Small Craft Advisory 1004, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
543 AM AKST THU DEC 17 2015

.ANALYSIS AND UPPER LEVELS...

A CUT-OFF UPPER LEVEL LOW HAS MOVED INTO THE GULF OF AK THIS
MORNING...WITH STRONG RIDGES OVER THE WEST COAST OF NORTH AMERICA
AND THE BERING SEA...AND ANOTHER UPPER LOW OVER KAMCHATKA. AT THE
SURFACE...A LOW IS SOUTH OF KODIAK ISLAND WITH AN ASSOCIATED
STORM FORCE FRONT DRAPED ALONG THE ENTIRE GULF COAST...AND A
SECOND LOW IS GAINING STRENGTH JUST OFF OF THE KAMCHATKA PENINSULA
IN THE EXTREME WESTERN BERING. ITS ASSOCIATED STORM FORCE FRONT IS
OVER THE WESTERN BERING AND ALEUTIANS. A RIDGE IS CENTERED OVER
THE BERING. COLD NORTHWEST FLOW STREAMING BETWEEN THE BERING RIDGE
AND THE LOW SOUTH OF KODIAK IS SPREADING SNOW SHOWER ACTIVITY
ACROSS THE EASTERN BERING AND ALEUTIANS.

&&

.MODEL DISCUSSION...

MODELS REMAIN IN EXCELLENT AGREEMENT. THE LOW AND FRONT IN THE
GULF WILL MOVE SOUTHEAST AND AWAY FROM LAND THROUGH FRI. THE
BERING RIDGE WILL MIGRATE ACROSS THE AKPEN TODAY AND THEN THE
GULF FRI AND FRI NIGHT. THE KAMCHATKA LOW AND WESTERN BERING FRONT
THEN FOLLOW SUIT...WITH THE FRONT MOVING INTO SOUTHWEST AK FRI AND
FRI NIGHT...AND THE LOW ITSELF REACHING THE EASTERN BERING IN THE
SAME TIME FRAME. THIS WILL RESULT IN A GRADUAL WEAKENING OF WINDS
OVER THE GULF FOR THE REST OF THE WORKWEEK...DRYING CONDITIONS
CROSSING MAINLAND AK AND THE GULF BEFORE THE WEEKEND...AND A STORM
FORCE LOW AND FRONT TRANSITING THE BERING AND ALEUTIANS BY THE
WEEKEND.

&&

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

A POTENT LOW PRESSURE SYSTEM LOCATED TO THE SOUTHEAST OF KODIAK
ISLAND HAS BEEN SUPPORTING GUSTY WINDS AND LOCALLY HEAVY
PRECIPITATION ACROSS PORTIONS OF SOUTHCENTRAL OVERNIGHT. ITS
ASSOCIATED FRONT LIES JUST TO THE SOUTH OF THE GULF COAST...AND
HAS BEEN SUPPORTING STORM FORCE WINDS ACROSS MUCH OF THE COASTAL
WATERS FROM JUST SOUTH OF PRINCE WILLIAM SOUND TO AUGUSTINE
ISLAND. THIS LOW PRESSURE SYSTEM HAS ALSO CREATED A FAVORABLE
PRESSURE GRADIENT FOR GUSTS TO OCCUR ALL NIGHT ACROSS THE
MATANUSKA VALLEY...WEST ANCHORAGE...AND EASTERN PRINCE WILLIAM
SOUND. THESE WINDS ARE EXPECTED TO GRADUALLY RELAX THIS MORNING
INTO EARLY AFTERNOON AS THE LOW PRESSURE SYSTEM WEAKENS AND
CONTINUES TO THE EAST.

