Small Craft Advisory 712, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
503 AM AKDT FRI SEP 11 2015

.ANALYSIS AND UPPER LEVELS...THE PATTERN REMAINS QUITE ACTIVE
ACROSS THE ENTIRE AREA. THE JET IS VERY AMPLIFIED RIDING UP AND
OVER A RIDGE OVER THE WESTERN BERING AT 85 TO 95 KT. IT THEN
DIVES DUE SOUTH SHARPLY OVER THE CENTRAL BERING IN SUPPORT OF THE
LONG WAVE TROUGH CENTERED OVER THE WESTERN HALF OF THE STATE. IT
THEN DRIVES INTO THE SOUTHEASTERN PANHANDLE OF AK AT 120 TO 130
KT. WITHIN THE TROUGH WE FIND OUR DECAYING UPPER LEVEL LOW CENTER
OVER BRISTOL BAY. SO WORKING FROM WEST TO EAST...SENSIBLE WEATHER
IS DRIVEN BY WIDESPREAD NORTH TO NORTHWEST FLOW BRINGING SOME COLD
AIR CUMULUS AND SHOWERS OVER MUCH OF THE BERING AND EASTERN
ALEUTIANS. BRISTOL BAY IS EXPERIENCING A MIX OF SHOWERS UNDER THE
LOW CENTER AND SOME FOG WITH ONSHORE FLOW ON THE BACKSIDE OF IT.
FOR SOUTHCENTRAL...THE PRIMARY FRONT HAS CLEARED THROUGH THE
COPPER RIVER BASIN AND WINDS HAVE GENERALLY BEGUN TO DIMINISH. ALL
OF THE CONVECTION WE SAW THU AFTERNOON HAS WANED DURING THE
OVERNIGHT HOURS. WEAK PERTURBATIONS WRAPPING AROUND THE UPPER
LEVEL CENTER ARE TRACKING FROM THE KODIAK AREA TOWARD THE GULF
COAST. THESE WILL BE THE BIGGEST CHALLENGES TODAY.

&&

.MODEL DISCUSSION...SYNOPTICALLY MODELS REMAIN IN SOLID SHAPE WITH
DECENT OVERALL AGREEMENT. BUT AS HAS BEEN THE CASE THE PAST FEW
DAYS IN THIS ACTIVE PATTERN...THERE IS DISAGREEMENT ON SOME OF
THE FINER DETAILS. AND THESE SMALLER SCALE FEATURES WILL BE
CRITICAL ELEMENTS FOR THE SHORT-TERM FORECAST. OUT WEST...A BLEND
OF THE EC AND GFS WAS USED WITH FAIRLY LARGE SYSTEMS DOMINATING
THE PATTERN. THE GLOBAL MODELS HAVE BEEN IN TIGHT AGREEMENT IN
HANDLING THE WINDS...PRECIPITATION...AND WAVES FROM THE REMNANTS
OF TYPHOON KILO. SO FORECAST CONFIDENCE IS HIGH IN THAT
DEPARTMENT. FOR SOUTHCENTRAL...THE NAM MODEL WAS USED TO IMPART
SOME MORE DETAIL. THE STRUGGLE WILL CONTINUE TO BE TIMING EACH
INDIVIDUAL IMPULSE AND THE SHOWERS AND WINDS ASSOCIATED WITH THEM.

&&

.MARINE...INSTABILITY OVER THE NORTHERN GULF COULD LEAD TO ANOTHER
ROUND OF SOME ISOLATED THUNDERSTORMS LATER TODAY. A SHORTWAVE IS
TAKING SHAPE ON SATELLITE JUST SOUTHEAST OF KODIAK. AS IT SLIDES
NORTHEAST WITH A COLD POOL ALOFT...IT SHOULD BE ENOUGH TO TRIGGER
SOME CONVECTION THROUGH THE NORTHERN GULF UP INTO PRINCE WILLIAM
SOUND. THIS DOES NOT LOOK TO BE A WIDESPREAD EVENT. BUT IF A FEW
CELLS DO DEVELOP...THEY COULD PRODUCE SOME SMALL HAIL AND GUSTY
WINDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...FRI AND
SAT)...ANOTHER WET AND GUSTY DAY IS IN STORE FOR FOR MOST OF THE
AREA. THE KENAI AND MIDDLETON RADARS ARE ALREADY PICKING UP ON THE
NEXT SHORTWAVE SWINGING THROUGH THE SOUTHERN KENAI PENINSULA. AS
THIS FEATURE MOVES THROUGH COOK INLET...THE SOUTHEAST TO
NORTHWEST GRADIENT SHOULD TIGHTEN UP THIS MORNING. THIS WILL LEAD
TO A SLIGHT UPTICK IN SOUTHEAST WINDS THROUGH TURNAGAIN ARM AND
THE COPPER RIVER BASIN. HOWEVER...UNLIKE THE PAST FEW DAYS...THESE
WINDS WILL NOT BE AS SIGNIFICANT ACROSS THE ANCHORAGE BOWL WITH
ONLY SOUTH AND WEST ANCHORAGE PICKING UP MAYBE 15 MPH. SIMILAR TO
THU THOUGH WILL BE THE CONVECTIVE POTENTIAL ACROSS PORTIONS OF THE
AREA. MODELS ARE STILL KEYING IN ON SOME INSTABILITY THIS
AFTERNOON...MAINLY OVER THE KENAI MOUNTAINS. AS THE REMNANTS OF
THE UPPER LEVEL LOW TRAVERSE THE AREA...AND IF WE CAN SEE SOME
BREAKS IN THE CLOUD COVER...IT SHOULD BE ENOUGH TO TRIGGER SOME
ISOLATED THUNDERSTORMS. THIS ALSO APPLIES TO EASTERN PRINCE
WILLIAM SOUND...INCLUDING VALDEZ AND CORDOVA.

