Small Craft Advisory 398, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKDT SAT MAY 9 2015

.ANALYSIS AND UPPER LEVELS...
A VERTICALLY STACKED LOW SITS TO THE SOUTHEAST OF KODIAK ISLAND
WHICH CONTINUES TO BRING RAIN TO AREAS ALL ALONG THE NORTH GULF
COAST. INSTABILITY AND SHORTWAVES FROM THIS LOW ARE ALSO BRINGING
SHOWERY ACTIVITY TO MORE INLAND LOCATIONS. WEAK RIDGING RESIDES TO
THE WEST OF THE LOW WITH ANOTHER LOW PUSHING THROUGH THE BERING.
THIS LOW IS ALSO WEAKENING BUT STILL HAS AN ASSOCIATED FRONT
PUSHING THROUGH THE EASTERN BERING. A THIRD LOW IS FORMING SOUTH
OF THE ALEUTIANS AND IS STRENGTHENING AS IT MOVES EAST.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT IN THE SHORT TERM. IN THE MID
TERM THERE IS SOME DISAGREEMENT WITH THE LOW IN THE GULF MONDAY
WITH THE EC AND GEM HAVING A SLIGHTLY MORE NORTHERN POSITION
COMPARED TO THE NAM AND GFS. HOWEVER...THIS DIFFERENCE SHOULD HAVE
MINIMAL IMPACT IN TERMS OF WEATHER IMPACTS FOR THE SOUTHCENTRAL
AND KODIAK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE CURRENT LOW IN THE GULF OF ALASKA WILL BRING ANOTHER NIGHT OF
RAINY AND WINDY CONDITIONS TO THE EASTERN KENAI PENINSULA...PRINCE
WILLIAM SOUND AND NORTHERN GULF COAST REGIONS. PRECIPITATION WILL
BEGIN TO GRADUALLY DIMINISH SUNDAY AND SUNDAY NIGHT AS THE SURFACE
LOW WEAKENS AND DISSIPATES. WHILE ALSO WEAKENING...THE BROADER
UPPER LEVEL LOW WILL DRIFT NORTH TO BE CENTERED OVER THE NORTHERN
GULF AND BRING A COOLER SLIGHTLY UNSTABLE AIR MASS TO SOUTH
CENTRAL ALASKA. AN UPPER LEVEL TROUGH WILL ROTATE NORTH AROUND THE
EAST SIDE OF THIS LOW ON MONDAY...LIFTING NORTH UP AND OVER THE
NORTHERN GULF COAST AND COPPER RIVER BASIN. IN ADDITION TO
BRINGING ANOTHER REINFORCING SHOT OF COOL AIR AND SOME SHOWERS
WITH IT THIS TROUGH WILL ALSO BRING A STRONG PUSH OF SOUTH TO
SOUTHEAST WINDS THROUGH THE COPPER RIVER MONDAY AFTERNOON AND
EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
MOST OF SOUTHWEST ALASKA WILL LIE UNDER WEAK UPPER LEVEL RIDGING
BETWEEN A LOW OVER THE WESTERN GULF...A SLOWLY APPROACHING FRONT
FROM THE BERING...AND LOW PRESSURE SOUTH OF THE AKPEN. THIS WILL
GIVE MOST OF THE AREA A CHANCE TO DRY OUT A BIT...THOUGH MINIMUM
HUMIDITY VALUES AND WINDS WILL LIKELY REMAIN WELL SHORT OF
REACHING CRITICAL FIRE WEATHER CONDITIONS.

BY MONDAY...THERE SEEMS TO BE GROWING CERTAINTY IN THE WEATHER
FRONT OVER THE BERING MOVING INLAND AND THEN SLOWLY FALLING APART
OVER SOUTHWEST ALASKA. FOR THIS REASON...HAVE INTRODUCED NUMEROUS
SHOWERS INTO THE FORECAST FOR MONDAY FOR THE KUSKOKWIM DELTA AND
BRISTOL BAY.

