Small Craft Advisory 172, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
414 PM AKST MON FEB 23 2015

.ANALYSIS AND UPPER LEVELS...

A LARGE UPPER LOW CONTINUES TO SPIN OVER FAR EASTERN RUSSIA AND
THE NORTHERN BERING SEA...WITH THE STRONG RIDGE OVER WESTERN NORTH
AMERICA NOW LOSING AMPLITUDE. BOTH OF THESE FEATURES ARE COMBINING
TO CREATE GENERAL SOUTHWESTERLY FLOW ACROSS A GOOD PORTION OF THE
MAINLAND AND GULF REGIONS...WITH A MORE ZONAL FLOW OVER THE FAR
WESTERN BERING. COLD AIR HAS FULLY ENTRAINED AROUND THE ANCHORING
UPPER LOW OUT WEST...AND AS A RESULT COLD AIR ADVECTION IS
OCCURRING IN THE SOUTHWESTERLY FLOW ACROSS ALL OF THE SOUTHERN
MAINLAND. A SHORTWAVE TROUGH IS ALSO MOVING THROUGH THIS
FLOW...AND IS SUSTAINING THE ONGOING SHOWER ACTIVITY AROUND COOK
INLET AND PRINCE WILLIAM SOUND. WITH SURFACE WINDS CONTINUING OUT
OF THE SOUTH...THERE IS AN UPSLOPE/OROGRAPHIC ENHANCEMENT TO
THESE SHOWERS OVER THE WESTERN CHUGACH...TALKEETNA...AND KENAI
MOUNTAINS. HOWEVER...THE STRENGTH OF THE AFOREMENTIONED SHORTWAVE
TROUGH IS PRETTY WEAK OVERALL...AND THIS IS THE LIMITING FACTOR AS
TO WHY MORE PRECIP IS NOT BUILDING BACK ACROSS ANCHORAGE PROPER
DESPITE THE OTHER FAVORABLE FACTORS MENTIONED ABOVE.

IN THE BERING SEA...WIDESPREAD CONVECTIVE SNOW SHOWERS ARE
OCCURRING AS COLD AIR MOVES OVER THE WARMER OCEAN WATERS. A WEAK
FRONT/TROUGH MOVING THROUGH THE CENTRAL BERING IS ENHANCING SNOW
SHOWER ACTIVITY AND GUSTY WINDS IN THE VICINITY OF THE PRIBILOF
ISLANDS.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN EXCELLENT SYNOPTIC AGREEMENT THROUGH THE FIRST
FEW DAYS OF THE FORECAST. THE ECMWF IS A LITTLE FASTER THAN ALL
OTHER MODELS WEAKENING THE LOW THAT WILL MOVE INTO THE SOUTHERN
GULF TOMORROW (MONDAY). THE MAIN IMPACT OF THIS DIFFERENCE WOULD
BE THE ECMWF ENDING RAIN ACROSS KODIAK ISLAND ABOUT 6 HOURS FASTER
THAN THE OTHER MODELS. HOWEVER...OVERALL FORECAST CONFIDENCE IS
ABOVE AVERAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

