Small Craft Advisory 454, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT SUN JUL 3 2011

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN CONSISTS PRIMARILY OF THREE UPPER LEVEL LOWS.
THE FIRST IS A PERSISTENT LOW IN THE SOUTHERN GULF THAT HAS BEEN
RESPONSIBLE FOR THE RAIN/EASTERLY WAVES ACROSS SOUTHCENTRAL AK THE
LAST SEVERAL DAYS. WHILE THIS LOW IS WEAKENING, IT IS CURRENTLY
GETTING A REINFORCING SHOT OF ENERGY FROM A STRONG SHORTWAVE THAT
CROSSED THE AK PENINSULA YESTERDAY AND IS DROPPING INTO THE GULF. THE
SECOND MAJOR LOW IS OVER EXTREME NORTHWEST CANADA HEADED QUICKLY INTO
NORTHERN ALASKA. A FINAL LOW IS DROPPING SOUTH ACROSS THE BERING
STRAIT. THE BERING LOW WILL ULTIMATELY BE THE MOST SIGNIFICANT OF THE
AFOREMENTIONED SYSTEMS AS IT IS NOW EXPECTED TO SHIFT THE OVERALL
WEATHER PATTERN FOR THE ENTIRE STATE FOR THE COMING WEEK.

AT THE SURFACE...GRADUALLY WEAKENING NORTHEAST FLOW IS SLOWLY
BRINGING AN END TO THE STEADY RAIN OVER THE SUSITNA VALLEY THIS
MORNING. AS CLOUD COVER ACROSS THE REGION DIMINISHES, DIURNALLY
DRIVEN SHOWERS ARE ALREADY DEVELOPING FROM THE COPPER RIVER VALLEY TO
THE MAT-SU AND DOWN TO THE KENAI PENINSULA. FURTHER WEST...A
WEAKENING FRONT PUSHING ONSHORE THE KUSKOKWIM DELTA IS EVIDENT ON
RADAR IMAGERY.

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT ON THE LARGE-SCALE WEATHER PATTERN
ACROSS THE STATE FOR THE FORESEEABLE FUTURE. THE UPPER-LEVEL BERING
STRAIT LOW WILL SPIN UP A NEW LOW AT THE SURFACE TONIGHT IN THE
NORTHERN BERING. THIS STORM WILL ABSORB THE ENERGY FROM THE LOW
CURRENTLY OVER NORTHWEST CANADA AND BECOME THE MAJOR WEATHER FEATURE
FOR THE NEXT WEEK AS IT REMAINS NEARLY STATIONARY IN THE NORTHERN
BERING SEA. SOME MODEL DIFFERENCES ARE NOTED WITH REGARD TO THE
CURRENT GULF LOW. WHILE ALL MODELS SLOWLY WEAKEN THE LOW THROUGH
MIDWEEK, THE EC/NAM AGREE ON A SLOW EASTERLY DRIFT TOWARD THE
PANHANDLE. MEANWHILE THE GFS IS AN OUTLIER IN KEEPING THE LOW IN
PLACE UNTIL DISSIPATION. FORECAST UPDATES TODAY WERE GENERALLY BASED
ON THE 12Z EC.

.SHORT TERM FORECAST...
SOUTHCENTRAL...WITH PARTIAL CLEARING/BREAKS IN THE CLOUDS ACROSS THE
REGION SCATTERED SHOWERS HAVE POPPED UP THIS AFTERNOON IN MOST
LOCATIONS. SOMEWHAT RARELY...VIGOROUS CONVECTIVE ACTIVITY HAS EVEN
DEVELOPED OVER THE NORTH GULF COAST...BRINGING PERIODS OF HEAVY RAIN
TO CORDOVA THIS AFTERNOON. AS GULF LOW CONTINUES TO WEAKEN...EXPECT
MOST OF SOUTHCENTRAL TO SLIDE INTO PREDICTABLE PATTERN OF DIURNALLY
DRIVEN SHOWERS AND MAYBE EVEN AN ISOLATED LIGHTNING STRIKE. THIS
PATTERN SHOULD PERSIST THROUGH AT LEAST MIDWEEK.

SOUTHWEST...LEFTOVER LIGHT RAIN/CLOUDS OVER BRISTOL BAY HAS
DIMINISHED THROUGHOUT THE AFTERNOON...GIVING RISE TO THE DEVELOPMENT
OF SHOWERS AND ISOLATED THUNDERSTORMS. OVER THE DELTA...WEAKENING
FRONT ABOUT TO MOVE THROUGH BETHEL WILL PROGRESS EASTWARD OVERNIGHT.
AS IT DOES, EXPECT DEVELOPING SHOWER ACTIVITY IN BRISTOL BAY/LOWER
KUSKOKWIM VALLEY TO BE SWEPT INTO A BROADER SHIELD OF STEADY RAIN
THAT WILL MOVE NORTHEAST TOWARD THE ALASKA AND ALEUTIAN RANGES BY
MORNING. MOVING FORWARD IN THE WEEK...UNSEASONABLY STRONG UPPER LOW
CURRENTLY OVER THE BERING STRAIT WILL PARK ITSELF IN THE NORTHERN
BERING...BRINGING WAVES OF ABUNDANT MOISTURE ONSHORE SOUTHWEST ALASKA
THROUGH THE END OF THE WEEK.

BERING SEA/ALEUTIANS...AS LOW PARKS NEAR SAINT MATTHEW ISLAND, EXPECT
EASTERN BERING/ALEUTIANS TO STAY IN AN UNSETTLED AND SHOWERY WEATHER
PATTERN WITH NORTHWEST FLOW. MEANWHILE, REMAINDER OF BERING WILL
LIKELY SEE A CONTINUATION OF RELATIVELY WEAK WINDS WITH WIDESPREAD
SEA FOG.

.LONG TERM FORECAST...
AS BERING SEA LOW MAKES FOR A WET WEEK OVER SOUTHWEST
ALASKA...SOUTHCENTRAL WILL INITIALLY REAP THE REWARDS OF RELATIVELY
WEAK HIGH PRESSURE. WHILE THIS HIGH WILL NOT BE STRONG ENOUGH TO
INHIBIT DIURNAL CONVECTION, IT SHOULD HELP LIMIT SHOWERS TO MAINLY
MOUNTAINOUS REGIONS. HOWEVER, BY MIDWEEK BERING LOW CIRCULATION OPENS
UP AND BEGINS TO SPREAD A SERIES OF WEATHER FRONTS EASTWARD TOWARD
THE COOK INLET REGION...INCREASING CHANCES FOR WIDESPREAD CLOUD COVER
AND STEADY RAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 180 185
FIRE WEATHER...NONE

AMD JUL 11