Small Craft Advisory 450, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
137 PM AKDT THU JUN 5 2014

.ANALYSIS AND UPPER LEVELS...AN UPPER LEVEL RIDGE IS CENTERED OVER
THE NORTHERN BERING SEA WITH A SPOKE EXTENDING EASTWARD ACROSS THE
SOUTHERN ALASKA MAINLAND...WITH CLEAR SKIES NOTED ACROSS MUCH OF
THIS AREA. HOWEVER...THE RIDGE OVER THE SOUTHERN MAINLAND IS BEING
SQUEEZED WITH A LARGE UPPER LOW/TROUGH DROPPING OUT OF THE ARCTIC
ACROSS THE NORTHERN MAINLAND AND ANOTHER VERTICALLY STACKED
LOW/TROUGH SOUTH OF THE ALASKA PENINSULA LIFTING NORTHWARD. CLOUDS
AND A FEW SHOWERS HAVE WORKED INTO THE VERY NORTHERN TIER OF THE
FORECAST AREA FROM THE KUSKOKWIM VALLEY TO THE NORTHERN SUSITNA
AND COPPER BASIN WHILE A MUCH MORE STABLE MARINE AIR MASS IS MOVING
NORTHWARD ACROSS THE GULF/KODIAK ISLAND AND THE ALASKA PENINSULA.

&&

.MODEL DISCUSSION...MODEL SOLUTIONS VARY WITH HANDLING OF COMPLEX
LOW SOUTH OF THE ALASKA PENINSULA INTO THE GULF. WITH GOOD UPPER
LEVEL DIVERGENCE ON THE DOWNSTREAM SIDE OF THIS SYSTEM EXPECT
DEVELOPMENT OF ONE OR MORE TRIPLE POINT LOWS OVER THE NEXT 24 HOURS.
MEANWHILE...ANOTHER MUCH SMALLER UPPER LOW DROPPING SOUTHWARD ACROSS
THE FAR WESTERN BERING WILL QUICKLY TRACK SOUTHEASTWARD AND
INTERACT WITH THE LOW SOUTH OF THE ALASKA PENINSULA CREATING YET
ANOTHER WEAK SURFACE LOW. AS WOULD BE EXPECTED WITH SUCH A COMPLEX
INTERACTION OF GENERALLY WEAK FEATURES...THERE IS A DECENT MODEL
SPREAD ON SURFACE LOW POSITIONS. FORTUNATELY THIS WILL ONLY IMPACT
WINDS IN THE OUTER PORTIONS OF THE COASTAL ZONES SOUTH OF THE
ALASKA PENINSULA. THE POSITION OF THE OCCLUDED FRONT ON THE NORTH
AND WEST SIDE OF THE SURFACE LOWS IS VERY CLOSE IN ALL OF THE
SOLUTIONS. LARGER AND MORE NOTABLE MODEL DIFFERENCES DEVELOP AS
THE COMPLEX LOW MOVES INTO THE GULF SATURDAY NIGHT AND SUNDAY WITH
MULTIPLE WAVES ROTATING AROUND THE GULF AND SOUTHCENTRAL. WILL USE
A VERY BROAD BRUSH APPROACH TO THE PRECIP FORECAST IN THIS TIME
PERIOD WITH LOW CONFIDENCE IN POSITION AND STRENGTH OF INDIVIDUAL
WAVES.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A SURFACE RIDGE OVER THE NORTHERN GULF WILL
LIFT NORTHWARD ONSHORE OF SOUTHCENTRAL OUT AHEAD OF THE LOW AND
FRONTAL SYSTEM OVER THE SOUTHERN GULF. THIS WILL CAUSE LOCALLY
GUSTY GAP WINDS IN THE USUAL PLACES (TURNAGAIN ARM/KNIK RIVER
VALLEY/COPPER RIVER) TODAY AND FRIDAY. HOWEVER THIS DOES NOT LOOK
LIKE A VERY STRONG WIND EVENT WITH LITTLE SUPPORT FROM ALOFT AND
FLAT TO VERY WEAK PRESSURE RISES. EXPECT RED FLAG FIRE WEATHER
CONDITIONS IN THE COPPER BASIN TODAY AND TOMORROW. THERE IS
CURRENTLY A FIRE WEATHER WATCH FOR THE KNIK RIVER VALLEY AND THE
LOWER HILLSIDE FRO FRIDAY AFTERNOON. WITH A RAPIDLY WEAKENING
SURFACE RIDGE AND ADVECTION OF MORE STABLE AIR AND CLOUDS FRIDAY
AFTERNOON IT IS LOOKING LESS AND LESS LIKELY THAT RELATIVE
HUMIDITY WILL REACH THE NECESSARY THRESHOLD. THEREFORE...WILL
LIKELY CANCEL THE WATCHES WITH THE AFTERNOON PACKAGE.

