Small Craft Advisory 469, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKDT SUN JUN 9 2013

.ANALYSIS AND UPPER LEVELS...A BROAD RIDGE EXTENDS FROM THE EASTERN
BERING SEA TO THE SOUTHERN MAINLAND AND GULF OF ALASKA. AN EXTENSIVE
STRATUS DECK COVERS MUCH OF THE EASTERN BERING AND SOUTHWEST ALASKA
COAST...BUT THE SPARSE NETWORK OF SURFACE OBSERVATIONS SHOWS THERE
ISN'T A WHOLE LOT OF FOG. INVESTIGATION OF AREA SOUNDINGS (COLD
BAY/SAINT PAUL/KING SALMON/BETHEL) SHOWS THE TOP OF INVERSIONS ARE
APPROXIMATELY TWO OR THREE THOUSAND FEET UP. WOULD LIKE TO SEE THESE
LOWER AND STEEPEN FOR FOG TO BECOME MORE WIDESPREAD. SOUTHCENTRAL
ALASKA IS CLEAR THANKS TO DRY OFFSHORE FLOW.

MEANWHILE...ON THE WEST SIDE OF THE RIDGE IS A WEAK LOW NEAR THE
WESTERN ALEUTIANS WHICH IS BEING FORCED SOUTHWARD. NORTH OF THE
RIDGE A FAIRLY VIGOROUS UPPER LEVEL LOW AND SHORT-WAVE TROUGH ARE
DIGGING EAST-SOUTHEAST INTO NORTHERN ALASKA.

.MODEL DISCUSSION...MODELS ARE ALL MORE AGGRESSIVE WITH DIGGING
OF UPPER TROUGH ALONG THE CANADIAN BORDER. THERE ARE MINOR
DIFFERENCES IN AMPLITUDE AND LOCATION OF THIS TROUGH WHICH WILL
PRIMARILY AFFECT HOW MUCH CLOUD COVER AND PRECIP FALLS ACROSS THE
COPPER RIVER BASIN. THE OTHER FEATURE MODELS DIFFER ON IS TRACK OF
A LOW MOVING UP FROM THE NORTH PACIFIC TOWARD THE EASTERN ALEUTIANS
ON TUESDAY. WILL TREND TOWARD THE MORE NORTHERLY SOLUTION OF THE
GFS/ECMWF WHICH SHOW GOOD RUN-TO-RUN CONSISTENCY SINCE THE 00Z RUNS
FROM YESTERDAY AFTERNOON.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE THERMAL TROUGH WILL REMAIN OVER
SOUTHCENTRAL ALASKA ONCE AGAIN TODAY PROVIDING THE FOCUS FOR
AFTERNOON AND EVENING CONVECTION. STORM MOTION IS BECOMING MORE
WESTERLY AS THE TROUGH OVER NORTHERN ALASKA PUSHES DOWN ON THE
RIDGE. THIS MEANS SHOWERS THAT FORM ON THE TALKEETNA AND CHUGACH
MOUNTAINS WILL TRACK AWAY FROM THE POPULATION CENTERS AND THE
COPPER RIVER BASIN WILL SEE THE BULK OF ACTIVITY TODAY. THE THERMAL
TROUGH WILL BE PUSHED SOUTHWARD ON MONDAY AS THE TROUGH BEGINS TO
DIG SOUTHEASTWARD TOWARD THE CANADIAN BORDER. LOOKS LIKE THERE
WILL STILL BE ENOUGH INSTABILITY TO PRODUCE SHOWERS AND PERHAPS
EVEN SOME WEAK LIFT FROM THE TROUGH...MAINLY OVER THE COPPER BASIN.
THE UPPER TROUGH WILL CONTINUE TO AMPLIFY ALONG THE CANADIAN BORDER
ON TUESDAY...PERHAPS TRIGGERING A FEW SHOWERS ALONG THE WRANGELL
MOUNTAINS. MUCH MORE STABLE AIR WILL ENCOMPASS THE REMAINDER OF
SOUTHCENTRAL... ENSURING DRY AND PARTLY TO MOSTLY SUNNY CONDITIONS.

