Gale Warning 518, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM AKDT FRI AUG 29 2008

.ANALYSIS AND UPPER LEVELS...A LONG-WAVE TROUGH CONTINUES TO
DOMINATE ALASKA WEATHER. FAIRLY HIGH AMPLITUDE SHORT-WAVE TROUGHS
ARE CENTERED OVER THE CENTRAL BERING SEA AND SOUTHEAST ALASKA
WITH A WEAK RIDGE IN BETWEEN. THERE IS ALSO A SLIGHTLY OUT OF
PHASE SHORT-WAVE SOUTH OF THE BERING TROUGH. A VORT-MAX MOVING
THROUGH THE BASE OF THIS TROUGH AS WELL AS A VORT-MAX DROPPING
INTO THE BACK SIDE OF THE BERING TROUGH ARE LEADING TO AMPLIFICATION
OF THE TROUGHS AND THE DOWNSTREAM RIDGE. AT THE SURFACE THERE IS A
1000 MB LOW CENTERED OVER THE CENTRAL BERING WITH FRONTAL SYSTEM
TRACKING SLOWLY TOWARD THE MAINLAND. A WEAK SURFACE LOW HAS FORMED
JUST AHEAD OF THE SOUTHERN TROUGH AND IS EXPECTED TO BE THE MAIN
FEATURE OF CONCERN THIS WEEKEND. THE SOUTHERN MAINLAND OBSERVED
AREAS OF STRATUS AND FOG THIS MORNING BUT THAT HAS BEGUN TO BREAK
UP. MOISTURE AND INSTABILITY EVIDENT IN 12Z ANCHORAGE SOUNDING ARE
RESULTING IN QUICK DEVELOPMENT OF CUMULUS AS THE STRATUS BREAKS.
THE COMBINATION OF RIDGE BUILDING INTO THE REGION AND NORTH GULF
COAST SURFACE TROUGH IS ALSO PRODUCING SOME LOCALLY WINDY CONDITIONS
THROUGH COASTAL GAPS.

.MODEL DISCUSSION...00Z MODEL RUNS WERE IN VERY GOOD AGREEMENT WITH
DEVELOPMENT AND TRACK OF NORTH PACIFIC LOW TO KODIAK ISLAND ON
SUNDAY. THE 12Z UKMET AND ECMWF HAVE COME IN WITH A SLIGHTLY FARTHER
WEST TRACK THAT BRINGS THE LOW TO SHELIKOF AND ACROSS INTO BRISTOL
BAY WHILE THE GFS REMAINS CONSISTENT WITH A TRACK JUST EAST OF
KODIAK ISLAND. WILL STICK WITH THE MORE CONSISTENT GFS-BASED FORECAST
FOR NOW. THE GFS IS ALSO MORE CONSISTENT WITH TRACK OF LOW SOUTH OF
ALEUTIANS SUNDAY THROUGH TUESDAY BRINGING TO THE LOW TO NEAR COLD BAY
WHILE THE 12Z ECMWF MADE A LARGE JUMP EASTWARD TOWARD KODIAK ISLAND.
THE CURRENT FORECAST WAS BASED OFF THE 00Z ECMWF FROM YESTERDAY WHICH
HAD A TRACK WEST OF THE GFS. THIS IS FAR ENOUGH OUT THAT WILL STICK
WITH CURRENT FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL...EXPECT ISOLATED TO SCATTERED SHOWERS TODAY...MAINLY
OVER THE MOUNTAINS. IT IS STILL UNSTABLE ENOUGH THAT WE COULD SEE
A STRAY LIGHTNING STRIKE OR TWO AS WELL. MORE STABLE CONDITIONS WILL
DEVELOP TONIGHT INTO SATURDAY AS THE AMPLIFYING UPPER RIDGE MOVES
OVER SOUTHCENTRAL. THUS...EXPECT ONLY A FEW SHOWERS OVER THE
MOUNTAINS ON SATURDAY. UNDER PARTLY CLOUDY SKIES THERE WILL BE
DECENT RADIATIONAL COOLING TONIGHT AND ONCE AGAIN EXPECT AREAS OF
FOG TO FORM. SATURDAY NIGHT AND SUNDAY THE IMPACTS OF THE STORM
TRACKING TOWARD KODIAK ISLAND WILL SPREAD TO SOUTHCENTRAL. EXPECT
A FAIRLY LARGE AREA OF GALE FORCE WINDS OVER THE GULF WATERS. MOST
OF THE RAIN SHOULD REMAIN ALONG THE COAST WITH A FEW SHOWERS MAKING
IT INLAND.

SOUTHWEST...THE FRONTAL SYSTEM OVER THE EASTERN BERING WILL MOVE
TO THE COAST TONIGHT AND THEN STALL OUT AS THE RIDGE BUILDS AHEAD
OF IT KEEPING INLAND AREAS MAINLY DRY. THE LOW TRACKING TO KODIAK
SUNDAY WILL BRING RAIN AND WIND FROM THE OPPOSITE DIRECTION AND
MAINLY AFFECT THE BRISTOL BAY REGION.

BERING SEA/ALEUTIANS...THE SURFACE LOW AND FRONTAL SYSTEM WILL
MOVE EASTWARD AND GRADUALLY DISSIPATE SATURDAY AND SUNDAY AS THE
NEW LOW TO THE EAST BECOMES DOMINANT. ANOTHER STORM WILL TRACK
SOUTH OF THE ALEUTIANS SUNDAY AND MONDAY WITH LITTLE IMPACT ON THE
ALEUTIANS...BUT THERE IS UNCERTAINTY IN THIS TRACK SO THIS COULD
CHANGE. MODELS ALSO INDICATE ANOTHER SHORT-WAVE DROPPING INTO THE
BACK SIDE OF THE TROUGH OVER THE WESTERN BERING.

.LONG TERM FORECAST...THE GFS 500MB 5-WAVE SHOWS THE UPPER TROUGH
REMAINING CENTERED OVER THE EASTERN BERING AND WESTERN ALASKA.
THEREFORE...EXPECT CURRENT STORM TRACK WITH LOWS DEVELOPING ALONG
THE JET OVER THE NORTH PACIFIC AND TRACKING TOWARD KODIAK ISLAND
AND THE ALASKA PENINSULA TO PERSIST. AS WOULD BE EXPECTED MOVING
INTO THE FALL SEASON STORMS WILL BEGIN TO GET STRONGER AND PRODUCE
MORE RAIN AND WIND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 132 150.
FIRE WEATHER...NONE.

SEB AUG 08