Small Craft Advisory 711, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
447 AM AKDT THU SEP 10 2015

.ANALYSIS AND UPPER LEVELS...

THE LOW THAT HAS BEEN HIGHLIGHTED FOR NEARLY A WEEK NOW HAS
FINALLY MATURED. IT IS CURRENTLY LOCATED IN BRISTOL BAY. IR
SATELLITE IMAGERY SHOWS AN OCCLUDED FRONT WRAPPING AROUND THE LOW
AND EXTENDING NORTHEASTWARD ACROSS INTERIOR SOUTHWEST ALASKA AND
MUCH OF SOUTHCENTRAL. MIDDLETON ISLAND AND KENAI RADARS INDICATE
EXTENSIVE MODERATE TO HEAVY RAIN ALONG NEARLY ALL OF THE NORTHERN
GULF COAST AND PRINCE WILLIAM SOUND...RAPIDLY PUSHING NORTH INTO
THE COAST. ACROSS COOK INLET...THE EXPECTED DOWNSLOPING DUE TO THE
SOUTHEAST WINDS CROSSING PERPENDICULAR TO THE CHUGACH HAS RESULTED
IN RELATIVELY LITTLE RAIN FROM THE MATANUSKA VALLEY ACROSS THE
ANCHORAGE BOWL AND MUCH OF THE WESTERN KENAI PENINSULA. SOME
LIGHTER AND LESS EXTENSIVE RAINFALL ACTIVITY IS OCCURRING FROM
DILLINGHAM NORTH AND WEST...WRAPPING AROUND THE WEST SIDE OF THE
LOW CENTER OVER BRISTOL BAY. FURTHER NORTH ALONG THE KUSKOKWIM
DELTA...A MORE OFF-AND-ON RAINFALL PATTERN HAS SET UP NORTH OF
BETHEL. OVER THE BERING...EXTENSIVE COLD AIR ADVECTION UNDER
STRONG NORTHERLY FLOW PERSISTS BETWEEN THE BRISTOL BAY LOW AND A
STRONG SURFACE HIGH NEAR THE SOUTHERN TIP OF THE KAMCHATKA
PENINSULA.

IN THE UPPER LEVELS...THE BRISTOL BAY LOW IS VERTICALLY STACKED.
A DEEP POSITIVELY TILTED TROUGH EXTENDS FROM THE LOW SOUTH INTO
THE NORTH PACIFIC. A 125 KT JET ROUNDS THE EASTERN PERIPHERY OF
THE TROUGH EXTENDING NORTHEASTWARD ACROSS THE GULF INTO THE
NORTHERN PANHANDLE.

&&

.MODEL DISCUSSION...

FOR THE PAST SEVERAL DAYS...THE MODELS HAVE MOVED THE TRACK OF THE
SURFACE LOW WEST WITH EACH DAY...AND ALSO SLOWED ITS FORWARD SPEED
DOWN. FOR VERIFICATION...THE LOW TRACK ENDED UP BEING EVEN FURTHER
WEST THAN ANY OF THE MODELS HAD SHOWN THE PAST SEVERAL DAYS...THUS
ANOTHER EXAMPLE OF THE EVOLVING NATURE OF THE SCIENCE OF
METEOROLOGY.

THE MODELS ARE LARGELY IN AGREEMENT TODAY WITH THE MOVEMENT OF THE
LOW MOVING FORWARD. THE MODELS TAKE THE LOW NORTHEAST INTO
INTERIOR ALASKA...BRINGING A FRONT ACROSS THE GULF THURSDAY NIGHT.
A NEW SURFACE LOW DEVELOPS IN THE COOK INLET AREA FRIDAY NIGHT
ASSOCIATED WITH ANOTHER SHORTWAVE. BUT MODELS DIVERGE ON HANDLING
THIS FEATURE...ESPECIALLY WITH REGARDS TO PRECIPITATION INTENSITY.
AT THIS TIME TIME THE GFS IS CLEARLY THE WETTEST. THE FINER
RESOLUTION MODELS WERE PREFERRED WITH THIS FORECAST PACKAGE DUE TO
THEIR AGREEMENT ON THE BROAD EVOLUTION OF THE PATTERN.
THUS...SHORT TERM FORECAST CONFIDENCE IS HIGH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...THU AND
FRI)...THE OCCLUDED FRONT MOVES NORTH ACROSS SOUTHCENTRAL ALASKA
TODAY. PRESSURE RISES ON THE BACKSIDE WILL PRODUCE GUSTY WINDS
ACROSS SOUTHCENTRAL...ESPECIALLY IN FAVORED GAPS LOCATIONS
(TURNAGAIN ARM/PORTAGE VALLEY/KNIK ARM) AND GENERALLY GUSTY SOUTH
WINDS ACROSS THE COPPER RIVER BASIN. WINDS ARE EXPECTED TO
DIMINISH THIS EVENING IN MOST AREAS...THOUGH THE COPPER RIVER WILL
EXPERIENCE ANOTHER SURGE WITH A PASSAGE OF A SECONDARY TROUGH ON
FRI. SHOWERS WILL BE THE GENERAL RULE ACROSS MUCH OF THE REGION
THROUGH FRI IN THE WAKE OF THE FRONTAL PASSAGE...THOUGH A
SECONDARY TROUGH MOVING TOWARD THE GULF TONIGHT MAY BRING MORE
STRATIFORM RAIN TO THE GULF COAST.

