Small Craft Advisory 275, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
456 AM AKDT SUN MAR 27 2016

.ANALYSIS AND UPPER LEVELS...

SURFACE AND UPPER LOW PRESSURE OVER THE NORTH GULF COAST IS
ROTATING MOISTURE NORTH INTO THE EASTERN COPER RIVER BASIN THIS
MORNING. AN UPPER LEVEL TROUGH IS MOVING EAST AND NORTH ACROSS
THE KUSKOKWIM VALLEY THIS MORNING AND WILL CROSS THE SUSITNA
VALLEY TODAY. THIS WILL PROVIDE THE DYNAMIC LIFT THAT WILL RESULT
IN SHOWERS ACROSS THE SUSITNA VALLEY AND COPPER RIVER BASIN TODAY.
WEAK RIDGING IS BUILDING IN ALONG THE GULF OF ALASKA COAST INTO
THE SOUTHERN MAINLAND AS THE LOW IN THE NORTH GULF COAST CONTINUES
TO MOVE OFF TO THE NORTHEAST AND THE UPPER LEVEL TROUGH MOVES
NORTH AND EAST.

OUT WEST WE HAVE A LARGE POTENT LOW SOUTH OF SHEMYA WITH A FRONT
THAT EXTENDS FROM SHEMYA EAST ACROSS THE BERING SEA TO A TRIPLE
POINT LOW FORMING NEAR COLD BAY. STORM FORCE WINDS HAVE BEEN
OBSERVED ALONG THIS FRONT NORTHWEST OF SHEMYA AND GALE TO STORM
FORCE WINDS ARE ALONG THIS FRONT IN THE SOUTHERN BERING SEA. SNOW
HAS BEGUN IN THE PRIBILOF ISLANDS ALONG WITH STRONG WIND. THE SNOW
THUS FAR HAS NOT BEEN SUFFICIENTLY HEAVY TO RESULT IN THE
ANTICIPATED BLIZZARD CONDITIONS.

&&

.MODEL DISCUSSION...

THE MAIN CONCERN IS WHETHER SUFFICIENT MOISTURE AND THUS HEAVY
ENOUGH SNOW WILL PUSH NORTH INTO THE PRIBILOF ISLANDS THIS
MORNING. THE HIGHER RESOLUTION MODELS ARE HOLDING THE PRECIP TO
JUST SOUTH OF SAINT PAUL WHILE THE EC AND GFS SPREAD THE SNOW OVER
SAINT PAUL.

