High Wind in Alaska, September 10, 2009

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
140 PM AKDT THU SEP 10 2009

.ANALYSIS AND UPPER LEVELS...LARGE DEEP UPPER LOWS ARE NOW LOCATED
JUST SOUTH OF THE GULF OF ALASKA AND AT THE SOUTHERN TIP OF THE
KAMCHATKA PENINSULA WITH RIDGING IN BETWEEN OVER THE CENTRAL
BERING SEA. SURFACE REFLECTION OF THE GULF LOW IS NOW BOTTOMING
OUT IN THE UPPER 960S. A SIGNIFICANT UPPER WAVE IN THE NORTHEAST
SECTOR OF THE LOW IS TRACKING NORTHWESTWARD ACROSS THE GULF (ALONG
WITH THE SURFACE FRONTAL SYSTEM WHICH IS SIMILARLY LOCATED).
MIDDLETON ISLAND SHOWS MODERATE TO HEAVY PRECIPITATION SPREADING
WESTWARD ACROSS PRINCE WILLIAM SOUND. OFFSHORE FLOW AHEAD OF THE
FRONT IS HELPING TO MITIGATE THE INTENSITY OF THE RAIN IN SOME
COASTAL LOCATIONS. QUIKSCAT WINDS FROM EARLIER THIS MORNING SHOW
A BAND OF GALE TO STORM FORCE WINDS AHEAD OF THE FRONT AROUND THE
ENTIRE GULF COAST. SEAS ARE RAPIDLY BUILDING WITH WAVE HEIGHTS
TOPPING 20 FEET AS OF NOON.

OUT WEST...THE FORMER TROPICAL SYSTEM WAS ABSORBED INTO A FRONTAL
SYSTEM AND HAS WEAKENED SIGNIFICANTLY WITH CENTRAL PRESSURE NOW
INTO THE 980S. HOWEVER...WITH RIDGING TO THE EAST IT IS STILL A
VERY STRONG FRONT. OBSERVATIONS FROM SHEMYA AND BUOY 46071 INDICATE
MAX GALES JUST AHEAD OF THE FRONT AS IT PUSHES TOWARD THE ALEUTIANS.

.MODEL DISCUSSION...SMALL DIFFERENCES CONTINUE IN TRACK OF LOW
ACROSS THE GULF...WITH THE GFS BEING THE BIGGEST OUTLIER AMONG
THE GROUP OF FOUR MODELS (GFS/NAM/UKMET/ECMWF). WILL STICK WITH
A BLEND OF CURRENT FORECAST COMBINED WITH AVERAGE POSITION OF
THE OTHER THREE MODELS. GFS IS ALSO QUICKEST IN TRACKING THE
LOW INLAND. ALL MODELS AGREE THE UPPER LOW/TROUGH WILL LIFT
NORTHEASTWARD TOWARD THE YUKON...SO THERE IS SUPPORT FOR MOVING
THE SURFACE LOW WITH IT...BUT IT LOOKS LIKE THE GFS IS SHOWING
ITS NORMAL BIAS OF BEING TOO FAST WITH THESE CASES. THE TIMING
OF THIS WILL DETERMINE WHEN THE STRONG EASTERLIES ALONG THE
NORTH GULF COAST DIE DOWN. PREFER A TIMING SOMEWHERE BETWEEN
THE GFS AND NAM SOLUTIONS.

