Small Craft Advisory 862, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
735 AM ADT WED SEP 20 2006

.DISCUSSION...

ANALYSIS...AN UPPER LEVEL TROUGH CENTERED OVER THE EASTERN BERING AND
WEAK RIDGING OVER THE EASTERN GULF OF ALASKA THIS MORNING ARE THE
LOCAL PLAYERS IN THE CURRENT 5 WAVE HEMISPHERIC PATTERN.  THE
DEPARTING SURFACE LOW THAT AFFECTED THE AOR THE LAST COUPLE OF DAYS
HAS MERGED WITH AN AREA OF LOW PRESSURE IN THE INTERIOR ALLOWING FOR
SOME RIDGING FROM THE STRONG PACIFIC HIGH TO WORK INTO SOUTH CENTRAL
AND SOUTHEAST ALASKA THIS MORNING.  A DEEPENING LOW 300 MILES SOUTH
OF THE AKPENN ASSOCIATED WITH STRONG UPPER LEVEL DYNAMICS WILL BE THE
NEXT WEATHER MAKER FOR SOUTH CENTRAL ALASKA. AS MUCH OF ALASKA SITS
POISED FOR THE NEXT IN A SERIES OF RELENTLESS LOWS...CLEAR TO PARTLY
CLOUDY SKIES OVERNIGHT WITH WEAK SURFACE FLOW HAVE ALLOWED
TEMPERATURES IN MANY LOCATIONS TO APPROACH THEIR DEWPOINTS IN THE MID
TO UPPER 30S...SETTING UP A DECOUPLED ATMOSPHERE UP TO 660 FT...PER
THE ANCHORAGE SOUNDING.  FOG HAS FORMED IN THE TRADITIONALLY PRONE
AREAS THIS MORNING...WITH THIS SHALLOW INVERSION IT WILL BURN OFF
QUICKLY THIS AM.

MODEL ANALYSIS...THE VARIOUS NUMERICAL SOLUTIONS CONTINUE TO STRUGGLE
WITH THE SHOULDER SEASON WEATHER PATTERN IN THEIR STRENGTH/TIMING/RUN
TO RUN CONSISTENCY. WITH THE STORM CENTER HIDDEN BENEATH HIGH CLOUDS
ON SATELLITE IMAGERY AND VERY LITTLE DATA IN THE NORTH PACIFIC...HARD
TO SAY HOW THE MODELS INITIALIZED OVERNIGHT IN REGARD TO THE LOW
APPROACHING SOUTH CENTRAL ALASKA FROM THE SOUTHWEST. THE 0Z
UKMET/GFS/GFS ENSEMBLE ARE IN PHASE THROUGH 42 HOURS WITH THE WRF
SOLUTION BEING MUCH SLOWER AND MORE AMPLIFIED...ALTHOUGH THE 06Z WRF
RUN SHOWS MORE AGREEMENT WITH THE GFS/UKMET.  THE NEWEST 0Z AND 6Z
RUNS OF THE GFS/UKMET SHOW THE SURFACE LOW TO TRACK TO THE WEST OF
THE KENAI PENINSULA...THIS HAS BEEN A POINT OF CONTENTION THE LAST
MANY MODEL RUNS AND HAS SIGNIFICANT RAMIFICATIONS ON THE SOUTH
CENTRAL FORECAST.  HAVE OPTED TO GO WITH THE LATEST GFS SOLUTION
GIVEN ITS BETTER TRACK RECORD.

SHORT TERM...HEALTHY UPPER LEVEL DYNAMICS WILL CONTINUE TO DEEPEN THE
PACIFIC LOW TO 980 MB AS IT APPROACHES COOK INLET TONIGHT BRINGING
WITH IT INCREASING CLOUDS THROUGHOUT THE DAY. THE CHOSEN WESTERLY
TRACK OF THE SURFACE LOW IS A DRIER PATTERN FOR THE ANCHORAGE BOWL
AND HAVE ADJUSTED THE GRIDS ACCORDINGLY...BUT RAIN IS STILL EXPECTED
ACROSS MUCH OF THE AOR TONIGHT AND TOWARDS THE END OF THE WEEK...TO
INCLUDE THE EASTERN ALEUTIANS AND INTERIOR ZONES.  TURNAGAIN ARM
WINDS WILL INCREASE THIS AFTERNOON AND EVENING IN RESPONSE TO THE
TIGHTENING PRESSURE GRADIENT AHEAD OF THE APPROACHING LOW. NEAR TO
SLIGHTLY ABOVE NORMAL TEMPERATURES SHOULD BE THE RULE THROUGH THE
WEEKEND.

EXTENDED...UNSETTLED WEATHER CONTINUES INTO THE WEEKEND INBETWEEN LOW
PRESSURE SYSTEMS. SATURDAY EVENING ANOTHER LOW COURTESY OF THE
EASTERN RUSSIA BAROCLINIC ZONE BEGINS TO DEEPEN SOUTH OF THE WESTERN
ALEUTIANS AND HEADS EAST. RELATIVELY LIGHT WINDS THROUGHOUT THE
ALEUTIAN CHAIN IN THE SHORT TERM CAN BE EXPECTED TO AMP UP DEPENDING
ON HOW FAR SOUTH THIS LOW SKIRTS...NOT EXPECTING ADVISORY/WARNING
LEVEL WINDS EITHER WAY.  MODELS DIVERGE ON THE POSITION OF THE LOW ON
BOTH SIDES OF THE AKPENN TUESDAY AFTERNOON...WITH THE GFS HAVING THE
MORE CONSERVATIVE STRENGTH...BEFORE YET ANOTHER MORE VIGOROUS
SOUTHERLY LOW ENTERS THE GULF THE SECOND HALF OF NEXT WEEK.  THE GFS
HAS THIS LOW DEEPENING TO 966 MB SOUTH OF KODIAK ISLAND WEDNESDAY
NIGHT...SEEMS A BIT AMBITIOUS AT THIS POINT.  THESE TWO LOWS NEXT
WEEK ARE GOING TO BE A FUNCTION OF THE AMPLITUDE OF THE RIDGE IN THE
EASTERN PACIFIC AND THE TIMING OF SHORTWAVES ROLLING ACROSS THE TOP
OF THAT RIDGE...AS PER HPC GUIDANCE THE 06Z ENSEMBLE MEAN FOR DAYS 6
AND 7 SHOWS HIGH UNCERTAINTY FOR THE GULF OF ALASKA AREA PROVIDING
LOW CONFIDENCE FOR THIS PERIOD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALES 120 130 132 150
FIRE WEATHER...NONE

SDM SEP 06