Small Craft Advisory 780, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
455 AM AKDT TUE OCT 6 2015

.ANALYSIS AND UPPER LEVELS...

THE MAIN FEATURE ACROSS THE AREA REMAINS A VERTICALLY STACKED
BERING SEA LOW THAT IS SLOWLY DRIFTING NORTHWARD INTO THE
NORTHERN BERING SEA. THE NORTHWARD MOVING LOW HAS STARTED TO LOSE
ITS SUPPORT FROM A STRENGTHENING UPPER-LEVEL JET STREAK...AS THE
JET STREAK PIVOTS INTO A MORE ZONAL ORIENTATION SOUTH OF THE
BERING SEA. THIS TAKES THE LOW OUT OF THE FAVORABLE LEFT EXIT
REGION OF THE JET...WHICH AIDED IN THE RECENT CYCLONE
INTENSIFICATION. A DECAYING OCCLUDED FRONT ASSOCIATED WITH THE LOW
IS BRINGING LIGHT RAIN SHOWERS IN A SOUTHEASTERLY ONSHORE FLOW
REGIME TO SOUTHWESTERN ALASKA...WITH DOWNSLOPING WINDS KEEPING
AREAS IN THE LEE OF THE MOUNTAINS DRIER. ALONG AND AHEAD OF THE
FRONT AT THE SURFACE...SOUTHEASTERLY WINDS ARE GUSTING TO SMALL
CRAFT ADVISORY FORCE.

FURTHER EAST...RIDGING OVER THE CENTRAL AND EASTERN MAINLAND IS
SLOWLY MOVING EAST IN RESPONSE TO THE STRENGTHENING BERING LOW.
AT THE SURFACE UNDER THE RIDGE...FOG AND LOW STRATUS CONTINUE TO
PRESENT A FORECAST CHALLENGE OVERNIGHT WITH MUCH OF SOUTHCENTRAL
UNDER CALM TO LIGHT WINDS. THE EXCEPTION IS AROUND PRINCE WILLIAM
SOUND...WHERE LIGHT OUTFLOW WINDS ARE ALLOWING ENOUGH MIXING TO
PREVENT FOG DEVELOPMENT.

&&

.MODEL DISCUSSION...

MODELS REMAIN IN GOOD AGREEMENT SYNOPTICALLY IN THE SHORT TO MID
TERM. SOME MINOR DIFFERENCES ARISE IN THE PLACEMENT OF THE
APPROACHING GULF LOW SOUTH OF KODIAK ISLAND THURSDAY
NIGHT...HOWEVER THE IMPACTS OF THESE DIFFERENCES ARE MINIMAL. FOR
THE PRECIPITATION APPROACHING SOUTHCENTRAL ALASKA EARLY
TOMORROW...THE HIGHER RESOLUTION MODELS WERE USED OVER THE GLOBAL
MODELS TO ACCOUNT FOR THE DOWNSLOPING EFFECTS OF TERRAIN WITH THE
EASTERLY FLOW. WITH THE MODELS IN GOOD AGREEMENT THROUGH THE END
OF THE WEEK..FORECAST CONFIDENCE IS HIGHER THAN NORMAL.

&&

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

THE SHORT TERM FORECAST THROUGH WEDNESDAY NIGHT WILL BRING THE
ONSET OF A WINDY AND WET PATTERN ACROSS THE GULF...KENAI PEN...AND
COOK INLET REGION. THIS WILL FOR NOW WILL BRING AN END TO THE
PERSISTENT LOW CLOUDS AND FOG OVER THE MAINLAND AND COOK INLET. A
WEAKENING FRONT SLOWLY HEADS NORTH TODAY AND WILL SPREAD RAIN
ACROSS THE NORTH GULF AND KENAI PEN. THE ONSET OF SOUTHWESTERLY
ALOFT WILL SPREAD THE RAIN NORTH TOWARD THE SUSITNA VALLEY
TONIGHT. FREEZING LEVELS SHOULD BE HIGH ENOUGH FOR MOST AREAS TO
BE RAIN EXCEPT FOR THE FAR NORTH SUSITNA VALLEY WHERE COLDER AIR
IN PLACE SHOULD KEEP PRECIPITATION TILTED TOWARD SNOW. ON
WED...THE BRUNT OF THE PRECIPITATION (RAIN) WILL SHIFT TOWARD THE
GULF WITH THE APPROACH OF THE NEXT FRONT MOVING NORTH ACROSS THE
GULF.

