Small Craft Advisory 217, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKST SAT MAR 9 2013

.ANALYSIS AND UPPER LEVELS...
A COMPLEX PATTERN ALOFT TODAY WITH THE JET STREAM DISPLACED WELL
SOUTH INTO THE PACIFIC. A WEAK CONGLOMERATION OF TROUGHS EXISTS WITH
A ROUGH AXIS EXTENDING FROM SIBERIA ARCING EASTWARD THROUGH THE
CENTRAL INTERIOR...CONNECTING TO TWO UPPER LOW CENTERS IN THE WESTERN
GULF OF ALASKA AND NORTHERN PACIFIC. THE MOST PROMINENT FEATURE ON
WATER VAPOR IMAGERY THIS MORNING IS A MATURE UPPER LOW IN THE
NORTHWESTERN PACIFIC...RESULTING IN HEAT/MOISTURE PUMPING INTO THE
WESTERN BERING AND BUILDING RIDGE FROM THE NORTH CENTRAL PACIFIC
THROUGH THE CENTRAL BERING ARCING TOWARD THE KAMCHATKA PENINSULA. A
SNEAKY FEATURE BETWEEN THE MAINLAND TROUGH AND THE PACIFIC LOW LURKS
OVER THE NORTHERN BERING. THE LOW AMPLITUDE SHORTWAVE EMBEDDED IN THE
FLOW WITH AN ATTENDANT 125KT JET STREAK WHILE WEAKENING ITSELF WILL
LIKELY AMPLIFY AS RIDGING BUILDS IN BEHIND IT OVER THE CENTRAL
BERING. AT THE SURFACE...THE PRESSURE PATTERN MIMICS THE UPPER LEVELS
PRETTY WELL. THE SOUTHCENTRAL IS EXPERIENCING SLIGHTLY ABOVE NORMAL
TEMPERATURES IN SOUTHEASTERLY FLOW. THE SOUTHWEST MAINLAND IS A MIX
BETWEEN NORTHWESTERLY FLOW/NEAR AVERAGE TEMPS BEHIND THE WEAK TROUGH
AND SOUTHWESTERLY FLOW OUT AHEAD OF THE APPROACHING WAVE.

.MODEL DISCUSSION...
GUIDANCE IS IN GOOD AGREEMENT WITH THE EVOLUTION OF THE UPPER LEVEL
PATTERN THROUGH THE MIDDLE OF THE WEEK. GENERAL CONSENSUS IS A
DEVELOPING SPLIT FLOW/REX BLOCK PATTERN AS A CLOSED HIGH BUILDS OVER
THE CENTRAL BERING SEA THROUGH THE CHUKCHI/BEAUFORT SEAS TO THE NORTH
OF A MIGRATORY UPPER LOW IN THE NORTH CENTRAL PACIFIC. THE DOMINANT
LONG-WAVE TROUGH WILL REMAIN CENTERED OVER KAMCHATKA WITH ANOTHER
OVER THE NORTHERN CANADIAN ARCTIC. SHORT RANGE ENSEMBLE FORECAST
WINDS PREFERRED FOR THE EAST WITH A GFS/ECMWF BLEND IN THE WEST.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...THE REMNANTS OF THE SOUTHWEST TROUGH FROM THE
PREVIOUS DAY SPINS IN THE WESTERN GULF KEEPING MUCH OF THE
SOUTHCENTRAL IN A WEAK SOUTHERLY FLOW AND NUMEROUS RAIN AND SNOW
SHOWERS ALONG THE NORTHERN GULF COAST. A WEAK DE-AMPLIFYING LEADING
TROUGH WILL CONTINUE TO OVERSPREAD A MID LEVEL CLOUD DECK OVER MOST
OF THE REGION TODAY EXCEPT FOR THE EASTERN PORTION OF THE COPPER
RIVER BASIN. A SLIGHT CHANCE FOR LIGHT SNOW IS POSSIBLE FOR THE COOK
INLET REGION WITH A BETTER CHANCE FROM TALKEETNA NORTHWARD. A HIGHER
PROBABILITY FOR SNOW WILL OVERTAKE THE REGION LATE MORNING SUNDAY
INTO SUNDAY AFTERNOON AS A SHORTWAVE TROUGH SLIDES FROM THE SOUTHWEST
INTERIOR INTO THE GULF OF ALASKA. MOST AREAS FROM TALKEETNA SOUTHWARD
THROUGH ANCHORAGE WILL SEE AROUND AN INCH OR LESS WITH AMOUNTS
INCREASING FROM KENAI SOUTHWARD THROUGH KACHEMAK BAY WITH 1 TO 3
INCHES POSSIBLE FOR KENAI SOUTHWARD. AFTER THE SYSTEM MOVES INTO THE
CENTRAL GULF LATE SUNDAY INTO MONDAY WE WILL TRANSITION TO A MORE
NORTHERLY FLOW ALOFT WITH INTERIOR HIGH PRESSURE RETURNING TO MORE OF
A COLDER OUTFLOW PATTERN NOT SEEN FOR A WHILE AROUND HERE. PERHAPS
WINTER 12/13'S DEATH RATTLE.

SOUTHWEST ALASKA...BRISTOL BAY AND KUSKOKWIM VALLEY REGIONS ARE
SEEING THE SNOW GRADUALLY TAPER OFF THIS AFTERNOON...MAINLY HANGING
AROUND THE ALASKA/ALEUTIAN RANGES. THE NEXT WAVE IS COMING ASHORE THE
KUSKOKWIM DELTA REGION. SNOWFALL WILL GRADUALLY INCREASE IN COVERAGE
AND INTENSITY THIS EVENING...SPREADING INTO BRISTOL BAY AND KUSKOKWIM
VALLEY REGIONS OVERNIGHT. WINDS WILL RAMP UP PRETTY QUICKLY AHEAD OF
THIS WAVE COMBINING WITH THE PRECIPITATION TO BRING A QUICK SHOT OF
BLIZZARD CONDITIONS TO THE SOUTHWEST. THE WORST CONDITIONS ARE
EXPECTED ALONG THE COASTAL AREAS WHERE WINDS WILL BE THE STRONGEST.
THE FRONT WILL EXIT THE AREA TOMORROW SETTING UP DRIER AND COLDER
CONDITIONS THROUGH MUCH OF THIS WEEK.

BERING SEA AND ALEUTIANS...A QUICK MOVING FRONT AND UPPER LEVEL
DISTURBANCE WILL SKIRT THE AREA TONIGHT BRINGING A QUICK SHOT OF SNOW
TO THE ALASKAN PENINSULA. GUSTY SOUTHERLY WINDS ASSOCIATED WITH A
KAMCHATKA LOW COMPLEX WILL CONTINUE THROUGH TUESDAY AS A FRONT SLOWLY
PUSHES EASTWARD AND STALLS OUT OVER THE WESTERN ALEUTIANS. GENERALLY
DRY CONDITIONS WILL EXIST OVER THE CENTRAL ALEUTIANS THROUGH MID
WEEK.

.LONG TERM FORECAST...
THE EXTENDED FORECAST IS A BIT MORE VARIABLE THAN USUAL CONSIDERING
WE ARE IN THE MIDDLE OF A LARGE SCALE PATTERN CHANGE IN THE COMING
DAYS. CURRENT GUIDANCE IS SUGGESTING A CONTINUATION OF A BLOCKING
PATTERN WITH COLD AIR REMAINING OVER MUCH OF THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155 161
MARINE...GALE 132 150 175 176 185
FIRE WEATHER...NONE

MTL MAR 13