Small Craft Advisory 948, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1225 PM AKST THU NOV 28 2013

.ANALYSIS AND UPPER LEVELS...A RIDGE IS BUILDING OVER THE BERING
SEA WHILE A COLD UPPER LOW SINKS SOUTHWARD ACROSS MAINLAND ALASKA.
THE TROUGH DIGGING OUT AHEAD OF THE UPPER LOW IS BRINGING SNOW TO
PORTIONS OF EASTERN PRINCE WILLIAM SOUND AND THE COPPER RIVER
BASIN...WITH MOST OF THE SNOW ACCUMULATION OCCURRING INLAND. ARCTIC
AIR WITH THE TROUGH IS POURING SOUTHWARD INTO THE GULF OF ALASKA
WITH STRONG GAP WINDS BEING OBSERVED ACROSS MUCH OF THE NORTHERN
AND WESTERN GULF. A WEAK SHORT-WAVE MOVING OVER TOP OF THE BERING
RIDGE IS TRACKING TOWARD THE SOUTHWEST COAST...WITH SNOW BEGINNING
TO MAKE ITS WAY INTO THE KUSKOKWIM DELTA THIS MORNING.

.MODEL DISCUSSION...MODELS ARE STRUGGLING WITH THE UPPER LOW OVER
MAINLAND ALASKA AND EMBEDDED WAVES ROTATING AROUND IT AS IT WOBBLES
ITS WAY SOUTH AND EASTWARD OVER THE NEXT COUPLE DAYS. THE MAIN
IMPACT OF THESE UPPER WAVES WILL BE ON THE STRENGTH OF GAP FLOW
ALONG THE NORTH GULF COAST/PRINCE WILLIAM SOUND. WITH LOW CONFIDENCE
IN THE DETAILS OF THESE WAVES...WILL JUST HOLD CLOSE TO EXISTING
FORECAST WHICH DOES INDICATE STRENGTHENING GAP WINDS AS WE HEAD
INTO THE WEEKEND.

MODELS ARE ALSO STRUGGLING WITH DETAILS OF TROUGH EXITING ASIA AND
MOVING INTO THE WESTERN BERING THIS WEEKEND. 12Z GFS AND ECMWF BOTH
REFLECT A SIMILAR SOLUTION OF PHASING OF UPPER SHORT-WAVES WHICH
PICKS UP A LOW OVER THE NORTHWEST PACIFIC AND LIFTS IT NORTHWARD
ACROSS THE WESTERN ALEUTIANS. OTHER SOLUTIONS ARE NEARLY AS
AGGRESSIVE BUT FLOW SEEMS TO SUPPORT THAT SOME SORT OF LOW WILL
LIFT NORTHWARD. SINCE THIS IS NOT REFLECTED AT ALL IN THE CURRENT
FORECAST WILL TREND HEAVILY THAT DIRECTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AS THE UPPER LOW SHIFTS SOUTH AND EAST AND A
SURFACE HIGH BECOMES WELL ESTABLISHED OVER INTERIOR ALASKA THE NEXT
COUPLE DAYS SOUTHCENTRAL WILL SETTLE INTO THE DEEP FREEZE. STRONG
GAP WINDS ALONG THE NORTH GULF COAST AND PRINCE WILLIAM SOUND WILL
PERSIST (AND STRENGTHEN IN SOME LOCATIONS) MAINTAINING WARMER
TEMPERATURES IN THOSE LOCALES. THERE IS POTENTIAL FOR HIGH WINDS
IN THE VALDEZ AREA THIS WEEKEND. THIS IS HIGHLY DEPENDENT ON THE
STRENGTH OF UPPER LEVEL WAVES TRANSITING THE AREA WHICH AS MENTIONED
ABOVE THERE IS A GREAT DEAL OF UNCERTAINTY WITH.

SOUTHWEST ALASKA...THE UPPER WAVE MOVING TOWARD THE KUSKOKWIM DELTA
WILL RAPIDLY DIVE SOUTHWARD ALONG THE EAST SIDE OF THE BERING RIDGE
SO SNOW WILL NOT LAST LONG IN ANY ONE PLACE AS IT MOVES THROUGH.
OTHERWISE...ARCTIC AIR WILL PROVIDE CLEAR AND DRY CONDITIONS THROUGH
THE WEEKEND. THE UPPER RIDGE OVER THE BERING WILL SHIFT EASTWARD
OVER SOUTHWEST ALASKA LATE THIS WEEKEND ALLOWING WARMER AIR ALOFT
TO BEGIN TO MOVE INTO THE REGION. SURFACE TEMPERATURES WILL BE SLOW
TO WARM WITH CLEAR SKIES AND LIGHT WINDS...BUT THE MOUNTAIN TOPS
WILL WARM SETTING UP A STEEP LOW LEVEL TEMPERATURE INVERSION.

BERING SEA/ALEUTIANS...THE RIDGE OVER THE BERING SEA WILL GRADUALLY
SHIFT EASTWARD ALLOWING A COLD FRONT OVER THE NORTHWEST PACIFIC TO
MARCH EASTWARD ACROSS THE WESTERN BERING AND WESTERN ALEUTIANS.
SOUTHERLY FLOW OUT AHEAD OF THE COLD FRONT WILL PROVIDE FOR SOME
WARMING ALONG THE WESTERN ALEUTIANS. THE FRONT WILL EVENTUALLY STALL
AS THE PARENT LOW TRACKS NORTHWARD OVER EASTERN RUSSIA AND FRONT
BECOMES ELONGATED. ARRIVAL OF AN UPPER LEVEL SHORT-WAVE TROUGH WILL
THEN LIFT A PACIFIC LOW NORTHWARD RIGHT ALONG THE FRONTAL ZONE
SATURDAY AND SUNDAY. WEATHER ACROSS THE CENTRAL TO EASTERN BERING
WILL REMAIN BENIGN UNDER THE INFLUENCE OF THE UPPER RIDGE.

.LONG TERM FORECAST...SHORT-WAVES MOVING UP AGAINST THE WEST SIDE
OF THE UPPER RIDGE WILL FORCE IT TO CONTINUE SHIFTING EASTWARD OVER
MAINLAND ALASKA EARLY NEXT WEEK. INITIALLY TEMPERATURES WILL WARM
SIGNIFICANTLY AT HIGHER ELEVATIONS OF MAINLAND ALASKA BUT MUCH MORE
GRADUALLY AT THE SURFACE. MODELS DISAGREE ON THE EXACT LOCATION AND
ORIENTATION OF THE RIDGE NEXT WEEK...BUT GENERALLY LOOKS LIKE A
GOOD CHANCE OF PRECIP RETURNING TO SOUTHWEST ALASKA MID WEEK WHILE
SOUTHCENTRAL MAY REMAIN DRY UNTIL LATE IN THE WEEK. WEATHER OVER
THE BERING SEA/ALEUTIANS WILL BECOME MUCH MORE ACTIVE WITH STORMS
TRACKING UP THE WEST SIDE OF THE RIDGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 131.
MARINE...GALE WARNING...127 130 131 132 150 170 172 173 174 176 178.
         HEAVY FREEZING SPRAY WARNING...121 126 127 128 129 130 131
                                        136 137 138 141.
FIRE WEATHER...NONE.

SEB NOV 13