Small Craft Advisory 512, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
324 PM AKDT MON SEP 10 2012

.SHORT TERM...CALM BEFORE THE STORM. SHOWERS HAVE DIMINISHED
THROUGH THE DAY FROM NORTH TO SOUTH IN THE WAKE OF A LOW THAT
DISSIPATED OVER THE CENTRAL PANHANDLE EARLY TODAY. NORTHWEST LOW
LEVEL FLOW OVER THE EASTERN GULF HAS CLEARED OUT THE CLOUDS FOR
THE MOST PART OVER WATER. PUBLIC ZONES AND INNER CHANNELS HAVE
REMAINED MOSTLY CLOUDY THROUGHOUT THE DAY BUT THERE HAVE BEEN
SOME VERY NICE SUN BREAKS AS WELL. CLOUD BASES STARTED OUT VERY
LOW THIS MORNING BUT HAVE RISEN AS THE SHOWER ACTIVITY HAS
DIMINISHED. A FEW LOCATIONS HAVE REMAINED MARGINAL VMC FOR
CEILINGS THROUGH THE DAY, BUT OVERALL SOUTHEAST ALASKA IS VMC AS
OF EARLY THIS AFTERNOON. TOO MUCH CLOUD COVER FOR TEMPS TO GET
MUCH ABOVE THE MID 50S THIS AFTERNOON. WINDS 10 KTS OR LESS THIS
AFTERNOON AND OVERNIGHT FOR MOST INNER CHANNEL LOCATIONS. WITH
THE GROUND SATURATED FROM RECENT PRECIPITATION, POTENTIAL IS HIGH
FOR FOG TONIGHT AND HAVE WRITTEN THIS INTO THE AFTERNOON TAFS.
NOT EXPECTING AND LARGE AREAS OF DENSE FOG, BUT AVIATION
ACTIVITIES WILL LIKELY BE IMPACTED EARLY TOMORROW MORNING.

A RIDGE WILL BUILD OVER THE PANHANDLE TOMORROW MORNING IN ADVANCE
OF AN APPROACHING WARM FRONT. THIS WILL ACT TO STABILIZE THE LOWER
ATMOSPHERE AND ANY RESIDUAL PRECIPITATION TOMORROW WILL TRANSITION
FROM SHOWERS BACK TO RAIN. THE WARM FRONT WILL NOT ARRIVE OVER THE
PANHANDLE BEFORE THE END OF THE SHORT RANGE FORECAST PERIOD, BUT
FRONTAL RAINS WILL ARRIVE ALONG THE SOUTHERN OUTER COAST TOMORROW
AFTERNOON. SOUTHEASTERLY WINDS WILL ALSO SET UP EARLY TOMORROW
AFTERNOON OVER THE COASTAL WATERS AND BEGIN TO STRENGTHEN, WITH AN
EASTERLY BARRIER JET BEGINNING TO FOR WEST OF ICY BAY LATE IN THE
DAY. WINDS NOT SO MUCH OF AN ISSUE, BUT RAINS THAT BEGIN TOMORROW
WILL CONTINUE AND BECOME VERY HEAVY AT TIMES EARLY ON IN THE
EXTENDED RANGE FORECAST PERIOD.

USED NAM FOR UPDATES TO PRESSURE AND WIND. BLENDED ECMWF, GEM,
AND GFS FOR POP AND QPF. TEMPS ADJUSTED WITH BIAS CORRECTED SREF
AND GFS. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...THE ONSET OF RAIN HEAVY AT TIMES IS STILL SET BEGIN
LATE TUE NIGHT, AND THE MOST PERSISTENT OF THE HEAVIER RAINFALL
WILL OCCUR IN THE CENTRAL AND SOUTHERN PANHANDLE THROUGH THURSDAY
MORNING. THE STRONGEST WINDS IN THE INNER CHANNELS ARE FORECAST TO
BE IN CLARENCE STRAIT WITH GALE FORCE EXPECTED WEDNESDAY. GALE
FORCE WINDS WILL ALSO OCCUR ON THE OUTSIDE WATERS FROM ICY CAPE TO
CAPE SUCKLING. CONFIDENCE IS ABOVE AVERAGE.

THE LARGE SCALE PATTERN IS PROGRESSIVE, AND A GALE FORCE JET-
FRONT SYSTEM WILL MOVE NE INTO THE GULF EARLY TUE WITH A STRONGER
THAN USUAL WARM FRONT. THIS WARM FRONT WILL EXTEND SE ACROSS THE
GULF ABOUT 200 NM SW OF THE EASTERN GULF COAST TUE NIGHT AND WILL
PROVIDE THE UPGLIDE LIFT OF AN AIRMASS OF SUBTROPICAL ORIGIN AND
THEREFORE THE HEAVIER RAINFALL. THE SOURCE REGION FOR THE AIRMASS
THAT WILL BE RUNNING UP OVER THE WARM FRONT IS READILY TRACED TO
ABOUT 1800 NM SW UPSTREAM USING THE WV AND IR IMAGES.

MODELS: THE CONSENSUS BETWEEN THE GFS AND THE ECMWF STILL HOLDS
WELL THROUGH THU. THE GFS HAS A DISTINCT FRONTAL WAVE BECOMING
CYCLOGENETIC BUT A SMOOTHED OPEN WAVE WAS RETAINED AS PER THE
ECMWF MODEL AND GUIDANCE FROM THE HYDROMETEOROLOGICAL PREDICTION
CENTER.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

FRITSCH/JBT