Heavy Freezing Spray Warning 83, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST MON FEB 20 2012

.ANALYSIS AND UPPER LEVELS...
SENSIBLE WEATHER IS DOMINATED BY TWO MAIN FEATURES. IN THE EAST...A
970 MB LOW NEAR MIDDLETON ISLAND IS FILLING AS IT MOVES TOWARDS
PRINCE WILLIAM SOUND. THE STRONGEST SURFACE WINDS HAVE PEAKED AROUND
50 KT FROM THE GULF TO SHELIKOF STRAIT AND ARE SLOWLY DIMINISHING. AN
ASSOCIATED FRONT HAS TRACKED TO THE NORTHERN GULF COAST WITH SNOW AND
RAIN AND IS ALSO WEAKENING. THIS SLUG OF MOISTURE IS GENERALLY
CONFINED TO THE SOUTHERN TO EASTERN KENAI PENINSULA AND PRINCE
WILLIAM SOUND...THOUGH SOME LIGHT SNOW IS FALLING ACROSS BRISTOL BAY
AND THE KUSKOKWIM DELTA WITH AN INVERTED TROUGH AXIS EXTENDING BEHIND
THE LOW. ABUNDANT CLOUDINESS PERSISTS FROM THE MAT-SU VALLEY THROUGH
THE ANCHORAGE BOWL AND NORTHERN KENAI PENINSULA...BUT BRISK NORTHEAST
FLOW HAS KEPT THE LOWER ATMOSPHERE APPRECIABLY DRY AND RETARDED
PRECIPITATION FROM REACHING THE GROUND.

OUT WEST...A 980 MB LOW JUST WEST OF THE PRIBILOF ISLANDS IS DRIFTING
EAST AND FILLING. IN GENERAL...VISIBLE SATELLITE IMAGERY DEPICTS A
MODEST AMOUNT OF CU OVER THE CENTRAL BERING AND ALEUTIAN CHAIN
SUGGESTING AN UNSTABLE AND SHOWERY REGIME. ANOTHER PACIFIC LOW IS
DEPICTED AS WELL AROUND 450 MILES SOUTHEAST OF DUTCH HARBOR ROTATING
EAST NORTHEAST.

.MODEL DISCUSSION...
IN THE EAST...THE NAM CONTINUES TO BE AN OUTLIER SOLUTION. THE 12Z
RUN CONTINUED A TREND OF POOR RUN TO RUN INITIALIZATION WITH A
POSITION AND TRACK TOO FAR TO THE WEST. THE 18Z RUN CAME IN LINE A
BIT BETTER WITH THE OTHER MODELS...BUT STILL PREFER THE GFS/ECMWF
DEPICTION OVER THE NEXT 24 HOURS OF THE RESIDUAL SURFACE FEATURE
DRIFTING INTO PRINCE WILLIAM SOUND AND CONTINUING TO WEAKEN.
ALOFT...THE ECMWF SEEMS TO BE KEYING IN ON A STRONGER SHORTWAVE
MOVING UP TOWARDS SOUTHCENTRAL AK EARLY TUESDAY MORNING WITH POSSIBLY
SOME LIGHT SNOW EVEN ACROSS INLAND AREAS. HOWEVER WITH THE
PRE-EXISTING AIRMASS AS DRY AS IT IS...AN EVEN STRONGER FEATURE WOULD
BE NEEDED TO GENERATE ANY STEADY PRECIPITATION. THE CHANCES FOR THIS
BEGIN TO LOOK BETTER BY TUESDAY NIGHT INTO WEDNESDAY AS THE FLOW
ALOFT BECOMES INCREASINGLY CYCLONIC WITH STRONGER SHORTWAVES...AND AS
A BIT MORE COLD ADVECTION BLEEDS EASTWARD. ALL OF THE MODELS
GENERALLY SUPPORT THIS TREND.

OUT WEST...MODELS DEPICT THE SURFACE LOW NEAR THE PRIBILOFS DRIFTING
EAST AND MOVING ASHORE THE KUSKOKWIM DELTA COAST ON TUESDAY. THE LOW
SOUTH OF DUTCH HARBOR WILL QUICKLY TRACK TO THE SOUTHEASTERN GULF AND
AWAY FROM THE AOR. THUS THE NEXT FEATURE OF SUBSTANCE THEN BECOMES A
LOW THAT TRACKS TO AROUND 300 MILES SOUTHWEST OF ATTU WEDNESDAY
AFTERNOON WITH A POSSIBLE STORM FORCE INTENSITY FRONT PRECEDING IT.
MODELS HAVE DECENT GOOD AGREEMENT WITH THIS DEVELOPMENT AND WE HAVE
LARGELY LEANED ON THE GFS/NAM FOR THIS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
THE STEADIEST PRECIPITATION THROUGH TUE AFTERNOON LOOKS TO BE FOCUSED
ALONG COASTAL AREAS...THOUGH EVEN THERE...INTENSITY WILL EBB AS THE
SUPPORTING LOW PRESSURE SYSTEM WEAKENS. FOR KODIAK ISLAND...BREEZY
WESTERLY FLOW TO PERSIST INTO TUE. HOWEVER WITH THIS BEING AN
OFF-SHORE WIND...EXPECT SOME SUNNY BREAKS. ACROSS INLAND AREAS OF
SOUTHCENTRAL...THE CHANCE FOR SOME LIGHT SNOW INCREASES WITH TIME
CONCURRENT WITH MORE FAVORABLE UPPER-LVL DYNAMICS.

SOUTHWEST...
FRONTOGENETIC LIFT OVER BRISTOL BAY WILL WEAKEN OVERNIGHT WITH LIGHT
SNOWS TAPERING OFF BY TUESDAY MORNING. MOISTURE FROM THE DISORGANIZED
SYSTEM NEAR THE PRIBILOF ISLANDS MOVES ASHORE THE KUSKOKWIM DELTA TUE
AFTERNOON...BUT LARGELY WITHOUT ANY SIGNIFICANT FORCING...AND THUS
SHOULD SEE MAINLY JUST SHOWERS.

BERING SEA/ALEUTIANS...
SHOWERS ACROSS THE BERING/ALEUTIANS WILL DIMINISH A BIT ON TUESDAY AS
SUBSIDENCE FROM TRANSITORY RIDGING MOVES IN FROM THE WEST. HOT ON
IT'S HEELS WILL BE THE NEXT STORM SYSTEM. STEADY SNOW AND STRONG
GALES ADVANCE TO THE FAR WESTERN CHAIN ON WEDNESDAY.

.LONG TERM FORECAST...
THE LONG WAVE PATTERN WILL AMPLIFY BY LATE WEEK. THE MID-WEEK WESTERN
ALEUTIAN SYSTEM SLOWLY CREEPS NORTHEASTWARD AS AN UPPER-LOW BEGINS
ESTABLISHING ITSELF OVER THAT REGION. MEANWHILE...A SHARP UPPER-LVL
RIDGE LOOKS TO BUILD INTO THE SOUTHERN MAINLAND. RESIDUAL MOISTURE
FROM THE BERING SYSTEM MAY BRUSH THE SW MAINLAND...BUT THE REMAINDER
OF SOUTHCENTRAL LOOKS TO DRY OUT A BIT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM...150 352
         GALE...132 155 351
FIRE WEATHER...NONE

JAM FEB 12