Gale Warning 580, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
120 PM AKDT TUE SEP 15 2009

.ANALYSIS AND UPPER LEVELS...
A LONG WAVE CARVED OUT BY A RELATIVELY STRONG 150 KNOT JET SPANS
ALL THE WAY FROM THE BERING TO THE GULF.  THE TWO KEY UPPER LEVEL
FEATURES ARE THE CLOSED LOW OVER THE ALEUTIANS AND THE CLOSED UPPER
LEVEL LOW SOUTH OF THE GULF.  THE ALEUTIAN LOW IS VERTICALLY STACKED
TO THE SURFACE AND IS CURRENTLY BRINGING STORM FORCE WINDS TO THE
WESTERN ALEUTIANS AND GALE FORCE WINDS TO THE CENTRAL ALEUTIANS.  A
990MB SURFACE LOW IS CURRENTLY SOUTH OF THE GULF AND WILL RAPIDLY
STRENGTHEN OVER THE NEXT 24 HOURS AS IT MOVES NORTH AND WEST.

.MODEL DISCUSSION...
MODELS HAVE A GOOD HANDLE ON THE ALEUTIAN LOW AS IT TRACKS EAST INTO
THE GULF. THIS IS A BIG IMPROVEMENT OVER YESTERDAYS RUNS THAT HAD
DISAGREEMENT ON TIMING.  THE MAIN FOCUS RIGHT NOW IS THE LOW
CURRENTLY JUST SOUTH OF THE GULF.  CURRENT FORECAST IS TRENDING
TOWARDS THE 12Z GFS WHICH APPEARS TO BE THE SUPERIOR SOLUTION.
IGNORING THE 06Z GFS THERE IS GREAT RUN TO RUN CONSISTENCY WITH THE
LOW AS IT TRACKS NORTH AND WEST TO KODIAK ISLAND. THE GFS IS
BOTTOMING THE LOW OUT IN THE MID 970S FRIDAY JUST SOUTH AND EAST OF
THE ISLAND AND THEN LEAVING IT RELATIVELY STATIONARY OVER THE ISLAND
AS IT WEAKENS OVER THE NEXT SEVERAL DAYS.  IT SHOULD BE NOTED THAT
THE LAST TWO RUNS OF THE ECMWF BRING THE LOW ALL THE WAY INTO THE
BRISTOL BAY REGION WHILE WEAKENING IT SIGNIFICANTLY.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
AN EXITING SHORTWAVE IS BRINGING NEGATIVE VORTICITY ADVECTION TO
THE REGION RESULTING IN MOSTLY SUNNY SKIES FOR TODAY.  CLOUDS SHOULD
BEGIN STREAMING INTO THE AREA TONIGHT IN ADVANCE OF THE RAPIDLY
DEVELOPING LOW IN THE GULF.  WINDS SHOULD ALSO BE INCREASING OVER
THE NEXT 24 HOUR FOR MOST COASTAL LOCATIONS...MOST NOTABILITY OVER
KODIAK ISLAND. THE 12Z MODELS HAVE BACKED OFF ON THE WINDS SLIGHTLY
AND THIS WILL BE REFLECTED IN THE NEW FORECAST. AS FOR
PRECIPITATION...RAINFALL ALONG THE COASTAL AREAS SHOULD BE WIDESPREAD
BUT WITH THE EASTERLY FLOW ALOFT...AREAS SITTING TO THE WEST OF
MOUNTAIN RANGES WILL BE IN THE TYPICAL RAIN SHADOW. HOWEVER...MOST
EVERYONE SHOULD RECEIVE A SHOT OF PRECIPITATION AS THE STRONGER
UPPER LEVEL WAVES ROTATE AROUND THE PERIPHERY OF THE LOW. IF THE GFS
SOLUTION PANS OUT...THE LOW WILL SIT OVER KODIAK ISLAND AND BRING A
SHOWERY REGIME TO THE REGION THROUGH THE WEEKEND.

.SOUTHWEST...
A SHORT WAVE MOVING THROUGH THE REGION IS TRIGGERING SHOWERS FROM
THE KUSKOKWIM DELTA DOWN TO THE AKPEN.  A BRIEF DRYING TREND WILL
ENSUE FOR THE MAINLAND TONIGHT AND INTO TOMORROW MORNING AS DRY
NORTHEASTERLY WINDS MOVE THOUGH THE AREA.  THE UPPER LEVEL GULF
LOW WILL MOVE NORTH AND WEST TO KODIAK ISLAND AND BRING AN INCREASED
CHANCE OF SHOWERS TO THE REGION LATE WEDNESDAY.  EXPECT A SHOWERY
PATTERN THROUGH THE EXTENDED TO CONTINUE AS THE LONG WAVE TROUGH
REMAINS OVERHEAD.

.BERING SEA AND ALEUTIANS...
RAIN ALONG WITH GALE AND STORM FORCE WINDS ARE CONTINUING TO PLAGUE
THE WESTERN AND CENTRAL ISLANDS...ALTHOUGH THE ALEUTIAN LOW WHICH
IS CURRENTLY AT 180 DEGREES LONGITUDE IS QUICKLY PROGRESSING
EASTWARD. AS IT DOES SO WIND SHOULD TAPER OFF AND TURN NORTHERLY
BEHIND THE LOW.  A RIDGE BUILDING INTO EASTERN RUSSIA LATE THIS
WEEK AND INTO THE WEEKEND SHOULD KEEP THE WESTERN BERING FAIRLY
QUIET WHILE THE EASTERN ISLANDS WILL SEE CLOUDS AND SHOWERS AS A
LOW DROPS OUT OF THE ARCTIC LATE THIS WEEK.

.LONG TERM FORECAST...
GENERAL TROUGHING OVER THE MAINLAND SHOULD KEEP THE SHOWERS AND
CLOUDS AROUND FOR MUCH OF THE MAINLAND.  AS MENTIONED EARLIER...A
RIDGE BUILDING INTO EASTERN RUSSIA SHOULD KEEP THINGS RELATIVELY
QUIET OVER THE WESTERN ALEUTIANS THROUGH MOST OF THIS WEEKEND.
EARLY NEXT WEEK REMNANTS OF EX-TYPHOON CHOI-WAN WILL TRACK TOWARD
THE WESTERN ALEUTIANS.  DEPENDING ON HOW STRONG THE RIDGE BUILDS
WILL BE A BIG FACTOR ON WHETHER THIS EX-TYPHOON WILL MAKE ITS WAY
INTO OUR FORECAST AREA.  AS OF RIGHT NOW THE GFS AND ECMWF KEEP
THE LOW WELL SOUTH OF THE ALEUTIANS...HOWEVER THIS WILL NEED TO BE
CLOSELY WATCHED AS THIS COULD CHANGE WITHIN THE NEXT FEW DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 120 130 152 172 175 176
FIRE WEATHER...NONE

WILSON SEP 09