Small Craft Advisory 278, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
425 PM AKDT SUN MAR 29 2015

.ANALYSIS AND UPPER LEVELS...
A LARGE LOW COMPLEX IS SITUATED OVER THE WESTERN GULF OF ALASKA
THIS AFTERNOON WITH RAIN EXTENDING ALONG THE NORTHERN GULF COAST
THROUGH SOUTHEAST ALASKA. RAIN IS ALSO PRESENT FROM KODIAK ISLAND
TO THE EASTERN ALEUTIANS. INLAND LOCATIONS ARE REMAINING DRY AT
THE MOMENT WITH A VERY DRY LOW LEVEL. SO...VIRGA IS PRESENT FROM
BRISTOL BAY TO THE ANCHORAGE BOWL. OUT WEST...A LOW NEAR THE
KAMCHATKA PENINSULA PUSHING A FRONT THROUGH THE WESTERN ALEUTIAN
CHAIN. WITH HIGH PRESSURE IN BETWEEN THE TWO SYSTEMS...MODERATE
NORTH WINDS FROM KODIAK ISLAND WEST TO THE EASTERN BERING SEA.
GRADIENT TO WEAKEN SOMEWHAT TONIGHT FOR LIGHTER WINDS AS THE LOW
OVER KODIAK ISLAND MOVES INLAND OVER SOUTHWEST ALASKA AND THE LOW
WELL SOUTH OF KODIAK ISLAND BEGINS TO SWING NORTHEAST INTO THE
GULF OF ALASKA.

AT UPPER LEVELS...A CLOSED LOW NEAR SHEMYA DRIVING THE WESTERN
ALEUTIAN LOW WITH THE JET ENTRANCE REGION. THIS IS WHAT IS
FAVORING THIS LOW TO MOVE RATHER SLOW TIL A SECOND JET STREAK
ARRIVES IN THE VICINITY TONIGHT. THE LOW IN THE GULF IS ASSOCIATED
WITH A CLOSED LOW SOUTH OF KODIAK ISLAND WITH A VORT MAX OVER THE
ISLAND THAT EXTENDS TO THE CHUGACH MOUNTAINS. THIS VORT MAX TO
ROTATE WEST TONIGHT INTO SOUTHWEST ALASKA SPREADING SOME MOISTURE
INLAND OVER SOUTHWEST ALASKA TONIGHT. MOST INLAND LOCATIONS WILL
REMAIN DRY. THIS VORT MAX TO MEET WITH A VORT MAX OVER THE
EASTERN BERING SEA CREATING AN AREA OF CONVERGENCE OVER SOUTHWEST
ALASKA FOR RAIN TO BEGIN...ALBEIT LIGHT.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT TODAY THROUGH MUCH OF WEDNESDAY ON
THE BIGGER FEATURES. THERE IS A BIT OF DISCREPANCY IN A VORT MAX
ROTATING IN THE GULF OF ALASKA MONDAY NIGHT INTO TUESDAY. THE NAM
WRAPS THIS FEATURE INTO THE LARGE LOW COMPLEX OVER THE GULF OF
ALASKA. THIS RESULTS IN A STRONGER SURFACE TROUGH LEADING TO A
BIT STRONGER WINDS AND PRECIP IN THE NORTHERN GULF. THE LOW
COMPLEX SOUTH OF THE GULF OF ALASKA BECOMES MORE CONCISE INTO
TUESDAY AS IT ROTATES INTO THE GULF OF ALASKA. THIS LOW WILL
EVENTUALLY LIFT ACROSS THE NORTHERN PANHANDLE BY WEDNESDAY
AFTERNOON. WHAT SPARKS THE LOW LIFTING OUT OF THE GULF IS ANOTHER
LOW MOVING INTO THE WESTERN GULF WEDNESDAY AFTERNOON. THIS LOW IS
MUCH LARGER THAN THIS FIRST ONE. HOW THIS ONE DEVELOPS IS
CURRENTLY BASED UPON THE LOW NEAR SHEMYA CURRENTLY. THE LOW NEAR
SHEMYA IS STALLING CURRENTLY WITH NO UPPER LEVEL ENERGY SUPPORT. A
NEW JET STREAK TO HELP THIS LOW ALONG TONIGHT INTO TOMORROW WITH A
TRIPLE POINT DEVELOPING INTO A LOW SOUTH OF ADAK TOMORROW
AFTERNOON AND SLIDING EAST WITH UPPER LEVEL SUPPORT DIVING INTO
AND AROUND THE LOW. THE LOW DEVELOPS INTO A CLOSED AND STACKED LOW
BY WEDNESDAY SOUTH OF AKPEN. ALL MODELS UP TO THIS POINT...ARE IN
FAIR AGREEMENT. IN THE MEANTIME...A STACKED LOW ARRIVES OVER THE
KAMCHATKA PENINSULA. THIS IS WHERE WE START TO SEE SOME
UNCERTAINTY START TO CREEP INTO THE FORECAST. A RIDGE STARTS TO
DEVELOP OVER THE BERING SEA BETWEEN THE LOW IN THE GULF AND THE
LOW NEAR THE KAMCHATKA PENINSULA. HOW THE ENERGY AROUND THE
KAMCHATKA LOW INTERACTS WITH THE RIDGE AND SMALLER CLOSED LOW IN
THE CHUKCHI SEA CHANGES THE AMPLIFICATION OF THE RIDGE AND HOW
PROGRESSIVE THE ENERGY LEAVING THE KAMCHATKA LOW BEHAVES. THE
MODEL RUN TO RUN CONSISTENCY IS NOT HELPING THE DETERMINATION OF
THE SOLUTION AS WELL. OVERALL...THIS DOES NOT CREEP INTO THE
SURFACE FEATURES UNTIL FRIDAY. WITH UNCERTAINTY HIGH FOR THE
WEEKEND.

