Small Craft Advisory 307, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
501 PM AKDT TUE APR 7 2015

.ANALYSIS AND UPPER LEVELS...
THE STRONG LOW THAT WAS IN THE WESTERN GULF OF ALASKA MOVED UP
COOK INLET TODAY AND IS HEADING INTO THE UPPER KUSKOKWIM VALLEY
THIS AFTERNOON. THE FRONT ASSOCIATED WITH IT HAS ALSO MOVED THROUGH
SOUTHCENTRAL ALASKA LEAVING GUSTY SOUTH TO SOUTHEAST WINDS BEHIND
IT. COLDER AIR ALOFT HAS ALREADY MOVED INTO SOUTHWEST ALASKA AND
IS ALSO MOVING INTO SOUTHCENTRAL THIS AFTERNOON.

THE JET STREAM IS PUSHING THROUGH THE CENTRAL BERING SEA AND THEN
HEADING SOUTHEAST OVER THE ALASKA PENINSULA. THIS IS FEEDING THE
DEVELOPMENT OF A LOW JUST WEST OF THE KAMCHATKA PENINSULA THAT WILL
MOVE THROUGH THE BERING SEA THE NEXT FEW DAYS.

&&

.MODEL DISCUSSION...
MODELS ARE IN VERY GOOD AGREEMENT WITH THE MOVEMENT OF BOTH THE
LOW THAT MOVED THROUGH COOK INLET THIS MORNING AS WELL AS THE
DEVELOPING SYSTEM IN THE FAR WESTERN BERING SEA. THERE IS SOME
MINOR DISAGREEMENT WITH HOW THE LOW WILL SPLIT WHEN IT CROSSES
THE ALEUTIAN RANGE INTO THE NORTHWEST GULF ON THURSDAY BUT THESE
DIFFERENCES DO NOT APPEAR TO BE MAJOR AT THIS POINT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AS THE COLD FRONT AND UPPER LEVEL TROUGH WEAKEN AND PUSH FURTHER
NORTH THIS EVENING...GUSTY WINDS ALONG MUCH OF SOUTHCENTRAL WILL
CONTINUE TO DIMINISH TONIGHT. SHOWERY PRECIPITATION WILL CONTINUE
THROUGH TONIGHT OVER THE AREAS SURROUNDING PRINCE WILLIAM
SOUND...WHILE AREAS TO THE WEST WILL BEGIN TO LOSE SOME OF THE
DOWNSLOPING SIGNATURE OVERNIGHT AS CROSS BARRIER WINDS BEGIN TO
SHIFT TO THE SOUTH. AS THESE CROSS BARRIER WINDS SHIFT AND AN
UPPER LEVEL WAVE APPROACHES THE WESTERN KENAI AND ANCHORAGE AREA
EARLY TOMORROW MORNING...RAIN AND SNOW WILL LIKELY FILL IN OVER
THE AREA. THIS SYSTEM WILL QUICKLY OPEN UP AND WEAKEN AS A STRONGER
LOW OVER THE EASTERN BERING SEA MOVES EAST INTO THE WESTERN COAST
OF ALASKA TOMORROW NIGHT. THE FRONT ASSOCIATED WITH THE AFOREMENTIONED
SYSTEM WILL MOVE ACROSS KODIAK AND INTO THE GULF OF ALASKA TOMORROW
EVENING. THIS SYSTEM WILL BRING ANOTHER ROUND OF GUSTY WINDS AND
PRECIPITATION TO THE COASTAL AREAS ALONG THE GULF...WITH AREAS TO
THE WEST EXPERIENCING SOME DOWNSLOPING AGAIN AS STRONG SOUTHEASTERLY
FLOW BUILDS BACK OVER THE AREA LATE TOMORROW NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL TROUGH IS CURRENTLY ROTATING FROM THE KUSKOKWIM
DELTA SOUTHEAST ACROSS THE BRISTOL BAY COASTAL AREAS THIS AFTERNOON
AND EVENING. THIS MOTION WILL ACT TO LIFT THE AREA OF LOW PRESSURE
CURRENTLY OVER THE ILIAMNA AREA AND LOWER KUSKOKWIM VALLEY FURTHER
NORTH THIS EVENING CHANGING THE MORE STEADY PRECIPITATION TO SHOWERS...
WITH MORE ABUNDANT SHOWER COVERAGE INLAND AND TO THE NORTH.
ADDITIONALLY THE SHORTWAVE TROUGH WILL INCREASE SHOWER COVERAGE
OVER BRISTOL BAY AND ALONG THE ALASKA PENINSULA FROM KING SALMON
SOUTH AS IT SWINGS THROUGH THIS EVENING.

