Small Craft Advisory 576, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
139 PM AKDT SAT AUG 2 2014

.ANALYSIS AND UPPER LEVELS...
THE SPRAWLING HIGH PRESSURE IN THE BERING SEA HAS BEGUN TO SLOWLY
WEAKEN...BUT REMAINS A SIGNIFICANT BLOCKING FEATURE AT THIS TIME.
THE MOST PROMINENT FEATURE ON SATELLITE IMAGERY THIS MORNING
REMAINS A LARGE LOW SPINNING SOUTH OF THE GULF OF ALASKA. SEVERAL
SIGNIFICANT SHORTWAVES ARE SPINNING AROUND THIS LOW...ONE
CURRENTLY ON THE NORTH SIDE AND ANOTHER ON THE SOUTH SIDE. THE
NORTH SIDE TROUGH IS ASSOCIATED WITH A CLUSTER OF CONVECTION JUST
SOUTH OF THE GULF OFFSHORE ZONES. A WEAK SURFACE LOW HAS LIKELY
DEVELOPED BENEATH THIS CONVECTION...AND THIS FEATURE WILL SLING A
WEAK WEATHER FRONT TOWARD THE GULF COAST LATE TONIGHT AND
TOMORROW. SIGNIFICANT CLOUD-COVER IS SLOWLY ERODING ACROSS
SOUTHWEST ALASKA...AND REPRESENTS THE REMNANTS OF THE WEATHER
SYSTEM THAT BROUGHT RAIN TO THE NORTH SIDE OF THE ALASKA RANGE AND
SOUTHWEST ALASKA YESTERDAY. THE BERING AND ALEUTIANS REMAIN LOCKED
IN THE GRIP OF SIGNIFICANT LOW CLOUDS AND FOG AS THE
AFOREMENTIONED HIGH PRESSURE IS STILL PLENTY STRONG TO SUPPRESS
MORE ACTIVE WEATHER.

&&

.MODEL DISCUSSION...
THE WEATHER PATTERN IS GENERALLY SLOW-CHANGING...SO NOT
SURPRISINGLY THE MODELS ARE IN VERY GOOD OVERALL AGREEMENT. THE
MOST SIGNIFICANT DISAGREEMENT IN THE MODELS INVOLVES THE SHORTWAVE
CURRENTLY SOUTH OF THE BIG LOW IN THE NORTHEAST PACIFIC. BY
MONDAY NIGHT THIS FEATURE WILL ROTATE ALL THE WAY AROUND TO THE
NORTH SIDE OF THE LOW AND BE SQUARELY IN THE MIDDLE OF THE GULF.
MUCH LIKE THE CURRENT SHORTWAVE THIS FEATURE WILL RESULT IN
SURFACE CYCLOGENESIS...THE QUESTION IS IN HOW STRONG THIS LOW WILL
BECOME. THE ECMWF IS SIGNIFICANT STRONGER THAN THE OTHER
SOLUTIONS...ALTHOUGH ALL SOLUTIONS DO STILL DEVELOP A DECENTLY
STRONG LOW. THE ASSOCIATED SHORTWAVE IS CURRENTLY PRODUCING
SIGNIFICANT MARITIME THUNDERSTORM ACTIVITY OUT IN THE CENTRAL
PACIFIC...SO THE CURRENT THINKING IS THAT THE 12Z ECMWF IS
SIMULATING THIS CONVECTION AND INJECTING A SIGNIFICANT AMOUNT OF
LATENT HEAT ENERGY INTO THE SYSTEM TO AMP UP THE STRENGTH OF THE
SURFACE LOW. THE INSTABILITY UNDER THE LARGE COLD CORE UPPER LOW
IS UNDENIABLE (BASED ON CURRENT OBS/SATELLITE)...SO WHILE THE 12Z
ECMWF WILL NOT BE USED WHOLE-HOG A TREND WILL BE MADE TOWARD A
STRONGER SOLUTION THAN PREVIOUSLY DEPICTED IN THE FORECAST.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
ANOTHER MOSTLY SUNNY AND PLEASANTLY MILD DAY IS UNFOLDING ACROSS
MUCH OF SOUTHCENTRAL ALASKA. SOME LOW CLOUDS AND DRIZZLE ARE
ONGOING ACROSS THE FAR NORTHERN SUSITNA VALLEY AND NORTHERN COPPER
RIVER BASIN...BUT CONDITIONS WILL IMPROVE THROUGH THE EVENING AS
THE ATMOSPHERE SLOWLY DRIES OUT. MEANWHILE...THE NEXT IN THE
SERIES OF WEAK FRONTS IS MOVING INTO THE SOUTHERN GULF AT THIS
HOUR AS THE OVERALL LOW PRESSURE CIRCULATION SLOWLY INCHES
NORTHWARD. KODIAK GOT CLIPPED BY CLOUDS AND RAIN WITH THE FIRST
FRONT EARLIER TODAY. THIS NEXT FRONT WILL BRING ANOTHER ROUND OF
RAINFALL TO NOT ONLY KODIAK BUT MUCH OF THE GULF COAST BY SUNDAY
MORNING. MODELS ARE TRYING TO DEPICT SOME RAIN ON THE LEE SIDES OF
THE MOUNTAINS IN ANCHORAGE AND THE MAT-SU VALLEY BY SUNDAY
AFTERNOON...BUT THINK THIS WILL NOT AMOUNT TO ANYTHING TOO
SIGNIFICANT AS THE SYSTEM WILL BE WEAKENING AND A WEAK CROSS-
BARRIER FLOW SHOULD INDUCE A LITTLE DOWNSLOPING IN THE USUAL
AREAS. THE BIGGER IMPACT WILL SIMPLY BE INCREASED CLOUDINESS
COMPARED TO RECENT DAYS. HEADING INTO THE FIRST HALF OF NEXT WEEK
THE UPPER LOW WILL SET UP SHOW IN THE WESTERN GULF AND SLOWLY
WEAKEN. A BARRAGE OF SHORTWAVES CAN BE EXPECTED TO BRING
SUCCESSIVE ROUNDS OF RAIN TO THE COAST...WITH CLOUDINESS AND
SIGNIFICANT DIURNAL CONVECTION LIKELY ACROSS INTERIOR AREAS.
KODIAK ISLAND WILL SEE THE MOST VARIABLE WEATHER...WITH DAILY CONDITIONS
OSCILLATING BETWEEN DRY/PARTY SUNNY AND WET/CLOUDY DICTATED
LARGELY BY SHORTWAVE TROUGH TIMING WHICH IS FUTILE TO PINPOINT
THIS FAR IN ADVANCE.

