Small Craft Advisory 606, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKDT SUN AUG 2 2009

.ANALYSIS AND UPPER LEVELS...THERE IS A LONG-LIVED AND HIGHLY
AMPLIFIED LONGWAVE TROUGH STILL RESIDING IN THE BERING SEA THIS
MORNING. A RELATIVELY WEAK LOW IS UNDERNEATH THIS UPPER TROUGH IN THE
NORTH PACIFIC AND IS PREPARING TO CROSS THE CENTRAL ALEUTIANS AND
ENTER THE BERING. THIS LOW IS BRINGING AREAS OF GENERALLY LIGHT
RAINFALL TO SOUTHWEST ALASKA AND THE EASTERN ALEUTIANS. SURFACE HIGH
PRESSURE IS LOCATED IN THE GULF...WITH SOUTHWEST FLOW ABOVE IT AT THE
UPPER LEVELS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...RELATIVELY BENIGN WEATHER ON TRACK FOR MOST AREAS
TODAY...WITH MAIN WEATHER CONCERN BEING HOW MUCH MIDLEVEL CLOUDINESS
WILL INFILTRATE THE AREA FROM THE LOW CURRENTLY NEAR DUTCH HARBOR. DO
EXPECT AFTERNOON SEA BREEZES IN MOST OF THE USUAL LOCATIONS TODAY.
DESPITE THE HIGH PRESSURE AND WEAK WINDS IN THE GULF...MARINE STRATUS
HAS NOT MATERIALIZED AND IS THUS NOT A MAJOR FORECAST CONCERN TODAY.
SOME AFTERNOON THUNDERSTORMS ALONG THE ALASKA RANGE TO THE NORTH OF
THE COPPER RIVER BASIN ARE  A POSSIBILITY THIS AFTERNOON...BUT SHOULD
NOT BE WIDESPREAD. ADDITIONALLY, ANY STORMS THAT DO DEVELOP WILL MOVE
TO THE NORTHEAST AND OUT OF THE AREA.

.SOUTHWEST AND BERING SEA/ALEUTIANS...
THE WEAK LOW CROSSING THE ALEUTIAN CHAIN NEAR DUTCH HARBOR WILL
CONTINUE TO WEAKEN THROUGH THE DAY. WIDESPREAD LIGHT RAIN THIS
MORNING THROUGH THE BRISTOL BAY...KUSKOKWIM DELTA...AND ALASKA
PENINSULA REGIONS THIS MORNING WILL TAPER TO SHOWERS THIS AFTERNOON
AS THE LOW QUICKLY LOSES STEAM. A SECONDARY LOW THAT DEVELOPS SOUTH
OF THE ALASKA PENINSULA WILL ONCE AGAIN BRING GOOD CHANCES OF
GENERALLY LIGHT RAINS TO THE CENTRAL ALEUTIANS AND ALL POINTS
EASTWARD STARTING MONDAY NIGHT. BY TUESDAY EVENING...RAIN WILL BE
POSSIBLE AS FAR INLAND AS THE UPPER KUSKOKWIM DELTA. WINDS THROUGHOUT
THE FIRST HALF OF THE WEEK WILL REMAIN GENERALLY GUSTY OUT OF THE
SOUTHEAST...WITH PERIODS OF STRONGER GUSTS ESPECIALLY THROUGH FAVORED
GAPS IN TERRAIN ALONG THE ALEUTIAN RANGE.

.MODEL DISCUSSION...THE MAJOR GLOBAL MODELS ARE IN GOOD AGREEMENT FOR
THE FIRST FEW DAYS OF THE FORECAST. DISCORD BEGINS TOWARD THE END OF
THE WEEK WITH REGARDS TO A POSSIBLE WAVE MOVING THROUGH THE BROAD
SOUTHWEST FLOW AND IMPACTING KODIAK ISLAND AND EVENTUALLY
SOUTHCENTRAL ALASKA. AS EXPECTED...THE MODELS ARE ALSO STRUGGLING
WITH THE EXACT DETAILS OF THE SURFACE FEATURES ASSOCIATED WITH THE
COMPLEX LOW PRESSURE THAT WILL CONTINUE TO RESIDE IN THE CENTRAL AND
EASTERN BERING SEA. THE NAM WAS PRIMARILY USED FOR THE SHORT TERM
FORECAST TODAY...TRANSITIONING TO A NAM/GFS BLEND IN THE MIDRANGE.
MINIMAL CHANGES WERE MADE TO THE LONG TERM FORECAST DUE TO PERSISTING
UNCERTAINTY WITH THE PATTERN CHANGE TO MORE ZONAL FLOW NEXT WEEKEND.

.LONG TERM FORECAST...
THE LONGWAVE TROUGH IN THE BERING WILL LOSE JET SUPPORT AND BECOME A
CLOSED UPPER LOW BY TUESDAY MORNING. THIS LOW WILL SPIN IN PLACE IN
THE EASTERN ALEUTIANS BEFORE BEING KICKED OUT BY A POSSIBLE PATTERN
SHIFT LATE IN THE WEEK. AT THIS POINT IT LOOKS LIKE THE AMPLIFIED
FLOW OF THE PAST WEEK WILL BREAK DOWN INTO LARGELY ZONAL FLOW.
CONFIDENCE IN ADDITIONAL DETAILS AT THIS POINT ARE QUITE LOW...BUT
LIKELY IMPACTS FOR MAINLAND ALASKA WILL INCLUDE AVERAGE TO SLIGHTLY
BELOW AVERAGE TEMPERATURES...WITH PERIODIC BUT SHORT-LIVED WAVES OF
PRECIPITATION...NOT AN UNUSUAL PATTERN FOR EARLY FALL.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY 121 145
MARINE...GALE 155 160
FIRE WEATHER...NONE.

AMD AUG 09