Small Craft Advisory 457, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
203 PM AKDT SUN JUN 8 2014

.ANALYSIS AND UPPER LEVELS...

THE REGION IS UNDER THE INFLUENCE OF BROAD SCALE TROUGHING
ALOFT...EXTENDING FROM THE BERING ACROSS SOUTHERN ALASKA. NUMEROUS
MOBILE SHORTWAVE TROUGHS ARE PASSING THROUGH THE FLOW...WITH THE
TWO MAIN IMPACTFUL FEATURES OF INTEREST FOR THE REGION BEING A
COLD UPPER VORTEX CENTERED NEAR THE Y-K DELTA...AND A WEAKENING
LOW IN THE NORTHEAST GULF. A STRETCHING DEFORMATION ZONE BETWEEN
THE SYSTEMS IS CENTERED OVER THE LOWER KUSKOKWIM VALLEY AND
INTERIOR BRISTOL BAY...WITH MUCH COLDER AIR TRACKING INLAND ACROSS
THE KUSKOKWIM DELTA. A WEAK SHORTWAVE RIDGE EXISTS OVER THE
EASTERN INTERIOR OF ALASKA...WITH AN ASSOCIATED WEAK THERMAL
TROUGH. THE PRESSURE GRADIENT REMAINS WEAK...WITH SOUTHERLY
ONSHORE FLOW DEVELOPING UP COOK INLET...AND WEAK FLOW NEAR PRINCE
WILLIAM SOUND AS THE NORTHEAST GULF LOW WEAKENS. WITH TIME...THE
COLD UPPER LOW OVER WESTERN ALASKA WILL MAKE SLOW EASTWARD
PROGRESS...CONTINUING THE THREAT FOR SHOWERS ACROSS SOUTHERN
ALASKA INTO MIDWEEK.

&&

.MODEL DISCUSSION...

THE NUMERICAL GUIDANCE IS IN GOOD AGREEMENT WITH THE LARGE SCALE
SYNOPTIC PATTERN THROUGH THE END OF THE WEEK...BUT IN AVERAGE TO
BELOW AVERAGE AGREEMENT WITH NUMEROUS SHORT WAVELENGTH TROUGHS
EMBEDDED WITHIN THE LARGER FLOW. THESE DISCREPANCIES BECOME
SOMEWHAT LARGE BY TUESDAY...WITH THE ECMWF SLOWER AND MORE
AMPLIFIED ALOFT AS A STRONGER SHORTWAVE TROUGH TRACKS ACROSS COOK
INLET INTO THE COPPER BASIN TUESDAY AFTERNOON AND WEDNESDAY. THE
FORECAST FAVORS THE CANADIAN RDPS EARLY BEFORE TRANSITIONING TO A
GFS AND ECMWF BLEND AS THEY DEPICT SIMILAR EVOLUTIONS THROUGH
MIDWEEK...ALBEIT WITH SLIGHT TIMING DIFFERENCES TUESDAY.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
WITH THE NORTHEAST GULF LOW WEAKENING AND MIGRATING
EAST...SUFFICIENT MOISTURE REMAINS ACROSS
SOUTHCENTRAL...SUPPORTING SCATTERED TO BROKEN SKIES. SUFFICIENT
HEATING IS HELPING TO SPARK OFF SHOWERS...ESPECIALLY OVER THE
KENAI RANGE AND ACROSS THE COPPER BASIN. SHOWERS WILL GENERALLY
REMAIN OVER THE MOUNTAINS...WITH A FEW MINOR SHOWERS ACROSS
INLAND LOCATIONS. AN ISOLATED THUNDERSTORM IS POSSIBLE ALONG THE
KENAI MOUNTAINS WITH THIS AFTERNOONS ACTIVITY. SEA BREEZES WILL
BE MOST PROMINENT ACROSS COOK INLET LATE THIS AFTERNOON AND EARLY
EVENING AS THE FLOW UP COOK INLET INCREASES.