SOUTHWEST ALASKA...
EXTENSIVE CLOUDINESS WILL GRADUALLY DIMINISH DURING THE OVERNIGHT
HOURS AS OFFSHORE MID-LEVEL FLOW STRENGTHENS. AS THE UPPER LOW
MOVES INTO THE GULF THE COLD POOL OF AIR ALOFT WILL SPREAD INTO
SOUTHWEST ALASKA AND STEEPEN LAPSE RATES. THIS RAISES THE CONCERN
THAT WITH INCREASED SUNSHINE AND THE CONTINUED PRESENCE OF A WEAK
THERMAL TROUGH THERE IS THE POTENTIAL FOR SIGNIFICANT CONVECTION
EACH OF THE NEXT FEW DAYS ACROSS PARTS OF THE REGION. THERE IS
STILL UNCERTAINTY ABOUT HOW LONG LOW-CLOUDS WILL LINGER (AND
INHIBIT HEATING TOMORROW) AND IF FAIRLY WEAK DYNAMIC FORCING WILL
BE ENOUGH TO KICK OFF FEW THUNDERSTORMS. THERE SEEMS TO BE ENOUGH
GOING AGAINST THUNDERSTORM FORMATION TO KEEP MENTION FOR NOW AS
SHOWERS...THOUGH IMPRESSIVE COLD AIR ALOFT COULD LEAD TO SOME
DOWNPOURS. WHATEVER HAPPENS SHOULD BE FOCUSED MAINLY ALONG THE
HIGHER TERRAIN OF THE KILBUCK AND AHKLUN MOUNTAINS WITH A GENERAL
SOUTH TO SOUTHWEST-MOVING CELL MOTION.

BERING SEA/ALEUTIANS...
TRANQUIL WEATHER WILL CONTINUE OVERALL FOR SEVERAL MORE DAYS AS
HIGH PRESSURE TAKES ITS TIME RETREATING. FOG AND LOW CLOUDS WILL
REMAIN THE PRIMARY FORECAST CHALLENGE...WITH CONDITIONS LIKELY
WORSE AND SURGING INLAND AT NIGHT WITH DIURNAL COOLING. THE NEXT
NOTEWORTHY WEATHER SYSTEM WILL BE A LARGE WARM FRONT MOVING INTO
THE WESTERN BERING ON TUESDAY WHICH WILL EVENTUALLY BRING
WIDESPREAD RAINS TO THE MAJORITY OF THE REGION.

&&

.LONG TERM FORECAST (WED AUG 6TH - SAT AUG 9TH)...

HIGH LATITUDE BLOCKING WILL REMAIN A DOMINANT FORCE ACROSS THE
REGION WEDNESDAY...WITH THE BERING RIDGE TRANSITIONING INTO A
CLOSED BLOCK CENTERED OVER THE NORTHERN CHUKCHI SEA. A STRONG
NORTHWEST PACIFIC JET...AIDED BY REMNANTS OF TYPHOON NAKRI NEAR
KOREA...WILL EVENTUALLY UNDERCUT THE BERING RIDGE WEDNESDAY AND
THURSDAY WITH A MOIST SUBTROPICAL WARM FRONT TRACKING ACROSS THE
BERING SEA AND ALEUTIANS. RAIN WILL BE MODERATE TO HEAVY ACROSS
THE ALEUTIANS...WITH RAIN OVERSPREADING KODIAK ISLAND AND THE
KENAI COASTLINE BY LATE FRIDAY INTO SATURDAY. ACROSS INTERIOR
SOUTHERN ALASKA...THE REMNANTS OF THE PERSISTENT GULF LOW WILL BE
IN THE PROCESS OF WEAKENING...WITH DIURNAL DRIVEN SHOWERS/CLOUDS
DRIVING THE SENSIBLE WEATHER ACROSS SOUTHERN ALASKA INTO SATURDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

DIXON/AHSENMACHER AUG 14