Blizzard in Alaska, December 16, 2002

SOUTH/SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTION
10 AM AST MON DEC 16 2002

ANALYSIS...THE ATMOSPHERE IS FINALLY LOOKING MORE WINTRY ON THE
500 MB HEMISPHERIC PATTERN. A CLOSED UPPER HIGH CELL IS JUST
SOUTH OF THE POLE ALONG 180. A CLUSTER OF DEEP COLD UPPER LOWS IS
SURROUNDING THIS HIGH INCLUDING A MAJOR LOW OVER MOST OF EASTERN
RUSSIA AND AN UPPER LOW OVER THE NORTH SLOPE WITH A TROUGH OVER
THE ALASKA PENINSULA.  AN ANOTHER UPPER LOW CENTER IS NEAR
56/143W. THE VERY STRONG PACIFIC JET IS AIMED RIGHT AT LAS VEGAS
WITH A SECONDARY BRANCH INTO WASHINGTON STATE. THE BERING SEA HAS
A HUGE BUT WEAK SURFACE LOW AROUND 985 MB EXTENDS INTO NORTON
SOUND. THE GULF UPPER LOW SUPPORTS TWO OLD SURFACE LOWS 960 MB
NEAR 57/143W AND A 961 MB CENTER IN THE CHARLOTTES. 500 MB
TEMPERATURES ARE SEASONABLE OVER ALASKA RANGING FROM THE LOWER
-40S TO AROUND -30C FOR ANCHORAGE KODIAK AND FAIRBANKS IN WEAK
EASTERLY TO SOUTHERLY FLOW ALOFT. SATELLITE IMAGERY SHOWS BIG
COLD TOP CUMULUS CLUSTERS OVER MOST OF THE BERING SEA AND A BROAD
AREA OF OVER-RUNNING OVER SOUTH CENTRAL MOVING OUT OF THE EAST.
RADARS SHOW THE SNOW SHOWERS OVER THE KUSKOKWIM DELTA AND A WEAK
BAND OF SNOW VIRGA OVER ANCHORAGE WITH LOTS OF PRECIPITATION
MONTAGUE ISLAND SOUTH.

FORECASTS...ALL 12Z MODELS REVIEWED SO FAR CONSOLIDATE A WEAK
NEGATIVELY TILTED TROUGH ALOFT FROM AN UPPER LOW NEAR THE BERING
STRAIT THROUGH THE BARREN ISLANDS THROUGH 12Z TUESDAY. THE ETA
CUTS OFF A WEAK UPPER LOW IN THE WESTERN GULF BY TUESDAY
AFTERNOON WHILE THE HEMISPHERIC MODELS MAINTAIN THE WEAK TROUGH.
ALL LEAVE A WEAK SURFACE LOW PRESSURE SYSTEM IN THE GULF INTO
WEDNESDAY. THERE IS A BIG CHANGE COMING. THE MODELS HAVE
FORECASTED A BIG STORM IN THE BERING SEA STARTING MIDWEEK BUT
HAVE FLIP-FLOPPED ON THE POSITION EAST OR WEST. BY 12Z WEDNESDAY
ALL MODELS NOW AGREE ON A STRONG SHORTWAVE ALONG 170E WHICH
SUPPORTS A 950 MB STORM NEAR SHEMYA. THIS ALSO BUILDS A RIDGE
ALONG 170W 12Z WED WHICH IS ACCEPTED AS THE WEAK WESTERN GULF
TROUGH BEGINS TO KICK OUT. THE STRONG SHORT WAVE MOVES THE RIDGE
TO ABOUT 148W OR SO BY 12Z FRIDAY WHICH ALLOWS STRONG SOUTHERLIES
TO DEVELOP ALONG WESTERN ALASKA. A COUPLE OF ENSEMBLE PACKAGES
AGREE IN THE MEAN ON THIS SCENARIO. THIS COULD BE UGLY FOR WIND
AND WARMING FOR THE WESTERN PART OF OUR FORECAST AREA DURING THE
WEEKEND.

.AFC...WATCH/WARNING SUMMARY
PUBLIC...WIND ADVSRY 125 131 135 171 191.
MARINE...GALES 2C1 3ABC 5A 12B.

JC DEC 02