Winter Weather Advisory 4, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
450 PM AKST MON JAN 31 2011

.ANALYSIS AND UPPER LEVELS...
OVERALL HEMISPHERIC PATTERN REMAINS UNCHANGED WITH A HIGH AMPLITUDE
RIDGE DOMINATING SOUTHEAST ALASKA AND THE PACIFIC NORTHWEST. ON
EITHER SIDE OF THIS RIDGE ARE VERY LARGE TROUGHS THAT STRETCH ACROSS
EASTERN RUSSIA AND THE BERING SEA UPSTREAM...AND OVER MUCH OF THE
CENTRAL AND EASTERN CONUS DOWNSTREAM. AN ACTIVE JET STREAM FLOWING
AROUND THE BASE OF THE BERING SEA TROUGH WILL BEGIN TO FEED MOISTURE
INTO SOUTHCENTRAL ALASKA THIS EVENING AND CONTINUE THROUGH MOST OF
THE WEEK. MULTIPLE SHORTWAVES EMBEDDED WITHIN THE CYCLONIC
CIRCULATION WILL BRING THE PERIODS OF ENHANCED PRECIPITATION TO THE
REGION.

.MODEL DISCUSSION...MODELS CONTINUE TO HAVE PROBLEMS RESOLVING THE
MULTIPLE LOWS DEVELOPING AND ROTATING AROUND THE BASE OF THE TROUGH.
THE FIRST LOW TO MOVE INTO THE NORTHWESTERN GULF TONIGHT APPEARS TO
BE BEST INITIALIZED BY THE GFS AND UKMET. THE ECMWF TAKES THE LOW TO
THE NORTHWEST WHILE THE NAM PUSHES THE LOW DUE NORTH. THE 115 MILE
DIFFERENCE BETWEEN THE TWO RESULTS IN A MUCH LARGER DIFFERENCE IN
PRECIP TYPE LATER THIS EVENING AND TUESDAY. THE PREFERRED SOLUTION IS
SOMEWHERE BETWEEN THE NAM AND GFS WHICH PUTS THE LOW IN A VERY
FAVORABLE POSITION FOR WIDESPREAD SNOW ACROSS SOUTHCENTRAL ALASKA
WHILE COASTAL SECTIONS WILL CONTINUE TO SEE A MIX OF RAIN AND SNOW.

BEYOND THE FIRST 36 HOURS...MODELS CONTINUE TO STRUGGLE WITH THE
DETAILS ALTHOUGH THE STORY REMAINS THE SAME. SEVERAL LOWS ARE LINED
UP TO FOLLOW A SIMILAR PATH INTO THE NORTHERN GULF. PERIODS OF
PRECIPITATION CAN BE EXPECTED THROUGH AT LEAST WEDNESDAY. NO CHANGES
WERE MADE TO THE FORECAST BEYOND THE FIRST 48 HOURS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...DIFFICULT FORECAST WITH STILL QUITE A BIT OF
UNCERTAINTY AS A LARGE PLUME OF MOISTURE APPROACHES FROM THE SOUTH.
CURRENT FORECAST IS LOOKING GOOD WITH SUB ADVISORY SNOWFALL TOTALS
FOR MOST AREAS. FLURRIES HAVE ALREADY BEGUN IN THE ANCHORAGE BOWL.
INTENSITY WILL INCREASE OVERNIGHT INLAND AS SNOW MIXES WITH OR
CHANGES OVER TO RAIN ALONG THE COAST. ON THE BACKSIDE OF THE LOW...AN
INVERTED TROUGH REMAINS OVER THE NORTHWESTERN GULF AND KENAI
PENINSULA WITH MOISTURE OVERRUNNING THE SURFACE FEATURE. PERIODS OF
LIGHT SNOW WILL CONTINUE THROUGH TUESDAY BEFORE THE NEXT UPPER WAVE
BRINGS SOUTHCENTRAL ANOTHER ROUND OF HEAVIER PRECIPITATION TUESDAY
NIGHT. SNOW WILL STAY IN THE FORECAST THROUGH WEDNESDAY...POSSIBLY
THURSDAY...BEFORE THE TROUGH AXIS SHIFTS SLIGHTLY EAST.

SOUTHWEST ALASKA...THE PARENT LOW OVER BRISTOL BAY WILL GO THROUGH
SEVERAL PHASES OVER THE NEXT 36-72 HOURS AS IT EVOLVES INTO AN OPEN
TROUGH AND THEN BACK TO A CLOSED LOW. MEANWHILE...PERIODS OF LIGHT
SNOW AND FOG WILL CONTINUE ACROSS THE REGION WITH TEMPERATURES NEAR
OR SLIGHTLY BELOW CLIMATOLOGICAL NORMAL FOR THIS TIME OF YEAR.

BERING SEA/ALEUTIANS...A LOW IS DEVELOPING SOUTH OF THE WESTERN
ALEUTIANS THIS AFTERNOON. IT WILL MATURE OVER THE NEXT 48 HOURS AS IT
DRIFTS NORTH OF THE CHAIN. THIS CLOSED LOW AND ASSOCIATED FRONTAL
BOUNDARY WILL PRODUCE GALE FORCE WINDS OVER THE COASTAL AND OFFSHORE
WATERS IN THE BERING SEA. OTHERWISE...VERY BENIGN WEATHER CONTINUES
OUT WEST FOR LATE JANUARY/EARLY FEBRUARY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 172 175 176
         HEAVY FREEZING SPRAY WARNING 160
FIRE WEATHER...NONE.

AB JAN 11