Small Craft Advisory 998, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
355 AM AKST FRI DEC 13 2013

.ANALYSIS AND UPPER LEVELS...

A BROAD UPPER TROUGH EXISTS OVER SOUTHCENTRAL THIS MORNING...WITH A
WELL DEFINED POLAR VORTEX OVER SOUTHWEST ALASKA CENTERED OVER THE
ALEUTIAN RANGE. A VERY WELL DEFINED WARM CONVEYOR BELT/UPPER JET
MAXIMA IS EVIDENT ON WATER VAPOR SATELLITE IMAGERY...ASCENDING FROM
THE NORTHERN GULF INTO THE COPPER RIVER BASIN. A TRAILING SHORTWAVE
TROUGH IS CURRENTLY NEAR 53N 145W...AND RAPIDLY PROPAGATING TOWARDS
THE ALASKA PANHANDLE. IN THE LOW LEVELS...A STRONG 975 MB SURFACE
LOW...AS INDICATED BY SURFACE OBSERVATIONS...HAS MADE LANDFALL OVER
THE WESTERN PRINCE WILLIAM SOUND COAST. AN ASSOCIATED WARM FRONT
NOSED INTO PRINCE WILLIAM SOUND NEAR MIDNIGHT...WITH A TRAILING COLD
FRONT CURRENTLY WRAPPING AROUND THE SYSTEM. A SECOND SURFACE LOW/WARM
FRONT ASSOCIATED WITH THE TRAILING SHORTWAVE WILL TRACK INLAND NEAR
YAKUTAT THIS AFTERNOON...WITH A SECOND LOW FORMING IN PRINCE WILLIAM
SOUND AS THE UPPER VORTEX SHIFTS SOUTHEAST.

SNOW HAS OVERSPREAD ALMOST ALL OF SOUTHCENTRAL OVERNIGHT AND THIS
MORNING. WITH THE FIRST WARM FRONT OCCLUDING AND WEAKENING ALONG THE
COAST...SNOW RATES WILL GENERALLY TAPER TO LIGHT AND PERIODIC
SNOW/SNOW SHOWERS REGION WIDE THIS MORNING THROUGH EARLY AFTERNOON. A
SECOND ROUND OF SNOW WILL COMMENCE LATER THIS AFTERNOON INTO THE
EVENING ACROSS MUCH OF SOUTHCENTRAL...BECOMING MODERATE TO HEAVY AT
TIMES WITH THE POSSIBILITY FOR RAPID SNOW ACCUMULATIONS FOR SELECT
LOCATIONS.

.MODEL DISCUSSION...

MODELS ARE IN EXCELLENT AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK.
WHILE SMALL DIFFERENCES EXIST WITH FINE SCALE DETAILS...THE OVERALL
DYNAMICS AND THERMODYNAMICS PAINT A SIMILAR PICTURE...WITH DETAILS
FROM ALL THE GUIDANCE BEING USED FOR THIS FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL...
MOST AREAS ACROSS THE REGION WILL TAPER TO PERIODIC SNOW SHOWERS THIS
MORNING...WITH GENERALLY LIGHT SNOW ACCUMULATIONS. A SECOND ROUND OF
SIGNIFICANT ACCUMULATING SNOW WILL DEVELOP ACROSS MOST OF
SOUTHCENTRAL BY THIS AFTERNOON AND EVENING. SNOW MAY BECOME HEAVY AT
TIMES DURING THE EVENING AND EARLY OVERNIGHT...INCLUDING THE
ANCHORAGE BOWL AS COLDER AIR ALOFT WILL SUPPORT DENDRITIC CRYSTAL
GROWTH. SNOW WILL BEGIN TO TAPER BY MORNING TO SNOW SHOWERS...THEN
END ACROSS MOST LOCATIONS BY SUNDAY EVENING. SKIES WILL CLEAR MONDAY
AND TUESDAY AS HIGH PRESSURE BUILDS IN...LEAVING BEHIND COLDER
TEMPERATURES AND REGIONS OF PATCHY FOG.

SOUTHWEST...
MOST OF SOUTHWEST WILL REMAIN UNDER THE INFLUENCE OF COLD OFFSHORE
FLOW...WITH CONTINUED BREEZY NORTH TO NORTHWEST WINDS. SNOW AND SNOW
SHOWERS WILL CONTINUE ALONG AND NEAR THE ALASKA/ALEUTIAN
RANGES...WITH SCATTERED SNOW SHOWERS SPREADING INTO THE FOOTHILLS.
OTHERWISE...THE REGION WILL COME UNDER THE INFLUENCE OF HIGH PRESSURE

MONDAY AND TUESDAY...WITH COLD NORTH TO NORTHWEST WINDS SLOWLY
DIMINISHING.

BERING SEA AND ALEUTIANS...
GUSTY NORTHERLY FLOW AND SNOW SHOWERS WILL CONTINUE TO BE THE THEME
THROUGH THE WEEKEND...WITH BLOWING SNOW ACROSS THE EASTERN ALEUTIANS
AND ALASKA PENINSULA. HIGH PRESSURE WILL BUILD IN FROM THE WEST EARLY
NEXT WEEK...WITH WINDS AND SNOW SHOWERS SLOWLY DIMINISHING BY MONDAY.

.LONG TERM FORECAST...

EARLY NEXT WEEK...HIGH PRESSURE WILL BE DOMINATING THE MAINLAND AND
BERING SEA...WITH UNUSUALLY QUIESCENT CONDITIONS REGION WIDE. THE
MAINLAND WILL REMAIN UNDER THE INFLUENCE OF HIGH PRESSURE...SO
TEMPERATURES WILL REMAIN ON THE COLD SIDE OF CLIMATOLOGY. A STRONG
WARM FRONT WILL PUSH INTO THE BERING LATE TUESDAY THROUGH
WEDNESDAY...THEN WILL PUSH INTO SOUTHCENTRAL LATE WEDNESDAY INTO
THURSDAY. WHILE THE UPPER AIR PATTERN WILL BE AMPLIFIED...THE LATEST
ECMWF AND GFS SUGGEST MUCH OF SOUTHERN ALASKA WILL REMAIN ON THE COLD
SIDE OF THE FRONT AS PRECIPITATION MOVES INLAND...POSSIBLY KEEPING
ALL LOCATIONS AS SNOW WITH A RAIN/SNOW MIX ALONG THE COAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY 101 121.
MARINE...GALE 131 132 138 150 155 160 165 180 181 185.
         STORM 130.
         HEAVY FREEZING SPRAY 121 129 130 131 132 136 137 138 139 150
         160 180 181 185.
FIRE WEATHER...NONE.

AHSENMACHER DEC 13