Small Craft Advisory 653, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKDT WED AUG 19 2009

.ANALYSIS AND UPPER LEVELS...A LONG WAVE TROUGH REMAINS OVER THE
STATE AGAIN TODAY. A UPPER LEVEL CUT OFF LOW HAS BEGUN TO DEVELOP
JUST SOUTH OF KODIAK ISLAND WITH A SURFACE LOW DEVELOPMENT NEARBY IN
REFLECTION OF THIS. THIS LOW WILL MOVE SLOWLY ACROSS THE SOUTHERN
PART OF THE GULF AND THEN HEAD INTO SOUTHEAST ALASKA FRIDAY.
THE UPPER LEVEL RIDGE IS OVER BRITISH COLUMBIA AND THE JEST STREAM IS
RIDING NORTHWARD BETWEEN THESE FEATURES AND IS EASILY SEEN ON
SATELLITE IMAGERY MOVING ONSHORE JUST EAST OF THE FORECAST AREA.
A WEAK UPPER LEVEL RIDGE IS MOVING OVER SOUTHWEST ALASKA AND BRINGING
SOME CLEARING TO THAT AREA. THIS FEATURE WILL MOVE OVER SOUTH CENTRAL
TOMORROW INTO FRIDAY.
ALSO VISIBLE ON SATELLITE IMAGERY IS A LOW JUST OF SHEMYA. THIS LOOKS
TO BE MAINLY AN UPPER LEVEL FEATURE WHICH MAY BRING A FEW SHOWERS TO
THE WESTERN ALEUTIANS BUT SHOULD NOT EFFECT THE WINDS MUCH.

.MODEL DISCUSSION...THE OVERALL PATTER IS BEING HANDLED WELL THROUGH
THE WEEKEND. HOWEVER THE MODELS ARE STILL HAVING SOME DIFFICULTY
RESOLVING THE LOW DEVELOPING JUST SOUTHWEST OF THE GULF. THE GFS
INITIALIZED A BIT TOO FAR NORTHEAST. THE NAM INITIALIZED MUCH BETTER
AND MATCHED UP WELL TO THE POSITION SHOWN ON A MORNING QUIKSCAT
IMAGE. EVEN AS THIS LOW PROGRESSES ACROSS THE GULF THE SOLUTIONS
DIFFER WITH THE NAM BEING FARTHER SOUTH THAT THE GFS ECMWF OR UKMET.
THE LATER THREE MODELS ARE ALL VERY SIMILAR. IN THE END IT WILL NOT
MAKE A LOT OF DIFFERENCE IN THE FORECAST EXCEPT FOR THE GULF OF
ALASKA OFFSHORE MARINE FORECAST.

.SHORT TERM FORECAST...SOUTH CENTRAL ALASKA WAS STILL MODERATELY
UNSTABLE THIS MORNING BUT THAT INSTABILITY IS MOVING EASTWARD WHICH
WILL ALLOW THE COPPER RIVER BASIN TO POSSIBLY SEE THUNDERSTORMS AGAIN
THIS AFTERNOON AND EVENING. THERE IS NOT A LOT OF INSTABILITY WEST OF
THE ALASKA RANGE...JUST ENOUGH TO GIVE A FEW SHOWERS ALONG THE ALASKA
RANGE AND IN THE BRISTOL BAY REGION.
BY TOMORROW THERE WILL BE VERY LITTLE INSTABILITY ACROSS THE ENTIRE
MAINLAND AREA SO AFTERNOON SHOWERS ARE NOT EXPECTED EVEN WITH SOME
DAYTIME HEATING.

.LONG TERM FORECAST...THE SUNNY REPRIEVE THE NEXT DAY OR TWO WILL NOT
LAST LONG AS A POTENT COLD FRONT WILL MOVE INTO SOUTHWEST ALASKA
FRIDAY AND INTO SOUTH CENTRAL ALASKA FOR THE WEEKEND.

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

EZ AUG 09