Small Craft Advisory 677, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT TUE AUG 21 2007

.ANALYSIS...
WEAKENING LOW IN BRISTOL BAY WITH SHOWERS SPREAD ACROSS SOUTHWEST AND
SOUTH CENTRAL ALASKA THIS AFTERNOON. AN UPPER LEVEL SHORT WAVE TROUGH
IS LIFTING THROUGH THESE AREAS TODAY WITH SOME LIGHT TO MODERATE
SOUTH WINDS. SO...UPSLOPE AREAS MOST LIKELY RECEIVING MODERATE TO
HEAVY RAINFALL FOR PERIODS TODAY AND THIS EVENING. ANOTHER LOW IS
NEAR ATKA STACKED BELOW AN UPPER LOW WITH SHOWERS AND LOW CLOUDS OVER
THE CENTRAL AND WESTERN ALEUTIANS. HIGH PRESSURE BUILDING BEHIND THE
LOW IN THE WESTERN ALEUTIANS...BUT LOW CLOUDS WILL REMAIN.

.MODEL DISCUSSION AND UPPER LEVELS...
MODELS AND ENSEMBLES IN BETTER AGREEMENT TODAY THROUGH FRIDAY OVER
THE GULF OF ALASKA. THE SAME CANNOT BE SAID FOR THE NEXT LOW WORKING
TO THE WESTERN ALEUTIANS STARTING WEDNESDAY NIGHT. DUE TO THE NEARLY
ZONAL FLOW THAT WILL DEVELOP BY FRIDAY AND LAST THROUGH
SATURDAY...THE SPEED OF THIS SYSTEM IS IN DOUBT. NO MATTER...THE LOW
WILL DIG AND SLOW DOWN SOUTH OF THE AKPEN LATE IN THE WEEKEND. THIS
IS IN BETTER AGREEMENT WITH ALL MODELS. THE TRANSITION FROM THE LOW
JUST EAST OF THE KAMCHATKA PENINSULA TO THE LOW SOUTH OF THE AKPEN IS
WHERE THE UNCERTAINTY WILL LIE. THE 12Z GFS HAS SLOWED A BIT...BUT
STILL NOT AS SLOW AS THE ENSEMBLES OR EURO MODELS WOULD SUGGEST.

CURRENTLY A LOW IN BRISTOL BAY TO WEAKEN AND ROTATE NORTH THEN EAST
OVER THE NEXT 24 HOURS AND MERGE WITH A LOW CURRENTLY NEAR ATKA. THIS
WILL OCCUR WEDNESDAY OVER THE EASTERN BERING. THIS WILL MEAN A
CONTINUED SOUTHERLY FLOW OVER SOUTH CENTRAL AND WESTERN ALASKA. A
RIDGE WILL BUILD INTO THE WESTERN BERING DURING THIS TIME AS WELL.
THE EASTERN BERING LOW WILL TRANSITION INTO THE GULF THURSDAY WITH
THE RIDGE MOVING OVER THE CENTRAL AND EASTERN BERING. MEANWHILE...A
NEW LOW MOVES TO THE WESTERN BERING. THE MOVEMENT OF THESE FEATURES
WILL ALL DEPEND ON THE SPEED OF THE WESTERN BERING LOW. OVERALL...THE
WESTERN BERING LOW WILL PUSH TO SOUTH OF THE AKPEN SATURDAY WHILE
PUSHING THE GULF LOW ACROSS THE PANHANDLE INTO THE ROCKIES OVER THE
WEEKEND. THE BERING LOW EVENTUALLY SITS IN THE SOUTHERN GULF BY EARLY
NEXT WEEK WITH A RIDGE OVER THE BERING.

