Small Craft Advisory 627, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
427 AM AKDT TUE AUG 11 2015

.ANALYSIS AND UPPER LEVELS...
A COMPLEX PATTERN ALOFT OVER THE GREAT LAND THIS MORNING. THE MAIN
PLAYER IS A BROAD ARCTIC TROUGH OVER MUCH OF THE STATE WITH
SEVERAL EMBEDDED TROUGHS. THE FIRST IS EXITING THE COPPER RIVER
BASIN INTO THE YUKON AND THE SECOND IS CROSSING THE SOUTHWEST
MAINLAND. FURTHER TO THE SOUTH THE JET STREAM STRETCHES FROM THE
WESTERN PACIFIC NORTHEAST TOWARD THE PANHANDLE WITH SEVERAL
EMBEDDED DISTURBANCES. OUT WEST...HIGH PRESSURE ALOFT IS BUILDING
IN FROM SIBERIA WHILE SEVERAL WEAK UPPER LEVEL LOW PRESSURE
SYSTEMS RESIDE IN THE CYCLONIC FLOW OVER THE ALEUTIANS.

LOTS OF CLOUD COVER LINGERS ACROSS MUCH OF THE MAINLAND WITH THE
CURRENT TROUGH WHILE SEVERAL AREAS OF SHOWERS LINGERING IN THE
COPPER RIVER BASIN AND WESTERN PRINCE WILLIAM SOUND AS MOISTURE
AND DEFORMATION ZONE FOCUS LIFT.

&&

.MODEL DISCUSSION...
SYNOPTICALLY MODELS ARE IN LOCKSTEP AS FAR AS THE LONGWAVE PATTERN IS
CONCERNED. THE PLANETARY WAVE PATTERN BECOMES MORE PROGRESSIVE
WITH TIME AS OPPOSED TO AN ACTIVE FLOW WITH EMBEDDED
DISTURBANCES. THE NORTHERN STREAM WILL DIG NEAR KAMCHATKA
DEEPENING THE BROAD TROUGH OVER THE WESTERN BERING SEA WHICH WILL
BUILD THE EASTERN BERING RIDGE AND BEGIN TO DISPLACE THE CURRENT
TROUGH OVER THE SOUTHCENTRAL.

&&

.FIRE WEATHER...
NO IMMEDIATE FIRE WEATHER CONCERNS WITH A COOL TROUGH OVERHEAD. A
DRYING TREND BEGINS ON WEDNESDAY MORNING AS RIDGING PUSHES ONTO
THE MAINLAND. RELATIVE HUMIDITY VALUES WILL DROP NEAR THIRTY
PERCENT BUT WINDS WILL REMAIN GENERALLY LIGHT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
ONE LAST SHORT-WAVE MOVING THROUGH THE LARGER TROUGH WILL TRANSIT
SOUTHCENTRAL TODAY...PHASING WITH A TROUGH CURRENTLY SOUTH OF THE
ALASKA PENINSULA THEN EXITING TO THE EAST TONIGHT INTO WEDNESDAY.
A LOW LEVEL CONVERGENCE ZONE FROM THE EASTERN KENAI PENINSULA
NORTH-NORTHEAST TO THE WESTERN COPPER RIVER BASIN HAS SERVED AS
THE FOCUS FOR SHOWERS OVERNIGHT. AS THE SHORT-WAVE ARRIVES IN
SOUTHCENTRAL DURING THE MORNING HOURS EVERYTHING WILL BEGIN TO
SHIFT EASTWARD. THIS MEANS THE BULK OF PRECIP TODAY WILL BE OVER
THE COPPER RIVER BASIN. ONCE AGAIN EXPECT A FEW THUNDERSTORMS AS
A COLD POOL MOVES OVERHEAD OF THE COPPER BASIN THIS AFTERNOON AND
EVENING.

OFFSHORE FLOW WILL STRENGTHEN AS THE TROUGH EXITS AND A RIDGE
BUILDS IN FROM THE WEST. DESPITE RELATIVELY COOL LOW LEVEL AIR
MOVING IN THIS WILL SERVE TO WARM DAY-TIME TEMPERATURES BACK
ABOVE NORMAL FOR MOST OF THE REGION. IT WILL ALSO LEAD TO LOCALLY
GUSTY WINDS ALONG PRINCE WILLIAM SOUND AND THE NORTH GULF COAST
BEGINNING TONIGHT AND PERSISTING INTO WEDNESDAY NIGHT. NIGHT-TIME
TEMPERATURES WILL BE BELOW NORMAL FOR MOST AREAS THE NEXT COUPLE
DAYS...ESPECIALLY WHERE SKIES CLEAR AND WINDS GO LIGHT. THE RIDGE
MOVING IN FROM THE WEST IS FAIRLY DIRTY...MEANING THERE ARE QUITE
A FEW CLOUDS ASSOCIATED WITH IT. THUS EXPECT SOME CLOUDS TO
OCCASIONALLY MOVE OVERHEAD...MAKING IT DIFFICULT TO PINPOINT THE
TEMPERATURE FORECAST.

