Small Craft Advisory 485, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
432 PM AKDT SUN JUN 7 2015

.ANALYSIS AND UPPER LEVELS...
CURRENTLY ACROSS THE ALASKAN AREA...THERE IS STILL A DOMINANT
UPPER LEVEL LOW NEAR THE BERING STRAIT WITH A TROUGH AXIS
EXTENDING BACK TO THE NORTHWEST BERING SEA. A BROAD TROUGH EXTENDS
EASTWARD FROM THERE TO THE GULF OF ALASKA. ALONG THE DATELINE NEAR
THE POLE SITS ANOTHER UPPER LOW. WITH THIS PATTERN...A MORE OR
LESS ZONAL JET EXTENDS FROM 170E TO 160W WITH A CORE OF 145 KT.
THE EXIT REGION OF THE JET IS SUPPORTING A SURFACE LOW NEAR THE
CENTRAL ALEUTIANS AS EVIDENCED BY SATELLITE IMAGERY. NO GALE FORCE
WINDS ACCOMPANY THIS LOW BUT AREAS OF RAIN ARE SPREADING TO THE
CENTRAL AND EASTERN ALEUTIANS. OVER THE MAINLAND...A COUPLE OF
SHORT WAVES COMBINED WITH A SOMEWHAT UNSTABLE AIR MASS ARE POPPING
CONVECTION. ONE SHORT WAVE TROUGH IS PUSHING INTO SOUTHWEST ALASKA
OUT OF THE BERING STRAIT LOW SPARKING SCATTERED TO NUMEROUS
SHOWERS OVER SOUTHWEST ALASKA. IT IS ALSO BRINGING SOME MODERATE
WINDS TO THE COAST. ANOTHER SHORT WAVE TROUGH IS LIFTING THROUGH
THE NORTHERN GULF OF ALASKA TODAY AND WILL PHASE WITH THE
SOUTHWEST ALASKA WAVE MOVING NORTH THROUGH THE MAINLAND TONIGHT.
THE AIR MASS OVER THE MAINLAND IS QUITE UNSTABLE AND WE HAD ONE
REPORT OF SMALL HAIL OUT OF A THUNDERSTORM THIS AFTERNOON.

&&

.MODEL DISCUSSION...
PATTERN CHANGE ON THE WAY FOR THE BERING SEA AS A DEEPER TROUGH
WILL GIVE WAY TO A MORE ZONAL PATTERN BY THE END OF NEXT WEEK.
GIVEN THIS TRANSITION...SURPRISINGLY NUMERICAL GUIDANCE REMAINS IN
FAIRLY GOOD AGREEMENT ON THE PATTERN SWITCH THROUGH THE WEEK.

