Small Craft Advisory 446, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
546 PM AKDT WED JUN 4 2014

.ANALYSIS AND UPPER LEVELS...

THERE IS A LARGE UPPER LEVEL RIDGE OF HIGH PRESSURE CENTERED OVER
THE NORTHERN BERING SEA. THERE IS AN UPPER LOW TO THE SOUTH OF
THIS HIGH OVER THE ALEUTIANS AND NORTH CENTRAL PACIFIC...AND
ANOTHER LOW OFF THE NORTHWEST COAST OF ALASKA. SOUTHWEST ALASKA IS
FIRMLY UNDER THE CONTROL OF THE HIGH WITH WARM AND DRY WEATHER.
SOUTH CENTRAL ALASKA IS IN AN AREA OF WEAK FLOW TO THE EAST OF THE
HIGH AND THUS THERE IS SOME MOISTURE AND DIURNAL SHOWERS (MAINLY
OVER THE MOUNTAINS). AT THE SURFACE THERE IS A HIGH OVER THE
NORTHERN GULF OF ALASKA AND ANOTHER UNDERNEATH THE NORTH BERING
RIDGE. A WEAK THERMAL TROUGH IS IN BETWEEN THESE FEATURES OVER
SOUTHWEST AND SOUTH CENTRAL ALASKA. A WEATHER FRONT ASSOCIATED
WITH THE PACIFIC/ALEUTIAN HIGH IS OVER THE EASTERN ALEUTIANS AND
THE ALASKA PENINSULA AND IS BRINGING SOME RAIN AND WINDS TO THOSE
AREAS.

&&

.MODEL DISCUSSION...

MODELS REMAIN IN GOOD AGREEMENT THROUGH THE MAJORITY OF THE SHORT
TERM WITH A RIDGE OF HIGH PRESSURE OVER THE EASTERN BERING SEA
RETROGRADING AS A LOW MOVES SOUTH OF THE ALASKA PENINSULA AND INTO
THE GULF THIS WEEKEND. DISCREPANCIES REMAIN IN THE TIMING OF
MULTIPLE WAVES ALONG THE FRONT ASSOCIATED WITH THE LOW...WITH THE
GFS BEING A BIT FASTER AND FURTHER EAST WITH THE FIRST WAVE ALONG
THE FRONT. THE MODELS ARE HAVING A BIT OF DIFFICULTY DISCERNING
HOW A DESCENDING ARCTIC TROUGH WILL INTERACT WITH THE LOW MOVING
INTO THE GULF. THE GFS IS TRYING TO PHASE THE LOW WITH THIS
ARCTIC TROUGH WHICH SEEMS TO BE THE CAUSE FOR THE DIFFERENCE IN
UPPER LOW PLACEMENT. THE NAM/ECMWF/GEM ARE IN BETTER AGREEMENT
WITH A SLOWER PROPAGATION OF THE FRONT THROUGH THE GULF AND KEEP
THE ARCTIC TROUGH AND LOW IN THE GULF SEPARATE. A MIX OF ECMWF/GEM
REGIONAL WERE UTILIZED IN THIS FORECAST PACKAGE FOR RUN- TO-RUN
CONSISTENCY AND DETAIL.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A WEAK SHORT WAVE PUSHING ACROSS THE
INTERIOR OF ALASKA HAS ALLOWED FOR SOME CONVECTIVE SHOWERS TO
DEVELOP ALONG THE INLAND MOUNTAIN RANGES OF THE MAT-SU VALLEY AND
COPPER RIVER BASIN. MOST OF THESE SHOWERS WILL BE CONFINED TO THE
IMMEDIATE VICINITY OF THESE MOUNTAINOUS AREAS BUT A FEW SHOWERS
MAY DRIFT AWAY FROM THE MOUNTAINS IN THE MATANUSKA VALLEY.
CONVECTIVE SHOWERS WILL ONCE AGAIN BE POSSIBLE TOMORROW AFTERNOON.
A COASTAL RIDGE HAS BEGUN TO STRENGTHEN ALONG THE GULF COAST AND
HAS ALLOWED FOR SOME GUSTY WINDS TO DEVELOP ACROSS SOUTHCENTRAL
ALASKA. THIS RIDGE WILL CONTINUE TO STRENGTHEN ON THURSDAY AND
FRIDAY...LEADING TO GUSTY WINDS IN THE MATANUSKA VALLEY...ALONG
THE COPPER RIVER AND ALONG TURNAGAIN ARM AND THE HILLSIDE. THESE
GUSTY WINDS WILL COMBINE WITH LOW RELATIVE HUMIDITIES IN THE
COPPER RIVER BASIN TO PRODUCE RED FLAG CONDITIONS ON THURSDAY AND
FRIDAY. POTENTIAL RED FLAG CONDITIONS WILL BE POSSIBLE FOR
ANCHORAGE AND THE MATANUSKA VALLEY ON FRIDAY. TEMPERATURES WILL
REMAIN ABOVE NORMAL THROUGH THE REMAINDER OF THE WEAK FOR MOST OF
SOUTHCENTRAL AS WEAK HIGH PRESSURE OVER THE REGION TAKES HOLD. A
FRONT HAS BEGUN TO MOVE INTO THE SOUTHERN GULF OF ALASKA AND WILL
BEGIN TO BRING RAIN CHANCES TO KODIAK ISLAND TOMORROW AFTERNOON
AND SPREAD TOWARD THE GULF COAST FRIDAY AND THROUGH THE WEEKEND.