SATURDAY WILL BRING ANOTHER SHORTWAVE SWEEPING THROUGH THE AREA
COURTESY OF AN UPPER LEVEL LOW PARKED NEAR THE SEWARD PENINSULA.
THIS WILL BRING MORE WIDESPREAD RAIN TO THE AREA. SOUTHWEST FLOW
OPENS UP IN ADVANCE OF THIS FEATURE AND HELPS TO ADD PLENTY OF
MOISTURE INTO THE COLUMN. THIS SHOULD MAKE FOR SOME MODERATE
RAINFALL...PARTICULARLY BETWEEN LATE MORNING AND MID-
AFTERNOON...FOR COOK INLET. THIS SYSTEM SHOULD TRACK QUICKLY
THROUGH THE COPPER RIVER BASIN BY EARLY SUNDAY MORNING. SUNDAY
SHOULD BRING A BRIEF DRYING TREND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

DISTURBANCES WILL MOVE ACROSS THE AREA IN RAPID-FIRE SUCCESSION
OVER THE NEXT COUPLE OF DAYS...CULMINATING WITH THE ARRIVAL OF
DEEP TROPICAL MOISTURE FROM A SYSTEM APPROACHING FROM THE WEST
TOWARD SUNDAY AND MONDAY. THIS WILL KEEP AT LEAST A CHANCE OF
RAIN IN THE FORECAST FOR MOST AREAS DURING THIS TIME

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

A WELL-DEFINED DISTURBANCE IS CURRENTLY MOVING SOUTH ACROSS THE
ALASKA PENINSULA. ITS PASSAGE LATER THIS MORNING WILL LIKELY HELP
RAISE WINDS ESPECIALLY THROUGH CHANNELED TERRAIN.
OTHERWISE...FAIRLY BENIGN CONDITIONS FOR THIS TIME OF THE YEAR
WILL ENCOMPASS MOST OF THE BERING UNTIL SATURDAY NIGHT...WHEN
WINDS WILL BEGIN TO INCREASE AND RAIN BEGINS TO DEVELOP AND
INTENSIFY OVER THE NORTHERN AND WESTERN BERING AHEAD OF A STRONG
DISTURBANCE WITH DEEP TROPICAL MOISTURE ASSOCIATED WITH IT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A WEAKENING LOW OVER THE NORTH GULF COAST LATE SATURDAY WILL BRING
A BRIEF PERIOD OF OUTFLOW WINDS TO THE GULF COAST WITH RAIN TO
MUCH OF SOUTHCENTRAL INTO SUNDAY WHEN IT WILL BEGIN TO DISSIPATE.
OVER THE SOUTHWEST COAST...A WEAK FRONTAL SYSTEM WILL BRING
WIDESPREAD RAIN TO THE SOUTHWEST MAINLAND...WHICH WILL QUICKLY
BECOME INVIGORATED ON SUNDAY BY THE APPROACHING REMNANTS OF
TYPHOON KILO THAT WILL BE MOVING FROM THE KAMCHATKA PENINSULA INTO
THE BERING SEA. THIS SYSTEM WILL THEN BECOME THE FOCAL POINT FOR
THE WEATHER THROUGHOUT THE FORECAST AREA INTO EARLY NEXT WEEK.
WHILE THE CENTRAL PRESSURE OF THIS SYSTEM WILL BE UNIMPRESSIVE
(AROUND 990 MB)...A TIGHT PRESSURE GRADIENT BETWEEN THIS LOW AND A
BROAD AREA OF HIGH PRESSURE OVER THE ALEUTIANS WILL BRING WESTERLY
GALE FORCE WINDS STRETCHING FROM THE BERING SEA TO THE SOUTHWEST
COAST LATE SUNDAY-MONDAY. BECAUSE OF THIS LONG FETCH...15 TO 20 FT
SEAS WILL DEVELOP FROM THE PRIBILOF ISLANDS TO NEAR THE KUSKOKWIM
DELTA COAST...BRINGING THE POSSIBILITY OF COASTAL EROSION FOR THAT
AREA INTO MONDAY. AFTER THE REMNANTS OF THIS LOW WEAKEN OVER THE
AREA ON TUESDAY...THE MODELS ARE TRENDING MUCH WEAKER WITH
RIDGING OVER THE BERING SEA AND INSTEAD BRING A SERIES OF WEAK
SYSTEMS TO THE REGION THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL
KEEP ACTIVE WEATHER OVER MUCH OF THE REGION INTO MID
WEEK...HOWEVER AT THIS POINT NO MAJOR SYSTEMS ARE EXPECTED.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 130.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...DEK