Small Craft Advisory 302, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
513 PM AKDT SUN APR 5 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURES ARE THE UPPER LEVEL RIDGE NOW EXTENDING INTO
THE MAINLAND WHILE THE UPPER LEVEL AND SURFACE LOW ARE OVER THE
CENTRAL BERING SEA WITH THE UPPER LEVEL TROUGH AND ASSOCIATED
SURFACE FRONT EXTENDING TO THE EASTERN BERING SEA JUST OFFSHORE OF
THE BERING SEA COAST TO A TRIPLE POINT FORMING ALONG THE ALASKA
PENINSULA. THIS TRIPLE POINT LOW WILL BRING ROUND TWO OF
PRECIPITATION TO THE SOUTHCENTRAL REGION ALONG WITH STRONG WIND
THROUGH CHANNELED TERRAIN AND ACROSS THE ANCHORAGE HILLSIDE. THE
MAIN BERING SEA STORM IS SUPPORTING GALE FORCE WIND ALONG THE
ALEUTIANS AND CENTRAL BERING SEA IN THE SOUTHERN AND WESTERN
QUADRANTS OF THE LOW. WARMER AIR IS ADVECTING NORTH ALONG THE
FRONT AND IN THE SOUTHERLY FLOW IN ADVANCE OF THE UPPER LEVEL
TROUGH INTO THE EASTERN BERING SEA. IT IS IS EXPECTED TO PUSH
INTO THE BRISTOL BAY AREA TODAY CHANGING SNOW OVER TO RAIN OR A
MIX OF RAIN AND SNOW. COLD AIR IS WRAPPING AROUND THIS LOW AND
WILL RETURN TO SOUTHWEST ALASKA TONIGHT AND MONDAY. AN UPPER LEVEL
DISTURBANCE HAS MOVED OUT OF THE COOK INLET REGION ACROSS PRINCE
WILLIAM SOUND INTO THE NORTHERN GULF OF ALASKA. AS IT EXITS TO THE
SOUTHEAST IT IS TAKING WITH IT THE PRECIPITATION THAT OCCURRED
ACROSS THE SOUTH CENTRAL REGION AND PRINCE WILLIAM SOUND OVERNIGHT
THROUGH THIS AFTERNOON.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN EXCELLENT AGREEMENT THROUGH TUESDAY AFTERNOON.
THEY CAPTURE THE FRONTAL STRUCTURE AND TRIPLE POINT FORMING ALONG
THE ALASKA PENINSULA AND ARE ALL IN GOOD AGREEMENT BRINGING THE
ENERGY OF THE STORM SYSTEM FROM THE MAIN LOW NOW OVER THE BERING
SEA AND TRANSFERRING IT INTO THE TRIPLE POINT WHICH BECOMES THE
MAIN LOW MON NIGHT INTO TUESDAY MORNING. THE MAIN UNCERTAINTY IS
IN THE DETAILS OF EXACTLY WHERE THIS ENERGY (AND THUS THE MAIN
LOW) ENDS UP. THE MODELS HAVE BEEN TRENDING TOWARD A SOLUTION OF
A LOW ON THE WEST SIDE OF THE ALASKA RANGE THAT MOVES NORTH TUESDAY.
