FXAK68 PAFC 231346
AFDAFC

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST WED DEC 23 2009

.ANALYSIS AND UPPER LEVELS...
A BROAD LONGWAVE TROUGH ENCOMPASSING THE BERING SEA AND GULF OF
ALASKA IS BEING SUPPORTED BY A NEARLY 200 KT JET RUNNING ALONG THE
BASE OF THE TROUGH NEAR 40N LATITUDE. A WEAKENING JET STREAK COMING
UP FROM THE SOUTH INTO THE GULF IS SUPPORTING A SURFACE LOW IN THE
LOW 980 MB RANGE. THIS LOW WILL BE THE PRIMARY FORECAST CHALLENGE FOR
THE DAY AS IT APPROACHES THE KENAI PENINSULA. MIDDLETON ISLAND RADAR
SHOWS A SUBSTANTIAL SHIELD OF HEAVY PRECIPITATION ASSOCIATED WITH
THIS LOW...WHICH IS NOT SURPRISING CONSIDERING THE LONG SOUTHERLY
FETCH OF THE JET STREAM. 

.MODEL DISCUSSION...
MODELS SEEM TO BE COMING TO A CONSENSUS ABOUT THE TRACK OF THE LOW IN
THE GULF. THE MOST LIKELY TRACK CONTINUES TO BE THAT THE LOW MOVES
ONSHORE SOMEWHERE BETWEEN SEWARD AND MONTAGUE ISLAND. ALL MODELS
RAPIDLY WEAKEN THE LOW AS IT CROSSES THE KENAI PENINSULA...WHICH
SEEMS LIKE A REASONABLE SOLUTION CONSIDERING THE WEAKENING DYNAMIC
SUPPORT FOR THE LOW AS WELL AS THE RUGGED TERRAIN THAT THE SYSTEM
WILL BE CROSSING. THE ONLY DISSENTING MODEL TO THIS TRACK IS THE HIGH
RESOLUTION NAM...WHICH STALLS THE LOW BRIEFLY AND WOBBLES TO THE
NORTH BEFORE MOVING ONSHORE AND MEETING THE SAME FATE OF RAPID
WEAKENING. WHILE IT IS POSSIBLE THE NAM IS SAMPLING THE KENAI
MOUNTAINS THE BEST OF ALL THE MODELS AND IS THUS ON TO
SOMETHING...THE PREPONDERANCE OF ALL OTHER MODELS HAVING A COMMON
SOLUTION IS HARD TO IGNORE. THE CORRECT SCENARIO IS MOST LIKELY A
COMBINATION OF THE TWO...WITH THE BULK OF THE ENERGY MOVING RAPIDLY
INTO COOK INLET...BUT A RESIDUAL WEAK CIRCULATION SPLITTING OFF AND
PERSISTING BRIEFLY NEAR MONTAGUE ISLAND. THUS THE MORNING FORECAST
WILL REFLECT A SHIFT TOWARD THE COMMON SOLUTION OF THE
GFS/EC/GEM/UKMET.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...ONSHORE FLOW AND STEADY PRECIPITATION...MOSTLY
RAIN...WILL CONTINUE THROUGHOUT THE DAY OVER PRINCE WILLIAM SOUND AND
THE EASTERN KENAI PENINSULA. SNOW WILL SPREAD OVER THE ANCHORAGE BOWL
AND WESTERN KENAI PENINSULA THIS MORNING. DEPENDING ON THE EXACT
TRACK OF THE LOW...SNOW WILL LIKELY MIX WITH RAIN AND/OR FREEZING
RAIN OVER THE ANCHORAGE AREA IN THE AFTERNOON AS WARM AIR ALOFT MOVES
IN. THIS MAY ALSO HAPPEN OVER THE KENAI PENINSULA...ESPECIALLY IF THE
LOW MOVES INLAND SLIGHTLY FURTHER SOUTH THAN EXPECTED. TEMPERATURES
WILL REMAIN COLD ENOUGH OVER THE COPPER RIVER BASIN TO SUPPORT
SNOW...WITH GREATER THAN 6 INCHES ACCUMULATION EXPECTED SOUTH OF
GLENNALLEN BY MIDDAY BEFORE ENDING IN THE AFTERNOON. AS FOR THE
SUSITNA VALLEY...IT LOOKS LIKE THE LOW WILL WEAKEN RAPIDLY ENOUGH
THAT THE WIDESPREAD PRECIPITATION WILL NOT MAKE IT THAT FAR
INTACT...WITH THE EXCEPTION OF THE IMMEDIATE VICINITY OF THE ALASKA
RANGE WHERE LOCAL UPSLOPE WILL ALLOW FOR A STEADIER RAIN/SNOW MIX.
WINDS WILL BE STRONG THROUGHOUT MUCH OF THE AREA...BUT SHOULD STAY
BELOW WARNING LEVELS WITH THE POSSIBLE EXCEPTION OF CORDOVA WHERE
GUSTS TO NEAR HURRICANE FORCE ARE POSSIBLE...ESPECIALLY THROUGH
CHANNELED TERRAIN.

.SOUTHWEST/BERING/ALEUTIANS...WEATHER WILL BE RELATIVELY BENIGN FOR
THE NEXT FEW DAYS ACROSS THE REGION. A LARGE AND WEAKENING LOW OVER
THE FAR WESTERN BERING WILL KEEP NUMEROUS SHOWERS OVER THE WESTERN
ALEUTIANS...WHILE ANOTHER SLOW-MOVING LOW SOUTH OF CHIGNIK WILL BRING
ONSHORE FLOW AND SHOWERS TO THE SOUTH SIDE OF THE ALASKA PENINSULA
AND EASTERN ALEUTIANS THROUGH THE WEEKEND.

.LONG TERM FORECAST...
LONG RANGE MODELS CONTINUE TO SHOW OVERALL LITTLE CHANGE IN THE
SYNOPTIC PATTERN THROUGH THE MIDDLE OF NEXT WEEK. IT LOOKS LIKE THE
MOST ACTIVE WEATHER WILL CONTINUE TO BE IN THE VICINITY OF THE
EASTERN ALEUTIANS AND FAR WESTERN GULF. INLAND AREAS OF MAINLAND
ALASKA LOOK TO STAY MOSTLY DRY WITH SLIGHTLY ABOVE NORMAL
TEMPERATURES THROUGH THE START OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM WARNING 120
         GALE WARNING 125 130 132 138 150 155 160 165 170 171 172
FIRE WEATHER...NONE

AMD DEC 09