Small Craft Advisory 858, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKST MON NOV 26 2012

.ANALYSIS AND UPPER LEVELS...
A LOOK AT THE MORNING WEATHER MAP SHOWS A BROAD AREA OF LOW PRESSURE
OVER THE FAR SOUTHERN GULF WITH A WEAK ASSOCIATED FRONT STALLED OVER
THE NORTHERN GULF. THIS IS THE SAME FRONT THAT BROUGHT RAIN AND SNOW
TO KODIAK ISLAND YESTERDAY AND IS NOW DISSIPATING IN PLACE...BRINGING
STEADY LIGHT RAIN TO KODIAK TODAY AND SCATTERED SHOWERS ACROSS MUCH
OF THE REST OF THE GULF. OUT WEST...HIGH PRESSURE OVER THE EASTERN
BERING EXTENDS INTO MAINLAND ALASKA...WHERE CLEAR AND COLD CONDITIONS
CONTINUE. FURTHER WEST...A SIGNIFICANT UPPER TROUGH IS DISPLACING THE
BERING RIDGE TO THE SOUTHEAST. BENEATH THIS TROUGH...AT THE
SURFACE...A 1005 MB LOW IS GRADUALLY STRENGTHENING IN THE CENTRAL
BERING AS AN INFLUX OF COLD AIR ENTERS FROM THE KAMCHATKA PENINSULA.
A WEAKENING GALE-FORCE FRONT IS BRINGING A ROUND OF RAIN AND SNOW TO
THE PRIBILOF ISLANDS AND EASTERN ALEUTIANS.

.MODEL DISCUSSION...
AS EXPECTED WITH A FAIRLY STEADY-STATE LONGWAVE PATTERN THE MODELS
ARE IN GOOD AGREEMENT ON THE BASIC EVOLUTION OF FEATURES TODAY. THE
RIDGE IN THE EASTERN BERING WILL BE PUSHED TO THE SOUTHEAST AND
DISSIPATED BY THE DIGGING TROUGH IN THE WESTERN BERING. AS THIS
TROUGH JOINS THE LONGWAVE TROUGH IN THE SOUTHERN GULF ON
TUESDAY...MODELS AGREE THAT AN EVEN STRONGER RIDGE WILL REDEVELOP IN
THE BERING SEA AND EXTEND NEARLY ALL THE WAY TO THE NORTH POLE BY
WEDNESDAY MORNING. THIS AMPLIFICATION OF THE UPPER LEVEL PATTERN WILL
RESULT IN STRONG NORTHERLY FLOW ACROSS ALL OF MAINLAND ALASKA THAT
WILL LIKELY USHER IN SOME OF THE COLDEST AIR OF THE SEASON. THERE ARE
A FEW MODEL ISSUES AS RELATES TO THE DEVELOPMENT OF THIS AMPLIFIED
PATTERN. THE FIRST ISSUE IS WITH THE TIMING AND STRENGTH OF A POTENT
SHORTWAVE THAT DROPS DOWN THE FRONT/EAST SIDE OF THE BERING RIDGE
WEDNESDAY EVENING...WHILE THE SECOND INVOLVES ANOTHER UPPER TROUGH
DIGGING INTO THE SOUTHERN MAINLAND FROM THE NORTHEAST ON THURSDAY. IN
ALL CASES THE COMMON THEME IS THAT THE 12Z NAM IS THE OUTLIER FROM
THE GOOD CONSENSUS OF THE OTHER MODELS...AND AS A RESULT A GFS/EC
COMBO HAS BEEN USED FOR THE SYNOPTIC PATTERN.

