Small Craft Advisory 964, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
530 PM ADT FRI OCT 20 2006

.DISCUSSION...

WATER VAPOR IMAGERY SHOWS A SLIGHTLY NEGATIVELY TILTED AMPLIFYING
TROUGH BETWEEN 150W AND 170W. MOISTURE IS STREAMING NORTHWARD FROM
THE TROPICS TO THE GULF OF ALASKA. THE CIRRUS SHIELD IS ALREADY
OVERSPREADING EASTERN PORTIONS OF SOUTHCENTRAL AND LOW LEVEL MOISTURE
IS NOW APPEARING ON THE MIDDLETON RADAR. A WEAK SURFACE LOW IS
LOCATED AROUND 52N 147W AND TRACKING NORTHWARD. THIS IS THE MAIN
FEATURE OF CONCERN FOR SOUTHCENTRALS FORECAST TONIGHT AND SATURDAY.
THE MODELS ARE IN FAIR AGREEMENT ON SLOWLY DEEPENING THIS LOW AS IT
TRACKS TOWARD PRINCE WILLIAM SOUND TONIGHT AND SATURDAY
MORNING...WITH COLD AIR FEEDING INTO THE BACK SIDE OF THE SYSTEM
AND THE UPPER TROUGH BECOMING SLIGHTLY MORE NEGATIVELY TILTED. THE
BIGGEST QUESTION IS THE EXACT TRACK WHEN IT REACHES THE NORTH GULF
COAST. THE 12Z MODEL RUNS WERE IN FAIR AGREEMENT THAT THE LOW WOULD
TRACK TO NEAR HINCHINBROOK ENTRANCE BY LATE SATURDAY MORNING AND THEN
ACROSS THE COPPER RIVER BASIN LATE SATURDAY. THE 18Z NAM INDICATES A
TRACK EAST OF CORDOVA. THIS WOULD HAVE HUGE RAMIFICATIONS ON THE
FORECAST FOR WEST OF THE COASTAL RANGE INCLUDING ANCHORAGE. TAKING
A CLOSER LOOK AT THE UPPER LEVEL FORCING...THERE IS A STRONG WESTERLY
JET RIDING SOUTH OF THE ALEUTIANS. THIS WILL AID IN MAINTAINING A
PROGRESSIVE PATTERN...MEANING THE UPPER TROUGH APPROACHING THE GULF
SHOULD CONTINUE TO PROGRESS EASTWARD WHILE THE LOW IS PUSHED
NORTHWARD. HOWEVER...AS THE TROUGH BECOMES MORE NEGATIVELY TILTED
THE LOW WOULD BE PUSHED SLIGHTLY WESTWARD. BOTTOM LINE...THERE IS
HIGH UNCERTAINTY IN THE PRECIP FORECAST FOR WEST OF PRINCE WILLIAM
SOUND. FOR NOW...WILL STICK CLOSE TO THE PREVIOUS FORECAST AND THE
12Z MODEL SOLUTIONS AND PROVIDE A LITTLE LESS DETAIL IN PARTS OF THE
FORECASTS UNTIL IT BECOMES CLEAR WHERE THE LOW IS HEADED.

HIGHLIGHTS OF THE FORECAST...GALE FORCE WINDS ALONG THE TRACK OF
THE LOW. LOTS OF RAIN FOR PRINCE WILLIAM SOUND AND SNOW IN THE
COPPER RIVER BASIN. PORTIONS OF THE COPPER RIVER BASIN WILL LIKELY
SEE ADVISORY AMOUNTS (6 INCHES)...BUT WILL HAVE TO WAIT TO FINE TUNE
LOCATIONS. FOR NOW WILL JUST UP CURRENT ADVERTISED AMOUNTS. WEST OF
THE COASTAL RANGE...A SLIGHT CHANCE OF OVERUNNING PRECIP AFTER
MIDNIGHT TONIGHT. COLD AIR ALOFT WILL WORK ITS WAY INTO COOK INLET
AND SUSITNA VALLEY SATURDAY...SO IF THERE IS MOISTURE PRESENT
FREEZING LEVELS WILL QUICKLY DROP AND THERE IS THE POTENTIAL FOR
THE FIRST SNOWFALL NEAR SEA LEVEL. EVEN WITH ENOUGH MOISTURE...DO
NOT EXPECT ANY SIGNIFICANT SNOWFALL AMOUNTS.

OUT WEST...A MATURE LOW CONTINUES TO SPIN WEST OF NUNIVAK ISLAND
AND PRODUCE DECENT SHOWERS OVER THE CENTRAL BERING AND INTO THE
KUSKOKWIM DELTA. THIS LOW WILL SLOWLY DRIFT OFF TO THE NORTH THE
NEXT COUPLE DAYS WITH DIMINISHING WINDS AND SHOWERS. A DEVELOPING
LOW IS CURRENTLY TRACKING TOWARD THE WESTERN ALEUTIANS. THE NEAR
ZONAL WESTERLY JET WILL TRACK THIS LOW QUICKLY EASTWARD ACROSS THE
SOUTHERN BERING SATURDAY AND THEN INTO THE GULF SUNDAY. MORE LOWS
WILL BE ON ITS TAIL HEADING INTO NEXT WEEK AS THE WESTERLY JET
REMAINS NEAR 50N.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 130 150 155 AND 176.

SEB OCT 06