Small Craft Advisory 79, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
550 AM AKST THU JAN 24 2013

.ANALYSIS AND UPPER LEVELS...
THREE UPPER LEVEL LOWS CURRENTLY SURROUND THE STATE OF ALASKA.  THE
FIRST OF WHICH IS CENTERED NEAR THE BROOKS RANGE IS SLOWLY WORKING
ITS WAY INTO SOUTHCENTRAL...AND WILL BE THE NEXT SNOW PRODUCING
SYSTEM FOR THE SOUTHCENTRAL AREA. THE SECOND IS A STORM FORCE LOW
THAT IS NEARLY TO THE SHEMYA AREA...AND WILL BRING THAT AREA A ROUND
OF RAIN AND SNOW TODAY. THE UPPER LEVEL LOW THAT HAD BEEN CENTERED
OVER THE GULF OF ALASKA FOR THE PREVIOUS TWO DAYS IS SLOWLY WEAKENING
SOUTH OF THE ALASKA PENINSULA....AND CONTINUING TO BRING RAIN AND
SNOW SHOWERS TO THE EASTERN ALEUTIANS AND ALASKA PENINSULA.

.MODEL DISCUSSION...
THE MODELS HAVE COME INTO BETTER AGREEMENT WITH THE UPPER LEVEL LOW
MOVING INTO SOUTHCENTRAL THURSDAY EVENING...SO THERE IS NOW ENOUGH
CONFIDENCE TO BRING ADVISORY LEVEL SNOWFALL ACCUMULATION FORECASTS
INTO THE SUSITNA VALLEY. THE MODEL AGREEMENT THEN CONTINUES INTO
SUNDAY...AND THEN QUICKLY BEGIN TO STRUGGLE LATE SUNDAY WITH A SERIES
OF COMPLEX LOWS MOVING INTO THE ALEUTIANS. THERE IS ALSO SOME
DISAGREEMENT AS TO WHETHER A WEAK LOW WILL FORM OFF OF KODIAK ISLAND
ON MONDAY...CURRENTLY WE PREFER THE GFS/HPC SOLUTION WHICH BRINGS A
WEAK LOW INTO THE GULF THROUGH MONDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...AS STATED IN THE MODEL DISCUSSION ABOVE...THERE IS NOW
ENOUGH CONFIDENCE TO BRING ADVISORY LEVEL SNOWFALL FORECAST
ACCUMULATIONS INTO THE SUSITNA VALLEY STARTING THURSDAY EVENING. THE
SNOWFALL WILL CONTINUE SPREADING INTO THE MATANUSKA VALLEY AND
ANCHORAGE BOWL LATE THURSDAY NIGHT THROUGH FRIDAY AFTERNOON...THEN
INTO THE COPPER RIVER BASIN THROUGH SATURDAY. AT THIS MOMENT THE
MATANUSKA VALLEY LOOKS AS IF IT WILL STAY JUST UNDER ADVISORY LEVEL
SNOWFALL...BUT GREATER ACCUMULATIONS ARE CERTAINLY POSSIBLE ALONG
HIGHER ELEVATIONS IN AREAS SUCH AS HATCHERS PASS. TEMPERATURES BEHIND
WILL THEN QUICKLY FALL STARTING FRIDAY EVENING AS SKIES CLEAR AND
STRONG COLD AIR ADVECTION BEGINS...AND CONTINUE THROUGH THE WEEKEND.
MOST OF THE INTERIOR SECTIONS OF THE SUSITNA VALLEY AND COPPER RIVER
BASIN WILL FALL WELL BELOW ZERO THROUGH SUNDAY MORNING.

SOUTHWEST...
RAIN AND SNOW SHOWERS WILL CONTINUE TO FALL OVER THE ALASKA PENINSULA
TODAY AS THE WEAKENING LOW CONTINUES TO MEANDER BACK INTO THE GULF
THIS AFTERNOON. OTHERWISE...THE KUSKOKWIM DELTA WILL BE THE FIRST
AREA TO EXPERIENCE THE STRONG COLD AIR ADVECTION FROM THE WEST SIDE
OF THE DESCENDING UPPER LEVEL LOW THIS EVENING. AS A RESULT...A WIND
CHILL ADVISORY HAS BEEN ISSUED FOR WIND CHILL VALUES TO 45 BELOW LATE
TONIGHT THROUGH TOMORROW MORNING. COLD AIR WILL ALSO MOVE INTO THE
KUSKOKWIM VALLEY AND BRISTOL BAY THROUGH THE WEEKEND...HOWEVER WINDS
WILL BE MUCH LIGHTER SO WIND CHILLS WILL BE LESS OF A PROBLEM.

BERING SEA AND ALEUTIANS...
THE NEXT STORM FORCE LOW WILL BRING STRONG WINDS...RAIN...AND SNOW TO
THE WESTERN AND CENTRAL ALEUTIANS STARTING THIS MORNING. THE SYSTEM
WILL THEN REMAIN IN THE WESTERN ALEUTIANS FOR THE REMAINDER OF THE
WEEK.

.LONG TERM FORECAST...
THE LONG TERM FORECAST CONFIDENCE IS CURRENTLY QUITE LOW AT THE
MOMENT...ESPECIALLY EARLY NEXT WEEK WHEN THE MODELS STRUGGLE WITH THE
INTERACTION BETWEEN AN ALEUTIAN LOW AND RIDGE HOLDING OVER INTERIOR
ALASKA. THE EC IS CURRENTLY THE STRONGEST WITH THE INTERIOR
RIDGE...AND AS A RESULT IS ALSO THE FURTHEST WEST WITH THE LOW. THE
CURRENT FORECAST RELIES HEAVILY ON HPC GUIDANCE...WHICH IS WEAKER
WITH THE INTERIOR RIDGE...ALLOWING THE LOW TO PROGRESS FURTHER EAST
INTO THE ALASKA PENINSULA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY 145. WIND CHILL ADVISORY 155.
MARINE...STORM 176. GALE 130 172 175 411. HEAVY FREEZING SPRAY 130
160
FIRE WEATHER...NONE

DEK JAN 13