MODELS CONTINUE TO HAVE PROBLEMS OUT WEST WITH HANDLING OF FRONTAL
LOW AND INTERACTION WITH MAIN UPPER CENTER AS IT TRANSITIONS FROM
THE KAMCHATKA PENINSULA INTO THE CENTRAL BERING. THE 00Z/10 GFS
LOOKS LIKE IT WAS AN OUTLIER IN COMPLETELY DISSIPATING FRONTAL LOW
AND MOVING IN SURFACE LOW FROM KAMCHATKA. PREFER THE SOLUTION THAT
THE ECMWF HAS BEEN ADVERTISING THE LAST COUPLE DAYS AND WHICH THE
12Z GFS AGREES WITH...WEAKENING THE FRONTAL LOW BUT THEN DEEPENING
IT AS THE UPPER CENTER MOVES OVERHEAD. SO...NEW FORECAST WILL BE A
BLEND OF CURRENT FORECAST WITH THE 12Z GFS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...BIGGEST CONCERN WITH THE GULF LOW REMAINS
WINDS. THE SURFACE OCCLUSION WILL PUSH WESTWARD TO COOK INLET
TONIGHT. RAPID PRESSURE RISES OF 1.5 MILLIBARS PER HOUR OR GREATER
WILL OCCUR BEHIND. A BARRIER JET WILL ALSO SET UP ALONG THE NORTH
GULF COAST. CURRENT FORECAST ADVERTIZES THIS FAIRLY WELL...SO WILL
JUST PERFORM SOME FINE-TUNING ON THESE WINDS. WOULD NOT BE SURPRISED
TO SEE A FEW GUSTS APPROACHING WARNING LEVEL FROM CORDOVA TO PORTAGE
VALLEY...BUT BASED ON WHAT MODEL WINDS ARE SHOWING IT DOES NOT LOOK
LIKE A FULL BLOWN WARNING EVENT. ALSO, AS THE FLOW SHIFTS FROM
NORTHEAST AHEAD OF THE FRONT TO SOUTHEAST BEHIND THE FRONT RAINFALL
RATES WILL INCREASE IN UPSLOPE FLOW. LOCATIONS ON THE LEE OF THE
KENAI AND CHUGACH MOUNTAINS SHOULD SEE A PERIOD OF LIGHT RAIN RIGHT
AS THE OCCLUSION CROSSES...BUT STRONG SOUTHEASTERLIES BEHIND THE
FRONT WILL QUICKLY SHUT OFF THE RAIN. ONE LARGE CHANGE TO THE
FORECAST WILL BE TO BRING CATEGORICAL RAIN INTO THE COPPER RIVER
BASIN BEHIND THE FRONT. SOUTHEAST LOW LEVEL FLOW IS FAVORABLE FOR
PRECIPITATION THERE AND MULTIPLE UPPER WAVES WILL ROTATE INTO THIS
REGION FROM THE SOUTHEAST. WINDS AND RAIN WILL DIMINISH FRIDAY AS
THE SYSTEM WEAKENS OVER THE NORTHERN GULF...WITH THE BULK OF RAIN
AND WIND REMAINING ALONG THE NORTH GULF COAST. AS THE SYSTEM EXITS
SATURDAY THE BERING TROUGH WILL BEGIN TO INFLUENCE SOUTHCENTRAL...SO
CLOUDS AND SHOWERS WILL BE ON THE INCREASE AGAIN. THINGS SHOULD
THEN START TO DRY OUT SUNDAY INTO MONDAY AS THE BERING LOW DROPS
INTO THE NORTHEAST PACIFIC. IT TOO EARLY TO PINPOINT HOW THIS
SYSTEM WILL AFFECT SOUTHCENTRAL...BUT IT LOOKS LIKE UPPER WAVES
WILL MAKE THERE WAY UP TOWARD SOUTHCENTRAL EARLY TO MID WEEK.

SOUTHWEST ALASKA...THE REMNANTS OF THE OCCLUSION MOVING ACROSS
SOUTHCENTRAL WILL BRING SOME RAIN TO AREAS ALONG THE WEST SIDE
OF THE ALASKA AND ALEUTIAN RANGES LATE TONIGHT AND FRIDAY.
MEANWHILE...ONSHORE FLOW ALONG THE WEST COAST WILL MAINTAIN
AREAS OF FOG AND STRATUS. THE FRONTAL SYSTEM ASSOCIATED WITH
THE BERING LOW WILL THEN BRING RAIN TO THE REGION FRIDAY NIGHT
THROUGH THE WEEKEND. DRYING SHOULD COMMENCE FOR THE BEGINNING
OF THE NEW WEEK AS THIS SYSTEM EXITS TO THE SOUTH AND A RIDGE
BUILDS IN FROM THE WEST.

BERING SEA/ALEUTIANS...THE FRONT ALONG THE ALEUTIANS WILL QUICKLY
WEAKEN TONIGHT AS IT STRETCHES OUT. HOWEVER...GALE FORCE WINDS WILL
PERSIST AS THE WEAKENING FRONTAL LOW STRENGTHENS AGAIN OVER THE
CENTRAL SEA. AS THE LOW TRACKS TO THE EASTERN BERING SATURDAY A
RIDGE WILL BUILD IN BEHIND IT AND A BIT OF ARCTIC AIR WILL ADVECT
SOUTHWARD BETWEEN THE RIDGE AND LOW. WITH PROGRESSIVE UPPER
FLOW...ANOTHER MAJOR STORM WILL MOVE INTO THE WESTERN BERING AND
ALEUTIANS SUNDAY NIGHT AND MONDAY.

.LONG TERM FORECAST...AS BERING SYSTEM MOVES TO THE NORTHEAST
PACIFIC THIS WEEKEND RIDGE WILL BUILD OVER WESTERN CONUS AND
CANADA AND THEN CONTINUE TO STRENGTHEN EARLY NEXT WEEK AS
SHORT-WAVES ROTATE UP THE EASTERN SIDE OF THE TROUGH. THIS WILL
BRING AN END TO THE PROGRESSIVE WAVE PATTERN. SO...THERE IS SOME
CONFIDENCE IN MEDIUM RANGE MODELS WHICH INDICATE THE SYSTEM
ENTERING THE WESTERN BERING LATE THIS WEEKEND MERGING WITH THE
NORTHEAST PACIFIC LOW MID WEEK TO FORM ONE HIGH AMPLITUDE TROUGH
CENTERED AROUND 160W BY THE END OF THE WEEK. SO...AS ONE WOULD
EXPECT THIS TIME OF YEAR...WEATHER WILL REMAIN ACTIVE ACROSS
MOST OF THE FORECAST AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...120.
         GALE WARNING...125 129 130 132 150 172 175 176 185.
FIRE WEATHER...NONE.

SEB SEP 09