Small Craft Advisory 786, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT SUN SEP 23 2007

.ANALYSIS AND UPPER LEVELS...
TWO VERTICALLY STACKED LOW PRESSURE SYSTEMS WILL BE INFLUENCING THE
WEATHER IN THE SHORT TERM. A 990 MB LOW IS JUST SOUTH OF KODIAK
ISLAND AND WILL BE PUSHING EASTWARD RELATIVELY QUICKLY BEFORE MOVING
ONSHORE NEAR YAKUTAT MONDAY MORNING. THIS SYSTEM HAS A STRONG
SOUTHERLY FETCH AND IS BRINGING RAIN TO THE SOUTHCENTRAL COASTAL
AREAS. A LARGER 960 MB LOW WILL BE SLOWLY TRACKING NORTHEASTWARD
BEFORE BECOMING NEARLY STATIONARY NEAR NORTON SOUND BY TUESDAY
AFTERNOON. THIS LATTER LOW HAS MUCH MORE UPPER LEVEL SUPPORT WITH A
130 KT JET STREAK RIDING AROUND THE UPPER LOW. BY THE MIDDLE OF NEXT
WEEK...ANOTHER LOW PRESSURE SYSTEM WILL BE APPROACHING THE WESTERN
ALEUTIANS AND WILL BECOME THE DOMINANT SYSTEM.

.MODEL DISCUSSION...
NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT ON THE SYNOPTIC FEATURES
IN THE SHORT TERM WITH THE GFS CONTINUING TO SHOW TERRIFIC
CONSISTENCY. THE NAM HAS FALLEN IN LINE WITH THE GFS IN BRINGING THE
GULF OF ALASKA LOW ONSHORE NEAR YAKUTAT. THERE ARE SUBTLE DIFFERENCES
WITH THE HANDLING OF THE BERING SEA LOW...THOUGH WILL NOT HAVE A
LARGE IMPACT ON THE OVERALL FORECAST. THE NEW RUN OF THE GFS BRINGS
THIS LOW TOWARDS NORTON SOUND SLIGHTLY FASTER THAN PREVIOUS RUNS DID.
GFS ENSEMBLE MEAN KEEPS THE LOW A FEW MILLIBARS WEAKER AND SLIGHTLY
SLOWER...AS DO A MAJORITY OF ITS MEMBERS. THE EUROPEAN MODELS WERE IN
GOOD AGREEMENT WITH THE GFS. THIS FORECAST PACKAGE TRENDED TOWARDS
THE NEW GFS SOLUTION THROUGH THE FIRST FEW DAYS...WITH MINIMAL
CHANGES BEYOND DAY 4 AS MODELS ARE HAVING A DIFFICULT TIME WITH THE
HANDLING OF THE NEXT LOW BY THE MIDDLE OF THE WEEK.

.SHORT TERM FORECAST...

BERING SEA AND ALEUTIANS...THE LOW IN THE WESTERN BERING SEA WILL
MOVE INTO THE CENTRAL BERING BY SUNDAY AFTERNOON AND NORTHEAST
TOWARDS SAINT MATTHEW ISLAND BY TUESDAY. THE STORM WILL MAINTAIN MUCH
OF ITS INTENSITY THROUGH TUESDAY AT WHICH POINT IT WILL BEGIN TO LOSE
UPPER AIR SUPPORT. WIDESPREAD RAIN AND GALE FORCE TO POTENTIALLY
MINIMUM STORM FORCE WINDS CAN BE EXPECTED COVERING A WIDE SWATH OF
THE BERING THROUGH TUESDAY. A WEAK OF RIDGE HIGH PRESSURE WILL MOVE
WEST TO EAST TUESDAY AND WEDNESDAY IN ADVANCE OF ANOTHER LOW PRESSURE
SYSTEM APPROACHING THE WESTERN ALEUTIANS BY WEDNESDAY.

SOUTHWEST ALASKA...PRECIPITATION PRIMARILY CONFINED TO THE BRISTOL
BAY REGION ASSOCIATED WITH THE GULF OF ALASKA LOW WILL BEGIN TO TAPER
OFF LATER TODAY AS THE LOW PULLS EASTWARD AND A WEAK RIDGE OF HIGH
PRESSURE BUILDS IN. HOWEVER...THE REPRIEVE WILL BE EXTREMELY
SHORT-LIVED AS A WEATHER FRONT ASSOCIATED WITH THE BERING SEA LOW
WILL PUSH ONSHORE MONDAY NIGHT. WIDESPREAD RAIN CAN BE EXPECTED FOR
MUCH OF THE AREA STARTING SUNDAY NIGHT AND LASTING A FEW DAYS AS THE
FLOW BECOMES PRIMARILY SOUTHWESTERLY AND AS MULTIPLE SHORTWAVES
ROTATE AROUND THE UPPER CLOSED LOW.

SOUTH AND EAST OF THE ALASKA RANGE...PRECIPITATION ASSOCIATED WITH
GULF OF ALASKA LOW WILL REMAIN PRIMARILY FROM KODIAK NORTH TO THE
ANCHORAGE BOWL AND EASTWARD TO THE COASTAL AREAS SURROUNDING PRINCE
WILLIAM SOUND AND THE GULF. IT LOOKS AS THOUGH THE LOW WILL STAY FAR
ENOUGH SOUTH TO KEEP MUCH RAIN FROM FALLING IN THE MATANUSKA AND
SUSITNA VALLEYS. A BARRIER JET IS SETTING UP ALONG THE NORTH GULF
COAST AND WILL LEAD GALE FORCE WINDS IN MARINE ZONES 120 AND 130. THE
STORM SYSTEM WILL MOVE OUT OF THE FORECAST AREA TONIGHT.
HOWEVER...THE FLOW ALOFT WILL BECOME SOUTHWESTERLY ON MONDAY. SEVERAL
SHORTWAVES WILL SWING AROUND SOUTHCENTRAL...LEADING TO GENERALLY
SHOWERY CONDITIONS THROUGH WEDNESDAY.

.LONG TERM FORECAST...
TRANSIENT PATTERN IS IN THE WORKS AS THE POLAR JET STREAM IS LARGELY
ZONAL BUT HAS MULTIPLE LOW AMPLITUDE PERTURBATIONS EMBEDDED. THE NEXT
SHOT FOR PRECIPITATION FOR SOUTHCENTRAL WILL COME LATE NEXT WEEK AS
ANOTHER STRONG JET STREAK DRIVES AND DEEPENS THE LOW THAT MAKES ITS
WAY ACROSS THE ALEUTIANS EARLY IN THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 120 125 130 138 150 170 172 185 179
         STORM 175 176
FIRE WEATHER...NONE

DANG SEP 07