TURNAGAIN ARM AND PORTAGE VALLEY WINDS ALONG WITH SMALL CRAFT TO
GALE CONDITIONS ACROSS THE WESTERN GULF ARE EXPECTED TO DEVELOP
THIS MORNING WITH A WEAK LOW MOVING TOWARD KODIAK ISLAND. THESE
WINDS WILL WEAKEN LATER TODAY AS PRESSURE GRADIENTS RELAX. A
SECOND AND MUCH STRONGER ROUND OF WINDS ARE EXPECTED ON WED AND
WED NIGHT WITH A NORTHWARD MOVING LOW AND ITS ASSOCIATED FRONT
OVER THE NORTHEAST PACIFIC. GALES ARE EXPECTED AHEAD OF THE FRONT
OVER THE NORTHERN GULF AND WESTERN GULF WED AFTERNOON. WINDS
LIKELY WILL INCREASE TO STORM FORCE ACROSS THE BARREN ISLANDS AND
THROUGH SHELIKOF STRAIT WED EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONTAL SYSTEM WILL GRADUALLY WEAKEN BUT CONTINUE TO BRING WET
WEATHER AT IT REMAINS STRETCHED OVER SOUTHWEST ALASKA TODAY.
ANOTHER SHORTWAVE TROUGH WILL ROTATE INLAND TONIGHT REINVIGORATING
SHOWERS OVER THE AREA. A LARGE LOW TRACKING INTO THE GULF FROM
THE SOUTH WILL SPREAD RAIN AND BREEZY NORTH TO NORTHEASTERLY
WINDS ACROSS THE ALASKA RANGE AND INTO SOUTHWEST ALASKA WEDNESDAY
AND WEDNESDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE RATHER LARGE VERTICALLY STACKED AREA OF LOW PRESSURE WILL
REMAIN IN THE NORTHERN BERING AS IT GRADUALLY FILLS THROUGH
WEDNESDAY...DRIFTING TOWARDS THE GULF OF ANADYR. SEVERAL SHORTWAVE
TROUGHS WILL ROTATE OUT OF RUSSIA AND ACROSS THE BERING SOUTH OF
THE LARGE UPPER LOW KEEPING THE WEATHER COOL AND SHOWERY WITH WESTERLY
WINDS IN THE 30 TO 35 KNOT RANGE. ON WEDNESDAY A DEEPER TROUGH
WILL SWING OFF OF THE KAMCHATKA PENINSULA AND DIG MORE TO THE
SOUTHEAST AND ACROSS THE CENTRAL ALEUTIANS. THIS WILL BOTH ACT TO
START PULLING THE LARGE UPPER LEVEL LOW TO THE SOUTH WEDNESDAY
NIGHT AND TO SHIFT THE WINDS IN THE WESTERN GULF MORE TO THE
NORTHWEST AND INCREASE THEM UP TO GALES OVER A BROADER AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MODELS CONTINUE TO TRACK THE RAPIDLY DEEPENING NORTH PACIFIC
LOW JUST SOUTH OF THE LOWER WESTERN GULF BY WEDNESDAY. BY LATE
WEDNESDAY EVENING AS THE LOW TRACKS CLOSER TO THE CHIRIKOF ISLAND
REGION THE PRESSURE GRADIENTS WILL STRENGTHEN RESULTING IN STRONG
NORTHEASTERLY GALE FORCE WINDS TO THE NORTHERN GULF EXTENDING
THROUGH THE BARREN ISLANDS...SHELIKOF STRAIT AND THE SOUTHERN COOK
INLET THROUGH THURSDAY MIDDAY. THE ASSOCIATED WEATHER FRONT WILL
BE MOVING THROUGH THE AFOREMENTIONED REGION BRINGING WIDESPREAD
RAIN AND STRATUS. THE ECMWF MODEL SEEMS TO BE THE OUTLIER WITH
THIS SYSTEM AS IT TRIES TO PUSH THIS SYSTEM FARTHER EAST THAN THE
OTHER MODELS BY THURSDAY AFTERNOON. THIS IS HIGHLY UNLIKELY DUE TO
AN UPPER LEVEL NEGATIVE TILTED RIDGE WILL BE POSITIONED ALONG THE
NORTHERN GULF REGION AS WE HEAD INTO THE WEEKEND. THE MODELS ARE
DEPICTING THIS SYSTEM BECOMING STATIONARY JUST SOUTH OF THE
EASTERN ALEUTIANS BY FRIDAY. THIS SYSTEM WILL THEN PHASE IN WITH A
ANOTHER NORTH PACIFIC LOW THAT IS TRACKING NORTHWARD INTO A BROAD
AREA OF LOW PRESSURE OVER THE CENTRAL GULF BY SATURDAY. THE
CONFIDENCE IS LOW WITH TOO MUCH UNCERTAINTY WITH THE PHASING IN
OF THESE TWO SYSTEMS DUE TO THE TIMING AND STRENGTH AS WE HEAD
INTO THE WEEKEND.

MEANWHILE...ON THE BERING SIDE THERE IS A DECAYING LOW THAT WILL
TRACK FROM THE NORTHERN TO CENTRAL BERING BY THURSDAY MORNING
BEFORE DISSIPATING BY THURSDAY AFTERNOON. THIS WILL CONTINUE TO
BRING A SHOWERY WEATHER REGIME WITH THE WINDS SHIFTING TO A MORE
NORTHERLY FLOW BY FRIDAY. THE NEXT SYNOPTIC FEATURE TO AFFECT THE
BERING WILL BE A NORTH PACIFIC LOW TRACKING CLOSER TO THE EASTERN
ALEUTIANS FROM THE PACIFIC SIDE HEADING INTO THE WEEKEND. THIS
WILL BRING ABUNDANT MOISTURE SPILLING OVER THE ALASKA PENINSULA
INTO THE EASTERN ALEUTIANS AND THE SOUTHWEST ALASKA REGION AS THIS
SYSTEM BECOMES ALMOST STATIONARY NEAR CHIRIKOF ISLANDS BY FRIDAY.
THIS SYNOPTIC FEATURE WILL KEEP THE BERING AND THE ALEUTIAN CHAIN
IN NORTHERLY FLOW SCATTERED SHOWERY WEATHER REGIME THROUGH THE
WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY 101 111.
MARINE...GALE 130 131 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RD
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JER
LONG TERM...PD