THE NEXT FRONTAL SYSTEM WILL APPROACH THE WEST COAST WEDNESDAY
MORNING THEN SWING INLAND IN THE AFTERNOON AND EVENING BRINGING
ANOTHER ROUND OF PRECIPITATION. THE ASSOCIATED SURFACE LOW WILL
REACH BRISTOL BAY WEDNESDAY NIGHT THEN SHIFT INLAND THURSDAY WITH
COLD NORTHWESTERLY FLOW PUSHING IN BEHIND IT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE NEXT RATHER STRONG FRONTAL SYSTEM IS CURRENTLY SPINNING UP IN
THE FAR WESTERN BERING. THIS LOW WILL CONTINUE RAPIDLY DEEPEN AND
STRENGTHEN AS IT TRACKS EAST TONIGHT AND WEDNESDAY PROPELLED BY A
VERY STRONG JET STREAM. THE MAIN IMPACTS WITH THIS SYSTEM WILL BE
WIDESPREAD WESTERLY GALES AS WELL AS A FAIRLY BROAD AREA OF STORMS
TO THE SOUTH OF THE LOW...STRENGTHENING AND FOLLOWING IT EAST AS
IT DEEPENS. ADDITIONALLY THE TRACK AND SPEED OF THE LOW IS FAVORABLE
FOR THE DEVELOPMENT OF RATHER LARGE SEAS TO ITS SOUTH. CURRENTLY
IT IS LOOKING LIKE THESE SEAS WILL BUILD TO AROUND 30 FEET AND
TRACK TOWARDS THE WESTERN ALASKA PENINSULA AND EASTERN ALEUTIANS
WEDNESDAY AND WEDNESDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS ARE IN AGREEMENT WITH THE ONSET OF UPPER LEVEL ZONAL FLOW
THU NIGHT THROUGH SUN. A 120 TO 150 KT JET WILL REMAIN NEAR 45N
AND EXTEND FROM NORTHERN JAPAN TO THE PACIFIC NORTHWEST. THIS
FEATURE WILL KEEP CYCLONIC FLOW OVER THE ENTIRE FORECAST AREA
THROUGH SUN. AT THAT TIME THE JET WILL BUCKLE...AND THE CYCLONIC
CIRCULATION WILL BREAK DOWN INTO A RIDGE OVER THE MAINLAND AND A
DEEP TROUGH SOUTH OF THE BERING BEGINNING ON MON. AT THE SURFACE...
A LOW CROSSING THE AKPEN WILL MOVE TO THE NORTHERN GULF THU NIGHT.
MODELS ARE HAVING A DIFFICULT TIME DETERMINING A TRACK FOR THIS
LOW. WPC USED AN ENSEMBLE APPROACH THAT BY FRI NIGHT MOVES THE LOW
WELL SOUTH OF CAPE SAINT ELIAS AND THEN BROADENS IT OVER THE NORTH
GULF COAST THROUGH EARLY NEXT WEEK. IN THE WEST...WEST TO NORTHWEST
FLOW WILL PERSIST OVER THE BERING AND ALEUTIANS INTO NEXT WEEK.
THE FORECAST UTILIZED THE EC UNTIL FRI EVENING AND THEN TRANSITIONED
TO WPC GUIDANCE.

SNOW SHOWERS WILL PERSIST OVER THE BERING...ALEUTIANS...AND SW AK
WITH WIDESPREAD GALE FORCE WINDS GRADUALLY DIMINISHING TO SMALL
CRAFT BY EARLY NEXT WEEK. IN THE EAST...RAIN IS EXPECTED ALONG THE
COAST...WITH DAYTIME RAIN SHOWERS AND NIGHTTIME SNOW SHOWERS
CROSSING THE KENAI AND CHUGACH MOUNTAINS. THESE WILL DIMINISH IN
INTENSITY AT THE END OF THE WEEKEND AS HIGH PRESSURE MOVES ACROSS
THE MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 165 170 173.
  GALE WARNING 131 150 155 171 172 174 175 176 177 178 179.
  HEAVY FREEZING SPRAY...185.
FIRE WEATHER...NONE.

&&

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