SOUTHWEST ALASKA...HIGH PRESSURE CENTERED OVER THE EASTERN BERING WILL
SLIDE WEST INTO THURSDAY. WITH OFFSHORE FLOW IN ITS WAKE..DRIER AIR
WILL  PUSH OFF THE COASTLINE. THIS SHOULD HELP TO LIMIT ANY AREAS OF
DENSE FOG LIKE WE SAW THIS MORNING ALONG THE KUSKOKWIM DELTA COAST.
IT WILL ALSO SET THE STAGE FOR MORE WIDESPREAD DIURNAL SHOWERS
THURSDAY AFTERNOON AND EVENING. THIS PATTERN WILL BE SHORT LIVED
THOUGH AS FRIDAY WE SEE A COLD FRONT DIVING DOWN FROM THE ARCTIC
COLLIDING WITH A WARM...MOIST SYSTEM SOUTH OF THE AKPEN. GUSTY EAST
TO SOUTHEAST WINDS WILL ACCOMPANY THIS SYSTEM. THEY WILL INCREASE
FROM THE AKPEN DURING THE DAY THURSDAY AND SPREAD TOWARD THE ALASKA
RANGE BY THURSDAY NIGHT. AND WHILE WETTING RAINS WILL NOT BE
WIDESPREAD WITH THIS FRONTAL BOUNDARY...THIS WILL BRING COOLER AND
MOISTER CONDITIONS FOR THE WEEKEND.

BERING SEA/ALEUTIANS...THE TWO MAIN WEATHER DRIVERS ARE A FILLING
LOW  SOUTH OF THE EASTERN ALEUTIANS AND HIGH PRESSURE OVER THE
EASTERN BERING.  FIRST...THE CLOCKWISE FLOW AROUND THE HIGH IS
CLEARLY EVIDENT IN SATELLITE IMAGERY THIS EVENING. THIS DRY AIR IS
PUSHING OFF THE YUKON-KUSKOKWIM DELTA  AND IS HELPING TO SLOWLY
CLEAR THE REMAINING FOG OUT OF THE PRIBILOFS.  THE WEAKENING LOW IS
TRACKING PARALLEL TO THE EASTERN ALEUTIANS. IT IS BRINGING CLOUDS
AND RAIN TO MUCH OF THE SOUTH SIDE OF THE CHAIN...HOWEVER THE NORTH
SIDE IS STAYING RELATIVELY DRY AND EVEN CLEAR IN SOME SPOTS. THE TWO
SYSTEMS ARE WORKING TOGETHER TO MAKE A TIGHT GRADIENT OVER 181 AND
EXTREME SOUTHWEST 161 TO PRODUCE SOME GUSTY SOUTHEASTERLY WINDS.
WHILE THE HIGH SLOWLY RETROGRADES OVER THE NEXT FEW DAYS...AN UPPER
LEVEL TROUGH WILL SLIDE SOUTH JUST WEST OF SHEMYA. THIS ENERGY WILL
CATCH UP TO THE PREVIOUSLY MENTIONED LOW AND HELP TO REINFORCE THE
BROAD TROUGH THAT WILL ESTABLISH ITSELF SOUTH OF THE AKPEN TOWARDS
THE WEEKEND. THIS WILL KEEP MOST OF THE BERING UNDER RELATIVELY WEAK
AND QUIET NORTH TO NORTHWEST FLOW.

&&

.LONG TERM FORECAST...

THE MODELS CONTINUE TO PAINT A SIMILAR PICTURE WITH THE LONG TERM
FORECAST STARTING LATE THIS WEEKEND. ONCE THE ARCTIC TROUGH SETS
UP AND BECOMES QUASI STATIONARY OVER THE EASTERN BERING ON
SUNDAY...MUCH OF THE MAINLAND WILL FALL UNDER A MORE ACTIVE
WEATHER PATTERN. THIS WILL BE ESPECIALLY TRUE FOR THE WEST
MAINLAND AND AREAS OF THE GULF COAST. INTERIOR LOCATIONS OF
SOUTHCENTRAL WITH LIKELY SEE MORE BREAKS IN RAINFALL AS A SERIES
OF WEAK LOWS MOVE THROUGH THE GULF BY THE EARLY OF NEXT WEEK...BUT
SKIES WILL REMAIN MOSTLY CLOUDY WITH BELOW NORMAL TEMPERATURES
STARTING LATE THIS WEEKEND. IT REMAINS QUITE UNCERTAIN HOWEVER HOW
LONG THIS PATTERN WILL LAST HOWEVER...AS THERE IS DISAGREEMENT IN
THE MODELS AS TO WHETHER IT WILL BEGIN TO BREAK DOWN MID WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE...138.
FIRE WEATHER...RED FLAG WARNING...141
               RED FLAG WATCH.....101 111

&&

MMC/MSO/BL JUN 14