AS THE COMPLEX LOW SOUTH OF THE ALASKA PENINSULA LIFTS
NORTHEASTWARD INTO THE GULF THE NORTHERN LOW/TROUGH WILL DIG
SOUTHWARD ACROSS THE BERING WHICH IN TURN WILL PROVIDE LESS
RESISTANCE TO THE NORTHWARD PROGRESSION OF THE SOUTHERN TROUGH.
THUS...FRIDAY WILL BE THE LAST IN A STRING OF SUNNY AND WARM DAYS
ACROSS SOUTHCENTRAL. THE REMNANTS OF THE OCCLUDED FRONT WILL MOVE
ONSHORE ALONG THE GULF COAST FRIDAY NIGHT AND SATURDAY BRINGING
STEADY RAIN TO THE COAST...SHOWERS INLAND...AND LOTS OF CLOUDS
AND COOLER TEMPERATURES TO ALL OF SOUTHCENTRAL. CROSS BARRIER
FLOW WILL INCREASE ACROSS THE KENAI AND CHUGACH MOUNTAINS SATURDAY
AFTERNOON HELPING TO LIMIT THE AMOUNT OF PRECIP MAKING IT OVER
THE MOUNTAINS AND PERHAPS EVEN CREATING A FEW BREAKS OF SUN.
FORECAST CONFIDENCE GOES DOWN SATURDAY NIGHT AND SUNDAY WITH
UNCERTAINTY IN TRACK OF UPPER LEVEL DISTURBANCES MOVING AROUND
THE UPPER LOW CENTER. THERE IS HIGHER CONFIDENCE THAT IT WILL BE
CLOUDY AND COOL WITH AREAS OF RAIN OR SHOWERS...BUT IT IS
IMPOSSIBLE TO PINPOINT THOSE AREAS.

SOUTHWEST ALASKA...WITH RIDGING HOLDING IN ALOFT OVER SOUTHWEST
ALASKA TODAY THE LOW LEVEL THERMAL RIDGE (PRESSURE TROUGH) WILL BE
CENTERED OVER THE KUSKOKWIM DELTA AND KUSKOKWIM MOUNTAINS. THE 12Z
BETHEL SOUNDING IS PRIMED FOR CONVECTION WITH 850-500 LAPSE RATES
OF 7.9 DEGREES C/KM. WITH A LITTLE HELP FROM THE APPROACHING
TROUGH THERE MAY EVEN BE A FEW ISOLATED THUNDERSTORMS. IT LOOKS
A LITTLE TOO CLOUDY IN THE KUSKOKWIM VALLEY TO REACH THE FULL
POTENTIAL OF INSTABILITY...SO BEST CHANCE LOOKS TO BE INTERIOR
KUSKOKWIM DELTA. HEIGHTS WILL ACTUALLY RISE IN THIS AREA FRIDAY AS
THE ARCTIC TROUGH DIGS FURTHER WEST ACROSS THE NORTHERN BERING.
STABILITY WILL INCREASE AS WELL...BUT THERE COULD STILL BE A FEW
DIURNAL SHOWERS.

MEANWHILE...THE OCCLUDED FRONT SOUTH OF THE ALASKA PENINSULA WILL
WORK ITS WAY NORTH INTO BRISTOL BAY. WITH MOST OF THE ENERGY
HEADING NORTHEASTWARD INTO THE GULF OF ALASKA THERE WILL BE A
TIGHT GRADIENT OF PRECIP ON THE NORTHWEST SIDE...WITH THE ALASKA
PENINSULA AND ALEUTIAN RANGE MOST LIKELY TO SEE RAIN OR SHOWERS.
ON SUNDAY SOUTHWEST ALASKA WILL RECEIVE LIFT FROM THE DIGGING
BERING TROUGH AND THE LOW IN THE GULF...SO EXPECT WIDESPREAD
CLOUDINESS...COOLER TEMPERATURES...AND A GOOD CHANCE OF RAIN.

BERING SEA/ALEUTIANS...THE RIDGE OVER THE BERING WILL BE QUICKLY
OVERTAKEN BY THE TROUGH DROPPING OUT OF THE ARCTIC AND ANOTHER
TROUGH DROPPING OUT OF EASTERN RUSSIA INTO THE WESTERN BERING.
EVEN SO...ASIDE FROM SOME WEAK SURFACE LOWS SOUTH OF THE ALEUTIANS
CONDITIONS WILL BE QUITE BENIGN WITH LITTLE IN THE WAY OF WIND OR
PRECIP.

&&

.LONG TERM FORECAST...THE COMPLEX LOW OVER THE GULF WILL EXIT TO
THE EAST EARLY NEXT WEEK WHILE THE ARCTIC LOW AND TROUGH SETTLES
IN PLACE OVER THE EASTERN BERING AND SOUTHWEST ALASKA COAST.
THIS WILL PRODUCE GENERALLY CLOUDY COOL AND WET CONDITIONS OVER
COASTAL SOUTHWEST. HEIGHTS WILL GRADUALLY RISE OVER THE EASTERN
HALF OF MAINLAND ALASKA AS A RIDGE BUILDS OVER WESTERN CANADA.
EXPECT WARMING TEMPERATURES AND A STRENGTHENING THERMAL TROUGH
OVER INTERIOR ALASKA. THIS PATTERN FAVORS DIURNAL SHOWERS AND SOME
SUNSHINE. THE PATTERN BECOMES MUCH MORE QUESTIONABLE LATE NEXT
WEEK WITH MODELS STRUGGLING WITH RUN-TO-RUN CONSISTENCY WITH
ULTIMATE DESTINATION OF THE EASTERN BERING LOW. MEANWHILE...THE
BERING SEA AND ALEUTIANS WILL REMAIN QUIET.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 131 138.
FIRE WEATHER...NONE.

&&

SEB JUN 14

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