BY FRIDAY EVENING...A FRONT WILL MOVE ACROSS KODIAK ISLAND AND A
TRIPLE POINT LOW WILL DEVELOP TO THE NORTHWEST OF THE ISLAND. THIS
FRONTAL SYSTEM WILL TAP INTO SUFFICIENT TROPICAL MOISTURE TO BRING
STEADY RAIN AND SNOW TO PORTIONS OF THE SOUTHCENTRAL MAINLAND
THROUGH SATURDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SNOW OVER BRISTOL BAY AND THE ALASKA PENINSULA WILL TAPER OFF
THROUGH THE MORNING AS THE LARGE LOW IN THE GULF SHIFTS EAST. THE
STRONG NORTHWESTERLY WINDS THROUGH THE GAPS AND PASSES IN THE
ALASKA PENINSULA WILL ALSO DIMINISH AS THE PRESSURE GRADIENT
RELAXES AS THE LOW EXITS THE AREA AND A TRANSIENT RIDGE BUILD OVER
THE AREA IN ADVANCE OF THE NEXT LARGE BERING LOW. THE ASSOCIATED
FRONTAL SYSTEM WILL REACH THE SOUTHWEST ALASKA COAST EARLY FRIDAY
MORNING THEN PUSH INLAND BRINGING SNOW AND BREEZY WINDS THROUGH
THE DAY FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FRONTAL SYSTEM ASSOCIATED WITH THE LARGE LOW DEVELOPING IN
THE FAR WESTERN BERING CURRENTLY STRETCHES FROM THE NORTH PACIFIC
ACROSS THE WESTERN ALEUTIANS AND WESTERN BERING. THIS FRONT WILL
TRACK EAST TODAY AND TONIGHT REACHING THE WESTERN MAINLAND FRIDAY
MORNING. THE PARENT LOW WILL FOLLOW MORE SLOWLY REACHING THE
CENTRAL BERING FRIDAY NIGHT. STORM FORCE SOUTHERLIES WILL FOLLOW
THE INITIAL FRONT EAST WITH A BROADER AREA OF WESTERLY STORMS
SOUTH AND WEST OF THE LOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
WEAKENING LOW PRESSURE WILL TRANSITION TO THE GULF WITH SECONDARY
LOW DEVELOPMENT OVER THE NORTHERN OR CENTRAL GULF. CONFIDENCE IN
THE EXACT LOCATION IS DEPENDENT ON THE LOCATION OF THE
ACCOMPANYING JET STREAM. SNOW CHANCES FOR SOUTHCENTRAL INCLUDING
THE LARGER POPULATION CENTERS WILL BE HIGHLY DEPENDENT ON HOW FAR
NORTH TOWARD PRINCE WILLIAM SOUND THIS SECONDARY LOW DEVELOPMENT
OCCURS...AS WELL AS ANY SOUTHEASTERLY MOISTURE PUSH PROVIDED BY
POTENTIAL JET DEVELOPMENT ON THE DOWNSTREAM SIDE OF THE NEGATIVE-
TILTED UPPER LEVEL TROUGH. OVERALL...CONFIDENCE IN SNOW CHANCES
FOR ANCHORAGE AND VICINITY HAVE DIMINISHED SOMEWHAT IN THE LAST
DAY...ESPECIALLY FOR SUNDAY INTO MONDAY.

MEANWHILE OVER THE BERING A SURFACE FRONT WILL ELONGATE FROM WEST
TO EAST ACROSS THE SOUTHERN BERING AND SERVE AS A FOCUSING
MECHANISM FOR SHOWERS AND GUSTY WINDS. BEHIND THIS FRONT...COLD
ADVECTION WITH SCATTERED SNOW SHOWERS WILL BE COMMON OVER THE
NORTHERN AND CENTRAL BERING.

BY THE EARLY TO MIDDLE PART OF NEXT WEEK...AN ARCTIC AIR MASS WILL
SETTLE OVER MUCH OF THE REGION...BRINGING BELOW NORMAL
TEMPERATURES (BY DECEMBER STANDARDS) TO MOST AREAS THAT MAY
PERSIST UNTIL THE END OF THE YEAR.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 191.
MARINE...GALE 130 131 132 138 139 141 155 165 170-172 180 181.
         STORM 119 120 150 173-179 185.
         HEAVY FREEZING SPRAY 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...CC