FXAK68 PAFC 151545 CCA
AFDAFC

AREA FORECAST DISCUSSION...CORRECTED
SOUTHCENTRAL AND SOUTHWEST ALASKA
645 AM AKST TUE DEC 15 2009

CORRECTED TIME/DATE STAMP

.ANALYSIS AND UPPER LEVELS...
DEEP UPPER LEVEL LOW OVER PRUDHOE IS SLOWLY DROPPING SOUTH. A TROUGH
EXTENDS SOUTH AND WEST FROM THE LOW DOWN THROUGH THE AKPEN. A LARGE
RIDGE OF HIGH PRESSURE OVER THE BERING IS SLOWLY WEAKENING AND
SHIFTING SOUTH. AT THE SURFACE A NORTH PACIFIC LOW SLOWLY MOVES EAST
AND CONTINUES TO DEEPEN. A TROUGH OF LOW PRESSURE EXISTS TO THE NORTH
AND A SURFACE LOW AT THE APEX OF THE TROUGH HAS FORMED OVERNIGHT AND
IS GOING TO REMAIN NEARLY STATIONARY IN PRINCE WILLIAM SOUND THROUGH
THURSDAY. HIGH PRESSURE OVER THE BERING AND A MODERATE GRADIENT
BETWEEN SOUTHCENTRAL ARE USHERING IN GOOD NORTHERLY WINDS AND STRONG
COLD AIR ADVECTION.

.MODEL DISCUSSION...
MODELS CONTINUE TO BE IN GOOD AGREEMENT IN THE SHORT TERM
SYNOPTICALLY...WITH SMALLER SCALE DIFFERENCES. LARGER DIFFERENCES
APPEAR BY TOMORROW AFTERNOON WITH THE EVOLUTION OF THE PWS LOW. THE
NAM AND GFS ARE HINTING AT BRINGING ANOTHER LOW INTO THE SOUND
OVERNIGHT TOMORROW AND REPLACING THE CURRENT ONE...BUT PLACEMENT AND
INTENSITY CHANGES FROM RUN TO RUN THUS FAR. OUT WEST THERE IS GENERAL
CONSENSUS WITH THE WEAKENING OF THE RIDGE AND THE NEXT LOW THAT WILL
SLIDE JUST SOUTH OF THE CHAIN TOWARDS THE END OF THE WEEK. 

.SHORT TERM FORECAST...
IN THE EAST...AN ACTIVE AND UNSTABLE WEATHER PATTERN CONTINUES FOR
THE MAJORITY OF SOUTHCENTRAL EARLY THIS WEEK. LIGHT SNOW WILL
CONTINUE ACROSS THE ANCHORAGE BOWL AND WILL EVENTUALLY INCREASE LATER
THIS EVENING IN RESPONSE TO THE UPPER LEVEL LOW OVER NORTHERN ALASKA
DROPPING FURTHER SOUTH AND THE TROUGH AXIS EXTENDING FROM SHIFTS TO
MORE OF A NEGATIVELY ORIENTATION. MODEL ISSUES HAVE KEPT ABSOLUTE
CONFIDENCE BELOW AVERAGE...HENCE THE LIKELY CLASSIFICATION VERSUS
CATEGORICAL...SNOW WILL CONTINUE ACROSS THE SOUND AND COAST THROUGH
TOMORROW AFTERNOON. SNOWFALL WILL REMAIN BELOW ADVISORY CRITERIA FOR
THE COASTAL SECTIONS...BUT HIGHER ELEVATIONS...SUCH AS THOMPSON
PASS... WILL SEE BLOWING SNOW CONDITIONS AND VISIBILITIES WILL FALL
BELOW ONE QUARTER MILE AT TIMES.

OUT WEST...COLD AIR ADVECTION IS SETTLING IN OVER THE AREA AND WILL
BRING ADVISORY LEVEL WINDCHILLS ACROSS THE MAINLAND LATE TONIGHT AND
INTO TOMORROW MORNING. SNOW SHOWER ACTIVITY WILL INCREASE ALONG THE
AKPEN AND EASTERN CHAIN. OTHERWISE BENIGN WEATHER WILL CONTINUE UNTIL
A LOW NORTH PACIFIC LOW MOVES SOUTH OF SHEMYA LATER THIS WEEK
BRINGING ANOTHER ROUND OF PRECIPITATION ACROSS THE CHAIN AS IT WORKS
EAST. 

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLOWING SNOW ADVISORY 131
.........WIND CHILL 152 155 161
.........SNOW ADVISORY 141
MARINE...STORM WARNING 130
.........HEAVY FREEZING SPRAY 130 132 140 150 160 165 179 180 185
FIRE WEATHER...NONE

SHEA DEC 09