Small Craft Advisory 563, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM AKDT THU JUL 17 2008

.ANALYSIS AND UPPER LEVELS...SATELLITE IMAGERY SHOWS A LARGE OCCLUDED
LOW SPINNING NEARLY STATIONARY JUST OFF THE KUSKOKWIM COAST. THE
FRONTAL SYSTEM EXTENDS ACROSS INTERIOR SOUTHWEST ALASKA TO JUST WEST
OF ANCHORAGE AND SOUTHWARD INTO THE WESTERN GULF. FRONTAL PROGRESSION
ACROSS THE MAINLAND HAS SLOWED DUE TO THE FORMATION OF A VERY WEAK
TRIPLE POINT LOW NEAR THE SOUTHERN TIP OF THE KENAI PENINSULA. A
STRONG WESTERLY UPPER LEVEL JET EXTENDS APPROXIMATELY ALONG THE
ALEUTIANS AND THEN BENDS NORTHWARD ACROSS THE GULF. JET DYNAMICS ARE
CONTRIBUTING TO A SOLID BAND OF RAIN ALONG THE FRONT. VORTICITY
MAXIMUMS EMBEDDED WITHIN THE UPPER LEVEL CYCLONIC FLOW ARE ALSO
HELPING TO INDUCE SHOWERS. RAIN TOTALS OVER THE SOUTHERN MAINLAND
THE PAST 24 HOURS HAVE RANGED FROM ABOUT ONE HALF INCH TO JUST OVER
ONE INCH. SOME STREAMS HAVE RISEN FAST WITH THIS RAIN BUT CONDITIONS
STARTED OUT FAIRLY LOW SO DO NOT EXPECT ANY FLOODING PROBLEMS AT THIS
POINT. A VERY WEAK SURFACE LOW IS EMBEDDED WITHIN THE WESTERLY FLOW
SOUTH OF THE WESTERN ALEUTIANS. STRONGER WINDS REMAIN SOUTH OF
ALEUTIANS...SO ONLY IMPACT IS RAIN AND FOG.

.MODEL DISCUSSION...MODELS CONTINUE TO BE TOO WEAK WITH CENTRAL
PRESSURE OF THE WESTERN ALASKA LOW. NEARBY SURFACE OBSERVATIONS
INDICATE A PRESSURE AROUND 995MB WHILE MODEL SOLUTIONS ARE AROUND
999MB. MODELS ARE ALSO HAVING PROBLEMS RESOLVING MOVEMENT OF WESTERN
ALEUTIAN LOW DUE TO FAST FLOW ALOFT. HOWEVER...SINCE LOW IS WEAK AND
EXPECTED TRACK IS EAST-SOUTHEAST...EVENTUALLY MOVING AWAY FROM THE
ALEUTIANS...THIS WILL NOT GREATLY IMPACT THE FORECAST.
OTHERWISE...MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT-TERM
WITH DECENT RUN-TO-RUN CONSISTENCY...SO ONLY MINOR ADJUSTMENTS WILL
BE MADE TO THE CURRENT FORECAST. IN THE MID TO LONG TERM THE ECMWF
SOLUTION IS PREFERRED DUE TO BETTER RUN-TO-RUN CONSISTENCY THAN THE
GFS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...MODELS INDICATE TRIPLE POINT LOW JUST OFF THE KENAI
PENINSULA WILL DRIFT NORTHWARD OVER WESTERN PRINCE WILLIAM SOUND AND
THEN DISSIPATE AS IT MOVES INLAND FRIDAY. AN UPPER LEVEL LOW WILL
ALSO FORM OVERHEAD TONIGHT. UPPER SHORT-WAVES EMBEDDED WITHIN THE
FLOW WILL ALSO CONTINUE TO MOVE ACROSS THE REGION. THUS...RAIN WILL
HANG IN FOR MOST OF SOUTHCENTRAL THROUGH THE DAY FRIDAY WITH SOME
IMPROVEMENT POSSIBLE FRIDAY NIGHT AS THE MAIN LOW BACK OVER WESTERN
ALASKA TRANSITIONS INTO THE GULF. HOWEVER...THE UPPER LEVEL LOW
COMPLEX WILL REMAIN OVER THE REGION THROUGH AT LEAST SATURDAY
RESULTING IN A SHOWERY PATTERN. BY SUNDAY ANOTHER TROUGH WILL SWING
IN FROM THE NORTHWEST...SO DONT EXPECT MUCH OF A BREAK IN THE
WEATHER.

SOUTHWEST ALASKA/ALASKA PENINSULA...THE WESTERN ALASKA LOW WILL
SLOWLY SINK SOUTHEASTWARD AND DISSIPATE OVER THE BRISTOL BAY ZONE
FRIDAY NIGHT AS THE UPPER LEVELS OPEN TO A TROUGH AND SWING INTO
THE GULF. RAIN/SHOWERS ALONG WITH LOW CLOUDS AND FOG ALONG THE COAST
WILL CONTINUE INTO FRIDAY WITH A DRYING TREND BEGINNING LATE FRIDAY.
SATURDAY LOOKS LIKE A BRIEF RESPITE FROM WET WEATHER A A TRANSIENT
SHORT-WAVE RIDGE MOVES THROUGH...BUT NEXT TROUGH WILL SWING DOWN
FROM THE NORTH ON SUNDAY BRINGING A RETURN TO RAIN.

BERING SEA/ALEUTIANS...THE LOW SOUTH OF THE WESTERN ALEUTIANS WILL
MOVE FAR ENOUGH SOUTH OF ALEUTIANS FRIDAY MORNING TO CLEAR OUT ALL
OF THE RAIN. WEAK HIGH PRESSURE WILL THEN BUILD OVER THE WESTERN
ALEUTIANS FRIDAY AND HOLD IN ON SATURDAY AND SUNDAY AS A PACIFIC
SYSTEM APPROACHES FROM THE SOUTHWEST.

.LONG TERM FORECAST...LONG-WAVE TROUGH WILL REMAIN CENTERED OVER
MAINLAND ALASKA THROUGH THE END OF NEXT WEEK...MAINTAINING COOL
AND WET CONDITIONS ACROSS MUCH OF THE STATE. MEANWHILE...THE
ALEUTIANS WILL BE IMPACTED BY A CLOSED LOW FOR MUCH OF NEXT WEEK.
NO MAJOR WINDS ARE EXPECTED...BUT LOTS OF CLOUDS AND RAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...ASHFALL ADVISORY 185.
MARINE...ASHFALL ADVISORY 170.
FIRE WEATHER...NONE.

SEB JUL 08