THE MODELS ARE IN GOOD AGREEMENT WITH THE SHOWERS ASSOCIATED WITH
THE UPPER TROUGH PASSING ACROSS THE INTERIOR TODAY. THE NAM AND
CANADIAN MODELS ARE SLIGHTLY SLOWER SPREADING THE RAIN INTO KODIAK
ISLAND THAN THE GFS AND EC THOUGH NOT SIGNIFICANTLY ENOUGH TO
IMPACT THE OVERALL FORECAST. THE MODELS REMAIN IN GOOD AGREEMENT
WITH RESPECT TO THE INTENSITY AND LOCATION OF THE LOW TRACKING SOUTH
OF THE ALEUTIANS AND WITH THE MOVEMENT OF THE ASSOCIATED FRONT AND
DEVELOPMENT OF THE TRIPLE POINT LOW ALONG THE FRONT ALONG THE
ALASKA PENINSULA. THE MODELS ALSO HAVE COME INTO VERY GOOD
AGREEMENT WITH RESPECT TO THE WARM ADVECTION EXPECTED OVER THE
NEXT SEVERAL DAYS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL TROUGH OVER SOUTHWEST ALASKA WILL BRING SOME
SHOWERS MAINLY TO THE SUSITNA VALLEY THIS MORNING BEFORE MOVING
NORTHEAST THIS AFTERNOON. SOME SHOWERS NEAR CORDOVA FROM A
REMNANT LOW OVER THE NORTHEAST GULF WILL ALSO SLIDE EAST TODAY.
THEN THE MAIN EVENT FOR THE NEXT COUPLE OF DAYS WILL BEGIN AS A
WARM MOIST AIR MASS SURGES NORTH INTO SOUTH CENTRAL ALASKA. THIS
IS BEING STEERED BY A LARGE UPPER LOW SOUTH OF THE ALEUTAINS.
THERE IS SIGNIFICANT UPPER LEVEL JET SUPPORT AND A LONG MOISTURE
FETCH FROM THE SUBTROPICS. PRECIPITATION FROM THIS SYSTEM IS
PUSHING INTO KODIAK ISLAND EARLY THIS MORNING AND WILL REACH
KACHEMAK BY BY LATE MORNING...AND SURGE NORTH INTO ALL OF SOUTH
CENTRAL BY LATE TODAY. VERY WARM TEMPERATURES ALOFT WILL ACCOMPANY
THIS MOISTURE AND MOST OF THE PRECIPITATION FOR THE NEXT COUPLE OF
DAYS WILL BE IN THE FORM OF RAIN. SOME HIGHER ELEVATIONS WILL SEE
SOME SNOW INITIALLY...ESPECIALLY IN THE SUSITNA VALLEY NORTH OF
TALKEETNA. BY MONDAY AFTERNOON ALL BUT THE HIGHEST ELEVATIONS WILL
HAVE TRANSITIONED TO RAIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A BIG PATTERN CHANGE UPCOMING FOR THE MAINLAND AS A WARM FRONT
WITH COPIOUS AMOUNTS OF MOISTURE APPROACHES FROM THE SOUTH.
CURRENTLY THIS MORNING A LINGERING UPPER LEVEL TROUGH WILL
CONTINUE LIGHT SNOW OVER THE KUSKOKWIM VALLEY TODAY...WHICH WILL
EXIT BY THIS AFTERNOON AS THE NEXT FRONT OVERSPREADS THE GREATER
BRISTOL BAY AREA. PRECIPITATION COULD START AS SNOW IN THE
AREA...ESPECIALLY INLAND...BUT WILL QUICKLY TURN TO RAIN AS THE
WARM AIR MASS MOVES OVER THE AREA. AREAS WEST AND NORTH OF
KOLIGANEK COULD REMAIN AS SNOW WITH MINOR ACCUMULATIONS. THIS
EVENING INTO THE OVERNIGHT HOURS SNOW WILL SPREAD INTO THE
KUSKOKWIM DELTA AND VALLEY. AS SNOW SPREADS FROM SOUTH TO NORTH
ALONG THE DELTA COAST...STRONGER WINDS WILL LOFT SNOW TO REDUCE
VISIBILITY...POTENTIALLY DOWN TO HALF MILE OR LESS AT TIMES.
PRECIPITATION IN THE VALLEY WILL BE MAINLY SNOW TOWARD ANIAK BUT
WILL CHANGE TO RAIN ELSEWHERE. TEMPERATURES WILL RISE WELL ABOVE
NORMAL FOR THIS TIME OF YEAR...EXCEPT FOR THE DELTA WHICH WILL BE
CLOSE TO CLIMATOLOGY. THE DRY SLOT WITH THE APPROACHING SYSTEM
QUICKLY MOVES OVERHEAD MONDAY DRYING SOME OF THE MAINLAND
OUT...EXCEPT FOR THE DELTA WHICH WILL CONTINUE WITH SNOW SHOWERS
THROUGH MONDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A STORM FORCE FRONTAL BOUNDARY SITS OVER THE SOUTHERN BERING SEA
THIS MORNING BRINGING SNOW AND RAIN TO THE AREA. A TRIPLE POINT
LOW WILL DEVELOP EAST OF THE PRIBILOFS THIS MORNING WHICH WILL
STALL THE NORTHWARD PROGRESSION OF THE FRONT SLIGHTLY...LINGERING
IT OVER SAINT PAUL WHERE FALLING AND BLOWING SNOW WILL SEVERELY
REDUCE VISIBILITY TODAY. THE FRONT WILL BARELY TOUCH SAINT PAUL
THIS EVENING AND TONIGHT BEFORE PRECIPITATION AND WINDS DIMINISH
MONDAY MORNING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

IN THE LONG TERM AN ACTIVE PATTERN PERSISTS WITH A DRAMATIC RIDGE
CONTINUING TO BUILD ACROSS THE EAST GULF OF ALASKA. THE UPPER
LEVEL JET ALONG THE WESTERN PERIPHERY OF THIS RIDGE IS EXPECTED TO
CONTINUE TO FUNNEL MOISTURE FROM THE PACIFIC TOWARDS THE ALASKA
PENINSULA AND SOUTH CENTRAL MAINLAND. MODELS ARE IN GENERALLY
GOOD AGREEMENT FOR THE LONG TERM...WITH CONSISTENCY BETWEEN
ENSEMBLE MEMBERS. TODAY...MODELS ARE TRENDING WITH LESS
PRECIPITATION IN TYPICALLY DOWNSLOPED REGIONS IN SOUTH CENTRAL...AS
A TIGHTER PRESSURE GRADIENT IS ANTICIPATED FROM PRINCE WILLIAM
SOUND TO ANCHORAGE. BUT OVERALL...THE DYNAMIC PATTERN CHANGE
OCCURRING IN THE SHORT TERM WILL CONTINUE INTO THE LONG
TERM...WITH COPIOUS AMOUNTS OF MOISTURE SURGING TOWARDS THE GULF
COAST AND WIDESPREAD ABOVE AVERAGE TEMPERATURES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SAM
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...EN

