Small Craft Advisory 563, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT SUN JUL 28 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL RIDGE IN NOW CENTERED
OVER THE INTERIOR OF THE STATE AND HAS FLATTENED SINCE YESTERDAY.
THIS IS PART OF ITS MOVE FROM THE EASTERN BERING SEA YESTERDAY INTO
SOUTHEAST ALASKA TOMORROW NIGHT. THERE ARE TWO AREAS OF UPPER LEVEL
LOWS IN THE WESTERN PART OF THE FORECAST AREA. THE FIRST IS CENTERED
NEAR NORTHERN KAMCHATKA WHILE THE SECOND ONE IS RELATIVELY BROAD AND
JUST SOUTH OF THE ALEUTIAN ISLANDS. THIS PATTERN IS KEEPING UPPER
LEVEL FLOW RELATIVELY WEAK OVER MOST OF THE FORECAST AREA.
THE SURFACE RIDGE IS IN THE GULF OF ALASKA AND REMAINS FARTHER SOUTH
THAN THE UPPER LEVEL RIDGE. IT WILL NOT MOVE MUCH FOR THE FIRST HALF
OF THIS WEEK.
DESPITE THE PRESENCE OF AN UPPER LEVEL RIDGE THE ATMOSPHERE REMAINS
QUITE UNSTABLE TODAY EXCEPT FOR COASTAL AREAS UNDER THE INFLUENCE OF
MARINE INVERSIONS. THIS CAN BE SEEN IN COMPARING THE 12Z SOUNDINGS
FROM KING SALMON AND MCGRATH. KING SALMON IS IN THE MARINE LAYER AND
HAS A LIFTED INDEX VALUE OF +3.7 WHERE MCGRATH IS NOT INFLUENCED BY
THE MARINE AIR AND HAD A LIFTED INDEX VALUE OF -3.4 FROM THIS
MORNING.

.MODEL DISCUSSION...THE MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH
EACH OTHER AND HAVE GOOD RUN TO RUN CONSISTENCY. THE ONLY SIGNIFICANT
DIFFERENCE IS THE ABILITY OF THE NAM TO PICK UP THE LOW LEVEL
MOISTURE FIELDS THAT ARE PRODUCING THE MARINE LAYERS IN COASTAL
REGIONS. THEREFORE THE NAM IS BEING USED AS GUIDANCE FOR MARINE
STRATUS ESPECIALLY IN COOK INLET AND THE GULF OF ALASKA REGION.

.SHORT TERM FORECAST...THERE IS A STARK CONTRAST IN THE WEATHER
BETWEEN THE COOL AND STABLE MARINE AIRMASS ALONG THE COASTS AND UP
COOK INLET AND THE WARM AND UNSTABLE AIRMASS OVER THE INLAND AREAS.
STRONG INSTABILITY HAS HELPED KEEP SHOWERS THROUGH LAST NIGHT AND
THIS MORNING IN THE INLAND PARTS OF THE BRISTOL BAY ZONE AND THE
KUSKOKWIM VALLEY. THESE WILL INCREASE AND THUNDERSTORMS WILL DEVELOP
IN THESE AREAS THIS AFTERNOON AND EVENING FROM THE KILBUCK MOUNTAINS
TO THE ALASKA/ALEUTIAN RANGES. WEST OF THE KILBUCK MOUNTAINS THE
KUSKOKWIM DELTA IS ENTRENCHED IN A MARINE LAYER AND THE THICK STRATUS
IS KEEPING THE ATMOSPHERE STABLE. THIS IS THE CASE FOR MOST OF THE
BERING SEA REGION.
THE SUSITNA VALLEY AND COPPER RIVER BASIN SHOULD SEE SHOWERS AND
ISOLATED THUNDERSTORMS DEVELOP AGAIN THIS AFTERNOON AND EVENING.
AREAS ALONG THE COAST INCLUDING COOK INLET AND PRINCE WILLIAM SOUND
WILL REMAIN UNDER THE MARINE AIRMASS AND WILL CONTINUE TO SEE A LOT
OF MARINE STRATUS FOR THE NEXT FEW DAYS.

.LONG TERM FORECAST...
A SUBSTANTIAL PATTERN SHIFT WILL BEGIN TO TAKE SHAPE BY MIDWEEK AS A
LARGE UPPER LOW FORMS SOUTH OF THE ALEUTIAN CHAIN AND SURGES A
SUBTROPICAL MOISTURE PLUME NORTHWARD. RIDGING AND GENERALLY WARMER
THAN AVERAGE CONDITIONS ACROSS SOUTHERN ALASKA WILL COME TO AN END
LATE IN THE WEEK AS THE LOW BEGINS IMPACTING SOUTHERN ALASKA WITH
RAIN AND CLOUDS THURSDAY THROUGH SATURDAY. THE WILL TROUGH LIKELY
REMAIN OVER SOUTHERN ALASKA AND THE EASTERN BERING INTO EARLY NEXT
WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

JUL 13