Small Craft Advisory 403, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
510 AM AKDT MON MAY 11 2015

.ANALYSIS AND UPPER LEVELS...
EARLY MORNING SATELLITE IMAGERY INDICATES THE SPRAWLING BERING SEA
LOW IS BEGINNING TO SPLIT INTO TWO DISTINCT LOWS. THE NORTHERN LOW
CAN BE SEEN HEADING THROUGH THE NORTHERN BERING AND IS EXPECTED TO
SLOWLY WEAKEN AS IT MOVES TOWARDS NORTON SOUND TODAY. TO THE
SOUTH...A NEW LOW DEVELOPING JUST SOUTH OF THE AKPEN IS BEGINNING
TO INTENSIFY AS IT WRAPS INTO THE UPPER TROUGH OVER THE GULF. THIS
LOW WILL CONTINUE TO DEVELOP AND BECOME THE FOCAL POINT FOR THE
WEATHER AROUND THE GULF FOR THE NEXT 48 HOURS. OVER THE NORTHERN
GULF THE REMNANTS OF THE SYSTEM THAT BROUGHT WIDESPREAD RAIN TO
THE GULF COAST THIS WEEKEND CONTINUES TO BRING CLOUD COVER INTO
SOUTHCENTRAL THROUGH THE OVERNIGHT HOURS...WITH SHOWERS CONFINED
TO THE GULF COAST. ANOTHER SYSTEM IS BEGINNING TO APPEAR IN THE
NORTHWEST PACIFIC AND IS HEADING TOWARDS THE WESTERN ALEUTIANS.
THIS SYSTEM WILL CONTINUE ON THIS TRACK AND DOMINATE THE WEATHER
OVER THE BERING SEA THROUGH THE MIDDLE OF THIS WEEK.

&&

.MODEL DISCUSSION...
MODEL AGREEMENT REMAINS VERY GOOD WITH THE DEVELOPING LOW SOUTH OF
THE AKPEN AS IT PROGRESSES TOWARDS THE GULF TODAY...SO CONFIDENCE
REMAINS GOOD WITH THIS SYSTEM AND ONLY MINOR CHANGES WERE REQUIRED
OVERNIGHT. OVER THE WESTERN ALEUTIANS THERE HAS BEEN A SIGNIFICANT
INCREASE IN MODEL AGREEMENT SINCE YESTERDAY WITH THE APPROACHING
NORTH PACIFIC LOW...ESPECIALLY WITH THE STRENGTH OF THIS SYSTEM.
THERE IS NOW GOOD CONFIDENCE THAT THIS WILL BECOME A MODERATE GALE
FORCE LOW AND REMAIN AT THAT INTENSITY INTO TUESDAY. THE MODELS
ARE NOW IN GREAT SYNOPTIC AGREEMENT...SO THE GEM REGIONAL WAS
PREFERRED EARLY ON FOR ITS HIGHER RESOLUTION. THE EC WAS THEN
FAVORED STARTING TUESDAY NIGHT AS MINOR DIFFERENCES IN LOW
POSITION DEVELOP.

