Small Craft Advisory 493, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
442 AM AKDT WED JUN 10 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN UPPER LEVEL LOW IS ANCHORED OVER THE ARCTIC AND CONNECTS
TO A CUT OFF LOW CURRENTLY PUSHING INTO THE WESTERN GULF
TODAY...WITH THE SURFACE LOW FOLLOWING CLOSELY BEHIND OVER WESTERN
KODIAK ISLAND. RAIN CONTINUES TO FALL OVER THE COASTAL AREAS
AROUND THE NORTHERN GULF COAST AND COOK INLET TODAY...AS THE FRONT
ASSOCIATED WITH THE AFOREMENTIONED LOW SLOWLY DECAYS OVER THE AREA
TODAY. A WEAK WAVE BEHIND THIS FRONT CURRENTLY TRACKING OVER THE
GULF TODAY WILL BRING ANOTHER ROUND OF RAIN TO THE NORTHERN GULF
COAST AND PRINCE WILLIAM SOUND TODAY. CURRENT OBSERVATIONS ARE
SHOWING GUSTY WINDS ALONG TURNAGAIN AND KNIK ARM BEGINNING TO PICK
BACK UP...AS THE ABOVE MENTIONED FRONT TIGHTENS THE GRADIENT BACK
UP OVER THE AREA TODAY. OUT WEST...WEAK RIDGING BEGINS TO BUILD
OVER THE ALEUTIANS AND SOUTHERN BERING FROM THE NORTH PACIFIC
TODAY...WITH SHOWERS OVER THE SOUTHWEST MAINLAND BEGINNING TO
TAPER OFF AS THE SURFACE LOW AND FRONT PUSH FURTHER EAST.

&&

.MODEL DISCUSSION...
NUMERICAL MODELS ARE ALL STILL PERFORMING VERY WELL THROUGH THE
END OF THE WEEK. THE MODELS ARE IN GOOD AGREEMENT WITH A RIDGE
BUILDING OVER THE EASTERN BERING BY THE END OF THE WEEK...THEN
PUSHING EASTWARD OVER MUCH OF THE SOUTHERN MAINLAND BY THE
WEEKEND. THERE IS A SHORT WAVE CAUGHT UP IN THE UPPER LEVEL FLOW
WHICH WILL SWEEP ACROSS THE NORTHERN BERING SEA TODAY AND INTO
SOUTHCENTRAL BY THURSDAY...WHICH ALL MODELS HAVE NOW PICKED UP ON.
WITH THE MODELS IN GOOD AGREEMENT...FORECAST CONFIDENCE REMAINS ON
THE HIGHER END INTO THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
UNSETTLED WEATHER CONTINUES THROUGH THU AS A SERIES OF TROUGHS
TRANSIT SOUTHCENTRAL. WITH THE EXCEPTION OF RAIN ALONG THE GULF
COAST MOST AREAS WILL BE SHOWERY TODAY. A TROUGH MOVING IN FROM
THE WEST THIS AFTERNOON SHOULD ADD ENOUGH LIFT TO AN ALREADY
UNSTABLE ENVIRONMENT TO KICK OFF THUNDERSTORMS OVER THE SUSITNA
VALLEY...TALKEETNA MOUNTAINS...AND THE COPPER RIVER BASIN. SHOWERS
ARE EXPECTED ACROSS MAINLAND AGAIN ON THU...BUT ANY THUNDERSTORM
THREAT LIKELY WILL BE OVER THE COPPER RIVER BASIN. A TROUGH
SKIRTING THE ALASKA RANGE THU NIGHT SETS UP FAIRLY DEEP SWLY FLOW
OVER THE SUSITNA VALLEY AND MAY BRING IN STEADY RAIN TO THE
NORTHERN VALLEY.

