Small Craft Advisory 534, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
120 PM AKDT SAT JUN 30 2012

.ANALYSIS AND UPPER LEVELS...A LARGE CLOSED LOW JUST INLAND FROM
SOUTHEAST ALASKA IS SLOWLY DRIFTING NORTHWARD TOWARD THE YUKON.
SHORT-WAVES ARE DROPPING DOWN THE WEST SIDE OF THE LOW FROM THE
YUKON TO EASTERN ALASKA INTERIOR AND THE COPPER RIVER BASIN
PRODUCING SHOWERS OR STEADY RAIN. A VERY WEAK UPPER RIDGE HAS
FORMED FROM THE ALASKA INTERIOR TO SOUTHCENTRAL...BUT AT THIS
POINT THERE ARE LOTS OF WEAK WAVES EMBEDDED WITHIN IT WHICH ARE
HELPING TRIGGER ISOLATED TO SCATTERED SHOWERS OVER THE MOUNTAINS.
WITH WEAK STEERING FLOW UNDER THE RIDGE THESE SHOWERS WILL REMAIN
ALONG THE MOUNTAINS.

ANOTHER UPPER LOW NEAR THE EASTERN ALEUTIANS IS TRACKING QUICKLY
EASTWARD TOWARD THE NORTHEAST PACIFIC. A VERY WEAK LOW CAN BE FOUND
UNDER THE UPPER LOW ALONG WITH AN OLD FRONTAL BOUNDARY ALONG THE
SOUTHWEST ALASKA COAST...BOTH OF WHICH ARE PRODUCING AREAS OF LOW
CLOUDS AND RAIN. WEAK WAVES OUT AHEAD OF THIS ARE PRODUCING SHOWERS
OVER INTERIOR SOUTHWEST ALASKA.

LOOKING UPSTREAM ANOTHER UPPER LOW IS DROPPING OUT OF EASTERN
SIBERIA WITH A MUCH STRONGER ONE OVER THE RUSSIAN ARCTIC POISED
TO FOLLOW.

.MODEL DISCUSSION...MODELS ARE IN VERY GOOD AGREEMENT WITH HANDLING
OF SYNOPTIC SCALE FEATURES OVER THE NEXT THREE DAYS. THERE ARE A
FEW MINOR DIFFERENCES IN TIMING PLACEMENT OF MESO-SCALE WAVES...BUT
THEY ARE VERY DIFFICULT TO FORECAST VERY FAR OUT IN TIME ANYWAY.
THUS FORECAST CONFIDENCE IS AVERAGE TO ABOVE AVERAGE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SHORT-WAVE MOVING THROUGH THE COPPER RIVER
BASIN TODAY WILL CONTINUE SOUTHWARD INTO THE GULF TONIGHT SPREADING
RAIN INTO EASTERN PRINCE WILLIAM SOUND. WEAKER WAVES WILL ROTATE
SOUTHWESTWARD AROUND THE RIDGE AXIS BRINGING SHOWERS TO THE TALKEETNA
AND WESTERN CHUGACH MOUNTAINS. DON'T EXPECT RAIN TO MOVE OVER THE
VALLEYS...BUT CLOUDY SKIES WILL DOMINATE ANCHORAGE AND THE MAT-SU
LATER TONIGHT THROUGH AT LEAST SUNDAY MORNING. EXPECT AT LEAST
SOME SUN TO BREAK THROUGH SUNDAY AFTERNOON AS THESE WAVES ROTATE
BACK NORTHWARD ON THE WEST SIDE OF THE RIDGE AXIS. MEANWHILE ANOTHER
STRONGER WAVE WILL TRACK SOUTHWARD ACROSS THE EASTERN COPPER BASIN
SUNDAY BRINGING MORE RAIN OR SHOWERS. THE COPPER BASIN WILL REMAIN
ON THE WESTERN PERIPHERY OF THE UPPER LOW MOVING INTO THE YUKON
THROUGH TUESDAY...SO CLOUDS AND SHOWERS WILL REMAIN LIKELY.
ELSEWHERE ACROSS SOUTHCENTRAL THE WEAK RIDGE WILL REMAIN OVERHEAD
WITH CONDITIONS BECOMING MORE STABLE WITH TIME. THUS DRY CONDITIONS
CAN BE EXPECTED OVER THE LOWLANDS THROUGH TUESDAY. SKY COVER
REMAINS A CHALLENGE AS WEAK WAVES MOVE THROUGH THE RIDGE...SO
EXPECT PERIODS OF CLOUDS AND SUN.

SOUTHWEST ALASKA...REMNANTS OF FRONT WILL CONTINUE TO DISSIPATE
ALONG THE SOUTHWEST COAST THIS AFTERNOON. THE UPPER LEVEL
SHORT-WAVE BRINGING SHOWERS TO INTERIOR SOUTHWEST ALASKA WILL
EXIT TO THE NORTH TONIGHT. THE FIRST UPPER LOW DROPPING OUT OF
RUSSIA TODAY WILL OPEN INTO A TROUGH AND CROSS SOUTHWEST ALASKA
SUNDAY AND MONDAY. MODELS MOST OF THE RAIN WITH THIS TO FALL
INLAND WHERE GREATER INSTABILITY WILL CONTRIBUTE TO VERTICAL
MOTION. ONSHORE FLOW WILL PERSIST ALONG THE COAST WHERE STRATUS
AND FOG WILL BE THE PRIMARY PROBLEM. A MUCH STRONGER SYSTEM WILL
DROP OUT OF RUSSIA SUNDAY NIGHT AND PUSH A FRONT INLAND ACROSS
SOUTHWEST ALASKA MONDAY NIGHT AND TUESDAY...LIKELY RESULTING IN
WIDESPREAD RAIN.

BERING SEA/ALEUTIANS...A SERIES OF WEAK UPPER WAVES WILL TRAVERSE
THE BERING SEA TONIGHT AND SUNDAY. A MORE SIGNIFICANT FRONT WILL
CROSS THE REGION SUNDAY NIGHT THROUGH MONDAY NIGHT AS A LARGE LOW
DROPS OUT OF THE RUSSIAN ARCTIC. HIGH PRESSURE WILL BUILD BACK IN
BEHIND THE FRONT PRODUCING WIDESPREAD STRATUS AND FOG.

.LONG TERM FORECAST...THE PRIMARY FEATURE DURING THE DAY 4 THROUGH
7 PERIOD WILL BE THE LOW WHICH DROPS OUT OF THE RUSSIAN ARCTIC
EARLY NEXT WEEK. IT WILL TRACK SOUTHEASTWARD ACROSS THE FAR EASTERN
BERING MID WEEK AND DROP SOUTH OF KODIAK ISLAND BY THE END OF THE
WEEK. RAIN OR SHOWERS WILL INCREASE OUT AHEAD OF THE LOW AFFECTING
THE SOUTHERN MAINLAND FOR MUCH OF THE WEEK. THUS EXPECT GENERALLY
CLOUDY CONDITIONS WITH PERIODS OF RAIN OR SHOWERS. MEANWHILE...AS
THIS LOW IS TRAVERSING THE EASTERN BERING WARM AIR AND MOISTURE
WILL OVERRIDE THE NORTH PACIFIC RIDGE AND MOVE OVER THE ALEUTIANS
AND SOUTHERN BERING. THIS WILL BE VERY CONDUCIVE TO FORMATION OF
DENSE FOG ALONG WITH ANY RAIN THAT FALLS.

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

SEB JUN 12