Small Craft Advisory 33, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
340 PM AKST THU JAN 10 2013

.ANALYSIS AND UPPER LEVELS...
THE SYSTEM WHICH BROUGHT LIGHT PRECIPITATION TO SOUTHCENTRAL EARLY
THIS MORNING HAS MOVED INTO FAR NORTHEASTERN AK AND YUKON TERRITORY
WITH RESIDUAL CLOUDY SKIES AND SOME PATCHY FOG IN IT'S WAKE.
TRANSITORY UPPER-RIDGING BEHIND IT IS SLIDING EAST AHEAD OF A
NORTHEAST MOVING VIGOROUS SHORTWAVE TROUGH IN THE EASTERN BERING SEA.
THE EASTERN BERING TROUGH SUPPORTS A NW TO SE ORIENTED FRONT WITH
VARIOUS WAVES OF SURFACE LOW PRESSURE ALONG IT'S AXIS. ONE IS
CENTERED JUST NORTHEAST OF THE PRIBILOF ISLANDS PUSHING NORTH TOWARDS
SAINT LAWRENCE ISLAND. ANOTHER HAS DEVELOPED TODAY AROUND 200 MILES
SOUTHEAST OF SAND POINT AND IS ROTATING NORTHEAST TOWARDS KODIAK
ISLAND. FURTHER WEST...BROAD CYCLONIC AND UNSTABLE FLOW EXISTS OVER
THE WEST-CENTRAL ALEUTIAN CHAIN EVIDENCED BY THE SHOWER COVERAGE ON
SATELLITE IMAGERY. THE FLOW ALOFT IS ANCHORED BY A COMPLEX UPPER-LOW
BETWEEN THE KAMCHATKA PENINSULA AND ATTU. ALSO OF NOTE IS A
STRENGTHENING LOW PRESSURE SYSTEM AROUND 900 MILES SOUTH OF ATKA
TRACKING NORTH.

.MODEL DISCUSSION...
MODELS HAVE AN ADEQUATE HANDLE ON THE MAIN WEATHER FEATURES AND HAVE
DECENT AGREEMENT ON THE TREND TO A SUBSTANTIALLY MORE AMPLIFIED
UPPER-LVL PATTERN FOR THE WEEKEND.

ACROSS THE BERING SEA AND CHAIN...THE PACIFIC LOW SOUTH OF THE CHAIN
WILL MOVE TO NEAR ATKA EARLY FRI EVENING AND TRACK TO AROUND 170
MILES WEST OF SAINT PAUL SAT EVENING BEFORE DRIFTING TO THE FAR
NORTHERN BERING SEA ON SUN. THE UKMET AND GEM GLOBAL ARE
APPROXIMATELY 100 MILES EAST OF THE GFS/ECMWF/NAM CONSENSUS ON THE
LOW'S POSITION SAT AND SUN...BUT GENERALLY AGREE ON THE SPIRIT OF THE
TRACK. MEANWHILE...ENERGY FROM THE BROAD COMPLEX UPPER-LOW BEGINS
DIGGING THE OVERALL LONGWAVE TROUGH OVER THE ALEUTIANS AND BERING
WHILE AMPLIFYING THE RIDGE IN THE GULF/NORTHEAST PACIFIC.

