Small Craft Advisory 600, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKDT THU JUL 30 2009

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT THROUGH THE WEEKEND.
WHILE CONSISTENT...THEY ARE ALL A LITTLE TOO FAR EAST ON THE LOW
MOVING OVER KODIAK THIS AFTERNOON.
GETTING DOWN TO FINER DETAILS...THE GFS WAS WEIGHED UPON A LITTLE
HEAVIER FOR PRECIPITATION AMOUNTS IN THE EASTERN KENAI PENINSULA AS
THE NAM LOOKS TO BE A LITTLE BIT ON THE HIGH SIDE AND THE FARTHER
WEST TRACK OF THE LOW.

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL PATTERN HAS THE LONGWAVE
TROUGH FIRMLY ENTRENCHED OVER THE EASTERN BERING SEA WITH THE LARGE
LONGWAVE RIDGE OVER SOUTHEAST ALASKA. AN UPPER LEVEL WAVE ROTATION
AROUND THIS TROUGH IS STRENGTHENING A LOW MOVING UP FROM THE PACIFIC
WHICH IS NOW NEAR KODIAK ISLAND. WEAK SURFACE HIGH PRESSURE WILL
BUILD IN BEHIND THIS SYSTEM.

.SHORT TERM FORECAST... THERE IS A GOOD POOL OF COOL AIR ALOFT
ASSOCIATED WITH THE FAST MOVING SYSTEM APPROACHING THE KENAI
PENINSULA. THIS IS EXPECTED TO ENHANCE THE VERTICAL LIFT SO THAT
THERE WILL BE HEAVY RAINFALL AT TIMES AS THIS SYSTEM MOVES THROUGH.
KODIAK ISLAND HAS BEEN EXPERIENCING THIS TODAY AS THE HAVE REPORTED
MODERATE RAINFALL RATES FOR A NUMBER OF OBSERVATIONS. THIS IS THE BIG
QUESTION REGARDING THE FLOODING POTENTIAL IN THE SEWARD AREA. THE
SYSTEM WILL BE MUCH SHORTER IN DURATION WITH LESS OF A DUE SOUTH FLOW
IN THE UPPER LEVELS...BUT THE DYNAMIC LIFT IS BETTER WITH THIS SYSTEM
SO THERE COULD BE PERIODS OF HEAVY RAINFALL FROM LATE THIS AFTERNOON
UNTIL AROUND MIDNIGHT. IN ADDITION THE SHORTER PERIODS OF HEAVY
RAINFALL AS MORE LIKELY TO CAUSE ADDITIONAL FLOODING ISSUES SO THE
FLOOD WATCH FOR THE SEWARD AREA HAS BEEN UPGRADED TO A FLOOD ADVISORY
FOR TONIGHT.
THE PRESSURE RISES BEHIND THIS SYSTEM WILL ALSO CAUSE GUSTY SOUTHERLY
WINDS TO DEVELOP OVER MUCH OF SOUTH CENTRAL ALASKA.

.LONG TERM FORECAST...WHILE THE OVERALL PATTERN DOES NOT CHANGE WITH
THE UPPER LEVEL TROUGH IN THE BERING SEA AND THE UPPER LEVEL RIDGE IN
SOUTHEAST ALASKA. THERE IS SOME RETROGRESSION OF BOTH FEATURES THIS
WEEKEND WHICH WILL SHIFT THE RAINY PATTERN FARTHER WEST TOWARD THE
ALASKA PENINSULA. IT WILL ALSO BRING PARTIAL CLEARING TO SOUTH
CENTRAL ALASKA WITH THE MARINE LAYER POSSIBLE BECOMING A PLAYER UP
COOK INLET.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY 121 125.
MARINE...GALE 138.
FIRE WEATHER...NONE.

JUL 09