Small Craft Advisory 538, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
121 PM AKDT TUE JUL 8 2008

.ANALYSIS AND UPPER LEVELS...THERE ARE TWO SLOW MOVING CUT-OFF LOWS
IN THE UPPER LEVELS THIS MORNING. ONE OVER THE GULF OF ALASKA IS
TRACKING TOWARD SOUTHEAST ALASKA. THE OTHER IS DROPPING SOUTHWARD
OUT OF THE RUSSIAN FAR EAST INTO THE BACK SIDE OF THE LONG-WAVE
TROUGH. THERE IS A DECENT 130KT JET ON THE WEST SIDE OF THIS LOW.
IN BETWEEN THE TWO LOWS IS A WEAK SHORT-WAVE RIDGE CENTERED OVER
SOUTHWEST ALASKA. THE BASE OF THE LONG-WAVE TROUGH IS CENTERED
BENEATH THIS RIDGE OVER THE NORTH PACIFIC.

EXTENSIVE CLOUDINESS CONTINUES OVER THE SOUTHERN MAINLAND THIS
MORNING. SATELLITE IMAGERY SHOWS SEVERAL WEAK WAVES EMBEDDED
WITHIN THE CYCLONIC FLOW AROUND THE GULF LOW TRACKING SOUTHWARD
ACROSS SOUTHCENTRAL PRODUCING AREAS OF RAIN...MAINLY OVER THE
WESTERN COPPER BASIN AND TALKEETNA MOUNTAINS SOUTHWARD TO PRINCE
WILLIAM SOUND. WEAK UPPER WAVES ARE ALSO PREVALENT OVER INTERIOR
ALASKA IN A COL REGION AND UNDERNEATH THE WEAK RIDGE OVER SOUTHWEST
ALASKA. ONSHORE FLOW OVER BRISTOL BAY HAS ALSO ADVECTED SOME STRATUS
AND FOG INLAND. A WELL DEFINED FRONT EXTENDING FROM THE LOW DROPPING
OUR OF RUSSIA IS DROPPING SOUTH AND EAST ACROSS THE WESTERN TO
CENTRAL BERING THIS MORNING. SURFACE OBSERVATIONS AND QUIKSCAT WINDS
INDICATE A FAIRLY NARROW BAND OF MAINLY SMALL CRAFT WINDS AHEAD OF
THE FRONT AND A SHARP WIND SHIFT ALONG THE FRONT.

.MODEL DISCUSSION...MODELS INITIALIZED WELL WITH SYNOPTIC FEATURES.
THEY CONTINUE TO HAVE PROBLEMS RESOLVING THE WEAK UPPER LEVEL WAVES
MOVING ACROSS THE MAINLAND. WILL BASE FIRST PERIOD OF FORECAST OFF
OF SATELLITE AND RADAR TRENDS. THROUGH 60 HOURS THE MODELS HAVE
CONVERGED ON A SIMILAR SOLUTION OUT WEST WITH HANDLING OF NEXT LOW
AND ITS COLD FRONT. THIS IS VERY CLOSE TO SOLUTION CURRENT FORECAST
WAS BASED OFF...SO LITTLE CHANGE WILL BE MADE. THERE ARE LARGE
RUN-TO-RUN INCONSISTENCIES BEYOND 60 HOURS SO WILL STICK WITH CURRENT
FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL...EXTRAPOLATION OF CURRENT RADAR AND SATELLITE IMAGERY
SHOULD KEEP MOST IF NOT ALL OF RAIN ON THE EASTERN PERIPHERY OF THE
MATANUSKA VALLEY TO ANCHORAGE AREA THIS AFTERNOON INTO EVENING.
UNLESS SOMETHING CHANGES WILL HAVE TO BACK WAY OFF ON THE RAIN THAT
IS FORECAST FOR TONIGHT. RIDGE BUILDING IN FROM THE WEST WILL HELP
PUSH THE PRECIPITATION FARTHER EAST TONIGHT. THE RIDGE WILL THEN
BUILD OVERHEAD ON WEDNESDAY...BRINGING A GENERAL DRYING TREND TO THE
REGION. SINCE RIDGE IS INITIALLY VERY WEAK AND THERE IS A LOT OF
MOISTURE IN PLACE SKIES WILL REMAIN MOSTLY CLOUDY THROUGH WEDNESDAY.
THE RIDGE WILL STRENGTHEN WEDNESDAY NIGHT AND THURSDAY AHEAD OF AN
AMPLIFYING BERING SEA TROUGH. SO EXPECT MORE SUN ON THURSDAY. THE
THERMAL TROUGH WILL ALSO BEGIN TO DROP SOUTHWARD THURSDAY...ALTHOUGH
REMAIN OVER THE INTERIOR. THIS WILL INTRODUCE THE POTENTIAL FOR
ISOLATED THUNDERSTORMS ALONG THE ALASKA RANGE. CHANCES WILL INCREASE
MORE ON FRIDAY AS THERMAL TROUGH DROPS DOWN EVEN FURTHER. IN SUMMARY
EXPECTIMPROVING CONDITIONS THE NEXT FEW DAYS WITH SOME SUN AND
TYPICAL SUMMERTIME CONVECTION...MAINLY ALONG THE MOUNTAINS.

