Small Craft Advisory 880, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST THU DEC 1 2011

.ANALYSIS AND UPPER LEVELS...THE BIG PICTURE IN THE UPPER LEVELS HAS
A RIDGE OFF THE WEST COAST OF THE UNITED STATES THAT FLATTENS AS IT
EXTENDS TO THE ALCAN BORDER. A LONG WAVE TROUGH EXTENDS OUT OF THE
ARCTIC AND OVER THE KAMCHATKA PENINSULA. IN BETWEEN THESE FEATURES A
SOUTHWEST TO NORTHEAST ORIENTED JET STREAM FLOWS OVER MOST OF THE
FORECAST AREA. THIS OVERALL PATTERN WILL AMPLIFY AS THE WEEKEND
APPROACHES WITH THE TROUGH DIGGING SOUTHWARD OVER THE WESTERN
ALEUTIANS AND THE RIDGE PUSHING NORTHWARD. THE RESULT WILL BE FOR THE
JET STREAM TO INCREASE IN STRENGTH AND BECOME ORIENTED SOUTH TO NORTH
OVER THE MAINLAND PART OF THE STATE. THIS PATTERN IS THE ONE THAT
BRINGS WARM WEATHER AND CHINOOK WINDS TO THE STATE.

.MODEL DISCUSSION...MODELS RANGE FROM DIFFERING ON SOME IMPORTANT
DETAILS IN THE EASTERN PORTION OF THE FORECAST ARE TO BEING A BIT OF
A MESS IN THE BERING SEA. THE BIG ISSUE IN THE BERING SEA WILL BE
WITH THE LOW THAT DEVELOPS SOUTH OF THE ALEUTIANS TONIGHT AND MOVES
INTO THE CENTRAL BERING SEA SATURDAY. THE GFS, NAM, AND ECMF ALL HAVE
THIS SYSTEM DEVELOPING AND STRENGTHENING BUT THE STORM TRACK AND
INTENSITY IS VERY DIFFERENT ON ALL THREE BY SATURDAY AFTERNOON. THE
GFS SHOWED VERY POOR RUN TO RUN CONSISTENCY BETWEEN THE 00Z AND 12Z
MODEL RUNS. THE 12Z NAM HAS BEEN A BIT OF A MIDDLE GROUND AND LOOKS
REASONABLE. THE 18Z NAM RUN SHOWS A SOLUTION CLOSE TO THE FASTER ONE
USED BY THE 12Z GFS SO THE HOPE IS THESE MODELS HAVE BEGUN TO LOCK ON
TO A GOOD SOLUTION.

.SHORT TERM FORECAST...PRECIPITATION FROM A DECAYING FRONT MOVING
THROUGH SOUTHWEST ALASKA WILL MOVE INTO SOUTH CENTRAL ALASKA THIS
EVENING. THIS WILL LEAVE SOME RESIDUAL SNOW SHOWERS IN SOUTHWEST
ALASKA AND BRING SOME MORE SNOW INTO SOUTH CENTRAL. WHILE SOUTH
CENTRAL HAS BEEN TEETERING ON THE EDGE OF THE RAIN SNOW LINE FOR THE
LAST DAY THERE HAS BEEN ENOUGH COLD ADVECTION SINCE THIS MORNING TO
KEEP PRECIPITATION AS SNOW OVERNIGHT. THE POSSIBILITY OF FREEZING
RAIN IN SOUTH CENTRAL ALASKA TONIGHT AND TOMORROW LOOKS MUCH LESS
THAN IT DID WHEN LOOKING AT THAT TIME FRAME YESTERDAY. ONE OF THE
MAIN FEATURES IS TO HAVE COLD NORTHERLY WINDS AT THE SURFACE THAT
KEEP IT BELOW FREEZING AS WARMER AIR ALOFT STREAMS OVER THE KENAI AND
CHUGACH MOUNTAINS FROM THE SOUTHEAST. SURFACE WINDS LOOK TO REMAIN
MOSTLY FROM THE SOUTH WHICH WILL KEEP THIS FROM HAPPENING. THEREFORE
IT LOOKS LIKE SNOW FOR TONIGHT INTO TOMORROW WITH THE NEXT SHOT OF
FREEZING RAIN BEING FRIDAY NIGHT.
THE BIG WARM UP AND MELTDOWN IN SOUTHERN ALASKA ON SATURDAY LOOKS TO
BE RIGHT ON COURSE. EXPECT STRONG SOUTH TO EAST WINDS AND RAIN
SATURDAY.

.LONG TERM FORECAST...ALSO ON COURSE IS THE BIG COOL DOWN BEGINNING
SUNDAY. FOR AS WARM AS SATURDAY LOOKS A COLD FRONT WILL MOVE IN
QUICKLY FROM THE WEST AND MAKE TO TO THE ALASKA AND ALEUTIAN RANGE BY
SATURDAY NIGHT. IT WILL MOVE THROUGH SOUTH CENTRAL SUNDAY AND COOL
THINGS DOWN AGAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 120 130 132 138 150 155 160 170 172 175 176 179 180 185
FIRE WEATHER...NONE.

DEC 11