.SHORT TERM FORECAST...
SOUTHCENTRAL...THE WEAK FRONT OVER THE NORTHERN GULF HAS STALLED AND
WILL BEGIN TO SLOWLY RETREAT TO THE SOUTH TONIGHT AS THE EASTERN
BERING RIDGE IS PUSHED INTO THE GULF. THIS WILL CONTINUE TO DIMINISH
THE LOW LEVEL PRESSURE GRADIENTS ACROSS THE REGION AND AS A RESULT
EVEN GAP WINDS SHOULD DIMINISH THIS EVENING. SOME AREAS OF FOG ARE
STILL LINGERING AROUND UPPER COOK INLET...AND MAY EXPAND IN COVERAGE
OVERNIGHT AS THE LOW-LEVEL TEMPERATURE INVERSION STEEPENS AND LOWERS.
FOG WILL REMAIN THE MAIN FORECAST CHALLENGE UNTIL NORTHERLY FLOW AND
COLD AIR ADVECTION RESUME ONCE AGAIN LATE TUESDAY NIGHT. ANY AREAS
THAT DO REMAIN CLOUD-FREE TONIGHT WILL LIKELY SEE THE COLDEST
TEMPERATURES OF THE YEAR SO FAR AS LIGHT WINDS AND CLEAR SKIES CREATE
AN IDEAL SCENARIO FOR RADIATIONAL COOLING. STARTING WEDNESDAY
NORTHERLY OUTFLOW WINDS WILL RESUME ONCE AGAIN...AND HAVE THE
POTENTIAL TO GET QUITE STRONG BY THE END OF THE WEEK.

SOUTHWEST...CLOUDS FROM THE BERING SEA FRONT ARE APPROACHING THE
DELTA AND BRISTOL BAY COASTS THIS AFTERNOON. MODELS HAVE CONTINUED TO
HALF THE PRECIPITATION BEFORE IT SPREADS INLAND...AND LIKELY WILL NOT
PRODUCE MORE THAN A FEW FLURRIES ALONG THE COASTS. THE LARGEST IMPACT
WILL BE WARMER TEMPERATURES PROVIDING A BRIEF REPRIEVE FROM THE
ARCTIC TEMPERATURES OF THE PAST SEVERAL WEEKS. OVERALL FLOW WILL
BECOME OFFSHORE BY EARLY WEDNESDAY MORNING AS COLD AIR AND CLEAR
SKIES RETURN TO THE REGION.

BERING SEA AND ALEUTIANS...RAIN WILL MIX WITH AND TURN TO SNOW
OVERNIGHT AROUND THE PRIBILOF ISLANDS AS WINDS SHIFT TO THE NORTHWEST
BEHIND THE FRONT. MEANWHILE...AS THE UPPER TROUGH SLIDES TO THE
SOUTHEAST THERE WILL BE ANOTHER TRIPLE POINT LOW THAT FORMS ALONG THE
FRONT SOUTH OF THE ALASKA PENINSULA LATE TONIGHT. THIS WILL HELP KEEP
THE WARM AIR TO THE SOUTH AND RESULT IN A RAIN/SNOW MIX AROUND COLD
BAY AND THE REST OF THE ALASKA PENINSULA. FURTHER WEST...HIGH
PRESSURE IS ALREADY BEGINNING TO BUILD INTO THE WESTERN BERING AND
WILL SPREAD EASTWARD DURING THE DAY TUESDAY. THIS WILL BRING
GENERALLY BENIGN WEATHER BACK TO THE REGION AND RE-ESTABLISH GUSTY
NORTHERLY FLOW OVER THE EASTERN TWO-THIRDS OF THE ALEUTIAN CHAIN THAT
CONTINUE THROUGH THE WEEKEND.

.LONG TERM FORECAST...FROM PREVIOUS DISCUSSION...

NO MAJOR CHANGES TO THE EXTENDED FORECAST. THE SENSIBLE WEATHER WILL
BE CONTROLLED BY TWO LONGWAVE TROUGHS...ONE IN THE NORTHEASTERN
PACIFIC...TOO FAR SOUTH TO AFFECT THE SOUTHCENTRAL...AND ANOTHER WEST
OF THE KAMCHATKA PENINSULA. RIDGING BETWEEN THESE TWO FEATURES WILL
KEEP THE DRY AND COLD CONDITIONS IN PLACE FOR THE FORESEEABLE FUTURE
FOR MOST OF THE STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE WARNING 132 150 170 171 172 176 179 180 185
FIRE WEATHER...NONE

DIXON NOV 12