THIS WILL USE THE NAM FOR THE MOST PART FOR THE GRIDDED FORECAST
PRODUCTION TODAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEAK FRONT OVER THE GULF WILL USHER IN DEEP SOUTHWEST FLOW
TONIGHT AND BRING ANOTHER PERIOD OF LIGHT RAIN AND SNOW TO THE
COOK INLET REGION AND GULF COAST...WITH ANY ACCUMULATION EXPECTED
TO BE MINIMAL. A STRONGER FRONT WILL THEN MOVE INTO THE WESTERN
GULF ON MONDAY AND APPROACH THE GULF COAST MONDAY NIGHT. THIS
WILL INCREASE CROSS BARRIER FLOW OVER THE CHUGACH MOUNTAINS AND
THUS KEEP LOCATIONS IN THE LEE OF THE MOUNTAINS IN A MORE SHOWERY
REGIME DURING THE EARLY PART OF THE WORK WEEK. THE APPROACHING
FRONT AND A STEADILY INCREASING PRESSURE GRADIENT ACROSS
SOUTHCENTRAL AK WILL ALSO LEAD TO THE DEVELOPMENT OF STRONG GAP
WINDS THROUGH TURNAGAIN ARM AND THE KNIK RIVER VALLEY...WITH THE
STRONGEST WINDS EXPECTED LATE MONDAY EVENING INTO TUESDAY MORNING
ALONG TURNAGAIN ARM AND HIGHER ELEVATIONS. A HIGH WIND WATCH HAS
BEEN ISSUED ACCORDINGLY FOR THAT TIME FRAME...ALTHOUGH AN
INCREASING DOWN INLET GRADIENT WILL HELP TO KEEP THE STRONGEST
WINDS OUT OF THE ANCHORAGE BOWL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
MIXED RAIN AND SNOW TONIGHT WILL TRANSITION TO A MORE SHOWERY
REGIME ON MONDAY. SHOWERS HOWEVER WILL REMAIN ABUNDANT AS
SOUTHWESTERLY FLOW STREAMS ADDITIONAL MOISTURE ONSHORE AND
INSTABILITY INCREASES AS A COLD UPPER LEVEL TROUGH SWINGS ACROSS
THE ALASKA PENINSULA AND WEST COAST ON MONDAY. DESPITE THE
SIGNIFICANT COOLING ALOFT...THE HIGHER SPRING TIME SUN ANGLE WILL
KEEP THE SURFACE TEMPERATURES SLOW TO DROP AND PRECIPITATION TYPE
OF THE MIXED VARIETY LONGER.

THE NEXT SIGNIFICANT FEATURE TO WATCH FOR SOUTHWEST ALASKA WILL
BE THE TRIPLE POINT LOW SPINNING NEAR SHELIKOF STRAIT MONDAY
AFTERNOON AND EVENING. AS THIS LOW DEVELOPS A SECONDARY SURFACE
LOW WILL ALSO SPIN UP JUST TO THE WEST OF ILIAMNA MONDAY EVENING.
THIS LOW WILL TRACK TO THE NORTH-NORTHWEST MONDAY NIGHT AND TUESDAY
BRINGING THE POTENTIAL FOR SOME FAIRLY HEAVY PRECIPITATION...ESPECIALLY
TO EASTERN PORTIONS OF THE BRISTOL BAY ZONE AND THE LOWER KUSKOKWIM
VALLEY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE SURFACE LOW CENTERED NEAR ST MATTHEW ISLAND WILL CONTINUE TO
DEEPEN A COUPLE MORE MILLIBARS IN THAT GENERAL LOCATION TONIGHT
THEN TRACK GRADUALLY EAST TO NUNIVAK ISLAND THROUGH THE DAY
MONDAY. ALSO DURING THIS TIME PERIOD A TRANSIENT SURFACE RIDGE
WILL SLIDE IN FROM THE WEST AND OVER THE WESTERN ALEUTIANS.
NORTHWESTERLY GALES WILL BUILD ACROSS MUCH OF THE BERING AND
ALEUTIANS IN RESPONSE TO THE TIGHTENING SURFACE PRESSURE GRADIENT
BETWEEN THESE TWO FEATURES. ADDITIONALLY COLD AIR ADVECTION WITH
THE SHARP UPPER TROUGH SWINGING THROUGH WILL ALSO HELP STRONGER
GUSTY WINDS MIX DOWN AND SUPPORT ABUNDANT SHOWERS.

THE NEXT IN THE SERIES OF MANY FRONTAL SYSTEMS WILL TRACK INTO
THE FAR WESTERN BERING MONDAY NIGHT. A VERY STRONG JET STREAK (110
KT AT 500 MB AND 160 KT AT 300 MB) AS WELL AS A COLD UPPER LEVEL
TROUGH WILL CATCH UP WITH THE INITIAL SURFACE LOW JUST TO THE EAST
OF THE KAMCHATKA PENINSULA LATE MONDAY NIGHT AND EARLY TUESDAY
MORNING RAPIDLY DEEPENING AND STRENGTHENING THE SURFACE LOW AS IT
ACCELERATES EAST INTO THE BERING ON TUESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...WEDNESDAY THROUGH SUNDAY)...
THE FAMILY OF STORMS WILL CONTINUE TO CHUG THROUGH THE BERING
INTO THE MAINLAND DURING THIS TIME PERIOD. ONE STORM WILL LINGER
OVER SOUTH CENTRAL ON WED WHILE THE NEW PARENT LOW WILL BE OVER
THE WESTERN BERING. STARTING IN SOUTH CENTRAL...LINGERING MOISTURE
OVER MUCH OF THE COOK INLET REGION FROM DEEP SOUTH TO SOUTHWESTERLY
FLOW WILL SYNC UP WITH A SHARP TROUGH DROPPING OVER THE AK RANGE.
