Small Craft Advisory 672, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
122 PM AKDT FRI SEP 5 2014

.ANALYSIS AND UPPER LEVELS...A SHARP UPPER LEVEL SHORT-WAVE OVER
BRISTOL BAY/ALASKA PENINSULA IS PROGRESSING SLOWLY EASTWARD
TOWARD SOUTHCENTRAL ALASKA AND THE GULF. A SOUTHERLY JET WHICH
BEGINS DOWN AROUND 35N LATITUDE IS TRANSPORTING DEEP TROPICAL
MOISTURE NORTHWARD TO SOUTHCENTRAL. THE END RESULT IS WIDESPREAD
RAIN...HEAVY AT TIMES. OBSERVED 24 HOUR RAINFALL TOTALS GENERALLY
RANGE FROM ONE THIRD OF AN INCH TO AROUND ONE INCH. RIVER LEVELS
ACROSS THE REGION STARTED OUT FAIRLY LOW...SO DO NOT EXPECT ANY
ISSUES WITH FLOODING...ALTHOUGH SMALL CREEKS WILL SEE SIGNIFICANT
RISES OVER A SHORT PERIOD OF TIME. A RIDGE OVER THE EASTERN
BERING IS ATTEMPTING TO MOVE IN BEHIND THIS TROUGH...ALTHOUGH
ANOTHER TROUGH OVER NORTHERN ALASKA IS POISED TO DROP SOUTHWARD
PRIOR TO THE RIDGE BUILDING INTO MAINLAND ALASKA.

OUT WEST A LARGE DEEP LOW OVER THE NORTH CENTRAL PACIFIC HAS
OCCLUDED AND IS BEGINNING TO REALLY WRAP UP. THIS HAS STALLED
MOTION OF THE LOW CENTER...BUT THE OCCLUDED FRONT CONTINUES
NORTHWARD TOWARD THE ALEUTIANS. THIS SYSTEM IS ALSO TAPPING INTO
TROPICAL MOISTURE...SO EXPECT FAIRLY HEAVY RAIN ALONG THE
ALEUTIANS AS THE FRONT HEADS NORTHWARD LATER TODAY.

&&

.MODEL DISCUSSION...MODELS ARE IN VERY GOOD AGREEMENT WITH MAJOR
FEATURES AND FORECAST CONFIDENCE IS ABOVE AVERAGE. LATEST
SOLUTIONS ARE SLIGHTLY MORE AGGRESSIVE IN DIGGING ARCTIC TROUGH
SOUTHWARD ACROSS SOUTHCENTRAL INTO THE NORTHERN GULF THIS WEEKEND.
THE PRIMARY IMPACT OF THIS WILL BE STRONGER OFFSHORE
FLOW...ESPECIALLY THROUGH GAPS ALONG THE NORTH GULF COAST AND
PRINCE WILLIAM SOUND. THERE ARE SOME MINOR DIFFERENCES IN CENTRAL
PRESSURE OF THE NORTH PACIFIC LOW WHICH COULD BE THE DIFFERENCE
BETWEEN HIGH END GALES AND MIN STORMS SOUTH OF THE ALEUTIAN CHAIN.
SATELLITE BASED (SCATTEROMETER) WINDS FROM OVERNIGHT SHOWED 40 TO
45 KNOTS ALONG THE NORTHERN QUADRANT OF THE LOW. THIS IS HIGHER
THAN CURRENT FORECAST...SO WILL BUMP WINDS UP AHEAD OF FRONT BUT
KEEP BELOW STORM FORCE.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...RAIN WILL DIMINISH FROM THE KENAI PENINSULA
UP TO THE SUSITNA VALLEY THIS AFTERNOON AND EVENING AS THE UPPER
LEVEL SHORT-WAVE PASSES BY. HOWEVER...THE SHORT-WAVE TO THE NORTH
WILL DIG SOUTHEASTWARD ARRIVING IN SOUTHCENTRAL SATURDAY
AFTERNOON. A MUCH DRIER AIR MASS WILL MOVE IN BEHIND THE FIRST
TROUGH...BUT WITH THE NEXT SHORT-WAVE ARRIVING AT PEAK HEATING AND
COLDER AIR MOVING ALOFT MODEL LAPSE RATES LOOK STEEP ENOUGH TO
SUPPORT ISOLATED SHOWERS. AREAS FURTHER EAST FROM EASTERN PRINCE
WILLIAM SOUND TO THE COPPER RIVER BASIN WON'T HAVE TIME TO DRY OUT
BEFORE THE SECOND TROUGH ARRIVES...SO EXPECT AREAS OF RAIN TO
PERSIST INTO SATURDAY NIGHT OR EVEN SUNDAY MORNING FOR THE FAR
EASTERN COPPER RIVER BASIN. THE FOCUS BEHIND THIS SYSTEM WILL
SHIFT TO STRONG OFFSHORE GAP WINDS. SURFACE PRESSURE GRADIENTS
OVER SOUTHCENTRAL WILL TIGHTEN AS HIGH PRESSURE BUILDS OVER
INTERIOR ALASKA. PASSAGE OF THE SECOND SHORT-WAVE WILL BRING SOME
WEAK LOW LEVEL COLD ADVECTION ALONG WITH STRONG SUBSIDENCE TO HELP
MIX DOWN HIGHER WINDS FROM ALOFT. ALL OF THIS SUPPORTS STRONGER
WINDS THAN CURRENTLY ADVERTISED. THIS WIND EVENT WON'T BE LONG
LIVED AS HIGH PRESSURE MOVES OVERHEAD SUNDAY...PROVIDING A CLEAR
AND CALM DAY. WINDS SATURDAY NIGHT WILL KEEP TEMPS FROM FALLING
TOO FAR. SUNDAY NIGHT LOOKS TO BE SIMILAR TO LAST WEEKEND WITH
SOME AREAS BOTTOMING OUT NEAR FREEZING OR BELOW...ESPECIALLY
INLAND.

