Small Craft Advisory 314, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
341 PM AKDT FRI MAY 11 2012

.SHORT TERM...A FRONTAL SYSTEM OVER THE EASTERN GULF AND
PANHANDLE WILL CONTINUE TO AFFECT THE REGION THROUGH SATURDAY
BEFORE MOVING OFF TO THE EAST. THE MAIN FEATURES OF THE THIS
FRONT ARE THE STRONG WINDS ALONG IT. A WAVE WILL LIFT NORTH ALONG
IT LATE TONIGHT WITH WINDS OF AROUND 60KT AT 850MB. THIS WILL
KEEP THE GALES GOING FOR THE OUTSIDE WATERS AND AS THE FRONT
MOVES INLAND WINDS THROUGH INSIDE WATERS WILL INCREASE TO GALE
FORCE WITH WINDS GUSTING 35 TO 45MPH OVER LAND. STRONGEST WINDS
OVER THE YAKUTAT AND OUTER COASTAL AREAS WILL BE TONIGHT AND
EARLY SATURDAY MORNING FOR THE INNER PANHANDLE AREAS INCLUDING
JUNEAU. THESE STRONG WINDS WILL CAUSE WIND SHEAR FOR AIRCRAFT
CONCERNS.

 RAIN WILL CONTINUE WITH THIS SYSTEM AS WELL. EXPECT THE HEAVIEST
RAINFALL TO ACCOMPANY THE STRONG WINDS...AGAIN WITH THE NORTHERN
COASTAL AREAS SEEING THE MOST. EXCEPTION TO THIS IS OVER THE FAR
SERN ZONES THAT HAS SEEN THE LEAST AMOUNT OF RAIN TODAY. AS THE
WAVE LIFTS NORTH THIS WILL BACK PRECIP OFF EVEN MORE FROM THAT
REGION...THEN THE RAIN WILL MOVE BACK IN OVER THE PANHANDLE AS IT
PASSES THROUGH SATURDAY WITH MORE QPF THAN SEEN TODAY.

 NUMERICAL MODELS HAVE HAD A GOOD HANDLE ON THIS SYSTEM OVER THE
PAST SEVERAL DAYS KEEPING FORECASTER CONFIDENCE ABOVE AVERAGE.
THE HIRES MESOSCALE MODELS HAVE PICKED UP ON THE WIND SPEED THE
BEST AND WERE USED TO ADJUST UP FROM BASE MODEL WINDS THEN
ADJUSTED UP FURTHER FOR PRONE AREAS.

.LONG TERM...PATTERN CHG FM RAIN TO DRIER IS STILL TO OCCUR THROUGH
NEXT WEEK. CHANGES TO THE FORECAST PACKAGE ARE LIMITED, AND ARE
PRINCIPALLY DUE TO A WEAKER SOLUTION FOR THE LOW TRACKING E THROUGH
THE EASTERN GULF TUE. CONFIDENCE IS AVERAGE.

SOME NOTES ABOUT THE TRANSITION FROM THE SHORT-RANGE DESK: GFS
HAS SLOWER TIMING FOR THE APCH OF THE SFC TROUGH SAT, WITH UKMET/EC/NAM
IN A USEFUL CONSENSUS FOR LANDFALL ABOUT 00Z SUN. THE NAM AS PRINCIPAL
WITH NAM/GFS/EC FOR MON AND TRANSITION TO EC ABT 00Z TUE. 03Z WED
ONWARD USED EXISTING GRIDS WHICH FITS THE NEW HPC.

RAPID TRACK OF 500H LOW, FM OVER BRISTOL BAY SUN 00Z TO OVR ERN
GLFALSK 12Z TUE, WILL BE FOLLOWED BY A STRNG DRYING SEQUENCE THRFTR
AS THE LOW DISSIPATES ONSHORE ABT 100 NM NW PASI. THE DISSIPATION
OF THE LOW IS AIDED BY INTSFYG RIDGE ALF THAT BY 12Z WED WILL XTD
FM THE NPAC TO NNW OVR A PAWD TO PABR LN. THIS RIDGE ALF WILL BE A
MUCH SLOWER FEATURE TO MOVE E AS A POORLY-ORGANIZED BLOCKING PATN
BECOMES MORE IMPORTANT.

