Small Craft Advisory 1032, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
522 AM AKST WED DEC 24 2014

.ANALYSIS AND UPPER LEVELS...THE PATTERN IS CERTAINLY GETTING MORE
COMPLEX AND A BIT MORE WINTER-LIKE ACROSS THE REGION. OUR
HURRICANE FORCE LOW NORTH OF THE WESTERN ALEUTIANS REACHED ITS
PEAK INTENSITY SOMETIME EARLY TUE AND WILL NOW SLOWLY WEAKEN.
HOWEVER...IT WILL STILL CONTINUE TO HAVE A MAJOR IMPACT ON THE
SYNOPTIC PATTERN THROUGHOUT THE AREA FOR THE REMAINDER OF THE
WEEK. IT WILL SERVE AS THE PARENT LOW OVER THE WESTERN BERING
FERRYING VARIOUS WARM FRONTS FROM THE CENTRAL ALEUTIANS TO THE
MAINLAND. MANY OF THESE WILL TRY TO CREATE TRIPLE POINT SURFACE
LOWS...BUT THESE WILL ONLY BE SUSTAINED FOR A BRIEF PERIOD OF
TIME BEFORE BEING REPLACED BY YET ANOTHER LOW. A POTENT SHORTWAVE
RIDGE IS CURRENTLY SET UP FROM THE KENAI PENINSULA TO THE ALCAN
BORDER. THIS ONCE AGAIN HAS MANY AREAS TRAPPED IN FOG AND STRATUS
THIS MORNING. AS A WEAKENING WARM OCCLUSION SLIDES UP THE COOK
INLET FROM KODIAK ISLAND...THIS SHOULD CREATE ENOUGH MIXING TO
HELP THE FOG TO DISSIPATE MORE SO THAN IT DID ON TUE. THE
EXCEPTION TO THIS COULD BE THE COPPER RIVER BASIN AS THE FRONT
WILL NOT MAKE IT VERY FAR INLAND.

REGARDING THE JET STREAM ALOFT...THE CORE OF THE JET CONTINUES TO
FLOW SOUTH OF THE AREA. THIS MEANS THERE IS NOT GREAT UPPER LEVEL
SUPPORT FOR ANY ONE FEATURE OVER OUR AREA. HOWEVER...BY CHRISTMAS
DAY WE START TO SEE THE NORTH AMERICAN RIDGE BUILDING OFF THE
COAST OF CALIFORNIA. THIS SHOULD HELP TO BRING THE JET NORTH FROM
THE GULF OF AK TOWARDS THE SOUTH CENTRAL COAST. THIS COULD PROVIDE
SOME ADDITIONAL LIFT AND ENHANCE PRECIPITATION CHANCES OVER SOUTH
CENTRAL INTO FRIDAY. INTO THE WEEKEND...THIS AMPLIFICATION OF FLOW
REALLY GETS GOING WITH THE JET ALMOST TURNING DUE SOUTH TO NORTH
BUILDING A SHARP RIDGE OVER THE EASTERN HALF OF THE MAINLAND. THIS
SCENARIO COULD BRING UP PLENTY OF MOISTURE FROM THE NORTH PACIFIC
BUT WILL ALSO BRING WARM TEMPERATURES.

&&

.MODEL DISCUSSION...MODELS CONTINUE TO BE ON MOSTLY THE SAME PAGE
AND HANDLING THE OVERALL PATTERN WELL. THE GENERAL IDEA OF THE
DOMINANT LOW REMAINING NORTH OF THE WESTERN ALEUTIANS AND SEVERAL
FRONTS SPINNING UP THROUGH THE CENTRAL ALEUTIANS IS CONSISTENT
AMONGST THE MEMBERS. THERE ARE SOME SUBTLE DIFFERENCES IN TIMING
AND PLACEMENT WITH EACH FRONT/LOW. OVERALL THIS FORECAST PACKAGE
LEANED ON THE EC AS IT HAS LED THE WAY WITH THIS PATTERN SO FAR.