.SHORT TERM FORECAST...
ALEUTIANS AND BERING...
LOW NEAR ATKA WITH LIGHT WINDS AND SHOWERS. LOW CLOUDS AROUND THE
BERING WITH AREAS OF FOG. LIGHT WINDS TO PERSIST THROUGH TONIGHT FOR
AREAS OF FOG. WINDS WILL BEGIN TO PICK UP TOMORROW AFTERNOON AS A
FRONT MOVES TO SHEMYA AND ITS PARENT LOW MOVES TO THE KAMCHATKA
PENINSULA. THE ATKA LOW MOVES TO THE EASTERN ALEUTIANS WITH SHOWERS.
IN BETWEEN THE TWO SYSTEMS...HIGH PRESSURE WILL DOMINATE WITH LOW
CLOUDS AND FOG. THE EASTERN ALEUTIAN LOW MOVES INTO THE GULF THURSDAY
WITH THE KAMCHATKA LOW MOVING TOWARD SHEMYA AND THE ASSOCIATED FRONT
MOVING TO THE CENTRAL BERING. STRONG WINDS ARE POSSIBLE WITH THIS
LOW. A STRONG JET WITH THIS FRONT WILL ALSO BRING MODERATE TO HEAVY
RAINFALL. THIS LOW MOVES TO THE CENTRAL BERING FRIDAY WITH THE FRONT
MOVING PAST SAINT PAUL AND UNALASKA. THE WIND WILL CONTINUE TO BE
STRONG WITH THE FRONT DUE TO THE GOOD UPPER LEVEL SUPPORT.

WESTERN ALASKA...
THE WEAK LOW IN BRISTOL BAY WILL CONTINUE TO SPREAD SHOWERS OVER THE
AREA THROUGH TONIGHT. IN THE FRINGE AREAS WHERE SUN WILL PROVIDE A
HEAT SOURCE TODAY...A FEW THUNDERSTORMS ARE POSSIBLE AGAIN THIS
AFTERNOON AND EVENING. THIS WILL BE TRUE THROUGH THURSDAY. THE NEXT
LOW TO MOVE TO THE EASTERN ALEUTIANS WILL CONTINUE THIS PERIOD OF
SHOWERS INTO THURSDAY MORNING. AS THE LOW MOVES INTO THE CENTRAL GULF
THURSDAY...SHOWERS WILL BE ON THE DOWNTURN OVER WESTERN ALASKA. ONLY
EXPECT AFTERNOON AND EVENING CONVECTIVE SHOWERS FRIDAY.

SOUTH CENTRAL ALASKA...
THE WEAK LOW IN BRISTOL BAY WILL CONTINUE TO SPREAD SHOWERS OVER THE
AREA THROUGH TONIGHT. THIS WILL BE TRUE THROUGH THURSDAY. THE NEXT
LOW TO MOVE TO THE EASTERN ALEUTIANS WILL CONTINUE THIS PERIOD OF
SHOWERS INTO THURSDAY MORNING. THE LOW WILL DEEPEN DURING THE NIGHT
WEDNESDAY WITH WINDS INCREASING OVER THE GULF TO GALE FORCE. THE
STRONG WINDS WILL LAST THROUGH MUCH OF THURSDAY WITH SHOWERS MAINLY
ALONG THE COASTAL LOCATIONS. WILL SEE SOME OF THIS PRECIPITATION
ACROSS THE KENAI AND POSSIBLY INTO ANCHORAGE VALLEY. WILL EXPECT SOME
CONVECTIVE ACTIVITY FARTHER INLAND WHERE SOME SUN BREAKS WILL BE
OCCURRING. THE LOW WILL FILL INTO FRIDAY WITH WINDS AND PRECIPITATION
ON THE DOWN SWING.

.LONG TERM FORECAST...
THE LOW IN THE BERING WILL CROSS THE ALEUTIANS SATURDAY AND PUSH TO
JUST SOUTH OF THE GULF SUNDAY THEN SIT THERE THROUGH MID NEXT WEEK.
SHOWERS AND WINDS WILL BE STRONG AS THE LOW PASSES THE ALEUTIANS.
STRONGER WINDS WILL ONCE AGAIN MOVE INTO THE GULF MONDAY BUT WEAKEN
OVER TIME. A RIDGE WILL MOVE OVER THE BERING WITH LIGHT WINDS AND LOW
CLOUDS AND FOG.

THE LOW IN THE GULF WILL MOVE OUT OF THE AREA SATURDAY WITH SOME
CONVECTIVE MOUNTAIN SHOWERS STILL EXPECTED INLAND WITH ENOUGH
RESIDUAL MOISTURE AND HEATING. THE BRIEF PERIOD OF LITTLE ACTIVITY IN
THE GULF IS REPLACED BY SUNDAY WITH ANOTHER LOW JUST SOUTH OF THE
GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 175 176
FIRE WEATHER...NONE

JN AUG 07