ACROSS THE SOUTHERN MAINLAND/GULF...THE FRONT IN THE EASTERN BERING
MOVES ASHORE SW AK OVERNIGHT AND THEN WEAKENS AND SHEARS APART AS THE
SUPPORTING SHORTWAVE ENERGY PARTIALLY SPLITS OFF WITH ONE LOBE
CONTINUING NORTH PAST ST LAWRENCE ISLAND INTO EASTERN SIBERIA...AND
THE OTHER EJECTING INTO THE NORTHERN GULF THROUGH FRI. WITH THIS
TROUGH PASSAGE...A PRONOUNCED UPPER-LVL RIDGE BEGINS TO BUILD AS THE
AFOREMENTIONED BERING/ALEUTIAN TROUGH DIGS. THE RIDGE AXIS LOOKS TO
BE NEAR 140W LONGITUDE...WHICH WOULD KEEP THE ENTIRE SOUTHERN
MAINLAND ON IT'S 'DIRTY' SIDE AS THE 300 MB JET BECOMES SOUTHWESTERLY
AND STRENGTHENS WITH TIME. THIS SHOULD ALLOW COPIOUS MOISTURE AND
ANOMALOUSLY WARM AIR TO ADVECT DIRECTLY AND PERSISTENTLY INTO THE
REGION. 850 MB TEMPERATURES OF -7 CELSIUS OVER THE ANCHORAGE AREA ARE
DEPICTED RISING TO NEAR 0 CELSIUS LATE SAT AND TO POSSIBLY +5 CELSIUS
ON SUN WITH COMMENSURATE NUMBERS OVER BRISTOL BAY AND KODIAK ISLAND.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
THE SOUTHERN WAVE OF LOW PRESSURE ALONG THE EASTERN BERING FRONT WILL
TRAVERSE KODIAK ISLAND TONIGHT AND THEN TRACK JUST SOUTHEAST OF
MIDDLETON ISLAND ON FRI BEFORE WEAKENING IN THE EASTERN GULF FRI
NIGHT. AREAS NORTH AND WEST OF THE CHUGACH/KENAI RANGES SHOULD
GENERALLY JUST SEEING PERIPHERAL SNOW SHOWERS DUE TO THE WAVE
REMAINING FAR ENOUGH OFF-SHORE AND THE FRONT ITSELF SHEARING APART AS
IT APPROACHES WITH THE BULK OF SUPPORTING UPPER-ENERGY DEFLECTED
SOUTH. THUS THE STEADIEST PRECIPITATION WITH THIS SYSTEM SHOULD BE
CONFINED TO COASTAL AREAS/PRINCE WILLIAM SOUND. KODIAK ISLAND SHOULD
SEE A BREAK IN THE ACTION AS THE FLOW BECOMES OFF-SHORE BRIEFLY ON
FRI.

FORECAST CHALLENGES THEN TURN TO THE FIRST OF MANY WAVES OF ENERGY
TRANSPORTING MOISTURE TO THE REGION. INITIALLY THIS WILL BE WITH A
WARM FRONT ASSOCIATED WITH THE NORTH PACIFIC SYSTEM TRACKING TO THE
ALEUTIANS/BERING. WHILE NEARLY ALL PRECIPITATION SHOULD EVENTUALLY
TREND TO RAIN AS THE WEEKEND WEARS ON...THERE IS A QUESTION AS TO
WHETHER AN INITIAL COOL DOWN-INLET COMPONENT TO THE WIND COUPLED WITH
THE WARMER AIR OVERRIDING IT COULD SUPPORT A PERIOD OF FREEZING RAIN
ACROSS THE ANCHORAGE BOWL AND/OR OTHER SHELTERED LOW-LYING AREAS
INLAND FROM THE COAST. FOR NOW...HAVE INCLUDED A SLIGHT CHANCE...BUT
IT BUT IT BEARS WATCHING. THERE IS ALSO SOME UNCERTAINTY WHETHER
THERE WILL BE SOME DOWNSLOPING TO RETARD PRECIPITATION INITIALLY ON
SAT ACROSS THE BOWL AND MATANUSKA VALLEY AS EASTERLY TURNAGAIN ARM
WINDS INCREASE. THE OVERALL FLOW ALOFT IS GOING MORE SOUTHERLY TO
SOUTHWESTERLY AND BELIEVE THIS STRENGTHENING UP INLET TREND SHOULD BE
ENOUGH TO ALLOW PRECIPITATION TO BE SOMEWHAT WIDESPREAD...ALBEIT
LIGHT. PRECIPITATION ON SUN HOWEVER HAS POTENTIAL TO BE MODERATE TO
HEAVY...AND CONSIDERING FREEZING LEVELS RISING TO NEAR OR ABOVE AREA
MOUNTAIN LEVELS AND A MELTING SNOWPACK...FLOODING MAY BECOME A
CONCERN IN SOUTHCENTRAL ALASKA. PLEASE SEE THE SPECIAL WEATHER
STATEMENT FOR MORE DETAILS. THE WARM ADVECTION SHOULD ALSO SUPPORT
RESPECTABLE AMOUNTS OF FOG OVER THE GULF OF AK THIS WEEKEND.

