Small Craft Advisory 684, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT THU AUG 23 2007

.ANALYSIS AND UPPER LEVELS...
VERTICALLY STACKED LOW PRESSURE SYSTEM CURRENTLY LOCATED OVER THE
NORTHERN GULF OF ALASKA. A STRONG JET STREAM WINDING AROUND THE UPPER
CLOSED LOW IS ADVECTING IN A FAIR AMOUNT OF MOISTURE AND OMEGA FIELDS
INDICATE THAT THERE IS A WIDE SWATH OF LIFT. THE LOW PRESSURE SYSTEM
WILL SLOWLY WEAKEN AND DRIFT SOUTHEAST INTO JUNEAUS FORECAST DOMAIN
BY EARLY SATURDAY. BEHIND THIS SYSTEM...A WEAK RIDGE CURRENTLY OVER
THE BERING SEA WILL SWEEP THROUGH SOUTHCENTRAL ALASKA OVER THE
WEEKEND AND BRING FAIR WEATHER. THE NEXT LOW CURRENTLY OVER THE
KAMCHATKA PENINSULA WILL MOVE TOWARDS THE ALASKA PENINSULA BY SUNDAY
AND ITS ASSOCIATED WEATHER FRONT WILL BEGIN INFLUENCING SOUTHCENTRAL
BY EARLY MONDAY.

.MODEL DISCUSSION...
MODELS INITIALIZED WELL THIS MORNING. MODEL DIFFERENCES ARE MINOR FOR
THE EASTERN DOMAIN THROUGH THE SHORT TERM. THEREFORE...THE NEW
FORECAST PACKAGE HAS NOT MANY CHANGES. ANY CHANGES ARE MINOR TO
UP/DOWN POP. OUT WEST...SIGNIFICANT MODEL ISSUES REMAIN REGARDING THE
KAMCHATKA LOW. THE OPERATIONAL NAM CONTINUES TO BE SIGNIFICANTLY
SLOWER THAN THE GFS UKMET AND ECMWF. THE GFS ENSEMBLE MEAN AND
(SURPRISINGLY ENOUGH) THE NAM-BASED SREF AGREE WITH THE GFS SOLUTION.
GFS REMAINS TO BE THE SUPERIOR NUMERICAL MODEL OUT WEST.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
ONSHORE FLOW AND GENERALLY SOUTHERLY FLOW ALOFT FROM THE LOW IN THE
GULF WILL MEAN CONTINUED RAIN THROUGH THIS EVENING FOR MOST OF
SOUTHCENTRAL. SHOWERS WILL BE MORE SCATTERED AWAY FROM THE COAST.
GALE FORCE WINDS WILL BE MAINTAINED THROUGH THIS EVENING IN MARINE
ZONE 120 AS A BARRIER JET IS ALONG THE COAST. THE LOW WEAKENS TONIGHT
WITH SHOWERS AND WINDS ON THE WANE OVERNIGHT. THE LOW WILL BEGIN TO
PULL AWAY FRIDAY...AND ISOLATED TO SCATTERED RESIDUAL SHOWERS WILL
LINGER. BY LATE FRIDAY...FLOW ALOFT WILL BECOME MORE NORTHERLY AND
BRING DRIER WEATHER FOR THE WEEKEND. THE KAMCHATKA LOW WILL MOVE INTO
THE EASTERN BERING BY EARLY SUNDAY...AND KODIAK ISLAND WILL BEGIN TO
RECEIVE PRECIPITATION IN ASSOCIATION WITH ITS WEATHER FRONT BY MIDDAY
SUNDAY WITH PRECIPITATION SPREADING NORTHWARD TO THE KENAI PENINSULA
BY EARLY MONDAY.

SOUTHWEST ALASKA...
SHOWERS LINGERING PRIMARILY IN THE BRISTOL BAY AREA AND ALONG THE
ALEUTIAN RANGE IN ASSOCIATION WITH THE GULF OF ALASKA LOW WILL BEGIN
TO TAPER OFF TONIGHT AND TOMORROW. HOWEVER...RESIDUAL LOW LEVEL
MOISTURE OVER MUCH OF WESTERN ALASKA HAS SET UP AREAS OF FOG OVER THE
KUSKOKWIM VALLEY AND ALONG THE BERING SEA COAST INTO THE EARLY
AFTERNOON HOURS TODAY. WOULD NOT BE SURPRISED TO SEE THAT FOG
REDEVELOP TONIGHT. CONVECTIVE FORCING IS WEAKER TODAY THAN IT WAS
YESTERDAY...AND SIGNIFICANT CLOUD COVER WILL INHIBIT THUNDERSTORM
DEVELOP THIS AFTERNOON. INSTABILITY LOOKS TO INCREASE SLIGHTLY
TOMORROW ALONG THE ALEUTIAN RANGE AND REMAINS INTO SATURDAY. SHOWERS
OVER HIGHER TERRAIN WILL BE THE RESULT OF THIS INSTABILITY.

ALEUTIANS AND BERING SEA...
WIDESPREAD FOG OVER THE BERING RESULTING FROM SUBSIDENCE AND WEAK LOW
LEVEL FLOW WILL BEGIN TO DISSIPATE TONIGHT AS A WEATHER FRONT
ASSOCIATED WITH THE KAMCHATKA LOW SWEEPS ACROSS THE BERING AND BRINGS
SMALL CRAFT TO GALE FORCE WINDS. THE FRONT WILL GRADUALLY WEAKEN
TONIGHT AS THE LOW MOVES INTO THE CENTRAL BERING. WIDESPREAD
PRECIPITATION CAN BE EXPECTED AS THE LOW SLOWLY DRIFTS ACROSS THE
ALASKA PENINSULA SUNDAY.

.LONG TERM FORECAST...
DRIER WEATHER APPEARS TO BE IN TAP FOR MUCH OF SOUTHCENTRAL ALASKA
FOR THIS WEEKEND. THE KAMCHATKA LOW PRESSURE SYSTEM WILL BRING THE
NEXT SYNOPTIC SCALE CHANCE FOR PRECIPITATION...BUT IT APPEARS AT THIS
POINT THAT PRECIPITATION WILL PRIMARILY BE CONFINED TO COASTAL AREAS.
THE UPPER PATTERN WILL AMPLIFY BY THE MIDDLE OF NEXT WEEK WITH TROUGH
AXIS N-S THROUGH ALASKA AS A POWERFUL JET STREAK WORKS ITS WAY AROUND
AND DEEPENS THE UPPER LOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 120 172 175
FIRE WEATHER...NONE

TD/JN AUG 07