Gale Warning 181, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 PM AKST WED FEB 11 2009

.ANALYSIS AND UPPER LEVELS...
A VERY ACTIVE PATTERN CONTINUES ACROSS THE STATE TODAY. A TRANSIENT
UPPER LEVEL RIDGE LOCATED OVER THE EASTERN BERING SEA IS SEPARATING
TWO TROUGHS...A NEGATIVELY TILTED SHORT WAVE TROUGH EXTENDING
SOUTHEAST FROM THE CHUKCHI SEA TO THE NORTHERN GULF AND A SECOND ONE
WHICH IS QUASI-STATIONARY TO THE WEST WITH AN AXIS NEAR THE KAMCHATKA
PENINSULA.

AT THE SURFACE...A STRONG LOW SPUN UP EARLY THIS MORNING SOUTH OF
KODIAK ISLAND ASSOCIATED WITH THE FIRST UPPER TROUGH. THE SURFACE LOW
IS CURRENTLY MOVING INTO THE CENTRAL GULF WHERE IT WILL QUICKLY
WEAKEN THIS EVENING. SOUTH OF THE WESTERN ALEUTIANS...ANOTHER SURFACE
LOW IS RAPIDLY DEVELOPING AND WILL BECOME THE FOCUS FOR THE WESTERN
HALF OF THE STATE OVER THE NEXT SEVERAL DAYS.

.MODEL DISCUSSION...
MODELS ARE HANDLING THE LOW NEAR KODIAK MUCH BETTER THIS AFTERNOON
AND ARE IN GOOD AGREEMENT THROUGH TOMORROW AFTERNOON. ALL MODELS
WEAKEN THE STACKED LOW NEAR KODIAK TONIGHT AND DEVELOP A LOW FURTHER
SOUTH OFF THE COAST OF WASHINGTON AS A SHORT WAVE RIDES DOWN THE JET
IN THE CENTRAL GULF. ANOTHER LOW SOUTH OF ADAK TO WORK INTO THE
BERING SEA TONIGHT AND TOWARD SAINT PAUL TOMORROW AS A RIDGE BUILDS
FARTHER WEST. AFTER THIS...MODELS START TO DIVERGE SOMEWHAT WITH THE
GFS BEING THE OUTLIER EVEN THOUGH THE UPPER LEVEL PATTERN REMAINS THE
SIMILAR. THE NAM AND ECMWF SEEMS TO HANDLE THE SITUATION A LITTLE
BETTER AS THE LOW IN THE BERING MOVES TOWARD THE WEST COAST OF ALASKA
FRIDAY. THE GFS DOES NOT DEVELOP A TRIPLE POINT LOW AS WOULD BE
EXPECTED WITH THE JET STREAM RIDING TO THE SOUTH OF THE MAIN LOW. THE
NAM LETS THE LOW MOVE INLAND BUT SLOWER THAN THE GFS FRIDAY NIGHT AND
MUCH FASTER THAN THE ECMWF. SO...FORECAST REALLY REFLECTS THE NAM
THROUGH THE FIRST FEW DAYS. ANOTHER LOW TO FOLLOW THE RIDGE IN THE
BERING OVER THE WEEKEND AND REMAINS PREDOMINANTLY SOUTH OF THE
ALEUTIANS. THE MODELS SEEM TO HANDLE THE GENERAL PROGRESSION OF THIS
LOW WELL AS IT MOVES TO THE COAST SATURDAY NIGHT AND STALLS SUNDAY
WITH STRONG HIGH PRESSURE OVER THE YUKON AND EASTERN ALASKA.  FARTHER
IN THE FORECAST...THE BERING FORECAST BECOMES RATHER UNCERTAIN AS THE
FLOW TURNS MORE ZONAL IN THE GFS AND ITS ENSEMBLE MEMBERS AND NOT SO
MUCH IN THE ECMWF.

.SHORT TERM FORECAST...

SOUTHCENTRAL...
AN UPPER SHORT WAVE THAT SPAWNED THE SURFACE LOW SOUTH OF KODIAK
ISLAND IS BECOMING A CUTOFF LOW IN THE NORTHERN GULF. WINDS
ASSOCIATED WITH THIS SYSTEM ARE MUCH STRONGER THAN ANTICIPATED WITH
GUSTS AS HIGH AS HURRICANE FORCE REPORTED AT AMATULI ISLAND. MAXIMUM
GALES WERE REPORTED OVER MUCH OF THE NORTHERN GULF AND EVEN THE
SOUTHERN HALF OF COOK INLET. OVERRUNNING MOISTURE SPREAD SNOW
NORTHWARD MUCH FASTER THAN ANTICIPATED FROM KODIAK UP TO THE SUSITNA
VALLEY. HEAVY SNOW ENDED IN KODIAK CITY EARLY THIS MORNING ALTHOUGH
MOISTURE ON THE BACK SIDE OF THE LOW IS WRAPPING AROUND AND BRINGING
ANOTHER SHOT OF MODERATE TO HEAVY SNOW. WINDS ACCOMPANYING THE WRAP
AROUND MOISTURE ARE ALSO HELPING TO REDUCE VISIBILITY TO LESS THAN
ONE MILE ACROSS THE ISLAND. THE WINTER WEATHER ADVISORY FOR KODIAK
WAS EXTENDED INTO THE EVENING TO ACCOUNT FOR THE WRAP AROUND MOISTURE
AND ADDITIONAL SNOWFALL.

