Small Craft Advisory 709, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
413 PM AKDT WED SEP 9 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE ALASKA PENINSULA. THE SURFACE
LOW IS NOW FULLY MATURE AND CENTERED NEAR CHIGNIK...NEARLY VERTICALLY
STACKED WITH THE UPPER LOW. THE LEADING OCCLUDED FRONT IS WORKING
ITS WAY NORTHWARD OVER THE NORTHERN GULF. THE TRAILING "COLD"
FRONT CURVES SOUTH THEN SOUTHEAST...JUST SOUTHEAST OF THE JET CORE
(MAXIMUM NEAR 130 KTS). PLENTY OF MOISTURE IS ENTRAINED IN THIS
SYSTEM. THERE IS A LARGE RIDGE OF HIGH PRESSURE OVER EASTERN
RUSSIA AND THE WESTERN BERING SEA. NORTHERLY FLOW ALOFT AND AT THE
SURFACE IS OVER THE CENTRAL BERING AND MUCH OF THE EASTERN BERING
BETWEEN THE RIDGE AND THE UPPER LOW.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN DECENT AGREEMENT FOR THE SHORT TERM
PORTION OF THE FORECAST. THERE ARE SOME MINOR DIFFERENCES IN HOW
THEY HANDLE THE SURFACE LOW AS IT MOVES INTO MAINLAND ALASKA THAT
DOES MAKE THE FORECAST MORE DIFFICULT. THIS MAINLY IMPACTS THE
TIMING OF WINDS ON THE BACK SIDE OF THE LOW DUE TO THE ISALLOBARIC
PRESSURE RISES. THEY ALL ARE SIMILAR IN THE MOVEMENT OF THE
SURFACE LOW INTO SOUTHWEST ALASKA...BUT THE NAM IS FASTEST TO
DEVELOP A SECOND LOW NORTH OF THE ALASKA RANGE AND THUS FASTER IN
BRINGING UP THE SOUTHERLY WIND PUSH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE APPROACHING FRONT FROM THE LOW OVER THE ALASKA PENINSULA
COMBINED WITH A STRONG PRESSURE GRADIENT FROM THE LOW WILL RESULT
IN INCREASING WINDS OVERNIGHT FOR MUCH OF THE SOUTHCENTRAL. THE
STRONGER WINDS WILL LAST THROUGH MUCH OF THURSDAY BEFORE TAPERING
OFF THURSDAY NIGHT. THE STRONGEST WINDS WILL BE IN THE EAST TO
WEST ORIENTED GAPS LIKE TURNAGAIN ARM WHERE WINDS WILL GUST TO
AROUND 65 MPH WITH THE PEAK ON THURSDAY. THE FRONT WILL ALSO BRING
RAIN TO WIDESPREAD AREAS AROUND THE SOUTHCENTRAL THAT WILL PICK UP
TONIGHT. AS THE FRONT PUSHES THROUGH LATE TONIGHT SOUTHWEST FLOW
WILL FOLLOW...KEEPING SHOWERS IN THE AREA THROUGH FRIDAY. THE
RAINFALL LOOKS TO BE HEAVIEST AROUND PRINCE WILLIAM SOUND WITH
AREAS AROUND COOK INLET AND THE COPPER RIVER BASIN HAVING SOME
PROTECTION FROM THE SURROUNDING MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE CHIGNIK LOW WILL SLOWLY MOVE NORTH TONIGHT ACROSS THE ALASKA
PENINSULA AND BE SITUATED NEAR KING SALMON BY LATE THURSDAY
MORNING. RAIN WILL SWEEP ACROSS MOST OF SOUTHWEST ALASKA TONIGHT
WITH SHOWERS BEHIND. THE LOW WILL WEAKEN THURSDAY AS A SECONDARY
SURFACE LOW DEVELOPS TO THE NORTH OF THE ALASKA RANGE. THIS
SECONDARY LOW WILL BECOME THE PRIMARY LOW THURSDAY NIGHT.
HOWEVER SHOWER ACTIVITY WILL CONTINUE THROUGH FRIDAY DUE TO UPPER
LEVEL SHORTWAVES CONTINUING TO MOVE THROUGH THE REGION. THE UPPER
LOW NEAR KING SALMON WILL ONLY VERY SLOWLY MOVE NORTH AS A TROUGH
SLIDES DOWN THE BACK SIDE OF THIS LOW. THIS TROUGH WILL CROSS THE
ALASKA PENINSULA THURSDAY NIGHT AND BE NEAR KODIAK ISLAND FRIDAY
AFTERNOON.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
BROAD NORTHERLY FLOW WILL CONTINUE ACROSS MOST OF THE BERING SEA
AND ALEUTIANS AT THE SURFACE AND ALOFT THROUGH THURSDAY NIGHT.
SOME SHOWERS ARE EXPECTED...MAINLY OVER CENTRAL AND EASTERN
PORTIONS DUE TO WEAK CYCLONIC FLOW AND SOME COLD ADVECTION. ON
FRIDAY THE FLOW WILL BECOME MORE WESTERLY AS THE EASTERN
RUSSIA/WESTERN BERING HIGH BECOMES FLATTENED BY A SYSTEM RIDING
OVER THE TOP OF THE RIDGE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE WEEKEND STARTS OFF AS A CONTINUATION OF THE CURRENT SYSTEM IN
THE NORTHERN PACIFIC WITH LINGERING CLOUDS AND MOISTURE PUSHING
FROM WEST TO EAST ACROSS THE SOUTHCENTRAL. A COOL POCKET OF AIR
OFF THE SURFACE WILL PUSH FROM THE SOUTHWEST MAINLAND TO THE
SOUTHCENTRAL BRINGING SOME OF THE COOLEST OVERNIGHT TEMPERATURES
OF THE SEASON. THE PATTERN ALOFT BEGINS CHANGING AND BECOMES
PROGRESSIVE FROM A WESTERLY/NORTHWESTERLY DIRECTION AS THE FIRST
SYSTEM AFTER THE CURRENT TROUGH IS THE EXTRA-TROPICAL REMNANTS OF
TYPHOON KILO. THAT SYSTEM WILL SPREAD RAIN AND WIND OVER MUCH OF
SOUTHERN ALASKA LATE SUNDAY NIGHT INTO MONDAY FOLLOWED BY ANOTHER
DISTURBANCE BY MID-WEEK. EXPECT VERY SEASONABLE CONDITIONS THROUGH
THE FORECAST PERIOD WITH NEAR AVERAGE TEMPERATURES AND
PRECIPITATION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 125 130 131 132150 155 179 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...ML