SOUTHWEST ALASKA...EXTENSIVE CLOUD COVER REMAINS OVER SOUTHWEST
ALASKA AND WILL BE SLOW TO CLEAR OUT. INLAND AREAS SHOULD SEE
GRADUAL IMPROVEMENT WEDNESDAY INTO THURSDAY UNDER INFLUENCE OF RIDGE.
BERING SEA FRONT WILL STALL OVER THE EASTERN BERING WEDNESDAY...WITH
ASSOCIATED MOISTURE ONLY MAKING IT TO THE IMMEDIATE COASTLINE. SO
DONT EXPECT MUCH IN THE WAY OF PRECIPITATION...BUT CLOUD COVER
WILL PERSIST. CHANCE OF THUNDERSTORMS WILL RETURN THURSDAY FOR VERY
NORTHERN KUSKOKWIM VALLEY AND THEN A BIT FARTHER SOUTH ON FRIDAY
AS THERMAL TROUGH SINKS SOUTHWARD TOWARD THE AREA.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...THE WELL DEFINED COLD FRONT
WILL HELP CLEAR OUT THE FOG AND STRATUS AS IT MOVES ACROSS THE
ALEUTIANS TONIGHT AND WEDNESDAY. VISIBLE SATELLITE SHOWS A CLEAR
AREA BEHIND THE FRONT SO SOME AREAS WILL ACTUALLY BRIEFLY CLEAR OUT.
A FRONTAL LOW WILL FORM SOUTH OF THE EASTERN ALEUTIANS LATE WEDNESDAY
IN RESPONSE TO UPPER LEVEL JET ON BACK SIDE OF THE TROUGH. MEANWHILE
THE PARENT LOW WILL STALL OVER THE NORTHERN BERING. THIS WILL CAUSE
THE FRONT TO STALL AND WEAKEN OVER THE EASTERN BERING. UPPER TROUGH
WILL BECOME NEGATIVELY TILTED ON FRIDAY AS THE UPPER JET DRIVES THE
LOW SOUTH OF THE ALEUTIANS EASTWARD TOWARD THE GULF. ADDITIONAL WEAK
SHORT-WAVES WILL MOVE INTO THE BACK SIDE OF THE TROUGH...BRINGING
RAIN AND FOG BACK TO THE WESTERN ALEUTIANS.

.LONG TERM FORECAST...MEAN TROUGH REMAINS CENTERED OVER THE BERING
THROUGH THE END OF THE WEEK. MODELS HAVE BEEN CONSISTENT IN
TRANSITIONING THE TROUGH EASTWARD TO MAINLAND ALASKA BY NEXT WEEK.
SO IT LOOKS LIKE A RELATIVELY DRY PATTERN INTO NEXT WEEKEND FOR THE
SOUTHERN MAINLAND WITH WETTER CONDITIONS LIKELY BY THE BEGINNING OF
NEXT WEEK. EXPECT TYPICAL SUMMER WEATHER OVER THE BERING REGION WITH
CLOUDS/FOG AND A CHANCE OF RAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 180 185.
FIRE WEATHER...NONE.

SEB JUL 08