A SHORTWAVE EMBEDDED WITHIN THE SOUTHERLY FLOW ON THE EASTERN SIDE OF
THE TROUGH IS CURRENTLY ENHANCING THE WINDS AND PRECIPITATION ACROSS
SOUTHCENTRAL. COOLING CLOUD TOPS ARE EVIDENT ON THE IR SATELLITE IN
THE LAST COUPLE OF HOURS AS THE UPPER WAVE MOVES INLAND.
PRECIPITATION WILL CONTINUE ALONG THE COAST AND SLOWLY TAPER OFF
INLAND OVERNIGHT. SNOWFALL INLAND WILL REMAIN LIGHT WITH THE
EXCEPTION OF UPSLOPE AREAS OF THE ALASKA RANGE. THE UPPER TROUGH AXIS
WILL NOT MOVE THROUGH UNTIL AROUND 18Z THURSDAY SO WILL KEEP LIGHT
SNOW IN THE FORECAST THROUGH THEN. CLEARING ON THE BACKSIDE OF THE
SYSTEM COUPLED WITH THE RECENT SNOWFALL AND A SHORTWAVE UPPER LEVEL
RIDGE WILL LIKELY LEAD TO AREAS OF FOG REDEVELOPING ALONG COOK INLET
LATER ON THURSDAY.

THIS CLEARING WILL BE SHORT-LIVED AS THE NEXT LOW PRESSURE SYSTEM
MOVES TOWARD BRISTOL BAY AND THE ASSOCIATED FRONT MOVES INTO THE
NORTHERN GULF ON THURSDAY NIGHT INTO FRIDAY. MODELS HAVE BEEN
INCONSISTENT WITH THE STRENGTH OF THE FRONT WHEN IT REACHES THE
GULF...SO WILL ONLY MENTION THE CHANCE OF PRECIPITATION AND STRONGER
WINDS THROUGH THE WEEKEND.

SOUTHWEST ALASKA...
VERY ACTIVE SHORT TERM FORECAST OUT WEST. A STRONG AREA OF LOW
PRESSURE WILL CROSS THE WESTERN ALEUTIANS AND MOVE INTO THE BERING
LATE TONIGHT...THEN TRACK EAST THROUGH THE SOUTHERN BERING THROUGH
FRIDAY. STRONG WINDS SURROUND THE LOW...BUT THE STRONGEST WINDS WILL
BE ON THE BACK SIDE OF THE LOW IN THE WESTERN AND CENTRAL ALEUTIANS
THURSDAY THROUGH FRIDAY MORNING. THESE WINDS WILL COINCIDE WITH COLD
ADVECTION...THUS FEEL THAT THESE WINDS WILL BE QUITE GUSTY IN NATURE.
WILL UPGRADE HIGH WIND WATCHES TO HIGH WIND WARNINGS FOR THE WESTERN
AND CENTRAL ALEUTIANS WITH THE AFTERNOON FORECAST PACKAGE. ALTHOUGH
THERE MAY BE SOME BLOWING SNOW AS WELL...OPTED FOR HIGH WIND WARNING
INSTEAD OF A BLIZZARD WARNING AS THE SNOW WILL BE RATHER WET IN
NATURE AND THE WINDS SHOULD BE A BIGGER DEAL THAN THE BLOWING SNOW.

A FAIRLY STRONG FRONT WILL MOVE OUT AHEAD OF THE LOW AS WELL...BUT
WINDS WITH THIS FRONT WILL REMAIN BELOW HIGH WIND CRITERIA YET
STRONG ENOUGH FOR STRONG WIND HEADLINES. WARM AIR WILL MOVE IN FAST
WITH THE SOUTHERLY WINDS...SO LITTLE CONCERN OF BLIZZARD CONDITIONS
FOR THE EASTERN ALEUTIANS...AKPEN...AND PRIBILOFS. HOWEVER...NOT
SURE THE WARM AIR WILL MOVE IN FAST ENOUGH AS THE FRONT REACHES THE
WEST COAST THURSDAY AFTERNOON AND EVENING...AND WE WILL HOIST A
BLIZZARD WATCH FOR THE KUSKOKWIM DELTA WITH THIS FORECAST PACKAGE. A
WEAK AREA OF HIGH PRESSURE WILL MOVE IN BEHIND THIS SYSTEM...BUT
THIS WILL BE SHORT-LIVED AS ANOTHER POTENT LOW PRESSURE SYSTEM MOVES
NORTHEAST TO THE CENTRAL ALEUTIANS SATURDAY.

LONG TERM FORECAST...
A LOW TO MOVE OUT OF THE CENTRAL ALEUTIANS SATURDAY WITH GALES AND
POSSIBLE STORM FORCE WINDS. THE LOW TO WEAKEN AS IT REACHES THE WEST
COAST OF ALASKA SUNDAY AND SLOWLY PROGRESS EAST AS IT BREAKS DOWN THE
HIGH OVER EASTERN ALASKA. VERY UNCERTAIN PATTERN OVER THE BERING
BEHIND THIS LOW THROUGH THE WEEKEND AND INTO NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY ZONE 171
         BLIZZARD WATCH THURSDAY ZONE 155 ALONG THE COAST.
MARINE...HURRICANE FORCE...172 175
         STORM WARNING...170 176 185
         GALE WARNING...120 130 132 138 140
                        150 155 160 165 171 179 180
         HEAVY FREEZING SPRAY WARNING...140
FIRE WEATHER...NONE.

AB/JN/TF FEB 09