Small Craft Advisory 863, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKDT MON OCT 26 2009

CORRECTION FOR TYPOS

.MODEL DISCUSSION...
OVERNIGHT...THE MODELS IN THE IMMEDIATE SHORT TERM WERE NOT
INITIALIZING WELL IN HANDLING A LOW MOVING TOWARDS YAKUTAT. ALL OF
THE MODELS SEEMED TO BE TOO FAST WITH WINDS THAT WERE GENERALLY
UNDERDONE. OUT WEST THE MODELS SEEMED TO HAVE A PRETTY GOOD HANDLE ON
A SERIES OF LOWS OVER THE BERING. THE OVERALL PACKAGE HAD HEAVY GFS
THROUGHOUT THE MAJORITY OF THE PACKAGE. BEYOND THE SHORT TERM ...
DIFFERENCES START TO DEVELOP...AND THOSE DETAILS ARE DISCUSSED IN THE
LONG TERM FORECAST BELOW.

.ANALYSIS AND UPPER LEVELS...
ALASKA REGION IS EMBEDDED WITHIN A HIGH AMPLITUDE LONG-WAVE TROUGH. A
WEAKENING UPPER LEVEL LOW OVER THE BERING IS DIPPING SOUTH. A
SHORTWAVE WEST OF THE KENAI PENINSULA IS WEAKENING AND A STRONG
VORT-MAX ON THE SOUTH SIDE OF THE LOW IS POISED TO EJECT OUT OF
THE CYCLONIC ROTATION INTO THE EASTERN BERING. AT THE SURFACE A
STACKED LOW NEAR YAKUTAT IS MOVING ONSHORE. MEANWHILE AN EAST - WEST
ORIENTED TROUGH EXTENDS TO THE WEST OF THE LOW THROUGH PRINCE WILLIAM
SOUND.  A SHORT-WAVE TROUGH AND LOW LEVEL ARCTIC FRONT ARE SLOWLY
PIVOTING OFF TO THE NORTHEAST RESULTING IN CONTINUED RAIN AND SNOW
SHOWERS ACROSS THE REGION. A CLOSED UPPER LOW CONTINUES TO DROP
SOUTHEASTWARD ACROSS THE CENTRAL BERING. MULTIPLE SURFACE LOWS HAVE
FORMED IN RESPONSE TO THE SHORT-WAVE ROTATING AROUND THE UPPER
CENTER.

.SHORT TERM FORECAST...
A WEAK LOW IN WESTERN PRINCE WILLIAM SOUND WILL BE DEVELOPING THIS
AFTERNOON. THIS LOW...COUPLED WITH COLD AIR ADVECTION AND AN
ADVANCING SHORTWAVE WILL HELP TO BRING SNOW TO THE ANCHORAGE AREA.
WHILE NOT AS IMPRESSIVE AS IT LOOKED YESTERDAY...SNOW WILL BE SEEN
ALONG TYPICAL UPSLOPE AREAS OF THE HILLSIDE TODAY. EVEN THOUGH THE
FREEZING LEVELS JUMPED CLOSE TO 1000 FEET OVERNIGHT...THE MID LEVELS
CONTINUE TO COOL ANYWHERE FROM 2 TO 4 DEGREES IN 12 HOURS. IT WILL
TAKE A WHILE TO COOL ANCHORAGE ENOUGH TO HAVE SNOW ACCUMULATE ... A
WINTERY MIX OF RAIN MIXING WITH SNOW WILL BE NOTED THROUGHOUT THE
DAY. THE BRUNT OF THE ENERGY ASSOCIATED WITH THE AFOREMENTIONED
VORT-MAX IS NOW FURTHER SOUTH AND EAST THAN LAST NIGHT...BRINGING
DOWN THE ACCUMULATION TOTALS TO AN INCH OR LESS. MID WEEK AN UPPER
LEVEL TROUGH WILL EXIT THE REGION LEADING TO A DRYING TREND ACROSS
SOUTHCENTRAL.

OUT WEST....THE SHORT-WAVE TROUGH SITTING OVER SOUTHWEST
ALASKA CONTINUES TO PIVOT NORTHEASTWARD ...RESULTING IN
CONTINUED AREAS OF LIGHT PRECIPITATION ALONG AND JUST AHEAD OF IT.
THE SHORT-WAVE TROUGH WILL COMPLETELY SHEAR APART TODAY AS THE STRONG
BERING SHORT-WAVE SHOOTS THROUGH THE AREA INTO THE GULF. WESTERLY LOW
LEVEL FLOW WILL INCREASE SO THAT AREAS OF LIGHT SNOW WILL LIKELY
PERSIST ALONG THE UPSLOPE OF THE ALASKA AND ALEUTIAN RANGES.
TEMPERATURES ALOFT WOULD APPEAR TO SUPPORT MAINLY SNOW ACROSS THE
REGION...BUT IT IS STILL EARLY IN THE SEASON AND SEA SURFACE
TEMPERATURES IN THE LOWER 40S ARE RESULTING IN A WARM MARINE LAYER
THEREFORE...EXPECT A MIX OF RAIN AND SNOW. RIDGE WILL BUILD IN BEHIND
THE LOW COMPLEX...PROVIDING A BRIEF BREAK IN THE WEATHER BEFORE A
MAJOR STORM FORCE LOW MOVES TO THE WESTERN BERING AND ALEUTIANS MID
WEEK.

.LONG TERM FORECAST...
THE LONG TERM GUIDANCE CONTINUES TO BE PLAGUED BY UNCERTAINTY. BEYOND
THURSDAY ... GLOBAL MODELS STRUGGLE WITH HOW TO HANDLE THE REMNANTS
OF TROPICAL STORM LUPIT IN THE WESTERN ALEUTIANS. THE LATEST RUNS OF
THE GFS FULLY DIVERGE FROM EACH OTHER WITH THE 25/12Z GFS DRIFTING
SOUTH OF THE ALEUTIAN CHAIN...THE 26/00Z GFS DRIFTING INTO THE BERING
AND THE 26/06Z GFS DRIFTING NORTH TOWARDS SHEMYA. THE GFS ALWAYS HAS
AN INHERENT PROBLEM OF BREAKING DOWN FAIRLY WELL ESTABLISHED RIDGES.
MEANWHILE THE ENSEMBLE MEAN GUIDANCE IS MUCH CLOSER TO THAT OF THE
LATEST 06Z SOLUTION...BUT THE INDIVIDUAL MEMBERS ARE ALL OVER...AND
THE 500MB HEIGHT ENSEMBLE STANDARD DEVIATION REMAINS MANY DEVIATIONS
BEYOND THE NORM...LEAVING LITTLE FAITH IN DETAILS. THE ECMWF HAS BEEN
A LITTLE MORE STABLE FROM RUN TO RUN...EVENTUALLY WORKING THE STORM
UP THE WESTERN PERIPHERY OF THE RIDGE ... TOWARDS SHEMYA BEFORE
DISSIPATING...SIMILAR TO THE LATEST GFS SOLN. PROBLEMS ARE NOT AS
EVIDENT OUT EAST AS THEY ARE IN THE WEST...BUT ALL BIG ISSUES ARE
DERIVED FROM THE INABILITY TO ACCURATELY DEAL WITH LUPIT. WHILE
CONFIDENCE IS SLOWLY INCREASING WITH A TREND TOWARDS STABLE
SOLNS...IT STILL REMAINS LOW BEYOND THE END OF THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...130 132 136 141 150 155 170
FIRE WEATHER...NONE

SHEA OCT 09