A WEAK TROUGH ACROSS THE KENAI AND ALONG THE NORTHERN GULF WILL BE
THE FOCUS FOR RAIN AND SNOW SHOWERS THIS EVENING. THE BEST CHANCE
TO SEE SNOW ACCUMULATION WILL BE ALONG THE MOUNTAIN RANGES AND
NORTHERN GULF COAST. THE TROUGH DIMINISHES OVERNIGHT BRINGING AN
END TO PRECIPITATION FOR THE SOUTHERN MAINLAND AND BRIEFLY FOR
THE GULF. THE TROUGH WILL BE REPLACED BY SURFACE RIDGING MOVING UP
FROM THE NORTHEAST GULF. PATCHY FOG IS LIKELY TO DEVELOP OVERNIGHT
ACROSS VALLEYS AND AREA WATERS AS TEMPERATURES DROP CLOSER TO DEW
POINT VALUES. THE NEXT FRONT MOVES UP FROM THE NORTH PACIFIC INTO
THE SOUTHWESTERN GULF LATE TUESDAY. GUSTY WINDS AND RAIN ARE
EXPECTED AROUND THE CORE OF THE LOW CENTER AS IT TRAVELS ACROSS
THE GULF...RIDING CLOSE TO THE JET STREAM AT 50N WHICH BECOMES
NEARLY ZONAL HEADING INTO MID WEEK. AS THIS STORM SYSTEM MOVES
INTO THE CENTRAL GULF THE PRESSURE GRADIENT TIGHTENS ALONG THE
COAST WITH OFFSHORE FLOW INCREASING IN RESPONSE. SHOWERS SPREAD
NORTH INTO PRINCE WILLIAM SOUND AND NORTHEAST GULF COAST BY LATE
TUESDAY NIGHT AND CONTINUE THROUGH WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL WAVE AND ASSOCIATED WEAK FRONT WILL BRING LIGHT
SNOW SHOWERS TO THE KUSKOKWIM DELTA REGION TONIGHT INTO TUESDAY AS
THEY PUSH INLAND AND QUICKLY MOVE OFF TO THE NORTHEAST. OTHERWISE...
THE SOUTHWEST MAINLAND WILL REMAIN MOSTLY DRY THROUGH THE MIDDLE
OF THE WEEK AS HIGH PRESSURE BUILDS IN AT THE SURFACE AND MORE
ZONAL FLOW USHERS IN A MODEST COOLING TREND. PATCHY FOG WILL BE
POSSIBLE NEAR BRISTOL BAY TONIGHT WITH LIGHT WINDS AND LINGERING
LOW LEVEL MOISTURE...BUT THOSE CONCERNS SHOULD BE ALLEVIATED BY
TUESDAY AS DRY NORTHERLY FLOW DEVELOPS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
SHOWER ACTIVITY WILL DIMINISH OVER THE EASTERN BERING TONIGHT AS
THE UPPER WAVE PUSHES INLAND ALONG THE KUSKOKWIM DELTA...YIELDING
A PERIOD OF DRY WEATHER THROUGH MIDDLE OF THE WEEK AS HIGH
PRESSURE BUILDS OVER THE AREA AND A NORTH PACIFIC LOW PASSES WELL
SOUTH OF THE ALASKA PENINSULA. ATTENTION THEN TURNS TO THE WESTERN
BERING AS A GALE FORCE FRONT MOVES OVER THE WESTERN ALEUTIANS ON
TUESDAY AND PUSHES SLOWLY EASTWARD THROUGH WEDNESDAY...BRINGING A
MIX OF RAIN AND SNOW TO THE WESTERN PART OF THE CHAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AS THE LOW SKIRTING THE SOUTHERN GULF BEGINS TO DISSIPATE AND
RIDGING BUILDS OVER THE MAINLAND ON WEDNESDAY EVENING...OUTFLOW
WINDS WILL QUICKLY DEVELOP ALONG THE GULF COAST...AND PERSIST INTO
THURSDAY. THIS SHOULD BE BOTH A WEAK AND SHORT LIVED EVENT WITH
WEAK COLD AIR ADVECTION AND PRESSURE GRADIENTS THAT WILL BEGIN TO
DIMINISH BY THURSDAY EVENING.

LATE THIS WEEK...THERE IS VERY GOOD AGREEMENT IN THE MODELS THAT
PERSISTENT RIDGING WILL DEVELOP OVER THE NORTHEAST PACIFIC...WHICH
IS A FAMILIAR PATTERN FROM THROUGHOUT THIS WINTER. THIS WILL BRING
A SERIES OF NORTH PACIFIC LOWS MOVING TOWARD THE AKPENN. THE FIRST
WILL BRING RAIN AND SNOW FROM THE SOUTHWEST MAINLAND INTO THE GULF
COAST FRIDAY THROUGH SATURDAY. THIS SYSTEM WILL ALSO BRING THE
BEST CHANCE OF RAIN OR SNOW TO SOUTHCENTRAL OVER THE NEXT 7 DAYS.
WITH A STRONG UPPER LEVEL JET RIDING OVER A BUILDING RIDGE THIS
SYSTEM WILL QUICKLY DEPART THE AREA BY SUNDAY...BRINGING A RETURN
TO CLEARING SKIES AND OUTFLOW WINDS TO THE MAINLAND. THIS PATTERN
LOOKS TO CONTINUE THROUGH EARLY NEXT WEEK...KEEPING TEMPERATURES
ABOVE NORMAL FOR MOST OF THE SOUTHERN MAINLAND WITH SHORT LIVED
PERIODS OF PRECIPITATION (MAINLY IN THE FORM OF RAIN).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 132 150 155 177 178 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...DEK