&&

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

THE COLD UPPER LEVEL LOW MOVING OVER SOUTHCENTRAL ALASKA IS
KEEPING THE ATMOSPHERE UNSTABLE ENOUGH FOR A FEW SHOWERS. THE MAIN
AREA OF SHOWERS WILL REMAIN ALONG THE NORTH GULF COAST WITH ONLY A
FEW MAKING IT INLAND. A RIDGE WILL BEGIN TO BUILD OVER THE AREA
TUESDAY AND TUESDAY NIGHT WHICH WILL DECREASE THE CLOUD COVER
BEFORE THE NEXT FRONT BEGINS TO MOVE INTO THE WESTERN PART OF THE
AREA ON WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAKENING FRONT LYING JUST OFF THE SOUTHWEST ALASKA
COAST WILL MOVE INLAND TODAY BRINGING WITH IT A CHANCE OF
SHOWERS OVER THE REGION BEFORE DISSIPATING ON TUESDAY. MOST OF THE
RAINFALL TODAY WILL BEGIN ALONG THE ALASKA/ALEUTIAN RANGE AND THE
NORTHWEST COAST BEFORE SPREADING INLAND AS THE FRONT MOVES
EASTWARD. IN THE LOWER LEVEL OF THE ATMOSPHERE THERE WILL BE SOME
WEAK UPSLOPE FLOW ON THE SOUTH AND WEST SIDE OF THE KILBUCK
MOUNTAINS AS WELL AS THE LOWER ALEUTIAN RANGE...SO THOSE AREAS ARE
LIKELY TO SEE THE BEST CHANCE FOR PRECIPITATION TODAY AND
TONIGHT.

THINGS WILL DRY OUT TOMORROW AS A WEAK RIDGE QUICKLY MOVES THROUGH
THE AREA. THE FRONT ASSOCIATED WITH THE DEEP LOW OVER THE FAR
WESTERN ALEUTIANS WILL BEGIN TO IMPACT THE COAST LATE TUESDAY
NIGHT. THIS SYSTEM HAS DEEP FETCH OF MOISTURE FROM ABOUT 25N...SO
WIDESPREAD RAIN IS EXPECTED AS THE FRONT MOVES ASHORE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE HEAVY RAINFALL OVER THE WESTERN PORTIONS OF THE ALASKA
PENINSULA HAS ENDED AND RAINFALL WILL TAPER OFF TODAY AS THE
FRONT MOVES INLAND OVER SOUTHWEST ALASKA. WINDS SHOULD GENERALLY
DECREASE OVER THE REGION TODAY AS THE LOW SOUTH OF THE ALASKA
PENINSULA MOVES EASTWARD AND A RIDGE QUICKLY MOVES THROUGH THE
AREA. SOME AREAS OF SHOWERS WILL REMAIN OVER THE EASTERN ALEUTIANS
AND THE ALASKA PENINSULA WITH ENOUGH INSTABILITY AND MOISTURE LEFT
FROM THE FRONT TO GENERATE ISOLATED SHOWERS.

BY LATE TONIGHT ATTENTION SHIFTS WESTWARD AS THE STILL DEEPENING
LOW APPROACHES THE WESTERN ALEUTIANS. THE FRONT ASSOCIATED WITH
THE LOW WILL BEGIN TO MAKE ITS PRESENCE KNOWN TONIGHT ALONG THE
WESTERN AND CENTRAL ALEUTIANS AS WINDS INCREASE TO GALE FORCE
ALONG THE SOUTHERN SIDE OF CENTRAL AND WESTERN ALEUTIANS TONIGHT.
THIS SYSTEM HAS A MOISTURE FETCH FROM DEEP IN THE TROPICAL
PACIFIC /ABOUT 25N/ WITH THE 00Z NAFES MODEL RUN INDICATING
PRECIPITABLE WATER ANOMALIES OF UP TO 4 STANDARD DEVIATIONS FROM
NORMAL ALONG THIS PLUME. THUS...RAINFALL AMOUNTS MAY BE HEAVY AT
TIMES WITH LOCAL TOTALS OF ONE HALF TO ONE INCH POSSIBLE TONIGHT
INTO TOMORROW.