&&

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

SHOWER ACTIVITY ACROSS THE KUSKOKWIM DELTA HAS BEGUN TO INCREASE
IN COVERAGE EARLY THIS MORNING AS A WEAK SHORTWAVE AT 700 MB
ROTATES AROUND THE UPPER LEVEL TROUGH AHEAD OF A BUILDING RIDGE.
THE COVERAGE OF THESE SHOWERS SHOULD CONTINUE TO INCREASE INTO
THE AFTERNOON HOURS BEFORE BEGINNING TO SHIFT EASTWARD INTO THE
LOWER KUSKOKWIM VALLEY AS THE UPPER LEVEL ENERGY WILL BE SHUNTED
EASTWARD BY THE BUILDING RIDGE OVER THE BERING SEA. SHOWERS WILL
TAPER OFF FROM WEST TO EAST THIS EVENING INTO WEDNESDAY MORNING AS
HIGH PRESSURE BEGINS TO SITUATE OVER THE REGION. CLOUD COVER WILL
LIKELY LINGER THROUGH WEDNESDAY AS SOME MID LEVEL MOISTURE WILL BE
TRAPPED UNDER THE RIDGE BUT THIS MOISTURE WILL SLIDE EASTWARD ON
THURSDAY WHICH SHOULD LEAD TO SOME CLEARING SKIES ON THURSDAY.
WEAK COLD AIR ADVECTION ALOFT WILL BEGIN TO WANE THIS AFTERNOON
AND A WARM AIR ADVECTION PATTERN WILL DEVELOP WHICH SHOULD BRING
SLIGHTLY WARMER TEMPERATURES EACH OF THE FOLLOWING DAYS THROUGH
THE WEEK. HOWEVER...TEMPERATURES SHOULD REMAIN NEAR NORMAL FOR
THIS TIME OF THE YEAR BUT COOLER THAN THOSE OBSERVED THROUGH THE
MAJORITY OF THE SUMMER.

&&

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

A CLOSED LOW OVER THE EASTERN ALEUTIANS WAS DEALT A MORTAL BLOW
LATE LAST NIGHT AS IT GOT CUT OFF FROM THE UPPER LEVEL JET THAT
HAD BEEN SUPPORTING IT. THIS LOW WILL BECOME A WEAK WAVE AS IT
TRANSITIONS INTO THE GULF OF ALASKA THIS AFTERNOON/EVENING. DECENT
PRESSURE RISES ACROSS THE ALASKA PENINSULA ASSOCIATED WITH THE
BUILDING RIDGE SHOULD SUPPORT SOME GUSTY GAP WINDS IN THE COASTAL
WATERS SURROUNDING THE ALASKA PENINSULA. WARM AIR ADVECTION
ASSOCIATED WITH THE SFC BASED AND UPPER LEVEL RIDGE WILL PROMOTE A
STABLE ENVIRONMENT ACROSS MUCH OF THE BERING SEA AND KEEP LOW
STRATUS/FOG IN THE FORECAST THROUGH THE REMAINDER OF THE WEEK.
THE RIDGE WILL BE SHUNTED EASTWARD ON WEDNESDAY AS THE UPPER
LEVEL TROUGH AMPLIFIES ACROSS THE WESTERN ALEUTIANS. THIS WILL
CREATE A WEAK SURFACE REFLECTION AND ONCE AGAIN BRING RAIN BACK
TO THE WESTERN HALF OF THE BERING SEA COME THURSDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A PROGRESSIVE WEATHER PATTERN IN THE LONG TERM IS EXPECTED TO
BRING SEVERAL FRONTS ALONG THE ALEUTIAN CHAIN AND NORTH THROUGH
THE GULF. DRIER CONDITIONS...INITIALLY ACROSS THE MAINLAND ON
THURSDAY...WILL BEGIN TO SATURATE THURSDAY NIGHT AS A NEW LONG
WAVE TROUGH CENTERS OVER THE BERING. PRECIPITATION CHANCES
INCREASE ACROSS THE BERING AND SOUTHERN MAINLAND FOR THE END OF
THE WEEK AS SHORT WAVES MOVE ALONG THE TROUGH. THE FIRST FRONT
MOVES INTO THE SOUTHWEST ON THURSDAY AND SPREADS EAST INTO FRIDAY.
THE SECOND FRONT MOVES ALONG THE ALEUTIAN CHAIN ON FRIDAY AND THEN
STAYS ALONG THE SOUTHERN GULF FRIDAY NIGHT.

MODELS HAVE LARGE DIFFERENCES IN SOLUTIONS BY THE UPCOMING
WEEKEND AS THE BROAD UPPER TROUGH DEVELOPS A LOW CENTER IN THE
WESTERN BERING. THE CURRENT PROJECTION WILL BRING A WET AND WINDY
PATTERN TO THE BERING AND WEST COAST. THE MOST AGGRESSIVE MODEL
SOLUTION WAS THE ECMWF WHICH BRINGS A FRONT THROUGH THE WESTERN
GULF AT THE END OF THE WEEKEND.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MMC
LONG TERM...KH