&&

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

CYCLONIC FLOW OVER THE GULF OF AK WILL CONTINUE TO SEND WAVES OF MOISTURE
TO THE NORTH GULF COAST THROUGH TUE. RAIN SHOWERS ALONG THE COAST WITH
SNOW INLAND OVER HIGHER ELEVATIONS WILL PERSIST. SOME RAIN SHOWERS WILL
CROSS THE CHUGACH AND KENAI MOUNTAINS AND AFFECT THE LEEWARD SIDE
OF THE INLAND ZONES...ALONG WITH SOME SNOW SHOWERS FOR THE
MATANUSKA VALLEY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...MON AND
TUE)...THE SLOW MOVING QUIET PATTERN WILL CONTINUE TO START THE
WEEK. THE OFFSHORE FLOW THAT HAS BEEN KEEPING THINGS DRY SHOULD
DIMINISH AND SHIFT TO A BIT MORE OF A NORTHERLY DIRECTION
OVERNIGHT. THIS WILL ALLOW SOME FOG TO FORM...ESPECIALLY FROM
ANIAK TO BETHEL.

BROAD MID-LEVEL CONVERGENCE WILL OVERTAKE THE ENTIRE AREA INTO
MONDAY. THE LOW NEAR KODIAK ISLAND WILL DRIFT SLOWLY TOWARD THE
ALEUTIAN RANGE TONIGHT. THIS WILL PUSH A HEALTHY AMOUNT OF
MOISTURE INTO SOUTHWEST ALASKA. PRECIPITATION SHOULD BE ABLE TO
MAKE IT OVER THE ALEUTIAN RANGE BY EARLY MONDAY MORNING AND THEN
TRACK WEST THROUGH THE DAY. AT THE SAME TIME...A WEAK UPPER LEVEL
WAVE ASSOCIATED WITH SOME COLDER AIR OUT OVER THE BERING WILL CHUG
NEAR NUNIVAK ISLAND. AS THESE TWO FEATURES PRESS UP AGAINST EACH
OTHER...THEY COULD WRING OUT ABUNDANT RAIN AND SNOW SHOWERS. THESE
SHOWERS WILL BE VERY DIFFICULT TO PIN POINT FOR TIMING AND
LOCATION....SO HAVE BROAD-BRUSHED POPS ACROSS MOST OF THE AREA.
NONE OF THEM LOOK TO PRODUCED MUCH IN THE WAY OF ACCUMULATION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...MON AND
TUE)...THE PATTERN WILL START TO MOVE A BIT MORE QUICKLY TO START
THE WEEK...BUT IMPACTS WILL REMAIN VERY MINIMAL. THE DECAYING
FRONT THAT IS CURRENTLY STRETCHED FROM ADAK TOWARDS THE KAMCHATKA
PENINSULA WILL CONTINUE TO DRIFT EVER-SO-SLIGHTLY EAST AND FALL
APART TONIGHT. THE BIGGER STORY WILL BE A NEW PHASING LOW THAT
DEVELOPS WITH MODEST UPPER LEVEL SUPPORT JUST SOUTH OF SHEMYA.
