Small Craft Advisory 677, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
507 AM AKDT FRI AUG 28 2015

.ANALYSIS AND UPPER LEVELS...
AN AMPLIFIED UPPER TROUGH SPANS FROM THE ALASKA ARCTIC COAST
THROUGH THE GULF. THE SPIN OF THE GULF LOW IS SEEN CLEARLY ON
IR/WV SATELLITE IMAGERY EARLY THIS MORNING...PULLING A DRIER AND
COOLER AIR MASS INTO THE GULF. TO THE WEST...THE PERSISTENT RIDGE
PATTERN REMAINS OVER THE CENTRAL ALEUTIANS WITH ABUNDANT MOISTURE
RIDING OVER THE RIDGE ACROSS THE NORTHERN BERING. AT THE
SURFACE...NORTH TO WEST FLOW SET UP ACROSS THE SOUTHERN MAINLAND
BEHIND A COLD FRONT THAT MOVED THROUGH LAST NIGHT. GUSTY
CONDITIONS WERE STRONGEST ACROSS ANTICIPATED AREAS ALONG PRINCE
WILLIAM SOUND...KENAI...AND WESTERN GULF WITH MAXIMUM GUSTS
RECORDED BETWEEN 60 TO 70 MPH. ACROSS THE BERING...A FRONT IS
STRETCHED ALONG THE NORTHERN WATERS BRINGING RAIN INTO THE
PRIBILOFS. AREAS OF FOG AND LOW CLOUDS CONTINUE ACROSS MUCH OF THE
SOUTHERN BERING AND ALEUTIANS.

&&

.MODEL DISCUSSION...
THERE IS A GREAT AMOUNT OF COMPLEXITY WITH THE EVOLVING PATTERN
THROUGH THE WEEKEND. MODELS HAVE TO HANDLE TWO CLOSED LOWS WITHIN THE
TROUGH OVER ALASKA AND STRONG SHORTWAVES THAT PASS FROM THE ARCTIC
TO GULF. MODELS ARE COMPARABLE WITH THE OVERALL SYNOPTIC
PATTERN...HOWEVER THERE IS UNCERTAINTY IN ALL OF THE SOLUTIONS
THROUGH THE WEEKEND. THE MODELS ARE ALL SHOWING SIGNIFICANT HEIGHT
FALLS FOR THE LOW OVER THE MAINLAND GOING FROM 543 DAM TO 528 DAM
BY EARLY SUNDAY MORNING. MODEL MOISTURE AND TEMPERATURE FIELDS DO
NOT LOOK REPRESENTATIVE OF THIS PATTERN AS THE SURFACE PATTERN
REMAINS RELATIVELY THE SAME...WHEREAS MODELS SHOULD BE SHOWING A
COOLER TREND WITH HIGHER SURFACE MOISTURE. THE CURRENT FORECAST
PACKAGE WAS UPDATED WITH THE NAM...GEM...AND ECMWF TO CAPTURE THE
THE TRENDS INTO THE WEEKEND WITH ONLY MINOR CHANGES MADE.

