Small Craft Advisory 297, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKDT TUE APR 26 2011

.ANALYSIS AND UPPER LEVELS...A TROUGH EXTENDING FROM THE EASTERN
BERING SEA TO THE NORTHEAST PACIFIC IS WEAKENING AS IT MOVES
EASTWARD INTO A DOWNSTREAM RIDGE. THIS RIDGE IS BUILDING OVER
TOP OF THE TROUGH INTO MAINLAND ALASKA. THE SOUTHERN MAINLAND
WHICH IS ON THE SOUTHERN PERIPHERY OF THE RIDGE IS OBSERVING
SHOWERS ASSOCIATED WITH WEAK UPPER LEVEL WAVES. OUT WEST...A
LOW JUST SOUTH OF THE WESTERN ALEUTIANS IS STRENGTHENING ALONG
THE SUBTROPICAL JET.

.MODEL DISCUSSION...ALL MODELS NOW SHOW A VERY SIMILAR SOLUTION
WITH TRACK OF ALEUTIAN LOW WHICH WILL BE THE PRIMARY WEATHER-MAKER
FOR THE REST OF THE WEEK. THUS...FORECAST CONFIDENCE IS ABOVE
AVERAGE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THERE IS ONE MORE DISTINCT UPPER WAVE NOTED
ON WATER VAPOR IMAGERY WHICH WILL CROSS SOUTHCENTRAL THIS AFTERNOON
AND EVENING HELPING TO PRODUCE AREAS OF SHOWERS. ANY FEATURES TO
FOLLOW WILL BE MUCH WEAKER...SO EXPECT LESS CLOUDS AND SHOWERS ON
WEDNESDAY. OF COURSE WITH MORE SOLAR HEATING ON WEDNESDAY INSTABILITY
WILL INCREASE AND LIKELY LEAD TO A FEW AFTERNOON/EVENING SHOWERS...
ESPECIALLY ALONG THE MOUNTAINS. THE MAIN UPPER TROUGH SITTING SOUTH
AND WEST OF THE AREA WILL STRETCH APART AS IT LIFTS NORTHEASTWARD
ACROSS SOUTHCENTRAL WEDNESDAY NIGHT AND DON'T EXPECT ANY IMPACTS
FROM IT. A SHORT-WAVE RIDGE WILL THEN BUILD OVERHEAD ON THURSDAY
PROVIDING A DRY AND SUNNY DAY ACROSS MOST OF THE REGION. HOWEVER...
A FRONTAL BOUNDARY FROM AN ALEUTIAN LOW WILL BE RIGHT ON ITS HEELS.
EXPECT INCREASING CLOUDS AND A CHANCE OF RAIN OR SHOWERS THURSDAY
NIGHT AND FRIDAY. THE FRONT WILL STALL OVER THE WESTERN GULF DUE
TO AMPLIFYING DOWNSTREAM RIDGE SO THE BULK OF PRECIPITATION WILL
BE FROM KODIAK ISLAND TO THE KENAI PENINSULA WITH LESS AS YOU HEAD
NORTH AND EAST.

SOUTHWEST ALASKA...THERE ARE CURRENTLY A LOT OF LOW CLOUDS ALONG
THE SOUTHWEST COAST ALONG WITH PATCHY FOG AND A FEW SHOWERS. THESE
WILL HOLD IN PLACE UNTIL UPPER TROUGH MOVES THROUGH LATE TONIGHT
INTO WEDNESDAY. THERE WILL BE A VERY BRIEF BREAK IN CLOUDS BEFORE
A FRONT ARRIVES FROM THE WEST WEDNESDAY NIGHT. WITH AMPLIFYING
DOWNSTREAM RIDGE FRONT WILL SLOW TO A CRAWL ALONG THE SOUTHWEST
COAST. IT WILL BE IN A MUCH WEAKENED STATE AS IT PUSHES INLAND
THURSDAY. MUCH WARMER AIR WILL ACCOMPANY THE FRONT SO EXPECT THE
PREDOMINANT PRECIPITATION TYPE TO BE RAIN. MODELS DO SHOW AN UPPER
WAVE MOVING ACROSS THE REGION FRIDAY WHICH MAY PROVIDE ANOTHER
SHOT OF RAIN.

BERING SEA/ALEUTIANS...STORM ALONG THE ALEUTIANS WILL CONTINUE TO
STRENGTHEN TONIGHT AND PROVIDE WIDESPREAD GALE FORCE WINDS AND
PRECIPITATION ACROSS THE REGION THROUGH WEDNESDAY. TEMPERATURES ARE
INITIALLY COLD ENOUGH OUT AHEAD OF THE STORM TO SUPPORT SNOW...BUT
EXPECT A RAPID CHANGEOVER TO RAIN AS MUCH WARMER AIR MOVES IN WITH
THE FRONT. COLDER AIR WILL FEED INTO THE BACK SIDE OF THE SYSTEM
WEDNESDAY NIGHT AND CHANGE PRECIPITATION BACK OVER TO SNOW ACROSS
THE WESTERN BERING AND ALEUTIANS. THE UPPER JET WILL HEAD DOWNSTREAM
WEDNESDAY SO THE STORM WILL SLOW DOWN ITS EASTWARD PROGRESSION...
WITH THE LOW CENTER NOT REACHING DUTCH HARBOR UNTIL FRIDAY.

.LONG TERM FORECAST...A PROGRESSIVE PATTERN WILL DOMINATE THE
EXTENDED FORECAST PERIOD WITH STORMS MARCHING FROM WEST TO EAST
AND CENTERED IN THE REGION BETWEEN 45N AND 60N LATITUDE. WITH THIS
STORM TRACK THE GREATEST IMPACTS OF WIND AND PRECIPITATION WILL BE
FELT ALONG THE ALEUTIANS ALASKA PENINSULA AND GULF COAST WHILE MOST
OF SOUTHWEST AND SOUTHCENTRAL ALASKA WILL REMAIN ALONG THE PERIPHERY
OF THESE STORMS. INLAND AREAS SHOULD SEE SOME SUN ON MOST DAYS ALONG
WITH SOME DIURNALLY DRIVEN SHOWERS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 150 155 160 165 170 171 172 175 179 180.
FIRE WEATHER...NONE.

SEB APR 11