THIS LOW WILL CONTROL MOST OF THE SENSIBLE WEATHER FOR THE NEXT
FEW DAYS AS IT TRACKS ALONG JUST SOUTH OF THE CHAIN AND BRINGS
AMPLE PRECIPITATION. IT WILL BE ABLE TO TAP INTO SOME WARMER AIR
FROM THE N PAC AND FORM A TRIPLE POINT BEFORE IT BEGINS TO OCCLUDE
MON NIGHT. THIS SHOULD LEAD TO MIXED PRECIPITATION FOR DUTCH
HARBOR AND COLD BAY TUESDAY. ON THE BACKSIDE OF THIS SYSTEM...WITH
COLD AIR STILL ENTRENCHED OVER THE BERING...WE DO EXPECT SOME
DECENT PRESSURE RISES. THIS SHOULD BRING AN RELATIVELY SMALL
SWATCH OF GALE FORCE NORTH TO NORTHWEST WINDS LATE TUESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODEL GUIDANCE IS IN GOOD AGREEMENT WITH A STACKED SYSTEM
MIGRATING FROM THE EASTERN ALEUTIANS/ALASKA PENINSULA INTO THE
GULF OF ALASKA BY LATE WEEK. THIS SYSTEM WILL BE WEAKENING AS IT
MOVES ACROSS WITH THE FRONTAL BOUNDARY JUST REACHING INTO THE
NORTHERN GULF. COLD TEMPERATURES ALOFT AND INCREASING CYCLONIC
FLOW SHOULD PROMOTE MOUNTAIN SHOWERS ACROSS MUCH OF THE NORTH GULF
COAST WHILE THIS SYSTEM STAYS OVERHEAD. AS THE UPPER LOW EXITS TOWARD
THE PANHANDLE A BRIEF PERIOD OF OUTFLOW TYPE CONDITIONS WILL
EXIST...HOWEVER THERE DOESN'T APPEAR TO BE ENOUGH COLD AIR TO
SUPPORT ANY KIND OF SIGNIFICANT WIND. OVER THE WEEKEND GUIDANCE IS
HINTING AT PATTERN AMPLIFICATION AS A SYSTEM OVER KAMCHATKA MOVES
INTO THE BERING SEA. THERE IS SOME DISAGREEMENT IN THE EVOLUTION
OF THE PATTERN BETWEEN FULL AMPLIFICATION OR CUTTING OFF OF THE
UPPER LEVEL ENERGY...LEADING TO A MORE PROGRESSIVE PATTERN. EXPECT
ABOVE NORMAL TEMPERATURES TO CONTINUE THROUGH MUCH OF THE PERIOD
WITH MAINLY DRY CONDITIONS...EXCEPT FOR THE CHANCE FOR RAIN AND
RAIN SHOWERS ALONG THE COAST LATE WEEK...DRYING OUT BY THE
WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 130.
 HEAVY FREEZING SPRAY 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JN
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...ML