Small Craft Advisory 705, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
345 AM AKDT SUN SEP 6 2009

.ANALYSIS AND UPPER LEVELS...
HIGH PRESSURE OVER THE MAINLAND IS QUICKLY DISSIPATING AS A
VERTICALLY STACKED ALEUTIAN LOW PROGRESSES EASTWARD.  AN ARCTIC
TROUGH IS CURRENTLY DIGGING INTO THE NORTHERN BERING BRINGING SOME
COLDER AIR ALONG WITH IT. THE UPPER LEVEL LOW THAT HAS BROUGHT WEAK
DISTURBANCES THROUGH SOUTHCENTRAL IS SWINGING INTO THE SOUTHERN PART
OF BRITISH COLUMBIA.  AT THE SURFACE...A FAIRLY QUIET NIGHT AS CLEAR
SKIES PERSIST OVER MUCH OF THE MAINLAND DUE TO THE HIGH PRESSURE.
THE 996 MB ALEUTIAN LOW IS BRINGING LIGHT RAIN AND CLOUDY SKIES TO
MOST OF THE ISLANDS.

.MODEL DISCUSSION...
IN THE SHORT TERM ALL MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE NEXT
SYSTEM MOVING ASHORE TUESDAY.  THE GFS IS THE EXCEPTION AS IT IS
HAVING TROUBLE WITH THE TIMING OF THE FRONT.  THERE IS GENERAL
AGREEMENT THAT THE TROUGH DIGGING OUT OF THE ARCTIC WILL COMBINE WITH
THE ALEUTIAN LOW TO FORM A LARGE CLOSED LOW SOUTH OF AKPEN MIDWEEK.
MODELS ARE STILL SHOWING A POWERFUL SURFACE LOW FORMING IN THE GULF
MID TO LATE WEEK.  THERE ARE STILL INCONSISTENCIES ON THE EXACT
STRENGTH AND PLACEMENT OF THE SYSTEM BUT CONFIDENCE IS GROWING ON A
STORMY PATTERN.  THE 00Z ECMWF SEEMS TO BE A GOOD MIDDLE OF THE ROAD
SOLUTION WITH THE TRACK OF THE LOW BEING VERY SIMILAR TO THE HPC
SOLUTION.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
PLEASANT WEATHER WILL PERSIST TODAY AND TOMORROW FOR MUCH OF
SOUTHCENTRAL. A BIG CONCERN FOR THIS MORNING WILL BE THE EXTENT OF
THE FOG FOR THE COOK INLET.  DEW POINT DEPRESSIONS ARE LESS THEN LAST
NIGHTS VALUES AT THIS TIME FOR ANCHORAGE...KENAI...AND HOMER.
RELATIVE HUMIDITIES VALUES AT 700 MB ARE RATHER MOIST WHICH IS NOT
OPTIMAL FOR MAXIMUM RADIATIONAL COOLING...HOWEVER THEY ARE SIMILAR TO
LAST NIGHTS VALUE.  CURRENT THINKING IS THAT THE LIGHT SOUTHERLY
WINDS SHOULD PERSIST THROUGHOUT THE NIGHT AND PREVENT THE FOG FROM
BECOMING TOO WIDESPREAD IN MOST LOCATIONS. TODAY...ENOUGH INSTABILITY
IN THE ATMOSPHERE EXISTS THAT SHOWERS ARE EXPECTED TO FROM IN THE
MOUNTAINS WITH THE DIURNAL HEATING. HOWEVER...LIGHT WINDS ALOFT
SHOULD KEEP THE SHOWERS FROM DRIFTING FAR AWAY FROM THE MOUNTAINS
INTO THE LOWLANDS. MOSTLY CLEAR SKIES SHOULD PERSIST THOUGH EARLY
MONDAY BEFORE THE NEXT STORM MOVES INTO OUR AREA.

.SOUTHWEST...
ONE MORE NICE DAY IS IN STORE BEFORE THE REGION BEGINS TO FEEL THE
AFFECTS OF THE ALEUTIAN LOW.  CLOUDS BEGIN MOVING INTO THE AREA
TONIGHT WITH PRECIPITATION BEGINNING FOR MOST AREAS MONDAY NIGHT.
THE AKPEN BEING THE EXCEPTION WITH RAIN STARTING TODAY PROGRESSING
EASTWARD UP THE PENINSULA THROUGH TONIGHT.  WINDS SHOULD ALSO PICK UP
OUT OF THE SOUTHEAST TODAY AND INTO TONIGHT ON THE AKPEN AS THE
SURFACE LOW MOVES CLOSER TO THE AREA.

.BERING SEA AND ALEUTIANS...
A LOW JUST SOUTH OF THE CENTRAL ALEUTIANS IS BRINGING CLOUDS AND
LIGHT RAIN TO THE REGION. THIS LOW WILL CONTINUE TO MOVE UP THE CHAIN
THROUGHOUT THE NEXT SEVERAL DAYS.  ON THE BACKSIDE OF THE
SYSTEM...GUSTY NORTH WINDS WILL DEVELOP MONDAY AND INTO THE DAY
TUESDAY ADVECTING COLDER ARCTIC AIR INTO THE REGION.  850 MB
TEMPERATURES OF -5 DEGREE CELSIUS COULD SUPPORT SOME MIXED
PRECIPITATION IN THE NORTHERN BERING TUESDAY AND WEDNESDAY.

.LONG TERM FORECAST...
THE BIG STORY FOR THE LONG TERM WILL BE THE STRONG SURFACE LOW THAT
COULD FORM IN THE GULF MIDWEEK.  MODELS HAVE BEEN CONSISTENT IN
FORMING THESE LOWS AND MOVING THEM INTO THE SOUTHERN MAINLAND.  THERE
IS STILL QUESTION ON THE EXACT TRACK BUT WE CAN EXPECT A STORMIER
WEATHER PATTERN FOR THE SOUTHERN MAINLAND MID TO LATE WEEK.  FURTHER
WEST MODELS ARE SHOWING THE REMNANTS OF TROPICAL STORM DUJUAN MOVING
TOWARDS THE WESTERN ALEUTIANS MID TO LATE WEEK.  MODELS ARE COMING
INTO BETTER AGREEMENT ON PLACEMENT TONIGHT BUT THERE IS STILL MUCH
UNCERTAINTY ON TIMING AND STRENGTH.  OVERALL...A VERY ACTIVE WEATHER
PATTERN IS SETTING UP AND WILL NEED TO BE WATCHED CLOSELY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 185 AND 412
FIRE WEATHER...NONE

WILSON SEP 09