Small Craft Advisory 807, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
506 AM AKDT THU OCT 15 2015

.ANALYSIS AND UPPER LEVELS...
ALASKA AND THE NORTHERN PACIFIC REMAIN IN A PROGRESSIVE HIGH
AMPLITUDE PATTERN THIS MORNING. OVER THE WESTERN HALF OF THE
REGION...A BROAD TROUGH WITH AN LARGE CLOSED LOW IS LOCATED ON THE
BERING SIDE OF THE KAMCHATKA PENINSULA WITH A BROAD RIDGE
MIGRATING EASTWARD THROUGH THE CENTRAL ALEUTIANS. TO THE
EAST...ANOTHER BROAD AND DEEP TROUGH WITH A CLOSED LOW IS CENTERED
ALONG 153W WITH A BUILDING RIDGE TO THE EAST SPANNING FROM
SOUTHEASTERN ALASKA SOUTHWARD TO THE NORTHERN CALIFORNIA
COAST. THE POLAR JET IS CURRENTLY LOCATED TO THE SOUTH OF THE
REGION WITH SPEED MAXIMA OF ABOUT 130 KT ALONG THE BERING RIDGE
AND ABOUT 90 KT ALONG THE RIDGE ALONG SOUTHEASTERN ALASKA.

AT THE SURFACE...AN OCCLUDED FRONT ASSOCIATED WITH A 983MB LOW
NEAR KAMCHATKA IS PROGRESSING THROUGH THE WESTERN BERING SEA WITH
A TRIPLE POINT SURFACE LOW FORMING SOUTH OF ADAK THIS MORNING. A
WEAK INVERTED TROUGH IS LOCATED JUST SOUTH OF THE PRIBILOF
ISLANDS. EMBEDDED IN THIS INVERTED TROUGH IS A DISSIPATING 1010 MB
LOW THAT IS BRINGING SCATTERED SHOWERS TO THE EASTERN ALEUTIANS
AND THE ALASKA PENINSULA. OVER THE GULF OF ALASKA...A WARM FRONT
ASSOCIATED WITH A COMPLEX LOW OVER THE NORTHEAST PACIFIC ALONG
150W IS APPROACHING THE SOUTHCENTRAL COAST AS THE LOW MOVES
NORTHWARD INTO THE GULF. A SHORTWAVE AHEAD OF THIS FRONT IS
BRINING RAIN TO SOUTHCENTRAL ALASKA FROM KODIAK EASTWARD TO PRINCE
WILLIAM SOUND AS IT LIFTS NORTHWARD.

