Small Craft Advisory 312, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
452 PM AKDT THU APR 9 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL CLOSED LOW IS NOW CENTERED NEAR THE BARREN ISLANDS
REGION WITH A 974 MB SURFACE LOW DIRECTLY UNDERNEATH...INDICATING
A CONTINUED STACKED LOW PRESSURE SYSTEM THROUGH ALL LEVELS OF THE
TROPOSPHERE. DESPITE THIS STACKED LOW MOVING EAST...THE UPPER
LEVEL JET TO THE SOUTH OVER THE ALEUTIANS IS REMAINING STATIONARY
WHICH IS ALLOWING FOR RESIDUAL UPPER LEVEL LOW PRESSURE TO DEVELOP
TO THE JET STREAK'S NORTH OVER THE NORTHERN BERING SEA IN AN AREA
OF STRONG SHEAR VORTICITY. RADAR IMAGERY IS DEPICTING A DEFORMATION
BAND WITH LOCALLY HEAVY SNOW THAT HAS BEEN IMPACTING INLAND PARTS
OF BRISTOL BAY.

AHEAD OF THE LOW OVER THE BARREN ISLANDS REGION...AN OCCLUDED
GALE-FORCE FRONT IS SITUATED FROM CENTRAL COOK INLET ACROSS THE
KENAI PENINSULA INTO THE NORTHERN GULF NEAR MIDDLETON ISLAND.

THE AFOREMENTIONED FRONT MOVES NORTH INTO SOUTHCENTRAL BUT
GENERALLY FALLS APART ALONG THE COASTAL MOUNTAINS TONIGHT. THE
UPPER LEVEL ENERGY WILL MAKE IT A BIT FURTHER INLAND BUT LOSE
STEAM AS THE CYCLONIC FLOW WILL CAUSE THIS ENERGY TO ROTATE BACK
TOWARDS THE SOUTH AND WEST AROUND THE STACKED LOW. THIS STACKED
LOW WILL CONTINUE TO MOVE SLOWLY EAST ACROSS THE NORTHERN GULF
BEFORE BEGINNING TO DISSIPATE SATURDAY NEAR PRINCE WILLIAM SOUND.
BROAD AND WEAK CYCLONIC FLOW WILL CONTINUE OVER THE REGION WITH
EMBEDDED UPPER LEVEL AND SURFACE LOWS ROTATING AROUND ONE ANOTHER.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD AGREEMENT THIS MORNING WITH THE GALE-FORCE
LOW AND ASSOCIATED OCCLUDED FRONT AS IT MOVES INLAND INTO
SOUTHCENTRAL ALASKA. THE NAM WAS THE PREFERRED MODEL OF CHOICE
FOR THE SHORT TERM FORECAST PERIOD.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL LOW OVER THE SOUTHWEST COAST OF ALASKA WILL
PROGRESS EASTWARD...PUSHING ACROSS KODIAK ISLAND TONIGHT AND INTO
THE CENTRAL GULF BY FRIDAY AFTERNOON. A FRONT ASSOCIATED WITH THIS
LOW HAS STARTED TO PUSH INTO GULF COAST KEEPING WET AND GUSTY
CONDITIONS ALONG THE AREAS SURROUNDING THE GULF COAST. AS THE
FRONT PUSHES FURTHER INLAND TONIGHT...GUSTY WINDS OVER THESE AREAS
WILL BEGIN TO DIMINISH AND PRECIPITATION WILL BECOME MORE SHOWERY.
AS THE LOW TRACKS FURTHER EASTWARD OVERNIGHT CROSS BARRIER FLOW
WILL DIMINISH AND THE FLOW WILL BEGIN TO BACK TO THE EAST AND
NORTHEAST OVER THE ANCHORAGE AREA. THIS CREATES THE POTENTIAL
FOR SOME OF THE PRECIPITATION LINGERING AROUND HIGHER ELEVATIONS
AND EASTERN ANCHORAGE TODAY TO START PUSHING SOME LIGHT SNOW
SHOWERS INTO THE ANCHORAGE BOWL TONIGHT. SOUTH CENTRAL ALASKA
REMAIN IN WEAK CYCLONIC FLOW WITH JUST ENOUGH MOISTURE AROUND TO
KEEP SOME SCATTERED SHOWERY CONDITIONS OVER MOST AREAS INTO THE
WEEKEND. THE SHOWER ACTIVITY...LIMITED AS IT WILL BE...MAY BE
THERMALLY DRIVEN (DIURNAL) AS WELL.
&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH SATURDAY)...
SNOWFALL FROM BRISTOL BAY INTO THE KUSKOKWIM DELTA WILL CONTINUE
TO FALL THROUGH THIS EVENING THE REMNANTS OF THE UPPER LEVEL
TROUGH CONTINUE TO SLOWLY DISSIPATE OVER THE AREA. ACCUMULATIONS
WILL NOT BE NEARLY AS HEAVY AS THAT EXPERIENCED IN INTERIOR
BRISTOL BAY EARLIER TODAY...AND WITH JUST A FEW INCHES OF
ADDITIONAL SNOWFALL EXPECTED THE ADVISORY WAS CANCELLED WITH THE
AFTERNOON PACKAGE. FURTHER NORTH IN THE KUSKOKWIM DELTA SNOWFALL
WILL BE MUCH LIGHTER WITH MOST OF THE ACCUMULATION EXPECTED ALONG
THE COAST. LOW STRATUS AND PATCHY FOG WILL THEN LIKELY DEVELOP
OVERNIGHT TONIGHT OVER INTERIOR BRISTOL BAY AND THE KUSKOKWIM
DELTA AFTER THE SNOWFALL DIMINISHES WITH LIGHT WINDS IN THE AREA.

