Small Craft Advisory 455, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT SUN MAY 25 2008

.ANALYSIS AND UPPER LEVELS...
UPPER LEVEL ANALYSIS CONTINUES TO SHOW A STRONG RIDGE OVER WESTERN
CANADA WITH THE LONGWAVE TROUGH SITUATED OVER THE BERING SEA. AT THE
SURFACE THE PATTERN IS SHIFTED SLIGHTLY TO THE WEST WITH THE SURFACE
HIGH BUILDING OVER THE GULF OF ALASKA.  THE UPPER LEVEL PATTERN IS
EXPECTED TO RETROGRADE SLIGHTLY AS WELL WHICH WILL BRING WARMER DRIER
WEATHER TO THE MAINLAND.

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT AGAIN THROUGH ABOUT 84 HOURS...HOWEVER
AFTER THAT THE SOLUTIONS BEGIN TO DIFFER.  GFS AND ECMWF ARE IN
CLOSER AGREEMENT THAN 12 HOURS AGO AS BOTH MODELS PLACE A 995 MB LOW
IN THE CENTRAL ALEUTIANS.  THIS IS A BIG DIFFERENCE FOR THE ECMWF
WHICH HAD A 977 MB LOW SOUTH OF COLD BAY IN THE 25/12Z RUN.  AS FOR
THE GFS...THE SOLUTION IS MORE CONSISTENT BUT THE RESOLUTION OF
POTENTIAL TRIPLE POINT LOWS IS NOT VERY GOOD.  THE OPERATIONAL RUN
INDICATES A TRIPLE POINT LOW FORMATION AT ABOUT 130 HOURS BUT THIS
SOLUTION IS DIFFERENT THAN MOST OF THE ENSEMBLE MEMBERS.  GIVEN THE
LACK OF CONSISTENCY WITH THE ECMWF AND THE GFS PROBLEMS RESOLVING THE
POTENTIAL MULTIPLE LOWS NOT MANY CHANGES WERE MADE TO THE EXTENDED
FORECAST IN THE WEST...WHILE THE GENERAL SLOWING OF THE SYSTEM WAS
CHOSEN IN THE EAST AS THIS SEEMS TO BE THE MODEL TREND.

.SHORT TERM FORECAST...
IN THE EAST...NOTHING BUT GROUND CLUTTER ON THE RADARS THIS MORNING
INDICATING THAT THE HIGH HAS INDEED MOVED OVER HEAD AND THIS MEMORIAL
DAY SHOULD BE A SUNNY ONE.  CONDITIONS ARE STABLE ACROSS THE AREA SO
SHOWERS ARE NOT EXPECTED FOR THE NEXT FEW DAYS...HOWEVER A SHORTWAVE
TROUGH ASSOCIATED WITH A WEAK SURFACE LOW OVER WESTERN CANADA IS
EXPECTED TO MOVE THROUGH TOMORROW AND INTO TOMORROW EVENING.  THE
TIGHTENED GRADIENT BETWEEN THE TROUGH AND THE RIDGE IN THE PACIFIC
WILL INCREASE NORTH TO NORTHWESTERLY WINDS AND INCREASE FIRE WEATHER
DANGER...IN PARTICULAR FOR THE COPPER RIVER BASIN WHERE RELATIVE
HUMIDITIES ARE ALREADY LOW. A WATCH WILL BE ISSUED WITH THIS MORNINGS
FIRE WEATHER PACKAGE FOR THE TOMORROW EVENING TIME PERIOD.  OTHERWISE
SMALL CRAFT ADVISORY WINDS ARE EXPECTED IN BAYS SUCH AS RESURRECTION
AND PRINCE WILLIAM SOUND.

OUT WEST...SHOWERS CONTINUE TODAY AS THE ENTIRE AREA IS STILL BEING
INFLUENCED BY THE UPPER LEVEL LOW.  THESE WILL BE MIXED WITH SNOW
ALONG THE WEST COAST IN THE MORNING BUT SHOULD SWITCH OVER TO RAIN
AGAIN IN THE AFTERNOON.  AS THE UPPER LEVEL LOW MOVES NORTHWARD AND
THE N PAC RIDGE BEGINS TO BUILD IN FROM THE SOUTH THE AREA OF
INSTABILITY SHOULD MOVE NORTHWARD AND CONDITIONS WILL IMPROVE BY
TOMORROW.  THIS WILL BE FAIRLY SHORT LIVED FOR THE ALEUTIANS IN
PARTICULAR AS THE N PAC RIDGE WILL SHIFT EASTWARD ON WEDS...ALLOWING
AN AREA OF LOW PRESSURE TO MOVE IN FROM THE SOUTH.  WHILE THE LOW
ITSELF WILL REMAIN OUT OF THE AREA FOR QUITE A WHILE THE MOISTURE
WILL BE WELL AHEAD OF THE LOW ITSELF AND THE ALEUTIANS CAN EXPECT TO
SEE RAIN BEGINNING WEDNESDAY MORNING AND LASTING THROUGH THE FORECAST
PERIOD.  HOWEVER THE WESTERN MAINLAND LOOKS LIKE IT WILL CONTINUE TO
IMPROVE AS THE N PAC HIGH MOVES SLIGHTLY EASTWARD.

.LONG TERM FORECAST...
AS PER THE MODEL DISCUSSION IT LOOKS LIKE THE FORECAST OF A 990 MB
LOW MOVING INTO THE ALEUTIANS BY THE END OF THE WEEK IS STILL A GOOD
BET. EXACT DETAILS ON TIMING AND PLACEMENT OF THE LOW PRESSURE
SYSTEMS ARE STILL PRETTY UNCERTAIN BUT THE LOW LOOKS TO BE FAIRLY
WEAK SO MIN GALES IN THE ALEUTIANS WOULD BE THE HIGHEST EXPECTATIONS
FOR WINDS RIGHT NOW.  OTHERWISE HIGH PRESSURE OVER THE MAINLAND IS
EXPECTED TO STICK AROUND UNTIL NEXT WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...NONE
FIRE WEATHER...WATCH 141

LEWF MAY 08