&&

.MODEL DISCUSSION...
ON THE SYNOPTIC SCALE...THE MODELS CONTINUE TO BE IN EXCELLENT
AGREEMENT THROUGH THE SHORT TERM WITH THE GENERAL MOVEMENT AND
DEVELOPMENT OF MAJOR FEATURES. AS PREVIOUSLY NOTED...THE
DIFFERENCES BETWEEN THE SOLUTIONS ARE MAINLY AT THE MESO TO LOCAL
SCALE. THE LARGEST DIFFERENCE IN THE SHORT TERM WITH THE MODELS IS
THEIR DEVELOPMENT OF THE LARGE LOW CURRENTLY IN THE NORTHEASTERN
PACIFIC AND ITS MOVEMENT INTO THE GULF OF ALASKA. THE MODELS ARE
IN GOOD AGREEMENT THROUGH THIS EVENING BUT BEGIN TO DIVERGE
TONIGHT AS THE LOW COMPLEX BEGINS TO FRAGMENT INTO MULTIPLE
VORTICITY CENTERS BY FRIDAY EVENING. THE MODELS ARE IN GENERAL
AGREEMENT IN PLACING A BROAD SURFACE LOW OVER THE ALASKA
PENINSULA BUT PLACEMENT AND STRENGTH OF THE MESOSCALE SURFACE
FEATURES VARY...WHICH REDUCES OVERALL FORECAST CONFIDENCE. FOR
THIS FORECAST PACKAGE...A COMBINATION OF THE GEM-REGIONAL AND THE
GFS WERE FAVORED IN THE SHORT TERM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE SOUTHCENTRAL ALASKA REGION IS BRIEFLY UNDER THE INFLUENCE
OF AN UPPER LEVEL WEAK RIDGE THIS MORNING. WHILE...THE NEXT
WEATHER SYSTEM IS CURRENTLY IN THE NORTHERN GULF AND MOVING
TOWARDS THE NORTHWEST. PRECIPITATION FROM THIS SYSTEM WILL
MOVE ONSHORE LATER TODAY AND THEN SPREAD INLAND TONIGHT. THE
UPPER LEVEL LOW ASSOCIATED WITH THIS SYSTEM IS CURRENTLY WELL
TO THE SOUTH...CENTERED AROUND 46 DEGREES NORTH LATITUDE/150
DEGREES WEST LONGITUDE. THIS ELONGATED LOW IS SLOWLY MOVING TO
THE NORTH AND WILL BECOME INCREASINGLY NEGATIVELY TILTED THROUGH
FRIDAY MORNING...BEFORE IT BEGINS TO LOSE COHESION AS ANOTHER
UPPER LOW APPROACHES FROM THE WEST. SOUTHCENTRAL ALASKA WILL BE IN
SOUTHERLY TO SOUTHEASTERLY FLOW ALOFT FROM LATE TONIGHT THROUGH
THE END OF THE SHORT TERM (SATURDAY MORNING). THIS WILL KEEP
MOISTURE AND RAIN/SHOWERS PUMPING INTO THE AREA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAKENING WARM FRONT ALOFT WILL BRING RAIN TO THE BRISTOL BAY
COAST THROUGH THIS MORNING BEFORE IT MOVES WESTWARD INTO THE
EASTERN BERING. ANOTHER MORE STOUT WARM FRONT WILL MOVE FROM EAST
TO WEST TONIGHT THROUGH FRIDAY NIGHT...BRINGING MORE WIDESPREAD
RAIN TO ALL OF SOUTHWEST. THE HEAVIEST RAIN WILL BE ACROSS THE
BRISTOL BAY REGION AND INTO THE LOWER KUSKOKWIM VALLEY. GIVEN THE
VERY WARM TEMPERATURES ALOFT MOVING IN WITH THIS FRONT...ALL RAIN
IS EXPECTED THROUGH THE SHORT TERM.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A STRONG GALE FORCE FRONT OVER THE WESTERN ALEUTIANS WILL MOVE
INTO THE CENTRAL BERING THEN WEAKEN...FORMING INTO A TRIPLE
POINT LOW BEFORE MOVING EAST INTO THE NORTH PACIFIC. THIS WILL
SPREAD MORE RAIN AND RAIN SHOWERS AS THE SYSTEM MAKES EASTWARD
PROGRESS THROUGH SATURDAY. THE ASSOCIATED SURFACE LOW...CURRENTLY
WEST OF SHEMYA...WILL ALSO DRIFT EAST AND WEAKEN KEEPING SOME
SHOWERY ACTIVITY OVER THE WESTERN BERING THROUGH SATURDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A FRONTAL SYSTEM ASSOCIATED WITH A WEAKENING LOW CENTERED NEAR
KODIAK ISLAND WILL BRING CONTINUED RAIN FROM THE GULF COAST INTO
BRISTOL BAY INTO SATURDAY MORNING. THIS RAINFALL WILL THEN BEGIN
TO LIFT INTO SOUTHCENTRAL AND THE INTERIOR SOUTHWEST MAINLAND ON
SATURDAY AS THE UPPER LEVEL TROUGH BEGINS TO LIFT INTO THE
MAINLAND. MEANWHILE OVER THE WESTERN ALEUTIANS A WEAK LOW WILL
BEGIN TO ENTER THE AREA ON SATURDAY MORNING...AND MERGE WITH THE
GULF LOW AS IT MOVES INTO THE BERING ON SUNDAY. THIS WILL PRODUCE
A BROAD TROUGH CENTERED OVER THE EASTERN BERING THAT WILL PERSIST
INTO EARLY NEXT WEEK...KEEPING THE JET AND ANY MAJOR WEATHER
SYSTEMS SOUTH OF THE AREA.

BY NEXT TUESDAY SIGNIFICANT MODEL DISAGREEMENT DEVELOPS WITH THE
PLACEMENT OF A LOW NEAR THE GULF. THE GFS HAS CONSISTENTLY BEEN AN
OUTLIER WITH THIS FEATURE BY BRINGING IT AS FAR NORTH AS KODIAK
ISLAND...WHILE THE GEM/EC HAVE BEEN EQUALLY CONSISTENT IN A MUCH
FURTHER SOUTH SOLUTION. FOR NOW THE CURRENT FORECAST HEAVILY
USES ENSEMBLES TO BRING A MUCH WEAKER LOW INTO THE GULF BY MID
WEEK...BUT FURTHER MODEL RUNS WILL NEED TO BE MONITORED TO
DETERMINE THE EXACT TIMING OF THIS SYSTEM. AS A RESULT FORECAST
CONFIDENCE IS LOW BEYOND EARLY NEXT WEEK...ESPECIALLY FOR THE
SOUTHERN MAINLAND AND THE GULF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 130 131 132 136 137 138 139 150.

&&

SYNOPSIS AND MODEL DISCUSSION...RF
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DEK