AS THE LOW MOVES ACROSS THE CHAIN JUST EAST OF SHEMYA AND INTO
THE SOUTHWESTERN BERING SEA...THE WIND FIELD WILL BE QUITE LARGE
WITH NEAR GALE FORCE WINDS EXPECTED OVER MOST OF THE BERING AND
ALEUTIAN CHAIN. THE STRONGEST WINDS TOMORROW AND TOMORROW NIGHT
WILL INITIALLY BE LOCATED ALONG THE FRONT AS IT MOVES NORTHWARD
THROUGH THE BERING BUT WILL SHIFT TOMORROW NIGHT TO THE BACKSIDE
OF THE LOW AND THE SOUTH SIDE OF THE ALEUTIAN CHAIN. WINDS SHOULD
BEGIN TO DECREASE LATE TOMORROW NIGHT AS THE LOW BEGINS TO
ELONGATE NORTHEASTWARD AND WEAKEN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A RIDGE OF HIGH PRESSURE WILL BUILD OVER THE SOUTHWEST MAINLAND
AND GULF FROM THE WEST TUESDAY AFTERNOON...AND CONTINUE TO AMPLIFY
AS IT SETS UP OVER SOUTHCENTRAL WEDNESDAY. SOME GUSTY GAP WINDS
ARE EXPECTED TO DEVELOP AS THE GRADIENT TIGHTENS UP OVER WESTERN
PRINCE WILLIAM SOUND AND TURNAGAIN ARM...AS WELL AS SOME WARMER
TEMPERATURES ADVECTING UP FROM THE NORTHERN PACIFIC WHICH WILL
PERSIST THROUGH THE BEGINNING OF THE WEEKEND. RAINY AND WINDY
CONDITIONS ARE EXPECTED TO TRACK INTO THE SOUTHWEST MAINLAND AND
GULF WEDNESDAY AS A FRONTAL SYSTEM ASSOCIATED WITH A NORTH
PACIFIC LOW NEAR THE WESTERN ALEUTIANS TRACKS THROUGH THE AREA.
THE FRONT WILL THEN WEAKEN AND PUSH INTO SOUTHCENTRAL WEDNESDAY
EVENING...WHERE THE RAINY AND GUSTY CONDITIONS WILL PERSIST
THROUGH EARLY THURSDAY MORNING BEFORE BRIEFLY TAPERING OFF. MODELS
ARE NOW INDICATING THAT THE ABOVE MENTIONED NORTH PACIFIC LOW OVER
THE WESTERN ALEUTIANS WILL BEGIN TO WEAKEN AND TRANSFER ENERGY TO
A TRIPLE POINT LOW FORMING SOUTH OF THE CENTRAL ALEUTIANS
WEDNESDAY AFTERNOON. THE FRONTAL SYSTEM ASSOCIATED WITH THIS
TRIPLE POINT LOW WILL INITIALLY BRING SOME GUSTY AND SHOWERY
CONDITIONS TO THE FAR EASTERN ALEUTIANS AND ALASKA PENINSULA
THURSDAY...WHERE OTHERWISE BROAD CYCLONIC FLOW OVER THE REMAINDER
OF THE ALEUTIANS/BERING WILL KEEP SOME SHOWERY CONDITIONS OVER THE
AREA THROUGH THE END OF THE WEEK. THE FRONTAL SYSTEM WILL THEN
QUICKLY CATCH UP TO THE WEAKENING FRONTAL SYSTEM OVER THE GULF
THURSDAY EVENING...REINFORCING THE GUSTY WINDS AND RAINY
CONDITIONS OVER SOUTHCENTRAL THROUGH THE BEGINNING OF THE WEEKEND.
MODELS THEN SHOW THE TRIPLE POINT LOW TRACKING NORTHWARD INTO THE
BRISTOL BAY/EASTERN BERING REGION BY FRIDAY AFTERNOON...WHICH
COULD KEEP SOME OF THE WET AND WINDY CONDITIONS OVER THE ALASKA
PENINSULA AND SOUTHWEST MAINLAND INTO THE WEEKEND. HOWEVER THERE
ARE STILL SOME TIMING AND STRENGTH DISCREPANCIES IN THE MODELS
REGARDING THIS SYSTEM...KEEPING FORECAST CONFIDENCE SLIGHTLY BELOW
AVERAGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE
MARINE...GALE WARNING 170 173 175 176 177 178
FIRE WEATHER...NONE

&&

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