Small Craft Advisory 702, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
433 PM AKDT MON SEP 7 2015

.ANALYSIS AND UPPER LEVELS...
THE BIG STORY OVER THE SOUTHERN MAINLAND ON THIS LABOR DAY IS
WIDESPREAD CLOUDS AND AREAS OF FOG (LOCALLY DENSE). AREA SOUNDINGS
SHOW NOT MUCH HAS CHANGED IN THE PAST 24 HOURS WITH NEARLY SATURATED
LOW TO MID LEVELS AND WEAK FLOW. THERE ARE A COUPLE VERY WEAK
UPPER LEVEL WAVES MOVING THROUGH. IT TAKES VERY LITTLE VERTICAL
MOTION TO GENERATE PRECIP IN THIS ENVIRONMENT...SO THESE WAVES
ARE PRODUCING A FEW SHOWERS FROM SOUTHWEST ALASKA TO THE SUSITNA
VALLEY IN SOUTHCENTRAL. A LITTLE BIT OF WEAK OFFSHORE FLOW FROM
THE COPPER BASIN TO EASTERN PRINCE WILLIAM SOUND BEHIND A DEPARTING
UPPER LOW OVER THE EASTERN GULF IS JUST ENOUGH TO PRODUCE DRIER
CONDITIONS IN THAT AREA...WITH QUITE A BIT OF SUNSHINE TODAY.

CHANGES ARE AFOOT OUT WEST WITH A POLAR JET DIVING SOUTHWARD ACROSS
FAR EASTERN RUSSIA CAUSING WHAT HAS BEEN A STATIONARY MATURE LOW
OVER THE FAR WESTERN BERING SEA TO START TRACKING SOUTHEASTWARD.
THIS WILL LEAD TO AMPLIFICATION OF THE UPPER LEVEL PATTERN AND
CYCLOGENESIS SOUTH OF THE ALEUTIANS/ALASKA PENINSULA OVER THE NEXT
COUPLE DAYS. IN THE MEANTIME AN OCCLUDED FRONT EXTENDING FROM THIS
LOW HAS ELONGATED EAST-WEST ACROSS THE BERING SEA. THE SOUTH END
OF THE FRONT CONTINUES TO PROGRESS EAST-NORTHEAST ACROSS THE
EASTERN BERING SEA THIS MORNING (ALONG WITH A CORRESPONDING UPPER
LEVEL SHORT-WAVE)...RESULTING IN A FAIRLY NARROW BAND OF RAIN FROM
THE PRIBILOF ISLANDS TO THE EASTERN ALEUTIANS AND SOUTHERN ALASKA
PENINSULA.

&&

.MODEL DISCUSSION...
MODELS CONTINUE TO HAVE A GOOD HANDLE ON THE OVERALL PATTERN
CHANGE AND LARGE SCALE FEATURES. THE BIGGEST CHALLENGE IN THE
IMMEDIATE-TERM REMAINS DETAILS OF CLOUD COVER AND FOG IN THIS
MOISTURE RICH ENVIRONMENT. HOWEVER FORECAST CONFIDENCE IS HIGH
IN DEVELOPMENT OF RAIN AS THE UPPER SHORT-WAVE OVER THE EASTERN
BERING SEA REACHES THE SOUTHERN ALASKA MAINLAND ON TUESDAY.
ATTENTION WILL THEN TURN TO THE DEVELOPING SURFACE LOW SOUTH OF
THE ALASKA PENINSULA ON WEDNESDAY. ALL MODELS HAVE TRENDED
STRONGER AND FARTHER WEST WITH THE LOW TRACK SINCE YESTERDAY
MORNING. WITH AN AMPLIFYING TROUGH AND GOOD UPPER LEVEL JET
SUPPORT FULLY BUY INTO THESE TRENDS. THERE ARE STILL SOME MINOR
DIFFERENCES IN TIMING AND PLACEMENT...BUT CAN AT LEAST TREND THE
FORECAST HEAVILY TOWARD THE LATEST GROUP OF SOLUTIONS.