AS THE SURFACE NOW MOVES INTO THE WESTERN GULF AND A TIGHT
PRESSURE GRADIENT IS CREATED LATE TONIGHT...GUSTY NORTHWESTERLY
WINDS ALONG THE WESTERN CAPES AND THROUGHOUT THE AKPENN THAT WILL
PERSIST THROUGH TOMORROW MORNING. SIGNIFICANT AREAS OF BLOWING
SNOW HOWEVER ARE NOT EXPECTED AT THIS TIME DUE TO THE WARM AND WET
NATURE OF THE NEW SNOWFALL AND LACK OF COLD AIR ADVECTION. A FEW
ISOLATED AREAS OF BLOWING SNOW MAY BE SEEN...ESPECIALLY ALONG THE
WESTERN CAPES...HOWEVER THESE SHOULD BE SHORT LIVED.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH
SATURDAY)...
THE NORTHWESTERLY FLOW AND SNOW SHOWERS WILL SLOWLY DIMINISH OVER
THE NEXT 2 DAYS AS THE GRADIENT SLOWLY WEAKENS. OTHERWISE THE
WEATHER SHOULD REMAIN FAIRLY QUIET FOR THIS TIME OF YEAR THIS WEEKEND
WITH SYNOPTIC SCALE SYSTEMS EXPECTED.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MID TERM WILL BEGIN WITH A BROAD UPPER LEVEL TROUGH
ENCOMPASSING MAINLAND ALASKA AS THE ZONAL JET CURRENTLY SITUATED
ALONG 50N BEGINS TO BUCKLE THIS WEEKEND. THIS WILL BRING SHOWERY
WEATHER TO MUCH OF THE REGION THROUGH SUNDAY...WITH A MIX OF RAIN
AND SNOW CONTINUING ALONG THE GULF COAST IN THE VICINITY OF A
SURFACE LOW OVER THE NORTHERN GULF AND MORE SPORADIC SHOWERY
CONDITIONS INLAND. SNOW SHOWERS WILL ALSO PERSIST ACROSS THE
BERING IN NORTHWEST FLOW ON THE BACK SIDE OF THE TROUGH.

SOUTHCENTRAL ALASKA WILL THEN UNDERGO A GRADUAL DRYING TREND
EARLY NEXT WEEK AS THE GULF LOW SLOWLY WEAKENS...WITH SHOWERS ALSO
DIMINISHING OVER MUCH OF THE BERING BUT CONTINUING ALONG THE
ALEUTIAN CHAIN AS A NORTH PACIFIC LOW PASSES JUST TO THE SOUTH.
WIDESPREAD PRECIPITATION LOOKS TO RETURN TO THE SOUTHERN MAINLAND
DURING THE MIDDLE OF NEXT WEEK AS THIS LOW TRACKS TOWARDS THE GULF
AND AN UPPER RIDGE BUILDS OVER THE WEST COAST OF NORTH AMERICA. IT
APPEARS THAT THE BULK OF THIS PRECIPITATION WOULD EVENTUALLY
TRANSITION TO RAIN AS WARMER AIR RETURNS TO SOUTHCENTRAL AK IN
SOUTHERLY FLOW ON THE WESTERN PERIPHERY OF THE RIDGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 132 150-178 180.
         HEAVY FREEZING SPRAY 180.
FIRE WEATHER...NONE.

&&