FXAK68 PAFC 241406
AFDAFC

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST THU DEC 24 2009

.ANALYSIS AND UPPER LEVELS...
A LARGE VERTICALLY STACKED 962 MB LOW IS NEARLY STATIONARY ABOUT 500
MILES SOUTH OF SAND POINT. THE CIRCULATION FROM THIS LOW IS
ENCOMPASSING THE ENTIRELY OF THE GULF OF ALASKA AS WELL AS THE
EASTERN BERING SEA. DESPITE THIS SIZE...STRONGEST WINDS ARE AROUND 35
TO 40 KTS THROUGH THE GULF AND ALASKA PENINSULA AREAS. THERE ARE
SEVERAL SHORTWAVES PINWHEELING AROUND THIS MAIN LOW...AND THESE
REPRESENT THE FORECAST CHALLENGE FOR THE NEXT FEW DAYS AS THEY IMPACT
SOUTHCENTRAL ALASKA. OVERALL...SOUTHERLY FLOW AND WARM AIR CONTINUE
TO INFILTRATE MAINLAND ALASKA. FURTHER WEST...A WEAKENING LOW IN THE
FAR WESTERN BERING IS DRIFTING SOUTHEAST AND WILL DISSIPATE BY
TONIGHT. 

.MODEL DISCUSSION...
MODELS ARE IN RELATIVELY GOOD AGREEMENT THROUGH SUNDAY MORNING. THE
MOST SIGNIFICANT DIFFERENCE IS IN THE GULF RELATING TO THE STRENGTH
OF A SHORTWAVE THAT IMPACTS SOUTHCENTRAL ON CHRISTMAS DAY. GFS IS
STRONGEST...DEVELOPING A CLOSED LOW...WHILE THE ECMWF IS THE WEAKEST
WITH ONLY A WEAK TROUGH. MEANWHILE THE NAM IS A COMPROMISE
SOLUTION...AND WILL BE USED FOR THE MORNING FORECAST. BEYOND THE
WEEKEND...MODELS FALL APART WITH THE GFS TRYING TO BRING LOWS INTO
THE GULF OF ALASKA...WHILE THE ECMWF AS WELL AS HPC GUIDANCE KEEP THE
ACTIVE WEATHER SOUTH OF THE AREA. SINCE PREVIOUS FORECAST WAS CLOSER
TO THE LATTER SOLUTION...WILL OPT TO LEAVE FORECAST LARGELY INTACT
FOR NOW.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...REMNANT SHOWERS FROM THE DECAYING LOW IN COOK INLET
WILL CONTINUE TO DECLINE THIS MORNING. NUMEROUS EMBEDDED WAVES IN THE
SOUTHEASTERLY FLOW WILL HAVE HIGHEST IMPACTS ALONG THE COAST...WHERE
PERIODS OF RAIN MIXED WITH SNOW WILL CONTINUE FOR THE NEXT SEVERAL
DAYS. FOR INLAND AREAS...A DRIER FORECAST WITH THE BEST CHANCE OF
PRECIPITATION ON CHRISTMAS DAY...DEPENDING ON THE STRENGTH OF THE
SHORTWAVE TROUGH MOVING OVER THE AREA THAT DAY. AT THIS TIME IT LOOKS
LIKE A TYPICAL DOWNSLOPING PATTERN MAY PERSIST OVER THE ANCHORAGE
BOWL...WESTERN KENAI PENINSULA..AND MATANUSKA VALLEY.

.SOUTHWEST/BERING/ALEUTIANS...RELATIVELY LIGHT EASTERLY TO
NORTHEASTERLY FLOW CONTINUES FOR NEXT SEVERAL DAYS...WITH STRONGER
WINDS TO MINIMUM GALE FORCE LIKELY OVER THE ALASKA PENINSULA AND
EASTERN ALEUTIANS. SCATTERED TO NUMEROUS SHOWERS WILL CONTINUE
THROUGHOUT MOST OF THE BERING SEA...WHILE SOUTHWEST MAINLAND WILL SEE
ONLY ISOLATED SHOWERS.

.LONG TERM FORECAST...
AS MENTIONED IN THE MODEL DISCUSSION...LONG TERM MODEL PICTURE
BECOMES UNCLEAR STARTING EARLY NEXT WEEK. IN GENERAL...IT LOOKS LIKE
THE DEEP LONGWAVE TROUGH IN THE BERING WILL CONTINUE TO KEEP MOST
LOWS JUST SOUTH OF OUR AREA...WITH LIGHT SOUTHERLY FLOW CONTINUING TO
BRING WARMER AIR TO MAINLAND ALASKA THROUGH SATURDAY...BEFORE A
SLIGHT COOLING TREND STARTING ON SUNDAY. EXPECT MOSTLY CLOUDY
CONDITIONS FOR THE START OF THE WEEKEND...WITH PARTLY CLOUDY SKIES
DEVELOPING INLAND BY SATURDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE WARNING 120 130 150 155 160 165 170 172
         HEAVY FREEZING SPRAY WARNING 180 185
FIRE WEATHER...NONE

AMD DEC 09