FXAK68 PAFC 252228
AFDAFC

AREA FORECAST DISCUSSION 
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM AKST FRI DEC 25 2009

.ANALYSIS AND UPPER LEVELS...
LONG WAVE PATTERN REMAINS UNCHANGED WITH A BLOCKING RIDGE AXIS ALONG
THE WESTERN CONUS COAST. A LARGE AREA OF LOW PRESSURE IS SPINNING
BETWEEN 150W AND 160W AROUND 48N. THE SUBTROPICAL JET IS FLOWING
SOUTH TO NORTH BETWEEN THESE TWO MAIN FEATURES WITH NUMEROUS EMBEDDED
SHORTWAVES. WHILE THE ORIENTATION AND STRENGTH OF THIS PATTERN WILL
FLUCTUATE...NO MAJOR CHANGES ARE EXPECTED THROUGH EARLY NEXT WEEK.

.MODEL DISCUSSION...MODELS IN EXCELLENT AGREEMENT WITH ALL FEATURES
THROUGH 60 HOURS. DIFFERENCES ARISE IN THE EVOLUTION OF THE MAIN LOW
IN THE NORTH PACIFIC SUNDAY NIGHT. PREFER THE ECMWF/UKMET SOLUTIONS
THAT KEEP A DOUBLE BARRELED SYSTEM LONGER. THE THE GFS/NAM DEEPENS
THE LOW RAPIDLY INTO A LARGE CONCENTRIC SYSTEM 12 TO 24 HOURS TOO
SOON. 

.SHORT TERM FORECAST...
SOUTHCENTRAL...THE LATEST SHORTWAVE IS PUSHING UP AGAINST THE NORTH
GULF COAST EARLY THIS AFTERNOON BRINGING MODERATE TO HEAVY RAIN TO
THE REGION ALONG WITH STORM FORCE WINDS. THE NORMAL WESTERN VALLEYS
ARE BEING DOWNSLOPED...WITH ONLY A FEW FLURRIES AND ICE PELLETS
MAKING IT TO THE SURFACE. THIS WILL BE THE LAST SIGNIFICANT WAVE THAT
MOVES THROUGH...THE NEXT SEVERAL WILL BE MUCH WEAKER. THE ENERGY WILL
NOW SHIFT TO THE ALASKA PENINSULA WHILE HIGH PRESSURE AT THE SURFACE
BUILDS FROM THE YUKON TERRITORY AND SPREAD WEST INTO SOUTHCENTRAL
ALASKA BY MONDAY...CHOKING OFF THE MOIST SOUTHEASTERLY FLOW AND
FINALLY BRINGING AN END TO THE RAIN ALONG THE COAST.

SOUTHWEST INTERIOR...PRECIPITATION ASSOCIATED WITH THE LATEST
SHORTWAVE IS SPREADING ACROSS THE ALASKA AND ALEUTIAN RANGES AND INTO
THE BRISTOL BAY ZONE. A CONCERN FOR THE EVENING WILL BE THE
POSSIBILITY OF FREEZING RAIN WHERE A FEW COLD POCKETS WILL HOLD ON.
THE WARM AIR ALOFT IS ADVECTING FROM THE SOUTHEAST INTO THE AREA AND
IT WILL TAKE SOME TIME TO MIX THE COLD AIR AT THE SURFACE OUT. SO
THERE COULD BE A PERIOD THIS EVENING ALONG THE NUSHAGAK RIVER
VALLEY...MAINLY DILLINGHAM NORTH. 

BERING SEA/ALEUTIAN CHAIN...EAST TO NORTHEASTERLY SMALL CRAFT WINDS
WILL PERSIST THROUGH SUNDAY AFTERNOON WHEN THE NEXT LOW ROTATES UP
AROUND THE ALASKA PENINSULA. THERE ARE MANY QUESTIONS STILL
CONCERNING THE EVOLUTION OF THIS LOW BUT CURRENTLY THINKING STRONG
GALES TO MINIMUM STORMS COULD AFFECT MUCH OF THE ALASKA
PENINSULA...BRISTOL BAY...AND EASTERN ALEUTIANS ON MONDAY. AS HIGH
PRESSURE BUILDS OVER SOUTHCENTRAL DURING THIS TIME FRAME...THE LONG
WAVE TROUGH AXIS WILL RETROGRADE BACK TO THE WEST A BIT PLACING THE
MOST ACTIVE WEATHER AGAIN OVER THE EASTERN BERING SEA EARLY NEXT
WEEK.

.LONG TERM FORECAST...LONG TERM FORECAST STILL CONSISTS OF A BUILDING
ARCTIC AIRMASS OVER CENTRAL CANADA. THIS WILL EVENTUALLY SPILL
WESTWARD INTO ALASKA LATE NEXT WEEK. THE TIMING AND STRENGTH VARIES
WILDLY FROM RUN TO RUN BUT THIS SEEMS TO BE THE TREND THAT THE MODELS
ARE TRYING TO NAIL DOWN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 132 140.
FIRE WEATHER...NONE.

AB DEC 09