MORE ON THAT 500H LOW: IT IS OVR PAGM/PASA ATTM HAS AN ASSOCD
TROF XTDG SE OVR PAKN AND TO THE SSE.  A STRONG VORT CNTR ASSOCD
WITH THIS LOW ALF WILL RAPIDLY TRACK SE ALONG THE TROF ALF AS
THE TROF MOVS E. THE LOW ALF SHOULD BE OVR BRISTOL BAY ABT 00Z,
AND ABT 100 NM S OF PAMD AT 12Z MON.  12Z TUE THE LOW SHOULD BE
OVR PAYA, BASED ON THE ECMWF. THE GFS HAS A FASTER TIMING FOR
THE LOW ALF, BUT THE EC SLOWER TIMING IS EASIER TO ACCEPT AS IT
HAS VARIED LESS FROM RUN TO RUN, AND THAT THE EC HAS THE UPPER
LEVEL VORT FEATURES BETTER COUPLED WITH BOUNDARY LAYER LOW SOLNS.

AS THE 500H LOW MOVES OVER THE GLFALSK, THE FLOW ALOFT TO THE SW
OF THE LOW WILL WILL PROVIDE LEESIDE TROUGHING IN GULF AND ALSO
SUPPORT BE ASSOCD WITH A WEAK SFC LOW REACHING WITHIN 120 NM SE OF
PAYA ABT 12Z TUE.

CONFIDENCE IS AVERAGE. NEED TO POINT OUT LOW CONFIDENCE FOR DETAILS
OF OF WEAK LOW WI 100 NM OF CROSS SOUND ABOUT 18Z TUE. THERE ARE A
VARIETY OF SOLUTIONS THAT THE MODELS HAVE GIVEN, I.E. A STATISTICAL
SHOTGUN PATTERN FOR THIS SMALL FEATURE. THE BEST GUESTIMATE IS FOR
THE WIND SHIFTS NEAR CROSS SOUND TO FOLLOW A TRANSITION FROM SW TO
NE AND BACK TO SW IN ABOUT 48 HOURS BEGINNING LATE MON, BUT GETTING
CLOSER TO THE EVENT SHOULD HELP CLARIFY THE TIMING.

SOME NOTES ABOUT THE TRANSITION FROM THE SHORT-RANGE DESK: GFS
HAS SLOWER TIMING FOR THE APCH OF THE SFC TROUGH SAT, WITH UKMET/EC/NAM
IN A USEFUL CONSENSUS FOR LANDFALL ABOUT 00Z SUN. THE NAM AS PRINCIPAL
WITH NAM/GFS/EC FOR MON AND TRANSITION TO EC ABT 00Z TUE. 03Z WED ONWARD
USED EXISTING GRIDS WHICH FITS THE NEW HPC.

SLOWER MODEL TRACK SOLUTIONS FOR LOW MOVG E ACRS THE GULF ENCOURAGED
THE USE OF THE EC OVER THE GFS, AS THE LATER SEEMS TO NOT BE ACTING
ENOUGH ON LEESIDE EFFECTS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
     AKZ027.
         STRONG WIND FROM 7 PM AKDT THIS EVENING THROUGH SATURDAY MORNING
     FOR AKZ022-023-025.
         STRONG WIND SATURDAY MORNING FOR AKZ018-019.
         STRONG WIND FROM 7 PM THIS EVENING TO 1 AM AKDT SATURDAY FOR
     AKZ018.
         STRONG WIND FROM 1 AM AKDT SATURDAY THROUGH SATURDAY MORNING FOR
     AKZ017.
MARINE...GALE WARNING FOR PKZ011>013-021-022-031>036-041>043-051>053.

&&

HANNON/JBT