&&

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

THE MAIN IMPACT IN THE SHORT TERM FORECAST WILL BE RAIN WHICH
DEVELOPS ALONG TWO SEPARATE SHORTWAVES...WITH THE SECOND WAVE
BRINGING THE HIGHEST ACCUMULATIONS DURING THE FIRST PART OF THE
WEEK. THE FIRST SHORTWAVE...CURRENTLY OVER THE ALASKA
PENINSULA...SWINGS ACROSS KODIAK ISLAND AND INTO THE SOUTHERN GULF
TONIGHT...THEN LIFTS NORTH ACROSS THE KENAI AND THE REST OF
SOUTHCENTRAL ON TUESDAY. THIS SYSTEM LACKS ORGANIZATION WITHOUT A
DISCERNIBLE SURFACE LOW OR TROUGH AT THE SURFACE...THEREFORE RAIN
ACCUMULATIONS WILL BE LIMITED TO TRACE AMOUNTS UP TO ONE TENTH OF
AN INCH.

THE SECOND WAVE TAKES A VERY SIMILAR TRACK TO THE FIRST AND IS
EXPECTED TO ARRIVE AT KODIAK ISLAND/SOUTHERN GULF BY TUESDAY MID
DAY. THIS SYSTEM WILL MOVE A SURFACE TROUGH AS IT PUSHES NORTH
INTO SOUTHCENTRAL AROUND TUESDAY AFTERNOON. WINDS ARE EXPECTED TO
INCREASE OUT OF THE SOUTH AND EAST...HOWEVER THEY REMAIN BELOW
SMALL CRAFT CRITERIA ACROSS THE GULF AND INLET. GUSTY WINDS ARE
EXPECTED TO INCREASE THROUGH CHANNELED TERRAIN ALONG TURNAGAIN ARM
LATE AFTERNOON WITH A SOUTHERLY FLOW PICKING UP ACROSS THE COPPER
RIVER BASIN TUESDAY NIGHT AS THE TROUGH TIGHTENS THE GRADIENT
ACROSS THE NORTHERN GULF. RAIN IS EXPECTED TO SPREAD INLAND
THROUGH TUESDAY NIGHT WITH THE HIGHEST AMOUNTS EXPECTED TO FALL
ACROSS THE EASTERN FACING MOUNTAINS AND PRINCE WILLIAM SOUND.
RAIN ACCUMULATIONS SHOULD AVERAGE BETWEEN ONE QUARTER TO ONE HALF
OF AN INCH WITH LOCALIZED HIGHER AMOUNTS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
PRECIPITATION CHANCES OVER SOUTHWEST ALASKA WILL BE ON THE
INCREASE OVERNIGHT AS THE FRONT ASSOCIATED WITH THE LOW IN THE
BERING SEA MOVES ONSHORE AND BEGINS TO STALL ON TUESDAY. THE FRONT
IS EXPECTED TO ROTATE INTO AN EAST-WEST ORIENTATION ON TUESDAY
MORNING AND WILL REMAIN THE FOCUS OF RAINFALL THROUGH WEDNESDAY.
AS THE LOW IN THE BERING IS ABSORBED INTO THE NEW AND DEEPER LOW
SOUTH OF THE ALEUTIAN CHAIN...WINDS WILL BE ON THE INCREASE OVER
THE AREA WITH PRIMARILY NORTHEAST FLOW NORTH OF THE KILBUCKS AND
EASTERLY FLOW PUSHING THROUGH THE KAMISHAK GAP.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FRONT CURRENTLY OVER THE EASTERN BERING SEA IS EXPECTED TO
MOVE INTO SOUTHWEST ALASKA AND ROTATE INTO AN EAST-WEST
ORIENTATION OVER THE NORTHERN BERING BY TOMORROW MORNING. AS THE
UPPER LOW SWINGS EASTWARD AND PHASES WITH THE TROUGH CENTERED
ALONG THE BERING STRAIT...THIS FRONT IS EXPECTED TO WRAP ALONG THE
BACKSIDE OF THE LOW KEEPING PRECIPITATION IN THE FORECAST FOR MOST
