Small Craft Advisory 690, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKDT THU SEP 11 2008

.MODEL DISCUSSION...
MODELS REMAINED IN GOOD AGREEMENT THROUGH 84 HOURS AGAIN.  AFTER THAT
TIME PERIOD THERE IS STILL SOME DIVERGENCE BETWEEN THE GFS AND THE
ECMWF.  THE LOW THAT MOVES INTO THE BERING AT THAT TIME FRAME TAKES A
MORE SOUTHERLY AND WEAKER TRACK WITH THE ECMWF SOLUTION WHILE THE GFS
RUNS IT JUST SOUTH OF THE ALEUTIANS AT ABOUT 10 MB STRONGER. THIS
SHOWS SLIGHT RUN TO RUN INCONSISTENCY FOR THE GFS HOWEVER THE ECMWF
IS MUCH MORE INCONSISTENT BETWEEN RUNS. AT THE VERY END OF THE
FORECAST PERIOD THE MODELS DO COME TOGETHER ON THE SOLUTION AGAIN.
GFS WAS THE MODEL OF THE DAY YESTERDAY SO THAT SOLUTION WAS CHOSEN
AGAIN WITH A SLIGHT NUDGE TOWARDS THE NEW SOLUTION TO MOVE THE LOW
THROUGH THE ALEUTIANS A SLIGHT BIT FASTER.

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LEVEL TROUGH OVER THE STATE IS CAUSING UNSTABLE
CONDITIONS THROUGH OUT THE REGION.  ON THE SURFACE A WEAK LOW
PRESSURE SYSTEM OVER THE MAINLAND IS SLOWLY FILLING AS A SHORTWAVE
RIDGE BUILDS IN FROM THE WEST.  THE LONGWAVE TROUGH IS EXPECTED TO
SHIFT SLIGHTLY TO THE EAST AND A STRONG CLOSED LOW WILL MOVE INTO THE
BASE OF THE LONGWAVE TROUGH.  THIS LOW WILL GAIN THE UPPER LEVEL
SUPPORT FROM THE NORTHERLY JET AND BUILD THE SHORTWAVE RIDGE AHEAD OF
IT OUT OVER THE MAINLAND.  AS THE RIDGE BUILDS THE LOW PRESSURE WILL
SLOW AND MOVE NORTHWARD OVER THE BRISTOL BAY REGION.

.SHORT TERM FORECAST...
IN THE EAST...CONDITIONS WILL IMPROVE TEMPORARILY AS THE SHORTWAVE
RIDGE MOVES IN OVER THE NEXT COUPLE OF DAYS.  LINGERING MOISTURE WILL
CAUSE SHOWERS TODAY BUT THESE WILL SLOWLY TAPER OFF AND FOG WILL FORM
OVERNIGHT AS STABILITY INCREASES.  BY FRIDAY AFTERNOON AS THE LOW OUT
WEST MOVES INTO BRISTOL BAY SOUTHERLY FLOW WILL INCREASE OVER THE
EASTERN ZONES AND RAIN IS EXPECTED.  CHANNELED WINDS WILL INCREASE
THROUGH THE CHUGACH RANGE WITH THIS LOW POSITIONING AND THE TURNAGAIN
ARM WIND WILL INCREASE FOR THE ANCHORAGE REGION.

OUT WEST...GALE FORCE WINDS ARE EXPECTED FOR THE WESTERN AND CENTRAL
ALEUTIANS TODAY AS THE LOW PRESSURE SYSTEM MOVES THROUGH THAT REGION.
ALTHOUGH CENTRAL PRESSURES ARE EXPECTED TO REMAIN THE SAME THROUGH
THIS AFTERNOON THE SOUTHERLY TRACK OF THE LOW WILL KEEP GALE FORCE
WINDS FROM MAKING IT INTO THE EASTERN ALEUTIANS.  BY THE TIME THE LOW
MOVES INTO BRISTOL BAY ON FRIDAY NIGHT IT WILL HAVE WEAKENED SLIGHTLY
SO ONLY SMALL CRAFT ADVISORIES ARE EXPECTED FOR THIS AREA.  BEHIND
THIS LOW A RIDGE WILL BUILD IN OVER THE WEST TEMPORARILY IMPROVING
CONDITIONS UNTIL THE NEXT LOW APPROACHES SATURDAY MORNING.  RAIN IS
EXPECTED TO MOVE ONTO THE WEST COAST BEGINNING SATURDAY MORNING AND
CONTINUE OVER THE MAINLAND THROUGH THE WEEKEND.

.LONG TERM FORECAST...
NOT MUCH CHANGE IN THE WEATHER PATTERN EXPECTED IN THE LONG TERM.  AS
SOON AS THE LOW IN BRISTOL BAY DIES OUT ANOTHER WILL TAKE ITS
PLACE...MOVING UP ALONG THE ALEUTIANS ALONG A VERY SIMILAR TRACK.
RAINY CONDITIONS WILL BE FOLLOWED BY A SHORT BREAK AND THEN BACK TO
MORE RAIN AGAIN...A VERY TYPICAL FALL PATTERN FOR
SOUTHCENTRAL/SOUTHWESTERN ALASKA AND THE ALEUTIANS.

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

LEWF SEP 08