Small Craft Advisory 666, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
151 PM AKDT WED SEP 3 2014

.ANALYSIS AND UPPER LEVELS...
THE LARGE COLD UPPER LEVEL LOW CENTERED NEAR THE ARCTIC COAST IS
STARTING TO MOVE SLOWLY EASTWARD. THE UPPER LEVEL RIDGE IN THE
NORTH PACIFIC EXTENDS INTO THE GULF OF ALASKA WHICH IS CAUSING
STRONG ZONAL FLOW OVER MOST OF MAINLAND ALASKA TODAY. THIS
ACCELERATED UPPER LEVEL FLOW IS ACTUALLY PART OF THE POLAR JET
STREAM THAT IS RUNNING SOUTH AND AROUND THE ARCTIC COAST LOW. THE
SUBTROPICAL JET STREAM IS TAKING A ROUTE FROM NEAR JAPAN TO JUST
SOUTH OF THE ALEUTIANS. THIS PORTION OF THE JET STREAM WILL BE
INSTRUMENTAL FOR THE DEVELOPMENT OF THE FIRST STRONG LOW OF THE
FALL SEASON TO MOVE INTO THE ALEUTIANS THIS WEEKEND.
AT THE SURFACE THE HIGH PRESSURE IN THE GULF IS MOVING TO THE
SOUTHEAST WITH ANOTHER HIGH OVER THE BERING SEA. HIGH PRESSURE IS
ALSO MOVING INTO THE MAJORITY OF MAINLAND ALASKA BEHIND THE FRONT
THAT PASSED THROUGH SOUTHCENTRAL ALASKA LAST NIGHT. THIS HIGH
PRESSURE WILL BE SHORT LIVED AS THE NEXT LOW PRESSURE SYSTEM IS
SOUTH OF THE ALASKA PENINSULA.

&&

.MODEL DISCUSSION...
MODELS CONTINUE TO DO WELL WITH THE HEMISPHERIC AND SYNOPTIC
SCALE FEATURES. THE ITEM THE MODELS ARE STILL STRUGGLING TO
RESOLVE IS THE DEVELOPMENT AND MOVEMENT OF A LOW SOUTH OF THE
ALASKA PENINSULA THAT WILL BECOME COMPLEX AS IT MOVES NORTH AND
NORTHEASTWARD. THIS LOW IS ELONGATING WITH A SECONDARY CENTER
NORTH OF THE MAIN LOW WHICH WILL MOVE INTO BRISTOL BAY TOMORROW.
THE MODELS ARE ALL IN GOOD AGREEMENT WITH THIS. THE MAIN LOW WILL
WEAKEN AS IT MOVES NORTHEAST AND THEN BEGIN TO STRENGTHEN AGAIN
AFTER IT MOVES INTO THE NORTHERN GULF OF ALASKA FRI NIGHT. BETWEEN
NOW AND THEN THE MODELS ARE OFFERING UP A NUMBER OF PLAUSIBLE
SOLUTIONS TO HOW THIS EVOLUTION IN THE LOW WILL OCCUR. HOWEVER
THE MODELS ARE NOT BEING VERY CONSISTENT WITH THIS FROM RUN TO RUN
OR WITH EACH OTHER. FOR FRIDAY NIGHT THROUGH THE WEEKEND THE
MODELS ARE BACK INTO GOOD ALIGNMENT WITH HIGH CONFIDENCE THAT A
STRONG LOW IN THE MID 970 RANGE WILL BE APPROACHING THE ALEUTIAN
ISLANDS OUT OF THE NORTH PACIFIC THIS WEEKEND.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE WEATHER FRONT THAT PASSED THROUGH THE REGION OVERNIGHT HAS
MOVED INTO THE YUKON LEAVING CLEARING SKIES IN ITS WAKE. THERE IS
ENOUGH COLD AIR ALOFT TO BUILD UP SOME CLOUDS ALONG THE MOUNTAINS
BUT NO SIGNIFICANT SHOWER ACTIVITY IS EXPECTED. A WEATHER FRONT
ASSOCIATED WITH THE LOW SOUTH OF THE ALASKA PENINSULA IS MOVING
INTO THE GULF OF ALASKA AND WILL BRING RAINFALL TO KODIAK
OVERNIGHT AND TO THE NORTH GULF COAST BY MORNING. IN AREAS THAT
HAVE NOT SEEN THEIR FIRST FREEZE THERE WILL PROBABLY NOT BE ONE
TONIGHT AS THE CLOUDS FROM THIS APPROACHING SYSTEM WILL MOVE FAST
ENOUGH TO KEEP TEMPERATURES ABOVE THE FREEZING MARK. AREAS FAR
ENOUGH NORTH TO NOT RECEIVE ANY CLOUD COVER BY LATE TONIGHT WILL
HAVE ALREADY DROPPED BELOW FREEZING ON SOME PREVIOUS NIGHTS.

SOUTHWEST ALASKA...
THE KUSKOKWIM DELTA AND VALLEY WILL SEE SOME CLEARING TONIGHT IN
ADVANCE OF THE LOW MOVING INTO THE REGION FROM THE SOUTH. THE
BRISTOL BAY AREA WILL SE RAINFALL BEGINNING OVERNIGHT AND
CONTINUE INTO TOMORROW.

BERING SEA/ALEUTIANS...

HIGH PRESSURE WILL PERSIST OVER THE CENTRAL AND WESTERN BERING SEA
THE NEXT FEW DAYS. THE LOW MOVING INTO THE EASTERN BERING SEA WILL
BRING RAINFALL TO THAT REGION.

&&

.LONG TERM FORECAST...
THE DOMINANT FEATURE THROUGHOUT MUCH OF THE EXTENDED FORECAST
TERM WILL BE THE LARGE SEASONABLY STRONG LOW APPROACHING THE
CENTRAL ALEUTIANS THIS WEEKEND AND THEN GRADUALLY TRACKING
EASTWARD ALONG THE CHAIN THROUGH THE MIDDLE OF NEXT WEEK. THIS
WILL RESULT IN WIDESPREAD RAIN ACROSS THE SOUTHERN BERING SEA
ALONG WITH A SWATH OF GALE FORCE WINDS MOVING NORTHWARD ACROSS THE
WESTERN AND CENTRAL BERING LATE SATURDAY INTO SUNDAY.
MEANWHILE...MUCH OF SOUTHCENTRAL AK WILL SEE A TEMPORARY BREAK IN
PRECIPITATION BY LATE THIS WEEKEND AS AN UPPER LEVEL TROUGH
DEPARTS TO THE EAST AND IS REPLACED BY HIGH PRESSURE BUILDING IN
FROM THE WEST THROUGH EARLY NEXT WEEK. THE SOUTHERN MAINLAND WILL
THEN QUICKLY BEGIN TO TRANSITION BACK TO A WETTER PATTERN BY
TUESDAY AS A FRONT ASSOCIATED WITH THE BERING LOW REACHES THE
NORTHERN GULF COAST AND DEEP SOUTHWESTERLY FLOW BECOMES RE-
ESTABLISHED OVER THE REGION FOR THE REMAINDER OF THE WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 130.
FIRE WEATHER...NONE.
&&

SEP 14