Small Craft Advisory 459, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT FRI JUN 5 2009

.ANALYSIS AND UPPER LEVELS...LONG-WAVE TROUGH REMAINS FIRMLY
ENTRENCHED OVER THE BERING SEA. EMBEDDED VERTICALLY STACKED LOW
NORTH OF THE PRIBILOFS IS LIFTING NORTH-NORTHWEST TOWARD EASTERN
RUSSIA. A SHORT-WAVE TROUGH EXTENDS FROM THIS LOW SOUTHEASTWARD
ACROSS THE LOWER KUSKOKWIM VALLEY TO THE SOUTHERN KENAI
PENINSULA...AND IT IS LIFTING NORTHEASTWARD PRODUCING EXTENSIVE
CLOUDINESS ACROSS SOUTHCENTRAL AND SOUTHWEST ALASKA AS WELL AS
A FEW SHOWERS. STRONG WINDS HAVE DEVELOPED ALONG THE SOUTHWEST
COAST DUE TO TIGHT PRESSURE GRADIENT BETWEEN BERING LOW AND STRONG
RIDGE OF HIGH PRESSURE SOUTH OF THE GULF OF ALASKA. PRESSURE RISES
BEHIND THE DEPARTING LOW ALONG WITH MIXING DOWN OF STRONGER WINDS
FROM ALOFT IN AN UNSTABLE BOUNDARY LAYER ARE ALSO CONTRIBUTING TO
THESE STRONG WINDS.

.MODEL DISCUSSION...MODELS ARE IN FAIR AGREEMENT THROUGH THE FIRST
THREE DAYS OF THE FORECAST. MAIN DIFFERENCES LIE WITH THE LOW
TRACKING SOUTH OF THE ALASKA PENINSULA. 12Z GFS AND ECMWF SOLUTIONS
ACTUALLY MATCH UP QUITE WELL. HOWEVER...THERE IS A LARGE SPREAD
AMONG THE GFS ENSEMBLE MEMBERS AND VERY POOR RUN-TO-RUN CONSISTENCY
WITHIN EACH MODEL. THEREFORE...WILL ONLY TREND TOWARD THIS NEW TRACK.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE BULK OF THE SHOWERS WILL FALL OUT AHEAD
OF THE TROUGH FROM THE COPPER BASIN TO EASTERN PRINCE WILLIAM SOUND.
HOWEVER...PARTIAL CLEARING BEHIND THE TROUGH THIS AFTERNOON COMBINED
WITH COOLING ALOFT SHOULD DESTABILIZE THE ATMOSPHERE ENOUGH TO
TRIGGER A FEW SHOWERS BACK OVER THE REST OF SOUTHCENTRAL. THE
UPPER RIDGE WILL BUILD NORTHWARD ACROSS THE GULF INTO SOUTHCENTRAL
ON SATURDAY AND SUNDAY. MEANWHILE...THE SURFACE HIGH WILL BUILD
NORTHWARD ACROSS SOUTHWEST ALASKA AND INTO THE INTERIOR. THIS WILL
SET UP OFFSHORE FLOW WHICH WILL ENHANCE WARMING VIA DOWNSLOPING.
THEREFORE...IT LOOKS LIKE A VERY WARM AND DRY WEEKEND ACROSS
SOUTHCENTRAL...INCLUDING COASTAL AREAS WHERE THE NORTHERLY FLOW
WILL WORK AGAINST THE COOLING EFFECTS OF SEA BREEZES. CLOUDS AND
THE THREAT OF SHOWERS WILL RETURN MONDAY AS THE SHORT-WAVE RIDGE
MOVES TO INTERIOR ALASKA ALLOWING A TROUGH TO MOVE INTO THE GULF.

SOUTHWEST ALASKA...STRONG WINDS WILL PERSIST ALONG THE SOUTHWEST
COAST...MAINLY THE KUSKOKWIM DELTA...THROUGH TONIGHT AND THE
RAPIDLY DIMINISH SATURDAY AS SURFACE HIGH BUILDS IN FROM THE SOUTH.
THE MAIN UPPER SHORT-WAVE WILL EXIT THE LOWER KUSKOKWIM VALLEY THIS
AFTERNOON. HOWEVER...OTHER WEAKER WAVES EMBEDDED WITHIN THE TROUGH
WILL MOVE ACROSS THE REGION THROUGH SATURDAY...RESULTING IN A
CONTINUED THREAT OF SHOWERS. THE UPPER RIDGE WILL BEGIN TO BUILD
INTO BRISTOL BAY SATURDAY AFTERNOON AND OVER THE REST OF SOUTHWEST
ALASKA SATURDAY NIGHT...PRODUCING CLEARING AND DRYING. THIS WILL
LAST INTO SUNDAY...WHICH WILL BE THE WARMEST DAY OF THE WEEK...BUT
THE RIDGE WILL THEN EXIT INTO THE INTERIOR MONDAY AS ANOTHER TROUGH
MOVES IN.

BERING SEA/ALEUTIANS...WEATHER OVER THE BERING SEA AND ALEUTIANS
WILL REMAIN UNSETTLED UNDER THE INFLUENCE OF THE UPPER TROUGH. AS
THE LOW NEAR THE PRIBILOFS LIFTS NORTHWARD TO RUSSIA ANOTHER LOW
WILL DROP DOWN THE BACK SIDE OF THE TROUGH...MOVING SOUTH OF THE
WESTERN ALEUTIANS SUNDAY AND DEVELOPING INTO ANOTHER LARGE LOW
COMPLEX WHICH WILL AFFECT THE REGION FOR THE WEEK TO COME.

.LONG TERM FORECAST...THE UPPER TROUGH WILL REMAIN CENTERED OVER
THE BERING SEA AND ALEUTIANS THROUGH THE END OF NEXT
WEEK...MAINTAINING GENERALLY CLOUDY AND WET CONDITIONS ACROSS THE
BERING SEA AND INTO SOUTHWEST ALASKA. SOUTHCENTRAL WILL REMAIN ON
THE OUTER FRINGE OF THE TROUGH...WHICH WILL ALLOW FOR A MIX OF DRY
SUNNY DAYS IN BETWEEN UPPER SHORT-WAVES...AND CLOUDIER SHOWERY DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...180.
FIRE WEATHER...NONE.

SEB JUN 09