OFFSHORE FLOW WILL PERSIST OVER THE NEXT FEW DAYS WITH A SURFACE
TROUGH STRENGTHENING ALONG THE NORTH GULF COAST. THIS WILL WORK
AGAINST SEA BREEZES...ESPECIALLY IN WESTERN PRINCE WILLIAM SOUND
WHERE THE PRESSURE GRADIENTS WILL BE STRONGLY IN FAVOR OF OFFSHORE
FLOW. THUS...EXPECT WARM TEMPERATURES ALONG THE COAST...ESPECIALLY
FOR SEWARD AND WHITTIER.

SOUTHWEST ALASKA...PERSISTENT ONSHORE FLOW HAS ALLOWED STRATUS TO
PENETRATE INTO SOME INTERIOR PORTIONS OF SOUTHWEST ALASKA INCLUDING
MUCH OF THE SOUTHERN KUSKOKWIM VALLEY AND A SMALL PORTION OF
INTERIOR BRISTOL BAY. THE RIDGE WILL BUILD OVER THE EASTERN BERING
THROUGH TOMORROW RESULTING IN A SHIFT TO MORE NORTHERLY FLOW. THIS
WIND SHIFT IN COMBINATION WITH THE POWER OF THE SUN SHOULD LEAD TO
DISSIPATION OF CLOUDS INLAND. THIS IN TURN WILL ALLOW A RETURN TO
WARMER TEMPERATURES OVER INTERIOR SOUTHWEST. COASTAL SECTIONS OF
THE KUSKOKWIM DELTA AND THE ALASKA PENINSULA WILL REMAIN FIRMLY
ENTRENCHED IN CLOUDS THROUGH TUESDAY WITH MORE OF AN ONSHORE
COMPONENT TO THE FLOW CLOSER TO THE RIDGE AXIS.

BERING SEA/ALEUTIANS...AS THE WEAK LOW ALONG THE WESTERN ALEUTIANS
EXITS TO THE SOUTH TODAY A MUCH LARGER TROUGH WILL EXIT ASIA AND
MOVE INTO THE WESTERN BERING SEA. UPPER FLOW WILL BRIEFLY BECOME
PROGRESSIVE WITH THE RIDGE SHIFTING EASTWARD TOWARD WESTERN ALASKA
AND THE TROUGH MOVING TO THE CENTRAL BERING SEA. A WEAK LOW PRESSURE
SYSTEM WILL DEVELOP AND MOVE INTO THE CENTRAL BERING AS WELL.
HOWEVER...THE BIGGER IMPACT WILL BE STRENGTHENING SOUTHERLY WINDS
WITH A TIGHTENING PRESSURE GRADIENT BETWEEN THE LOW AND HIGH.

.LONG TERM FORECAST...A CLOSED LOW WILL DEVELOP OVER THE WESTERN
BERING TUESDAY AND SET UP SHOP OVER THE BERING THROUGH NEXT WEEKEND.
THE RIDGE WILL SHIFT EASTWARD OVER MAINLAND ALASKA MID WEEK AND THEN
INTO CANADA LATE IN THE WEEK. THIS WILL RESULT IN A WETTER MORE
ACTIVE PATTERN OVER THE BERING SEA AND SOUTHWEST ALASKA. SOUTHCENTRAL
WILL SEE INCREASING CLOUDS LATE IN THE WEEK...BUT MAY HOLD OFF ON
RAIN AND COOLER TEMPERATURES UNTIL THE WEEKEND. THIS WILL ALL DEPEND
ON MOVEMENT OF INDIVIDUAL WAVES AROUND THE BERING LOW...WHICH MODELS
CANNOT RESOLVE THAT FAR OUT IN TIME.

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

SEB JUN 13