SOUTHWEST ALASKA...SKIES WILL CONTINUE TO CLEAR FROM WEST TO EAST
THIS AFTERNOON AND EVENING IN THE WAKE OF THE EXITING SHORT-WAVE.
WEAK OFFSHORE FLOW COMBINED WITH SOME LOW LEVEL MIXING FROM THE
SECOND SHORT-WAVE DIGGING DOWN FROM THE NORTH SHOULD BE ENOUGH TO
PREVENT FOG FORMATION. WITH SHORT-WAVE APPROACHING OVERNIGHT INTO
SATURDAY MORNING IT DOES NOT LOOK FAVORABLE FOR ANY PRECIPITATION
TO FALL OVER SOUTHWEST ALASKA...BUT THERE CERTAINLY WILL BE ENOUGH
INSTABILITY FOR SOME FAIR WEATHER CUMULUS CLOUDS. THE FRONTAL
SYSTEM FROM THE NORTH PACIFIC LOW LOOKS LIKE IT WILL COMPLETELY
FALL APART BEFORE REACHING SOUTHWEST ALASKA. THUS THE NEXT CHANCE
OF RAIN WILL NOT BE UNTIL SUNDAY NIGHT INTO MONDAY AS THE ENTIRE
SYSTEM DRIFTS NORTH AND EASTWARD ACROSS THE BERING.

BERING SEA/ALEUTIANS...THE BRUNT OF STRONG WINDS AND HEAVY RAIN
WILL BE FELT ALONG THE ALEUTIAN THIS AFTERNOON THROUGH TONIGHT.
THE STORM SYSTEM WILL THEN UNDERGO A VERY SLOW WEAKENING PROCESS
OVER THE NEXT FEW DAYS AS IT SETTLES IN OVER THE BERING SEA.
THUS...EXPECT AREAS OF RAIN AND FOG TO DOMINATE THE WEATHER
THROUGH EARLY NEXT WEEK.

&&

.LONG TERM FORECAST...
A SERIES OF RELATIVELY PLEASANT DAYS ACROSS SOUTHCENTRAL AK THIS
WEEKEND WILL GIVE WAY TO THE RETURN OF A MUCH WETTER PATTERN BY
EARLY NEXT WEEK AS HIGH PRESSURE MOVES OFF TO THE EAST AND MOIST
SOUTHERLY FLOW BECOMES RE-ESTABLISHED OVER THE AREA FOR THE
REMAINDER OF THE WEEK AHEAD OF THE BROAD UPPER LOW IN THE BERING
SEA. MEANWHILE...THE BERING ALSO LOOKS TO REMAIN RAINY AND WINDY
THROUGH MUCH OF NEXT WEEK AS THE FIRST LOW MOVES EAST AND WEAKENS
BUT IS THEN REINFORCED BY AN UPPER TROUGH DIGGING SOUTHWARD OVER
THE WESTERN BERING FROM EASTERN RUSSIA MONDAY NIGHT INTO TUESDAY.
A JET STREAK ROUNDING THE BASE OF THIS TROUGH WILL MERGE WITH
SOUTHERN STREAM JET ENERGY IN PLACE OVER THE NORTHERN
PACIFIC...PROVIDING FAVORABLE UPPER LEVEL SUPPORT FOR MORE
RAINFALL OVER THE ALEUTIAN CHAIN AND SOUTHERN BERING THROUGH THE
MIDDLE OF THE WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 173 174 175 176 177 178.
FIRE WEATHER...NONE.

&&

SEB/CB SEP 14