&&

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
NORTHWESTERLY FLOW ALOFT WILL CONTINUE OVER THE AREA INTO
SATURDAY. THIS WILL KEEP SOUTH CENTRAL ALASKA DRY WITH SOME
OFFSHORE FLOW AT THE LOWER LEVELS. THE PRESSURE GRADIENT WILL
WEAKEN TODAY HOWEVER AS THE LOW OVER THE SOUTHEAST GULF OF ALASKA
CONTINUES TO EXIT TO THE SOUTHEAST. WITH A DRY AND COLD AIR MASS
OVER THE AREA TEMPERATURES ARE EXPECTED TO BY QUITE COOL OVER THE
NEXT COUPLE OF DAYS...WITH SOME BELOW FREEZING TEMPERATURES
POSSIBLE TONIGHT AND FRIDAY NIGHT OVER MUCH OF THE AREA. THIS
INCLUDES EAST ANCHORAGE AND THE MATANUSKA VALLEY. A STRONG
ARCTIC LOW WILL SLOWLY PUSH SOUTH THROUGH SATURDAY NIGHT AND COVER
MUCH OF ALASKA BY EARLY SUNDAY MORNING. THIS WILL TURN THE UPPER
LEVEL MORE WESTERLY RATHER THAN NORTHWESTERLY AND BRING IN SOME
CYCLONIC FLOW. THIS WILL RE-INTRODUCE A CHANCE OF SHOWERS TO SOUTH
CENTRAL...BEGINNING IN THE SUSITNA VALLEY SATURDAY AFTERNOON AND
PUSHING SOUTH THROUGH ANCHORAGE AND THE KENAI PENINSULA SATURDAY
NIGHT. BUT THE CHANCES OF SHOWERS WILL BE FAIRLY LOW DUE TO THE
DOWN-SLOPING OFF THE ALASKA RANGE AND THE LINGERING DRY AIR MASS
OVER THE AREA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)... A
FRONTAL SYSTEM STRETCHED OVER TOP THE LARGE RIDGE IN THE BERING
WILL START BRINGING RAIN TO THE WESTERN CAPES AND WESTERN
PENINSULA THIS MORNING THEN THE BRISTOL BAY AREA AND REMAINDER OF
THE ALASKA PENINSULA THIS AFTERNOON AND EVENING. RAIN ALONG AND
NEAR THE COAST WILL CONTINUE THROUGH THE OVERNIGHT HOURS AND INTO
SATURDAY MORNING AS A SURFACE LOW TRACK FROM NORTHWEST TO
SOUTHEAST ALONG THE COAST OF MAINLAND SOUTHWEST ALASKA. CONDITIONS
WILL DRY OUT FAIRLY QUICKLY SATURDAY AFTERNOON AND EVENING AS
NORTHWEST FLOW PUSHES ACROSS THE AREA...THOUGH SCATTERED SHOWERS
WILL LIKELY PERSIST FURTHER INLAND ESPECIALLY ALONG THE MOUNTAINS
WITH A SHORTWAVE DROPPING SOUTH SUNDAY AND SUNDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
STRONG RIDGING WILL CONTINUE TO PERSIST OVER THE CENTRAL ALEUTIANS
AND EXTEND INTO THE BERING. A TROUGH WILL SWING TOWARDS THE
WESTERN ALEUTIANS LATE FRIDAY NIGHT AND EARLY SATURDAY MORNING
WITH A VERTICALLY STACKED LOW FOLLOWING SATURDAY NIGHT AND
REMAINING FAIRLY STATIONARY TO THE WEST OF SHEMYA THROUGH SUNDAY
NIGHT. A SMALL LOW TRACKING ACROSS THE NORTHEASTERN SIDE OF
BRISTOL BAY WILL BRING SOME WESTERLY GALES BEHIND IT LATE FRIDAY
NIGHT THROUGH SATURDAY MORNING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BEGINNING THE EXTENDED PERIOD ON SATURDAY EVENING...THE STATE OF
ALASKA WILL BE UNDER THE INFLUENCE OF A LARGE ARCTIC TROUGH
CENTERED OVER WESTERN ALASKA...WITH A WEAKLY PHASED SHORTWAVE
TROUGH IN NORTHWEST FLOW TRACKING INTO THE GULF OF ALASKA. AN
ASSOCIATED 140 KT UPPER LEVEL JET STREAK WILL BE TRACKING OVER
THE GULF AS THE ARCTIC TROUGH MAKES SOUTHWARD PROGRESS THROUGH
MONDAY. THIS WILL REINVIGORATE THE OFFSHORE FLOW PATTERN AS A
SURFACE LOW FORMS IN THE GULF OF ALASKA AND TRACKS TOWARD THE
PANHANDLE. RAIN AND SNOW SHOWERS WILL REMAIN LARGELY OVER THE
MOUNTAINS THROUGH MONDAY...ALTHOUGH LOWER ELEVATION SHOWERS WILL
BE MORE PREVALENT ACROSS THE LOWER KUSKOKWIM VALLEY AND BRISTOL
BAY REGIONS. OTHERWISE...RAPID DRYING WILL COMMENCE ON MONDAY AS
THE TROUGH CONTINUES TO DIG THROUGH THE SOUTHEAST GULF...AND
OFFSHORE AND DOWNSLOPE FLOW DRIES THE ATMOSPHERIC COLUMN. WEAK
RIDGING ALOFT WILL MOVE OVER THE STATE FROM WEST TO EAST TUESDAY
AND WEDNESDAY...WITH A SLOW WARMUP BUT CONTINUED DRY CONDITIONS.
PRECIPITATION CHANCES REDEVELOP TOWARD LATE WEEK AS A SERIES OF
WEAK LOWS TRACK FROM THE BERING INTO SOUTHWEST ALASKA. WITH THAT
SAID...THE UPPER LEVEL FLOW WILL REMAIN RATHER WEAK...WITH NO
SIGNIFICANT STORMS OR WET PERIODS ANTICIPATED WITH THE CHANGE IN
PATTERN. DUE TO SLIGHT UNCERTAINTY IN THE EXTENDED PERIOD TOWARD
THE END OF NEXT WEEK...A BLENDED WPC ENSEMBLE APPROACH WAS FAVORED
WITH SOME BLEND OF ECMWF AND GFS SATURDAY EVENING THROUGH MONDAY
TO CAPTURE OUTFLOW WINDS ALONG THE COAST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 125 131.
MARINE...GALE WARNING 119 121 127 128 130 131 132 150 155 165.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...JA