&&

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

THE REMNANTS OF A STRONG LOW WILL REMAIN OVER THE REGION TODAY
BEFORE WEAKENING AND MOVING EAST ON FRIDAY. PERIODS OF RAIN WILL
TURN MORE TO SHOWERS THIS AFTERNOON...WITH AN OUTSIDE THREAT FOR
ISOLATED THUNDERSTORMS ACROSS PARTS OF THE BRISTOL BAY REGION
NORTH OF KING SALMON. SHOWER ACTIVITY WILL DIMINISH GRADUALLY
TONIGHT BEFORE A WEAK UPPER LEVEL TROUGH AXIS MOVES OVER THE AREA
FROM NORTHWEST TO EAST FRIDAY AFTERNOON AND EVENING...REORGANIZING
PRECIPITATION INTO LIGHT STEADY RAIN MAINLY ACROSS THE LOWER
KUSKOKWIM DELTA AND BRISTOL BAY REGION...WITH PRECIP LASTING THE
LONGEST ALONG THE WESTERN SLOPES OF THE ALEUTIAN/ALASKA
RANGES...WITH MOST OF THE REMAINDER OF THE REGION DRYING OUT
FRIDAY NIGHT.

&&

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

A SHORTWAVE TROUGH IN NORTHERLY FLOW IS DROPPING SOUTH OVER THE
CENTRAL AND EASTERN BERING THIS MORNING...WHICH WILL ENHANCE
NORTHERLY WINDS AND SHOWERS TODAY AND TONIGHT BEFORE THE PRESSURE
GRADIENT RELAXES THROUGH THE REMAINDER OF FRIDAY AND FRIDAY NIGHT.
NORTHERLY WINDS WILL THEREFORE SLOWLY DIMINISH...ALONG WITH
SHOWERS...LINGERING THE LONGEST ACROSS THE EASTERN ALEUTIANS AND
ALASKA PENINSULA. LARGELY BENIGN AND QUIET WEATHER DEVELOPS FRIDAY
NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE WEEKEND STARTS OFF AS A CONTINUATION OF THE CURRENT SYSTEM IN
THE NORTHERN PACIFIC WITH LINGERING CLOUDS AND MOISTURE PUSHING
FROM WEST TO EAST ACROSS THE SOUTHCENTRAL. A COOL POCKET OF AIR
OFF THE SURFACE WILL PUSH FROM THE SOUTHWEST MAINLAND TO THE
SOUTHCENTRAL BRINGING SOME OF THE COOLEST OVERNIGHT TEMPERATURES
OF THE SEASON. THE PATTERN ALOFT BEGINS CHANGING AND BECOMES
PROGRESSIVE FROM A WESTERLY/NORTHWESTERLY DIRECTION AS THE FIRST
SYSTEM AFTER THE CURRENT TROUGH IS THE EXTRA-TROPICAL REMNANTS OF
TYPHOON KILO. THAT SYSTEM WILL SPREAD RAIN AND WIND OVER MUCH OF
SOUTHERN ALASKA LATE SUNDAY NIGHT INTO MONDAY FOLLOWED BY ANOTHER
DISTURBANCE BY MID-WEEK. EXPECT VERY SEASONABLE CONDITIONS THROUGH
THE FORECAST PERIOD WITH NEAR AVERAGE TEMPERATURES AND
PRECIPITATION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 150 185 351 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...ML