THE CURRENT BERING LOW WILL SPLIT AND PHASE WITH THE POLAR LOW AS
WELL AS THE LOW MAKING ITS WAY OUT OF THE KAMCHATKA REGION OVER
THE NEXT 48 HOURS. THE PIECES THAT PHASE TOGETHER WITH THE NORTH
PACIFIC JET HELP TO CONSTRUCT A MODERATE LOW NEAR THE ALASKA
PENINSULA MONDAY EVENING INTO TUESDAY WITH A GOOD FRONT PUSHING
INTO THE WESTERN GULF OF ALASKA. AHEAD OF THIS FEATURE...THE SHORT
WAVE TROUGHS FROM SOUTHWEST ALASKA AND THE NORTHERN GULF LIFT OVER
THE MAINLAND LATE TONIGHT AND INTO MONDAY. A SHORT WAVE TROUGH
AHEAD OF THE MAIN LOW WILL ACCOMPANY THE FRONT MOVING INTO THE
WESTERN GULF MONDAY AFTERNOON/EVENING. AT THE SAME TIME...THE
PHASING OF THE UPPER FEATURES PUMPS UP THE RIDGE OVER THE EASTERN
GULF INTO THE YUKON. RIDGE BUILDS IN THE WESTERN BERING BEHIND
THIS FEATURE IN THE EASTERN BERING. THE SURFACE LOW/UPPER LEVEL
LOW SWING INTO THE GULF TUESDAY NIGHT/WEDNESDAY AND START TO LOSE
INTENSITY AS THE JET REMAINS SOUTH AND POINTED TO BRITISH
COLUMBIA. AT THIS SAME TIME...THE POLAR LOW DIVES INTO THE CHUKCHI
SEA WEDNESDAY. AS THE PATTERN MOVES FORWARD THURSDAY...THE LOW
TRANSITIONS TO A TROUGH OVER THE GULF OF ALASKA AND CONTINUES TO
SWING EAST TOWARD THE PANHANDLE AS THE RIDGE IN THE WESTERN BERING
STRETCHES OVER THE ENTIRE BERING SEA. THE POLAR LOW DIGS A TROUGH
OVER EASTERN RUSSIA AS ANOTHER LOW DEVELOPS SOUTH OF THE KAMCHATKA
REGION. A PIECE OF THE POLAR LOW PHASES WITH THE KAMCHATKA LOW
FRIDAY INTO SATURDAY BUILDING THE UPPER RIDGE AND SURFACE HIGH
PRESSURE OVER THE SOUTHERN MAINLAND AND EASTERN BERING SEA THROUGH
SUNDAY. MEANWHILE...THE OTHER PORTION OF THE POLAR LOW REMAINS IN
THE ARCTIC/BEAUFORT SEA AREA KEEPING NORTHERN ALASKA COOL AND WET.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...MONDAY
AND TUESDAY)...A FEW SHOWERS AND THUNDERSTORMS HAVE ONCE AGAIN
POPPED UP ACROSS THE AREA THIS EVENING WITH EVEN SOME SMALL HAIL
REPORTED IN PALMER. THESE SHOULD BE SHORT LIVED AS THEY MUST
CONTEND WITH THE LOSS OF DAYTIME HEATING AND SHORTWAVE RIDGING
BUILDING IN FROM THE SOUTHWEST.

AS WE HEAD INTO MONDAY...THE BIGGER STORY WILL BE THE DEVELOPING
SOUTHEASTERLY WINDS. A NEW AREA OF LOW PRESSURE WILL CONTINUE TO
RIDE THE JET RIGHT ALONG THE ALEUTIAN CHAIN AND INTO THE WESTERN
GULF BY TUESDAY. A COASTAL RIDGE WILL BUILD ALONG THE NORTHERN
GULF AHEAD OF THIS SYSTEM. THIS WILL PRODUCE A RATHER TIGHT
GRADIENT OVER MUCH OF THE REGION MAKING FOR WINDS UP TO 55 MPH IN
TURNAGAIN ARM AND 35 MPH FOR THE COPPER RIVER BASIN. IN THE
COPPER RIVER BASIN...THESE DOWNSLOPING WINDS WILL HELP RELATIVE
HUMIDITIES TO REACH CRITICAL DRY LEVELS AS WELL. WE HAVE ISSUED A
RED FLAG WARNING TO ADDRESS THIS.

FOR THE ANCHORAGE BOWL AND MAT-SU VALLEY TONIGHT INTO EARLY
MONDAY...A WEAK DEFORMATION ZONE WILL DEVELOP BETWEEN THE PARENT
LOW OVER THE BERING STRAIT AND THE WEAKENING SYSTEM IN THE
NORTHEASTERN GULF. THIS WILL MAKE FOR AN AREA OF LIGHT RAIN
DEVELOPING AFTER MIDNIGHT AND PERSISTING THROUGH MUCH OF MONDAY.
BY MONDAY AFTERNOON INCREASING DEEP LAYER SOUTHEASTERLY FLOW
SHOULD BE ENOUGH TO START TO DRY OUT THESE AREAS IN THE LEE OF THE
CHUGACH.