RAIN SHOWERS WILL LINGER ACROSS THE EASTERN COPPER BASIN THROUGH
TONIGHT...WITH MOST LOCATIONS STARTING OUT LARGELY DRY MONDAY
BEFORE ANOTHER WAVE DISTURBANCE TRACKS IN DURING THE
AFTERNOON...SPREADING MORE CLOUDS AND SHOWERS INTO SOUTHCENTRAL. IT
IS BECOMING MORE LIKELY THAT A SLUG OF MOISTURE MOVING IN FROM THE
SOUTH SOUTHWEST WILL SUPPORT PERIODS OF LIGHT RAIN AND OVERCAST
SKIES IN THE LATE AFTERNOON AND EVENING ACROSS THE COOK INLET
AREA...SPREADING NORTH INTO THE SUSITNA VALLEY. ANOTHER DISTURBANCE
WILL IMPACT SOUTHCENTRAL ON TUESDAY...WITH MORE THREATS FOR RAIN AND
RAIN SHOWERS.

SOUTHWEST ALASKA...

COLDER AIR WILL CONTINUE TO TRACK THROUGH SOUTHWEST ALASKA BEHIND
A FRONT THIS EVENING AND TOMORROW...WITH MOIST AND COOL WEST-
SOUTHWEST FLOW LASTING THROUGH WEDNESDAY. SHOWERS WILL BE MOST
PREVALENT OVER THE LOWER KUSKOKWIM VALLEY AND THE KUSKOKWIM
DELTA. TONIGHT...A MORE VIGOROUS LOW WILL MOVE INTO THE KUSKOKWIM
DELTA...WITH THE POSSIBILITY OF LIGHT SNOW ACCUMULATIONS UNDER
HEAVIER BANDS OF PRECIP. SNOW SHOWERS WILL CONTINUE THROUGH THE
MORNING BEFORE CHANGING TO RAIN AND SNOW SHOWERS DURING THE DAY.

BERING SEA/ALEUTIANS...

A RELATIVELY QUIESCENT PATTERN EXISTS IN THE BERING...WITH
COPIOUS AMOUNTS OF CLOUD COVER ACROSS THE CHAIN. A COLD FRONT
MOVING ACROSS THE PRIBILOF ISLANDS WILL SUPPORT A FEW ISOLATED
RAIN SHOWERS...POSSIBLY BRIEFLY MIXING WITH SNOW TONIGHT. A WEAK
LOW WILL TRACK ACROSS THE CHAIN FROM WEST TO EAST TONIGHT THROUGH
WEDNESDAY...WITH A RETURN TO RAIN AND RAIN SHOWERS.

&&

.LONG TERM FORECAST...

BY THURSDAY...A TROUGH ACROSS THE EASTERN BERING AND WESTERN
MAINLAND WILL REFORM...WITH BROAD SOUTHWEST FLOW ACROSS MOST OF
SOUTHERN ALASKA. THIS WILL SUPPORT MORE RAIN AND RAIN SHOWER
THREATS THROUGH FRIDAY BEFORE A SLIGHT DRYING OCCURS AS THE LOW
TRACKS INTO THE GULF. THE PATTERN BECOMES QUITE CONVOLUTED BY THE
WEEKEND IN TERMS OF INDIVIDUAL WAVES IN THE FLOW ALOFT...WITH ALL
THE ENSEMBLE GUIDANCE FROM THE GFS...ECMWF...AND NAEFS HINTING AT
BROAD AND WEAK TROUGHING OVER MAINLAND ALASKA...KEEPING THE
PATTERN ACTIVE...WITH NEAR CLIMATOLOGICAL TEMPERATURES. NO
SIGNIFICANT WARM AND DRY CONDITIONS ARE THUS FORESEEN THROUGH NEXT
WEEKEND.

&&

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

AHSENMACHER JUN 14