THIS COULD LEAD TO SOME LINGERING SNOW OVER THE SUSITNA VALLEY
BEFORE IT STARTS TO MIX WITH RAIN CLOSER TO COOK INLET. THERE WILL
BE VERY LITTLE TIME FOR ANYTHING TO DRY OUT AS THE BERING LOW
TRACKS QUICKLY TOWARDS THE STATE. THE PRECIPITATION ASSOCIATED
WITH THIS FEATURE SHOULD REACH THE WEST COAST AROUND MID-DAY WED.
THINGS WILL LIKELY START AS SNOW AROUND BRISTOL BAY BUT THEN SOME
WARMER AIR PUSHES IN AND WILL LEAD TO MORE OF A MIXED PRECIP TYPE.
COLDER AIR FOR THE YK DELTA SHOULD KEEP THINGS PRIMARILY SNOW UP
THAT FAR NORTH.

ON THURSDAY WE SEE THE ENERGY ASSOCIATED WITH THIS EXPANSIVE
SYSTEM START TO CROSS THE ALEUTIAN AND ALASKA RANGES. AS IT DOES
SO...A NEW TRIPLE POINT LOW SHOULD FORM SOMEWHERE NEAR KODIAK
ISLAND THURSDAY MORNING. THIS PATTERN COULD BE NEARLY IDENTICAL TO
THE ONE WE SEE EARLY IN THE WEEK. IMPACTS WILL ONCE AGAIN INCLUDE
STRONG WINDS FOR MUCH OF SOUTHCENTRAL...ESPECIALLY AREAS THAT
FAVOR A NORTHEAST TO SOUTHEAST FLOW. A WIDE AREA OF PRECIPITATION
WILL TRACK UP FROM KODIAK ISLAND...INTO THE KENAI PENINSULA...AND
QUICKLY INTO THE MATANUSKA-SUSITNA VALLEY BY LATE THU. THE COASTAL
AREAS WILL ONCE AGAIN SEE THE HEAVIEST AMOUNTS OF RAIN WHILE
INLAND AREAS ON THE LEE SIDE OF THE MOUNTAINS WILL BE SPARED FROM
THE HEAVIEST AMOUNTS BY SOME CROSS BARRIER FLOW. THIS SYSTEM WILL
ALSO BRING ANOTHER ROUND OF WARM AIR...ESPECIALLY WITH THE STRONG
WINDS...BEFORE IT PULLS SOME COLD AIR FROM THE WEST AND NORTHWEST
AS IT DEPARTS. THIS MEANS THAT WHILE THINGS WILL LIKELY START AS
RAIN FOR MOST PLACES...WE COULD SEE IT CHANGE TO A MIX AND EVEN
ALL SNOW THROUGH FRI. WE ARE STILL WATCHING THIS EVENT QUITE
CLOSELY AS MANY OF THE MODELS TRENDED SLIGHTLY FURTHER NORTH WITH
THE LOW CENTER IN THE GULF IN THE LATEST RUNS. IF THAT LOW SHOULD
BE ABLE TO SNEAK INTO THE PRINCE WILLIAM SOUND AND BRING THE RIGHT
AMOUNT OF MOISTURE AND COLD AIR INTO THE COOK INLET REGION COULD
SEE SNOW HANG ON A BIT LONGER.

HEADING INTO NEXT WEEKEND...THE PATTERN WILL SLOW DOWN IN A
RELATIVE SENSE. A VERY BROAD UPPER LEVEL TROUGH WILL STRETCH FROM
EASTERN RUSSIA TO THE ALCAN BORDER AND DOWN INTO THE GULF OF AK.
THIS WILL KEEP TEMPERATURES ON THE COOL SIDE WITH ABUNDANT CLOUD
COVER. BY LATE IN THE WEEKEND...A NEW AREA OF LOW PRESSURE
IMPINGES ON THE WESTERN ALEUTIANS FROM THE NORTHWEST PACIFIC. THIS
SYSTEM THEN LEADS TO A FAIRLY CLASSIC SPRING CLASH OF LINGERING
COLD WINTER AIR AGAINST A WARM RIDGE TRYING TO BUILD OVER THE
ALASKA PENINSULA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 125 129 130 131 132 155 165 170 171
         172 173 174 175 176 177 179 185.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...MO