FOR TUESDAY...THE BULK OF THE PRECIPITATION WILL SPREAD FROM THE
EASTERN KENAI PENINSULA UP THROUGH PRINCE WILLIAM SOUND. THE
STRONG SOUTHEASTERLY FLOW WILL PERSIST KEEPING STRONG GUSTS
THROUGH CHANNELED TERRAIN. THESE WINDS WILL ALSO KEEP MAINLY
INLAND LOCATIONS MOSTLY DRY WITH JUST A FEW STRAY SHOWERS MAKING
IT OVER THE MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SCATTERED TO NUMEROUS SHOWERS WILL CONTINUE TO DEVELOP THIS
EVENING AS A SHORTWAVE MOVES ACROSS THE SOUTHWEST. ISOLATED
THUNDERSTORMS ARE POSSIBLE ACROSS THE KUSKOKWIM VALLEY AND THE
ALEUTIAN RANGE THIS EVENING WHERE THE ATMOSPHERE IS MOST UNSTABLE.
A FRONT MOVES INTO THE SOUTHWEST COAST MONDAY MORNING AND STALLS
ACROSS THE SOUTHWEST THROUGH MIDWEEK BRINGING COOLER CONDITIONS
WITH PERIODS OF RAIN THROUGH TUESDAY. GUSTY WINDS ALONG THE FRONT
CAN BE EXPECTED WITH A LONGER DURATION OF HIGHER WINDS ACROSS THE
ALEUTIAN RANGE WHERE THE PRESSURE GRADIENT INCREASES BETWEEN A
SURFACE LOW FROM THE ALASKA PENINSULA AND RIDGING ACROSS THE
NORTHERN GULF.

&&

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

A FRONT MOVES ACROSS THE EASTERN ALEUTIANS TONIGHT WITH A SECOND
FRONT PUSHING UP FROM THE NORTH PACIFIC TO CENTRAL ALEUTIANS EARLY
MONDAY MORNING. BOTH FRONTS PROGRESS EASTWARD SPREADING RAIN FROM
THE ALASKA PENINSULA AND THEN NORTH INTO THE BERING AND SOUTHWEST
MAINLAND THROUGH TUESDAY. MOSTLY CLOUDY CONDITIONS ACROSS THE
WESTERN BERING WILL ALSO SEE ISOLATED SHOWERS AS THE PARENT LOW
NEAR THE BERING STRAIT CONTINUES TO SEND SHORTWAVES TO THE SOUTH.
NORTH TO WEST FLOW RETURNS ACROSS THE BERING AND ALEUTIANS BEHIND
THE FRONT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE POLAR LOW IN THE ARCTIC WILL WEAKEN AND MOVE NORTHWARD LATE
IN THE WEEK. THE LONGWAVE TROUGH EXTENDING OUT OF THIS LOW AND
OVER SOUTHWEST ALASKA TUESDAY NIGHT WILL MOVE OVER SOUTHCENTRAL
ALASKA WEDNESDAY. THE COOLER AIR ALOFT ON TUESDAY NIGHT AND
WEDNESDAY WILL MAKE THE ATMOSPHERE CONDUCIVE FOR SHOWERS AND A FEW
THUNDERSTORMS FROM THE ALASKA RANGE EASTWARD. THURSDAY THE UPPER
LEVEL FLOW BECOMES MORE ZONAL WHICH WILL KEEP A FEW SHOWERS AROUND
BUT THE AIR ALOFT WILL BE WARMING WHICH WILL LIMIT MOST OF THE
SHOWER ACTIVITY. ON FRIDAY HIGH PRESSURE BEGINS TO BUILD BACK
OVER SOUTHWEST AND SOUTHCENTRAL ALASKA. THIS WILL BRING WARMER
WEATHER TO MOST OF THE FORECAST AREA BY LATE IN THE WEEK AND INTO
NEXT WEEKEND. THIS IS A CHANGE FROM PREVIOUS FORECASTS AS
CONFIDENCE IS INCREASING THAT THE RIDGE WILL BE BUILDING INTO
SOUTHERN ALASKA LATE IN THE WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...120 130 131.
FIRE WEATHER...141.

&&

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