Small Craft Advisory 605, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT FRI AUG 26 2011

.ANALYSIS AND UPPER LEVELS...THIS AFTERNOONS WEATHER MAP SHOWS A
STRONG UPPER LEVEL LOW IN THE NORTHWESTERN BERING SEA WITH A
SECONDARY UPPER LOW NEAR THE DUTCH HARBOR AREA. THE JET STREAM AT 250
MB RUNS WEST TO EAST FROM KAMCHATKA TO THE WESTERN ALEUTIAN ISLANDS
BEFORE HEADING SOUTHEAST AND UNDER THE UPPER LOW NEAR DUTCH HARBOR.
THE PRESENCE OF THE JET STREAM WILL CAUSE THIS LOW TO MOVE RAPIDLY
EASTWARD AND INTO THE GULF OF ALASKA BY SATURDAY. BEHIND THIS LOW AN
UPPER LEVEL RIDGE WILL AMPLIFY OVER THE BERING SEA THIS
WEEKEND...FORCING THE UPPER LOW IN THE NORTHWEST BERING SEA TO
RETROGRADE.
A SURFACE LOW IN THE MID 980 MB RANGE IS SOUTH OF THE ALASKA
PENINSULA AND BRINGING GALE FORCE WINDS TO THAT AREA.
THE SURFACE LOW IN THE GULF OF ALASKA...WHILE STILL LOOKING
IMPRESSIVE ON VISIBLE SATELLITE...IS WEAKENING RAPIDLY AND BECOME AN
INVERTED TROUGH OVER THE KENAI PENINSULA OVERNIGHT AS THE LOW NEAR
THE ALASKA PENINSULA MOVES INTO THE GULF OF ALASKA.

.MODEL DISCUSSION...THE BIGGEST SHORT TERM MODEL ISSUES REVOLVE
AROUND THE COMPLEX LOW MOVING INTO THE GULF OF ALASKA SATURDAY. THE
NAM AND ECMWF ARE MORE AGGRESSIVE IN DEVELOPING A TRIPLE POINT LOW
JUST EAST OF KODIAK ISLAND WHILE THE GFS MEANS OUT THE PRESSURE
DIFFERENCE WHILE KEEPING THE MAIN LOW CENTER FARTHER SOUTH. MODELS
CONVERGE AGAIN ON SUNDAY WITH THE LOW. MODELS GENERALLY AGREE ON THE
LONG WAVE PATTERN THROUGH EARLY NEXT WEEK BUT THEN RAPIDLY DIVERGE
AFTER THAT.

.SHORT TERM FORECAST...THE GALE FORCE WINDS NEAR THE ALASKA PENINSULA
WILL DIMINISH AND BECOME MORE NORTHWESTERLY OVERNIGHT AS THE LOW
PULLS EASTWARD. THE COMBINATION OF THIS LOW AND THE WEAKENING ONE IN
THE GULF WILL BRING RAINFALL INTO THE KODIAK AREA TOMORROW. THE
INVERTED TROUGH WILL ALSO BRING SOME RAINFALL ALONG THE NORTH GULF
COAST TONIGHT AND TO THE KENAI PENINSULA AND ANCHORAGE AND MAT-SU
AREAS TOMORROW MORNING.
THE ONLY CONVECTIVE POTENTIAL IN THE FORECAST AREA THIS AFTERNOON AND
EVENING IS IN THE SUSITNA VALLEY...HOWEVER THE HIGH CLOUD COVER WILL
PROBABLY KEEP THE CONVECTIVE TRIGGER FROM OCCURRING.

.LONG TERM FORECAST...LONG RANGE MODELS CONTINUE TO INDICATE A
PATTERN SHIFT ACROSS THE ALASKAN FORECAST AREA THIS WEEKEND. THE DEEP
AND PERSISTENT LONG WAVE TROUGH IN THE BERING SEA SHOULD CUT OFF AND
MOVE SOUTH OF THE GULF OF ALASKA WHILE A RIDGE OF HIGH PRESSURE
BUILDS OVER THE BERING SEA. THE OUTLOOK BECOMES LESS CLEAR BY THE
MIDDLE OF NEXT WEEK AS THE GFS AND ECMWF DIVERGE RAPIDLY AND
SIGNIFICANTLY IN THE LONG WAVE PATTERN.
HOWEVER UNTIL THEN...IT DOES APPEAR THE STATE WILL SEE A BREAK TOWARD
LESS ACTIVE AND DRIER WEATHER...WITH A RETURN TO SEASONAL
TEMPERATURES AT MOST LOCATIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 120 130 150 155 165 172 176.
FIRE WEATHER...NONE.

AUG 11