SOUTHWEST/AKPEN...
PARTIAL SPLITTING OF THE UPPER ENERGY DOES NOT OCCUR OVER THE SW
MAINLAND AS THE FRONT SWINGS THROUGH FROM THE AKPEN...SO SHOULD SEE A
SWATH OF SNOW ENVELOP THE REGION TONIGHT...MIXING WITH RAIN OVER FAR
SOUTHERN BRISTOL BAY WHERE TEMPERATURES ARE WARMER. WEAK SHORTWAVE
RIDGING IN IT'S WAKE ON FRI IS SHORT-LIVED FOR SW AK...WITH A RETURN
OF MOISTURE FROM THE APPROACHING WARM FRONT BRINGING MORE
PRECIPITATION (SNOW AND RAIN) OVERNIGHT FRI INTO SAT. INITIAL BRIEF
SOUTHEASTERLY FLOW MAY DOWNSLOPE AREAS IMMEDIATELY WEST OF THE
ALEUTIAN/ALASKAN RANGE...BUT PRECIP SHOULD QUICKLY FILL IN AS FLOW
GOES MORE SOUTHERLY. SHOULD SEE GALES RE-EMERGE ALONG MARINE AREAS
ADJACENT TO THE KUSKOKWIM DELTA AND BRISTOL BAY. WINDS MAY GUST TO
NEAR STORM FORCE OUT BAYS BAYS/PASSES/CHANNELED TERRAIN FRI NIGHT
ALONG THE AKPEN AND WESTERN CAPES. PRECIPITATION ALONG THE AKPEN
LOOKS SAFELY ALL RAIN.

BERING SEA/ALEUTIANS...
FORECAST CHALLENGES MAINLY REVOLVE AROUND THE STRONG NORTH PACIFIC
LOW. A SQUEEZED PRESSURE GRADIENT WITH IT'S APPROACH WILL SUPPORT
WIDESPREAD GALES TO MIN STORM FORCE WINDS. WINDS WILL BE BRISK BUT
ARE NOT EXPECTED TO REACH HURRICANE FORCE/HIGH WIND WARNING
LEVELS...AS THE LOW WILL ALREADY HAVE REACHED PEAK INTENSITY AND BE
SLOWLY FILLING BY THE TIME IT'S CORE OF WINDS ADVANCE ON THE CHAIN.
WARM ADVECTION SHOULD REACH THE PRIBILOF ISLANDS AS WELL...THOUGH
PRECIPITATION  WILL PROBABLY START AS WET SNOW AS THE PRECIP SHIELD
ARRIVES THERE FRI NIGHT. FURTHER WEST...AS THE COMPLEX UPPER-LOW
DRIFTS A BIT SOUTH AND AWAY FROM THE FAR WESTERN CHAIN...TEMPERATURES
ALOFT SHOULD WARM A TOUCH...WITH THE DECREASED INSTABILITY HELPING TO
REDUCE THE SHOWER COVERAGE IN THE AREA.

.LONG TERM FORECAST...
UPPER-LVL PATTERN STILL LOOKS MILD AND WET TO START THE NEXT WEEK
OVER THE SOUTHERN MAINLAND...THOUGH THE UPPER JET MAY LOOSEN IT'S
STRANGLEHOLD TUE/WED AND ALLOW TEMPS TO MODERATE AND COOL. THE
PATTERN DOES NOT LOOK DRY...BUT DOES NOT LOOK QUITE AS BLOCKED AND
WET. ACROSS THE BERING/ALEUTIAN CHAIN...CONDITIONS LOOK RATHER BENIGN
WITH WEAK DISTURBANCES ROTATING THROUGH THE FLOW BUT NO STRONG
DEFINED FEATURES.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM...170 172 175
         GALE...120 130 132 136 137 138 140 150 155 165 171 176 351
                352 412 413 414
         HEAVY FREEZING SPRAY...140
FIRE WEATHER...NONE

MALOY