&&

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

AS LOW PRESSURE MOVES NORTH THROUGH THE BERING AND DOWNSTREAM
RIDGING BECOMES STATIONARY OVER THE SOUTHWEST MAINLAND TONIGHT
INTO SUNDAY...THE BERING FRONT WILL BECOME SEMI-STATIONARY AND
ELONGATE NORTH-SOUTH FROM NUNIVAK ISLAND TO UNIMAK ISLAND. AS
MENTIONED ABOVE...THE NORTH PACIFIC LOW IS EXPECTED TO MOVE SOUTH
OF THE EASTERN ALEUTIANS AND ALASKA PENINSULA TONIGHT INTO
SUNDAY. THIS SYSTEM HAS A DEEP SOURCE OF MOISTURE FROM THE CENTRAL
PACIFIC WITH SATELLITE IMAGERY THIS MORNING INDICATING PW VALUES
OVER 200 PERCENT OF NORMAL. THIS WILL PROVIDE AMPLE MOISTURE FOR
CONTINUOUS RAIN ALONG THE FRONT THROUGH SUNDAY NIGHT WITH THE
HEAVIEST TOTALS FROM DUTCH HARBOR EASTWARD TO SAND POINT.

AS THE SECOND LOW APPROACHES THE REGION FROM THE SOUTH...WINDS
SHOULD INCREASE SUNDAY AFTERNOON SOUTH OF THE ALEUTIAN CHAIN BUT
SHOULD REMAIN BELOW GALE FORCE. AS A WEAK RIDGE BUILDS IN BEHIND
THE FRONT...THE FLOW WILL TURN WESTERLY AND WILL GENERALLY STAY
BELOW 25 KTS WITH SOME SCATTERED SHOWERS OVER MOST OF THE BERING
SEA AND WESTERN ALEUTIANS.

A TRAILING WEAK AND FAST-MOVING DISTURBANCE WILL LIKELY BRING SOME
RAIN TO THE CENTRAL ALEUTIANS SUNDAY NIGHT BEFORE BEGINNING TO
FALL APART AS IT APPROACHES THE EASTERN ALEUTIANS MONDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE NORTH PACIFIC LOW POSITIONED IN THE CENTRAL GULF WILL
GRADUALLY MOVE EASTWARD BEFORE DISSIPATING BY TUESDAY AFTERNOON.
THIS SYSTEM WILL BRING MOISTURE TO THE NORTHERN GULF AND THE
MAJORITY OF THE PRECIPITATION WILL BE ALONG THE COASTAL
AREAS. AN AMPLIFIED RIDGE OF HIGH PRESSURE WILL BEGIN TO MOVE
INTO THE SOUTHCENTRAL REGION FROM THE WEST BY WEDNESDAY. THIS
WILL BRING WARMER TEMPERATURES WITH DIURNAL SHOWERS IN THE
AFTERNOON AND EVENING ACCOMPANIED BY A THERMAL TROUGH FORMING IN
THE INTERIOR HEADING INTO THE MIDWEEK TIME FRAME. THE MODELS WERE
IN DECENT AGREEMENT WITH THESE FEATURES AND FORECAST CONFIDENCE IS
AVERAGE.

ON THE BERING SEA SIDE...THE NORTHERN BERING WILL HAVE A WEAK LOW
DISSIPATING BY EARLY TUESDAY MORNING. WHILE...THE WESTERN
ALEUTIANS WILL HAVE A NORTH PACIFIC GALE FORCE LOW APPROACHING BY
LATE MONDAY EVENING WITH AN ASSOCIATE WEATHER FRONT MOVING
THROUGH THE CENTRAL ALEUTIANS. THIS SYSTEM WILL TRANSITION INTO
A BROAD AREA OF LOW PRESSURE OVER THE BERING SEA. THIS WILL BRING
WIDESPREAD RAIN WITH GUSTY WINDS THROUGH THE EARLY PART OF NEXT
WEEK BEFORE TRANSITIONING TO SHOWERY PRECIPITATION BY MIDWEEK.
DOWNSTREAM...AN AMPLIFIED RIDGE BUILDS THROUGH THE EASTERN
BERING/ALEUTIANS BY MONDAY AND MOVES EASTWARD. THIS WILL BRING
WARMER TEMPERATURES THROUGH THURSDAY. THE MODELS CONTINUE TO
STRUGGLE WITH THE PLACEMENT/STRENGTH OF THIS NORTH PACIFIC LOW. THE
FORECAST CONFIDENCE REMAINS BELOW AVERAGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 155 AND 172.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...PD