THE AREA BRIEFLY. DUE TO THE STRONG ZONAL JET STREAK OVER
THE PRIBILOF ISLANDS THIS WILL HELP IN STREAMING HIGH/MIDS CLOUDS IN
TO THE SOUTHCENTRAL REGION. A HIGH WIND WATCH WAS ISSUED THIS MORNING
FOR LATE MONDAY NIGHT THROUGH TUESDAY AFTERNOON ALONG THE TURNAGAIN
ARM AND HIGHER ELEVATIONS. THIS IS DUE TO A RAPIDLY INTENSIFYING LOW
THAT WILL TRACK TO THE SOUTHWEST ALASKA TOMORROW COMBINED WITH A
INCREASED PRESSURE GRADIENT. THEREFORE...SOME OF THE WINDS ALOFT WILL
MIX DOWN AT TIMES INTO THE ANCHORAGE BOWL ALONG THE TURNAGAIN ARM AND
HIGHER ELEVATIONS.

SOUTHWEST ALASKA...
THE SATELLITE IMAGERY IS SHOWING A SWATH OF LOW CLOUDS FROM THE
PRIBILOF ISLAND EXTENDING TO THE KUSKOKWIM DELTA AND WESTERN CAPES.
THIS COINCIDES WITH THE SOUTHWEST WINDS THROUGH THE CENTRAL TO
EASTERN ALEUTIANS. THIS WILL CONTINUE TO STREAM IN CLOUDS AND
SCATTERED RAIN SHOWERS ALONG THE COAST. THERE WILL BE A RAPIDLY
INTENSIFYING NORTH PACIFIC LOW THAT WILL CROSS THE EASTERN ALEUTIANS
NEAR UNALASKA BY MONDAY AFTERNOON. THE STORM TRACK WILL TARGET THE
KUSKOKWIM DELTA REGION BY EARLY TUESDAY MORNING BRINGING STRONG
GALE/STORM FORCE WINDS AND POSSIBLY HIGHER WINDS WITH WIDESPREAD RAIN
TO THE SOUTHWEST ALASKA REGION.

THE ALEUTIAN CHAIN AND BERING SEA...
THE PREDOMINANT FEATURE IS THE SOUTHWEST WIND FLOW ALONG THE ALEUTIAN
CHAIN WITH A SURFACE LOW POSITIONED WEST OF THE SAINT MATTHEW ISLAND.
THIS LOW WILL GRADUALLY DROP SOUTHWARD AND DISSIPATE BY MONDAY
AFTERNOON. THERE WILL BE A STRONG NORTH PACIFIC LOW THAT WILL TRACK
ACROSS THE EASTERN ALEUTIANS MONDAY AFTERNOON AND THEN RAPIDLY
INTENSIFY AS IT TRACKS TOWARDS THE KUSKOKWIM DELTA AREA BY EARLY
TUESDAY MORNING. THIS SYSTEM WILL BRING GALE/STORM FORCE WINDS WITH
POSSIBLY STRONGER WINDS TO THE EASTERN BERING SEA AND SOUTHWEST
ALASKA REGION.

.LONG TERM FORECAST...
WE WILL STAY IN THE SAME WEATHER REGIME WITH ANOTHER LOW PRESSURE
SYSTEM ENTERING THE WESTERN BERING SEA BY WEDNESDAY AND TRACKING
TOWARDS THE SAINT LAWRENCE ISLAND BY FRIDAY. THE SOUTHWEST ALASKA
WILL CONTINUE TO HAVE ONSHORE FLOW WITH STRATUS/FOG AND WIDESPREAD
RAIN WITH THE NEXT SYSTEM. THE SOUTHCENTRAL WILL BE SLIGHTLY DRIER
WITH A RIDGE OF HIGH PRESSURE OVER THE REGION FROM WEDNESDAY THROUGH
FRIDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH 101.
MARINE...GALE 155 165 170 172 173 174 175 180
FIRE WEATHER...NONE.

PLD OCT 13