Small Craft Advisory 1011, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST SAT DEC 12 2009

.ANALYSIS AND UPPER LEVELS...
AN ELONGATED UPPER LEVEL RIDGE IS STILL SPREAD ACROSS MUCH OF SOUTH
CENTRAL AND WESTERN ALASKA.  A STRONG UPPER LEVEL LOW IS CENTERED
OVER THE ARCTIC SEA JUST NORTH OF THE NORTH SLOPE.  A SECOND TROUGH
STRETCHES FROM THE SOUTHWESTERN BERING SEA SOUTHEASTWARD INTO THE
PACIFIC.

AT THE SURFACE...A WEAK AREA OF RIDGING EXTENDS THROUGH INTERIOR
ALASKA UNDERNEATH THE UPPER LEVEL RIDGE WHILE A WEAK SURFACE LOW IS
CENTERED BENEATH THE ARCTIC LOW.  TWO SURFACE LOWS ARE UNDERNEATH THE
ALEUTIAN TROUGH WITH ONE CENTERED OVER SHEMYA AND THE OTHER SEVERAL
HUNDRED MILES SOUTH OF DUTCH HARBOR

.MODEL DISCUSSION...
MODELS ARE GENERALLY CAPTURING THE CURRENT WEATHER PATTERN WELL.
MODELS ARE IN GENERAL AGREEMENT ON THE WESTERN RETROGRADE OF THE
UPPER LEVEL RIDGE AND THE SOUTHWESTERN PROGRESSION OF THE ARCTIC LOW
OVER THE NEXT SEVERAL DAYS. MODELS BEGIN TO DIVERGE EARLY TUESDAY IN
THE PROGRESSION OF THE UPPER LEVEL TROUGH OVER WESTERN AND CENTRAL
ALASKA. THIS ADDS MORE UNCERTAINTY IN SNOWFALL AMOUNTS ACROSS SOUTH
CENTRAL ALASKA.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...AREAS OF DENSE FOG WILL CONTINUE TO PERSIST THROUGH
TONIGHT AS LIGHT WINDS AND STEEP INVERSIONS PERSIST. HOWEVER...BY
SUNDAY EVENING AN UPPER LEVEL LOW OVER WESTERN ALASKA WILL BRING MUCH
COOLER TEMPERATURES WHICH WILL WEAKEN THE SURFACE INVERSION.  THIS
WILL ALLOW FOR MORE MIXING TO OCCUR AND THE REDUCTION OF FOG.   A
TROUGH OF LOW PRESSURE AT THE SURFACE WILL BRING THE POSSIBILITY OF
SNOW STARTING MONDAY AND CONTINUE TO BRING THE CHANCE OF SNOW THROUGH
MUCH OF THE WEEK...ESPECIALLY ALONG THE GULF COAST. SNOWFALL AMOUNTS
IN THE ANCHORAGE BOWL AREA WILL DEPEND ON THE PROGRESSION OF THE
SURFACE TROUGH.

.WEST...THE STRATUS AND FOG THAT HAS BEEN COVERING MUCH OF THE AREA
WILL BEGIN TO DISSIPATE AS THE ARCTIC LOW MOVES SOUTHWESTWARD INTO
THE AREA BRINGING OFFSHORE WINDS AND COOLER TEMPERATURES ALOFT.
CURRENT MODELS INDICATE THE REGION WILL REMAIN RELATIVELY
PRECIPITATION FREE OVER THE NEXT FEW DAYS AND SURFACE TEMPERATURES
WILL CONTINUE TO DROP.

.ALEUTIANS...
THE SURFACE LOW CENTERED NEAR SHEMYA WILL RETROGRADE NORTHWESTWARD
WHICH WILL SLOWLY LOWER PRECIPITATION AND ASSOCIATED WINDS OVER THE
WESTERN ALEUTIANS. A SURFACE LOW SOUTH OF THE ALEUTIAN ISLANDS WILL
PROGRESS NORTHEASTWARD OVER THE NEXT FEW DAYS WHICH WILL INCREASE THE
CHANCE FOR PRECIPITATION AND WIND OVER THE CENTRAL AND EASTERN
ALEUTIAN ISLANDS.

.LONG TERM FORECAST...

AS THE ARCTIC LOW CONTINUES TO PROGRESS SOUTH AND WESTWARD...IT WILL
BRING MUCH COOLER TEMPERATURES ACROSS MUCH OF WESTERN AND PARTS OF
CENTRAL ALASKA.  MODELS ARE SUGGESTING ANOMALOUSLY COLD TEMPERATURES
ACROSS SOUTH CENTRAL ALASKA BY THE END OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...NONE
FIRE WEATHER...

EN DEC 09