THE COASTAL RIDGE WILL STRENGTHEN SOME TODAY AND COMBINED WITH
LOWER PRESSURE INLAND WILL MAINTAIN...ALTHOUGH WEAKER...GAP FLOWS
ACROSS THE COPPER RIVER BASIN...TURNAGAIN ARM...AND KNIK VALLEY
THROUGH THIS EVENING. TONIGHT AND THU...GAP FLOWS WILL WEAKEN
OVERNIGHT...THEN REDEVELOP OVER THE COPPER RIVER BASIN THU...WITH
GENERALLY SEABREEZES ELSEWHERE. COOK INLET...ALTERNATE PERIODS OF
GUSTY SOUTH WINDS ARE EXPECTED THROUGH THU NIGHT WITH THE PRESSURE
SQUEEZE BETWEEN LOWER PRESSURE INLAND AND A BUILDING HIGH PRESSURE
RIDGE TO THE SW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE BROAD CYCLONIC CIRCULATION ALOFT RESPONSIBLE FOR THE SHOWERY
PATTERN IS PUSHING EASTWARD INTO THE GULF OF ALASKA. THIS WILL
TRANSITION THE UPPER LEVEL PATTERN TO A PROGRESSIVE WESTERLY FLOW
FOR A COUPLE OF DAYS. A SLUG OF WARM AIR DISLODGED FROM AN EASTERN
SIBERIAN RIDGE HAS CREATED A THERMAL BOUNDARY BETWEEN THAT WARM
AIR AND COOLER TROUGHY AIR TOWARD THE BERING STRAIT. THIS
DIVISION WILL DRIVE THE JET AND PROPAGATE A COUPLE OF DISTURBANCES
TOWARD THE SOUTHWEST MAINLAND BEGINNING THIS MORNING AS A STRONG
TROUGH MOVES FROM WEST TO EAST. SHOWERS ASSOCIATED WITH THIS
TROUGH WILL SKIRT THE KUSKOKWIM DELTA AND INCREASE IN
COVERAGE/STRENGTH AS THE WAVE MOVE OVER THE KUSKOKWIM VALLEY NEAR
PEAK HEATING WHICH WILL MAKE THUNDERSTORMS A POSSIBILITY
OVER/ALONG THE ALASKA RANGE. THE SOUTHERN EDGE OF THIS DISTURBANCE
WILL SKIRT INTERIOR BRISTOL BAY AS WELL INCREASING SHOWER COVERAGE
MAINLY FROM DILLINGHAM EASTWARD WITH THE BEST CHANCES IN THE
NORTHEASTERN PORTION OF THE ZONE. A WEAKER DISTURBANCE WILL BRING
A CHANCE FOR RAIN TO THE DELTA ON THURSDAY WHILE THE KUSKOKWIM
VALLEY WILL SEE ANOTHER ROUND OF DIURNAL SHOWERS ALONG THE ALASKA
RANGE. BROAD WESTERLY FLOW OVER THE BERING SEA WILL BRING A RETURN
OF THE MARINE LAYER LATE THURSDAY INTO FRIDAY ALONG COASTAL
LOCATIONS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
PRETTY BENIGN CONDITIONS OVER THE BERING SEA AS THE AREA LIES
BETWEEN WEATHER SYSTEMS. AREAS OF LOW CLOUDS AND FOG REMAIN
POSSIBLE OVER A LARGE PORTION OF THE BERING FOR THE NEXT COUPLE
DAYS. GENERALLY LIGHT WESTERLY FLOW WILL PERSIST UNTIL A FRONT
APPROACHES THE WESTERN BERING LATE THURSDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A BROAD UPPER LEVEL RIDGE WILL BUILD INTO THE EASTERN ALEUTIANS
AND EXTEND THROUGH THE SOUTHWEST/SOUTHCENTRAL REGION BY FRIDAY.
THIS SYNOPTIC FEATURE WILL BECOME AMPLIFIED HEADING INTO THE
WEEKEND AND WILL EXTEND INTO THE NORTHERN SLOPE. WEAK SHORTWAVE
TROUGHS WILL PUSH THROUGH ON THE BACKSIDE OF THE RIDGE COINCIDING
WITH THE SOUTHWESTERLY FLOW IN THE BERING WILL EXTEND INTO THE
SOUTHWESTERN ALASKA REGION THROUGH TUESDAY. THIS WILL BRING
SHOWERY PRECIPITATION TO THE SOUTHWEST REGION AND WILL SPILL OVER
INTO THE NORTHERN SUSITNA VALLEY. WHILE...THE AMPLIFIED RIDGE
BRINGING WARMER TEMPERATURES THROUGHOUT THE ALASKA REGION THROUGH
TUESDAY. THE BIGGEST CONCERN WILL BE THE DRIER CONDITIONS AND
LOWER RELATIVE HUMIDITIES THROUGH THE COPPER RIVER BASIN...MATSU
VALLEY AND INTERIOR PORTIONS OF SOUTHWEST ALASKA. THIS WILL LEAD
TO POSSIBLE RED FLAG WARNING CONDITIONS THROUGH THE WEEKEND INTO
MONDAY. BY EARLY TUESDAY MORNING A TROUGH WILL PUSH THROUGH THE
SOUTHWEST ALASKA REGION. THIS WILL BRING A SHOWERY REGIME TO THE
SOUTHWEST AND WILL FALL APART AS IT RUNS INTO THE RIDGE OF HIGH
PRESSURE. WHILE...THE WESTERN ALEUTIANS WILL HAVE A KAMCHATKA LOW
TRACK NEAR SHEMYA BY FRIDAY AND WILL BRING SOUTHERLY GALE FORCE
WINDS ACCOMPANIED BY RAIN/FOG. THIS SYSTEM WILL DISSIPATE BY
SATURDAY WITH THE SOUTHERLY WINDS MOVING INTO THE CENTRAL/EASTERN
BERING SEA. THESE SOUTHERLY TO SOUTHWESTERLY WINDS WILL REMAIN
THROUGH THE BERING SEA THROUGH TUESDAY WITH THE HIGH PRESSURE
REMAINING ANCHORED SOUTH OF THE EASTERN ALEUTIANS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...PD