OF THE BERING SEA THROUGH WEDNESDAY AFTERNOON. ALONG WITH
THIS...WINDS OVER MOST OF THE REGION WILL BECOME NORTHERLY BY
WEDNESDAY AFTERNOON IN THE 20 TO 30 KT RANGE. THE NEW SURFACE LOW
FORMING SOUTH OF THE ALEUTIAN CHAIN WILL BECOME THE DOMINATE
WEATHER FEATURE BY TUESDAY NIGHT...KEEPING RAINFALL IN THE
FORECAST FOR MOST OF THE EASTERN ALEUTIANS AND THE ALASKA
PENINSULA. WINDS IN THE MARINE AREAS SOUTH OF THE EASTERN
ALEUTIANS AND THE ALASKA PENINSULA ARE EXPECTED TO REMAIN BELOW
GALE FORCE AT THIS TIME. HOWEVER...THE CONFIDENCE IN THE EXACT
LOCATION AND STRENGTH OF THIS LOW IS BELOW AVERAGE AT THIS TIME
AND A CHANGE IN THE TRACK OR INTENSITY COULD BRING GALE CONDITIONS
TO THIS AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE STRONG LOW SPINNING UP TO THE SOUTH OF THE ALASKA PENINSULA ON
WEDNESDAY CONTINUES TO BE THE MAJOR WEATHER FEATURE WHICH WILL
IMPACT THE MIDTERM FORECAST. IN COMPARISON TO YESTERDAY...MODELS
HAVE BROUGHT THE TRACK OF THE SURFACE LOW FURTHER TO THE WEST WITH
THE LOW TRACKING THROUGH THE WESTERN GULF SUCH THAT IT BRUSHES
OVER THE EASTERN COAST OF KODIAK ISLAND WEDNESDAY NIGHT BEFORE
CONTINUING NORTH TOWARDS THE KENAI PENINSULA THURSDAY AND TO THE
NORTHERN GULF THURSDAY NIGHT. EXPECTING TO SEE BARRIER JET WINDS
IN THE NORTHERN GULF...EAST WINDS IN PRINCE WILLIAM SOUND AND EAST
TO NORTHEAST WINDS THROUGH THE BARRENS INCREASE TO GALES WEDNESDAY
NIGHT AS THE INITIAL FRONTAL SYSTEM LIFTS NORTH ACROSS THE GULF
AHEAD OF THE LOW. SOUTHERLY GALES WILL ALSO SPREAD NORTH ACROSS
THE GULF ON THURSDAY TO THE EAST OF AND FOLLOWING THE LOW NORTH.
IN ADDITION ALSO EXPECTING STRONG GAP WINDS THROUGH PASSAGE CANAL
AND TURNAGAIN ARM WEDNESDAY NIGHT AND THURSDAY BEFORE BEGINNING TO
TAPER OFF THURSDAY NIGHT.

A COLD UPPER LEVEL LOW CENTERED OVER NORTHERN ALASKA AND SEVERAL
SHORTWAVE TROUGHS SWINGING IN FROM THE WEST AND NORTHWEST WILL
KEEP CONDITIONS COOL WITH SCATTERED SHOWERS AROUND THROUGH THE
WEEKEND. THE NEXT MAJOR LOW PRESSURE SYSTEM WILL APPROACH THE
WESTERN ALEUTIANS AROUND SATURDAY. MODEL UNCERTAINTY REMAINS
RATHER HIGH WITH REGARDS TO THE TIMING...TRACK AND STRENGTH OF
THIS FEATURE AS WELL AS THE SURFACE RIDGE AMPLIFYING OUT AHEAD OF
IT OVER THE ALEUTIANS AND BERING. HOWEVER IT IS ONE THAT DEFINITELY
BEARS WATCHING AS IT WILL CONTAIN QUITE A BIT OF REMNANT TROPICAL
MOISTURE. FOR THE GULF OF ALASKA...THE NEXT LOW WILL TRACK UP
FROM THE SOUTH SOMETIME AROUND SUNDAY OR MONDAY AND WILL ALSO
LIKELY BE A RATHER WARM AND MOIST SYSTEM

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...JR