Storm Warning 178, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
300 PM AST MON DEC 31 2007

.MODEL DISCUSSION...OVERALL THE MODELS ARE STILL PERFORMING WELL.
THERE IS GOOD AGREEMENT ON THE GULF OF ALASKA LOW PAST 60 HOURS AND
EVEN THEN THE DIFFERENCES ARE NOT SHOW STOPPERS...ESPECIALLY SINCE
THE GFS HAS BEEN VERY CONSISTENT WITH IT. OUT WEST THE OVERALL
PATTERN IS GOOD BUT THE MODELS ARE STRUGGLING A LITTLE WITH THE
COMPLEX LOW AND DEVELOPMENT OF TRIPLE POINT LOWS IN THE WEST AND
CENTRAL ALEUTIANS AND BERING SEA THROUGH WEDNESDAY. AFTER THAT THE
MODELS CONVERGE ON A LOW DEVELOPING SOUTH OF DUTCH HARBOR AND MOVING
SOUTH OF THE GULF OF ALASKA. THIS SHOWS THAT THE OVERALL PATTERN IS
GOOD...THEY ARE JUST STRUGGLING WITH THE DETAILS OF THE COMPLEX LOW
AS IT MOVES THROUGH THE ALEUTIANS.

.ANALYSIS AND UPPER LEVELS...THE BIGGEST WEATHER FEATURE TODAY IS A
LARGE LOW SOUTH OF THE GULF OF ALASKA. THIS LOW IS TIGHTENING THE
PRESSURE GRADIENT IN AND NEAR THE GULF AS WELL AS BRINGING
PRECIPITATION INTO THE AREA. THIS LOW WILL DEVELOP A DOUBLE CENTER
OVER THE NEXT DAY AS THE MAIN LOW HEADS NORTHEAST AND A SECONDARY
CENTER WILL DEVELOP ALONG THE FRONT. THIS CAN ALREADY BE SEEN
HAPPENING ON THE SATELLITE IMAGE NEAR 55N 145W THIS AFTERNOON. DURING
THE LATER HALF OF THE WEEK THERE WILL BE A RESIDUAL TROUGH IN THE
NORTHERN GULF THAT WILL STRENGTHEN INTO A LOW NEAR PRINCE WILLIAM
SOUND.
    IN THE WEST A STRONG FRONT IN THE WESTERN BERING SEA AND ALEUTIAN
ISLANDS WILL MOVE INTO THE NORTHERN BERING SEA AS A MODERATE LOW WILL
MOVE INTO THE BERING SEA BEHIND IT.
    THE JET STREAM REMAINS MOSTLY SOUTH OF THE FORECAST AREA WITH
JUST THE SOUTHERNMOST PART OF THE CENTRAL ALEUTIANS ON THE EDGE OF
IT. THE JET CURRENTLY COMES OFF OF JAPAN AND THEN INTO THE LARGE LOW
SOUTH OF THE GULF OF ALASKA BEFORE TURNING NORTH INTO THE ALASKA
PANHANDLE. THIS PATTERN WILL REMAIN CONSISTENT IN THE WEST WITH JUST
A SLIGHT DRIFT SOUTH IN THE JET THROUGH THE MIDDLE OF THE WEEK WHILE
THE PORTION IN SOUTHEAST ALASKA WILL WEAKEN AND MOVE INTO CANADA
LEAVING THE JET WELL SOUTH OF THE MAINLAND PORTION OF THE STATE FOR
AWHILE.

.SHORT TERM FORECAST...
RAIN OR A RAIN SNOW MIX WILL FALL ALONG THE GULF COAST OVERNIGHT
BEFORE COLDER AIR CAN MOVE BACK INTO THE AREA AND TURN ALL
PRECIPITATION BACK TO SNOW. THE SNOW ADVISORY IN NORTHERN AND WESTERN
SUSITNA VALLEY IS EXPECTED TO END THIS AFTERNOON AND ALL SNOW SHOULD
TAPER OFF EARLY THIS EVENING. SNOW IN THE ILIAMNA AREA SHOULD CUT OFF
OVERNIGHT AS WELL.

.LONG TERM FORECAST...BIGGEST ITEM OF INTEREST IN THE LATER PART OF
THE WEEK IS THE POTENTIAL FOR SOME SIGNIFICANT SNOW IN SOUTH CENTRAL
ALASKA. THE PATTERN OF A 500 MB TROUGH OVER WESTERN ALASKA AND 850 MB
THERMAL PACKING OVER COOK INLET THROUGH THE SUSITNA VALLEY IN
COMBINATION WITH A SURFACE LOW IN THE NORTH GULF OR PRINCE WILLIAM
SOUND HAS THE POTENTIAL TO BRING SNOW INTO SOUTH CENTRAL ALASKA
INCLUDING ANCHORAGE. IT STILL IS A LITTLE EARLY TO CALL IN A SURE
THING BUT THE PATTERN SETTING UP IS FAVORABLE FOR SNOWFALL IN THE
ANCHORAGE AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 125 140 150 155 170 172 185.
         STORM 120 130 132 138 175 176.
         HEAVY FREEZING SPRAY 140 155 160 165 180 185.
FIRE WEATHER...NONE.

DEC 07