Small Craft Advisory 519, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
420 PM AKDT WED SEP 12 2012

.SHORT TERM...THE HEAVY RAIN EVENT IS NOW IN TWO SEPARATE
COMPONENTS WITH THE FIRST IN THE NORTHERN THIRD OF THE PANHANDLE,
AND THE SECOND COVERING THE SOUTHERN HALF OF THE PANHANDLE. THE
NORTHERN HEAVY RAIN WILL RAPIDLY END BY EARLY THIS EVENING. THE
HEAVY RAINFALL IN THE SOUTHERN PANHANDLE WILL TAPER OFF THIS
EVENING BEFORE REDEVELOPING THURSDAY.

 THE FRONTAL SYSTEM MOVED ON SHORE THIS AFTERNOON AND AT THIS
TIME THE OCCLUSION IS DISSIPATING OVER THE NORTHERN PANHANDLE.
THE ASSOCIATED COLD FRONT IS ALOFT OVER THE SOUTH CENTRAL
PANHANDLE AND DRIFTING TO THE SOUTHEAST. THE COLD FRONT EXTENDS
TO THE SW OFFSHORE AND THE GOES IR IMAGE IS CONSISTENT WITH THE
MODEL SOLUTION OF THE COLD FRONT EXTENDING TO THE SOUTHWEST TO A
DEVELOPING LOW ABOUT 800 NM TO THE SW OF SITKA. THE APPROACH OF
THE DEVELOPING LOW IS ASSOCIATED WITH THE COLD FRONT BECOMING
STATIONARY OVER THE SOUTHERN PANHANDLE LATE TONIGHT. FOR MORE
ABOUT THE LOW ITSELF PLEASE SEE THE LONG RANGE SECTION BELOW.

 AFTER THE OCCLUSION ALOFT HAS DISSIPATED AND MOVED NORTH OF THE
PANHANDLE, COLD ADVECTION WILL OCCUR. SNOW CAN OCCUR AS LOW AS
2500 FT BEFORE THE PRECIP ENDS LATE TONIGHT. NOTE THE CHANCE OF
SNOW GIVEN FOR WHITE PASS.

.LONG TERM...CURRENTLY...AN UPPER LOW IS MOVING SLOWLY ACROSS THE
NORTHERN GULF. THE ASSOCIATED FRONT IS SLOWLY MOVING SOUTHEASTWARD
ACROSS THE PANHANDLE. THE BEGINNING OF THE LONG RANGE PERIOD HAS A
DEVELOPING LOW MOVING NORTHEASTWARD INTO SOUTHERN PANHANDLE. KEEP
THE WINDS IN SOUTHERN WATERS AND CLARENCE STRAIT AT 30 KT FOR THE
FIRST HALF OF THURSDAY NIGHT. AS THE LOW PRESSURE CONTINUES TO
PULL NORTHEASTWARD ACROSS CENTRAL PANHANDLE INTO INTERIOR BRITISH
COLUMBIA...WINDS IN THE SOUTHERN AREAS SHOULD DIMINISH DURING THE
COURSE OF THE NIGHT. WINDS IN THE NORTHERN INSIDE CHANNELS WILL
SHIFT TO THE NORTHERLY DIRECTION BRIEFLY AS THEY ARE ON THE WEST
SIDE OF THE LANDFALLING LOW PRESSURE SYSTEM.

USED ECMWF AS THE MODEL OF CHOICE AS IT HAS A BETTER HANDLE ON
THE DEVELOPING LOW MOVING INTO SOUTHERN PANHANDLE. THE NEW 12Z
ECMWF CONTINUES TO LOWER THE CENTRAL PRESSURE TO THE LOW 1000S MB.
ECMWF SOLUTION AGREES WITH THAT OF NAM AND UKMET. GFS IS STILL
HAVING DIFFICULTIES IN DIAGNOSING THE INTENSITY OF THIS DEVELOPING
LOW.

KEPT THE PRECIPITATION IN THE SOUTHERN AREAS A LITTLE BIT LONGER.
CATEGORICAL POPS FOR ZONES 27 THROUGH 29 FOR THE EVENING. RAIN
WILL LINGER OVER 28 AND 29 LATE THURSDAY NIGHT. HEAVY PRECIPITATION
WILL TAPER OFF AFTER THAT.

RIDGING WILL BUILDS ACROSS THE PANHANDLE ON FRIDAY. WITH UPPER
LEVEL SHORT WAVES MOVING ACROSS THE NORTHERN PANHANDLE...KEPT
LIKELY POPS THERE. PRECIPITATION SHOULD BE CONVECTIVE BEHIND THE
FRONT DUE TO UPPER LEVEL COLD AIR MOVING INTO THE AREA. OVER
SOUTHERN AREAS...INCERASING NORTHWEST FLOW MAY PROMOTE DRIER
CONDITIONS AND SUNNY BREAKS IN CLOUD COVER.

THE BIG WEATHER STORY THIS WEEKEND IS THE STRONG UPPER TROUGH
DEVELOPING OVER CENTRAL ALEUTIANS AND THE STRONG RIDGING DEVELOPING
OVER SOUTHEAST ALASKA. SOUTHERN AREAS SHOULD REMAIN DRY WITH PARTLY
CLOUDY SKIES FOR SATURDAY. SHOWERS WILL LINGER IN THE CENTRAL
PANHANDLE. A STRONG WEATHER FRONT WILL PUSH EASTWARD INTO YAKUTAT
AREA BY SUNDAY...AND THERE IS A POTENTIAL FOR HEAVY RAIN AND WINDY
CONDITIONS. RIGHT NOW PUT IN SOUTHERLY GALES IN THE WESTERN
OUTSIDE WATERS. WITH A HIGH MAGNITUDE LONGWAVE RIDGE/TROUGH
COUPLETS OVER NORTH PACIFIC...MODELS ARE HINTING ON PERSISTENT
RIDGING OVER SOUTHEAST ALASKA INTO MIDDLE OF NEXT WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ036.
         SMALL CRAFT ADVISORY FOR PKZ012-022-041.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043-051-052.

&&

JBT/RCL/ABJ