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1124 AM AKDT SUN MAR 27 2016

AKZ101-111-121-125-131-135-141-145-280730-
ANCHORAGE-MATANUSKA VALLEY-WESTERN KENAI PENINSULA-
WESTERN PRINCE WILLIAM SOUND-NORTHEAST PRINCE WILLIAM SOUND-
SOUTHEAST PRINCE WILLIAM SOUND-COPPER RIVER BASIN-SUSITNA VALLEY-
INCLUDING THE CITIES OF...ANCHORAGE...EAGLE RIVER...INDIAN...
EKLUTNA...PALMER...WASILLA...SUTTON...CHICKALOON...KENAI...
SOLDOTNA...HOMER...COOPER LANDING...WHITTIER...SEWARD...
GIRDWOOD...MOOSE PASS...VALDEZ...THOMPSON PASS...CORDOVA...
GLENNALLEN...EUREKA...MCCARTHY...PAXSON...SLANA...TALKEETNA...
WILLOW...CANTWELL
1124 AM AKDT SUN MAR 27 2016

...UNUSUALLY WARM AND WET CONDITIONS TO IMPACT SOUTHCENTRAL ALASKA
THIS WEEK...

LOCALIZED FLOODING WILL BE A CONCERN FOR MUCH OF SOUTHCENTRAL
ALASKA THIS WEEK AS A VERY WARM AND MOIST SUBTROPICAL AIR MASS
MOVES OVER THE STATE. CURRENTLY THE HEAVIEST RAIN IS EXPECTED
MONDAY INTO TUESDAY...WITH THE GREATEST AMOUNTS OCCURRING ACROSS
PRINCE WILLIAM SOUND. AT THIS TIME...THE POTENTIAL IMPACTS FOR
THE EARLY TO MIDDLE OF THIS WEEK APPEAR TO BE PONDING OF RAIN AND
SNOWMELT ON ROADS...PARTICULARLY IN URBAN AREAS. AN ADDITIONAL
THREAT MAY COME FROM LOCALIZED BREAK-UP OF FROZEN STREAMS AND
RIVERS THROUGH THE WEEK. MODELS CURRENTLY INDICATE THAT
DOWNSLOPING SHOULD PARTLY LIMIT RAINFALL AMOUNTS ACROSS ANCHORAGE,
THE MATANUSKA VALLEY AND WESTERN KENAI PENINSULA...BUT MODERATE TO
HEAVY RAIN IS STILL POSSIBLE AT TIMES THROUGH WEDNESDAY.

TEMPERATURES FOR MUCH OF THE SOUTHERN MAINLAND WILL RISE WELL
ABOVE FREEZING DURING THE DAY ON SUNDAY...THEN PERSIST OR CONTINUE
TO WARM THROUGH THE REMAINDER OF THE WEEK. AFTER SUNDAY
NIGHT...TEMPERATURES MAY REMAIN UNUSUALLY WARM (IN THE 40S) EVEN
AT NIGHT ACROSS ANCHORAGE AND SURROUNDING AREAS THROUGH THE
REMAINDER OF NEXT WEEK. FREEZING LEVELS MAY REACH AS HIGH AS 5000
FEET ACROSS SOUTHCENTRAL...WHICH COULD RESULT RAPID MELTING AND
INCREASED RUNOFF IN LOCAL STREAMS IN ADDITION TO THE MODERATE TO
HEAVY RAINFALL EXPECTED. WITH THIS INCREASED RUNOFF AND
TEMPERATURES...THERE IS AN INCREASED RISK FOR AVALANCHES OR
ROCKSLIDES IN AREAS OF STEEP TERRAIN.

PLEASE STAY ABREAST OF THE LATEST WEATHER FORECASTS BY VISITING
WEATHER.GOV/ANCHORAGE AND THE LATEST RIVER AND STREAM FORECASTS
BY VISITING WEATHER.GOV/APRFC. YOU CAN ALSO GET ADDITIONAL
INFORMATION BY FOLLOWING ALONG ON FACEBOOK OR ON TWITTER BY
FOLLOWING @NWSANCHORAGE.