BUT THE MODELS ARE NOT GRASPING SOME OF THE SMALL BUT IMPORTANT
DETAILS WELL. NONE OF THE MODELS REALLY RESOLVE THE LOW STRATUS
AND FOG EVENT THAT CONTINUES TO PLAGUE MUCH OF SOUTH CENTRAL.
THUS...WE HAVE RELIED ON PERSISTENCE AND FORECASTER DISCRETION.
UNLIKE TUE...IT DOES APPEAR THAT THE FRONT APPROACHING THE AREA
WILL BE STRONG ENOUGH TO MIX THINGS OUT BY THIS AFTERNOON. THE NAM
WAS PREFERRED IN HANDLING THIS FRONT BECAUSE OF ITS HIGHER
RESOLUTION. THE NEXT SLIGHT BUT SIGNIFICANT DIFFERENCE COMES FROM
THE TIMING OF PRECIPITATION ACROSS SOUTH CENTRAL ON CHRISTMAS DAY.
IF THE EC HAS ITS WAY...SNOW WOULD START AROUND THE ANCHORAGE BOWL
THURSDAY MORNING WHILE THE GFS WOULD NOT BRING IT IN UNTIL CLOSER
TO SUNSET. AN EC/NAM BLEND WAS USED TO HANDLE THIS AND LIKELY POPS
REMAIN IN THE FORECAST THROUGH THE DAY THURSDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
DENSE FOG IS RAPIDLY DISSIPATING AROUND SOUTHCENTRAL ALASKA THIS
MORNING AS A SHORT WAVE MOVES INTO THE AREA FROM THE SOUTHWEST
AND INCREASES CLOUD COVER AT MID AND UPPER LEVELS. PRECIPITATION WITH
THIS DISTURBANCE WILL BE MOSTLY ALONG THE GULF COAST AND KODIAK
ISLAND AHEAD OF THIS WAVE AS LEEWARD INLAND AREAS WILL DOWNSLOPE
OUT TODAY. THE UPPER LEVEL FLOW WILL BECOME SOUTHWEST LATE THIS
AFTERNOON AND THIS EVENING WHICH WILL BRING IN A PERIOD OF SNOW
SHOWERS BEFORE DRIER AIR MOVES INTO THE AREA AHEAD OF A SECOND AND
STRONGER DISTURBANCE WHICH WILL MOVE OVER THE AREA THURSDAY. THIS
SECOND DISTURBANCE IS EXCEPTED TO BRING IN MORE WIDESPREAD
SNOWFALL OVER SOUTHCENTRAL ALASKA FOR CHRISTMAS DAY WITH
ACCUMULATIONS GENERALLY IN THE 1 TO 3 INCH RANGE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
AS THE FRONT PUSHES THROUGH THE FLOW OVER THE AREA WILL DIMINISH
AND BECOME MORE SOUTHERLY. HOWEVER...WINDS WILL REMAIN STRONG
ENOUGH AROUND THE KUSKOKWIM DELTA FOR AREAS OF BLOWING SNOW TO
CONTINUE THIS MORNING. OVERALL SNOWFALL WILL LIGHTEN BUT CONTINUE
THROUGH CHRISTMAS UNDER THE SOUTHERLY FLOW. THEN WEAK HIGH
PRESSURE WILL MOVE IN FRIDAY DIMINISHING THE SNOW EVEN MORE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
AS THE LOW OVER THE WESTERN BERING BROADENS OUT ACROSS THE REST OF
THE BERING STRONG WINDS WILL CONTINUE FOR THE ALEUTIANS. THE
PRECIPITATION SHOULD REMAIN MOSTLY RAIN BUT WITH THE COLDER AIR
BEING ADVECTED IN SNOW WILL BECOME MORE PRESENT. ON THURSDAY
ANOTHER SYSTEM WILL APPROACH THE WESTERN ALEUTIANS FROM THE NORTH
PACIFIC AND BRING WARMER SOUTHERLY FLOW TO THE AREA. THE FRONT
WILL PUSH EAST MAKING IT TO THE EASTERN ALEUTIANS FRIDAY WHERE IT
WILL DISSIPATE.

&&

.LONG TERM FORECAST (FRI DEC 26 - WED DEC 31)...

LARGE SCALE AMPLIFICATION OF THE PATTERN WILL COMMENCE IN EARNEST
FRIDAY AND SATURDAY AS A DEEP WESTERN ALEUTIAN LOW BEGINS TO
INTERACT WITH A STOUT NORTHEAST PACIFIC RIDGE. A HIGH AMPLITUDE
RIDGE WILL RAPIDLY BUILD INTO MAINLAND ALASKA LATE SATURDAY INTO
SUNDAY. A WELL DEFINED ATMOSPHERIC MOISTURE RIVER WILL FORM OVER
THE ALASKA PENINSULA LATE SATURDAY BEFORE MOVING INTO THE NORTHERN
GULF OF ALASKA AND KODIAK SUNDAY THROUGH TUESDAY. SIGNIFICANT
SUBTROPICAL MOISTURE AND WARM AIR WILL PUMP NORTHWARD TOWARD THE
GULF COAST...WITH A CHINOOK MOVING THROUGH MOST OF SOUTHERN ALASKA
MONDAY AND TUESDAY. HEAVY RAIN WILL IMPACT COASTAL LOCATIONS
THROUGH TUESDAY...WITH THE POTENTIAL FOR PURE RAIN ACROSS INLAND
LOCATIONS BEHIND THE CHINOOK THROUGH TUESDAY. SLIGHTLY COOLER
TEMPERATURES MOVE IN WEDNESDAY...WITH SHOWERY RAIN AND SNOW
CONDITIONS REMAINING ACROSS SOUTHERN ALASKA AS THE ATMOSPHERIC
RIVER AND WARM AIR MOVE EASTWARD AND THE UPPER RIDGE FLATTEN OUT
OVER SOUTHERN ALASKA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY 101.
         BLOWING SNOW ADVISORY 155.
MARINE...GALE 150 155 160 165 170 172-175 177-180 185.
         STORM 176.
         HEAVY FREEZING SPRAY 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...AHSENMACHER