Small Craft Advisory 837, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
600 AM AKST SUN NOV 20 2011

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN FEATURES AN AMPLIFYING LONGWAVE TROUGH OVER
MAINLAND ALASKA AND A DEVELOPING RIDGE OVER THE WESTERN BERING SEA. A
QUICK LOOK AT SATELLITE THIS MORNING SHOWS A WEAKENING VERTICALLY
STACKED LOW PRESSURE SYSTEM OVER THE SOUTHERN BERING SEA MOVING
SOUTHEAST TOWARD DUTCH HARBOR. A LARGE AND DISORGANIZED FRONT
STRETCHES EASTWARD FROM THIS LOW ACROSS THE ALEUTIAN RANGE AND INTO
THE GULF OF ALASKA. A NEW TRIPLE POINT LOW IS DEVELOPING SOUTHEAST OF
KODIAK ISLAND. THIS NEW LOW WILL CONTINUE TO PULL ENERGY FROM THE
DECAYING LOW OUT WEST AS THE UPPER LOW FOLLOWS SUIT AND DROPS INTO
THE LONGWAVE TROUGH IN THE GULF. WIDESPREAD SNOW ACROSS SOUTHWEST
ALASKA IS TAPERING OFF AS THE BERING LOW DROPS RAPIDLY SOUTHWARD.
MEANWHILE...RAIN AND SNOW SHOWERS IN THE GULF ARE ON THE INCREASE AS
AN INVERTED TROUGH IS SWINGING TOWARD THE PRINCE WILLIAM SOUND AREA.

.MODEL DISCUSSION...
THERE IS ONE MAIN WEATHER SYSTEM AFFECTING THE STATE CURRENTLY...AND
THE MODELS ARE IN REASONABLY GOOD AGREEMENT ON THE EVOLUTION OVER THE
NEXT FEW DAYS. THERE IS A IT OF DISAGREEMENT ON THE TRACK OF THE
TRIPLE POINT LOW CURRENTLY DEVELOPING NEAR KODIAK ISLAND. THE NAM AND
ECMWF ARE FURTHER WEST THAN THE GFS LOW POSITION. LOOKING AT CURRENT
SATELLITE IMAGERY IT SEEMS LIKE THE GFS HAS INITIALIZED A BIT BETTER
THAN THE OTHERS...SO THE GFS TRACK HAS BEEN CHOSEN AS THE MODEL OF
CHOICE FOR THE SHORT TERM FORECAST. FOR THE EXTENDED GRIDS...A BLEND
OF HPC GUIDANCE AND THE ECMWF WERE USED TO MAKE RELATIVELY MINOR
TWEAKS TO THE INHERITED FORECAST.

.SHORT TERM FORECAST...
SOUTHCENTRAL...A FEW AREAS OF LIGHT SNOW ARE FALLING ACROSS THE
SOUTHERN KENAI THIS MORNING AS THE ALREADY-RAGGED FRONT AFFECTING THE
REGION CONTINUES TO FALL APART. SHOWER ACTIVITY ACROSS THE GULF HAS
EXPANDED INTO A MODERATE SHIELD OF PRECIPITATION IN RESPONSE TO THE
DEVELOPING LOW NEAR KODIAK. THIS AREA OF SNOW IS ABOUT TO MOVE INTO
THE EASTERN KENAI PENINSULA AND PRINCE WILLIAM SOUND REGION.
MEANWHILE...CLOUD-COVER HAS OVERTAKEN MANY OF THE INTERIOR
AREAS...LEADING TO MODERATELY WARMER TEMPERATURES THIS MORNING THAN
HAVE BEEN SEEN FOR SEVERAL DAYS. WINDS ACROSS KODIAK ISLAND SHOULD
BECOME MORE NORTHWESTERLY THIS MORNING...SWITCHING PRECIPITATION BACK
TO SNOW EVEN FOR THE LOWER ELEVATIONS OF THE ISLAND. HIGHER INLAND
ELEVATIONS WILL LIKELY SEE ADVISORY LEVEL ACCUMULATIONS TODAY.

MEANWHILE...AN INVERTED TROUGH WILL DEVELOP IN THE GULF THIS EVENING
AND ROTATE AROUND THE LOW TOWARD PRINCE WILLIAM SOUND THIS EVENING.
AT THE SAME TIME...AN UPPER LEVEL TROUGH SHOULD ROTATE SOUTHWARD
ACROSS THE ALASKA RANGE INTO THE COOK INLET REGION. THE COMBINATION
OF SOME UPPER LEVEL FORCING AND LOW LEVEL MOISTURE FROM THE GULF
SHOULD ALLOW SOME LIGHT SNOW TO FALL FROM THE KENAI PENINSULA UP
THROUGH ANCHORAGE AND THE MAT-SU VALLEY TONIGHT AND PERHAPS LASTING
INTO MONDAY.

SOUTHWEST AND BERING SEA...SNOW TO DIMINISH ACROSS THE DELTA AND
BRISTOL BAY REGIONS TODAY AS LOW IN THE BERING WEAKENS AND MOVES
RAPIDLY SOUTHWARD. NORTHERLY FLOW WILL DEVELOP AND A REINFORCING
SURGE OF BITTERLY COLD ARCTIC AIR WILL STREAM INTO THE SOUTHWEST
MAINLAND FROM THE NORTH FOR THE NEXT SEVERAL DAYS. AT THE SAME...WEAK
HIGH PRESSURE WILL DEVELOP OVER THE WESTERN BERING...SPREADING TO
MUCH OF THE REST OF THE BERING REGION BY TUESDAY.

.LONG TERM FORECAST...ANOTHER COLD WEAK ON TRACK FOR PRETTY MUCH ALL
OF MAINLAND ALASKA. AT THIS POINT IT LOOKS LIKE THE UPPER LEVEL
TROUGH WILL SET UP FAR ENOUGH WEST THAT A REPEAT OF THE STRONG
NORTHERLY WINDS OVER MUCH OF SOUTHCENTRAL THAT HAPPENED THIS PAST
WEEK WILL NOT REPEAT AGAIN WITH THIS EVENT. A LARGE BUT RELATIVELY
WEAK LOW PRESSURE SYSTEM WILL LINGER AROUND THE NORTHERN GULF FOR
MUCH OF THE WEEK...KEEPING THE THREAT OF SNOW SHOWERS AROUND FOR
COASTAL LOCATIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 131
         WINTER WEATHER ADVISORY FOR SNOW 171
MARINE...STORM 130 140 150
         GALE 120 127 128 132 138 155 160 165 170 172 179 185
         HEAVY FREEZING SPRAY 121 126 127 128 129 130 138 140 141 160
                              180
FIRE WEATHER...NONE

DIXON NOV 11