Small Craft Advisory 545, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
414 PM AKDT FRI SEP 16 2011

.SHORT TERM...AN EXTENSIVE CLOUD SHIELD COVERS THE PANHANDLE AND
THE RADAR IS PAINTING PLENTY OF PRECIPITATION WITH A NNW
TRAJECTORY. BOTH THE RADAR ECHOS AND INFRARED SATELLITE IMAGERY
ARE INDICATING OF A SLOW TRANSITION TO A MORE CONVECTIVE
ENVIRONMENT. THERE IS VERY LITTLE TEMPERATURE CONTRAST FROM ONE
SIDE OF THE FRONT TO THE OTHER AND THE STRONG NEGATIVE TILT IS
SUGGESTIVE OF A STATIONARY FRONT. SO FAR, FRONTAL PASSAGE HAS NOT
YET OCCURRED OVER ANY LAND STATIONS BUT HAS HAPPENED OVER THE
SOUTHERN MOST COASTAL MARINE ZONE. AS OF EARLY THIS AFTERNOON,
SPOTTY PRECIP IS BEING REPORTED OVER THE SOUTHERN HALF OF THE
PANHANDLE, TO INCLUDE SITKA.

FRONTAL PROGRESS AND THE ASSOCIATED PRECIPITATION WILL CONTINUE
TO BE SLOW THROUGHOUT THE NIGHT AND HAVE ADJUSTED THE POP GRIDS TO
REFLECT THIS. EVENTUALLY ALL LOCATIONS WILL SEE CATEGORICAL POPS
EXCEPT THOSE LOCATIONS ALONG NORTHERN LYNN CANAL WHERE POPS HAVE
BEEN LIMITED TO LIKELY THROUGH THE SHORT TERM FORECAST PERIOD.
RAIN WILL TRANSITION TO SHOWERS OVERNIGHT AND ALL REMAINING PRECIP
WILL BE CONVECTIVE BY TOMORROW MORNING. 6-HOURLY QPF RATES LIMITED
TO A QUARTER OF AN INCH OR LESS.

WINDS ASSOCIATED WITH THE FRONT HAVE NOT BEEN AS STRONG AS
ORIGINALLY EXPECTED EITHER AND THIS IS IN KEEPING WITH THE IDEA
THAT AS THE FRONT LOSES JET SUPPORT, MID LEVEL ENERGY AND DYNAMIC
SUPPORT WILL DIMINISH. ADJUSTED PRE-FRONTAL WINDS OVER THE COASTAL
MARINE ZONES DOWN BY 5 TO 7 KTS TO A MAX OF 25 KTS, WHICH ARE THE
MAX CONDITIONS OBSERVED UPSTREAM AS THE FRONT HAS CROSSED THE
CENTRAL GULF. HAVE ALSO LEFT THE EAST-WEST CHANNELS AS WELL AS
CLARENCE STRAIT BELOW 25 KTS, SO NO SMALL CRAFT ADVISORIES FOR ANY
OF THE INSIDE WATERS IN ADVANCE OF THE FRONT IN THE AFTERNOON
FORECAST ISSUANCE.

USED NAM FOR ADJUSTMENTS THROUGH SATURDAY MORNING. FORECAST
CONFIDENCE IS ABOVE AVERAGE.

&&

.LONG TERM /SAT NIGHT THROUGH FRIDAY/...
A VERTICALLY STACKED LOW PRESSURE SYSTEM WILL MOVE INTO THE SOUTHEASTERN
GULF SATURDAY NIGHT. THE INCREASED PRESSURE GRADIENT BETWEEN THIS
LOW AND THE COASTAL RIDGE OF HIGH PRESSURE ALONG WITH A LOW LEVEL
JET MAX WILL CAUSE WINDS TO INCREASE OUT OF THE E-SE. WINDS REACHING
GALE FORCE SATURDAY NIGHT FOR THE SOUTHERN OUTSIDE WATERS...AND
SOON SPREADING INTO THE SOUTHERN INSIDE WATERS AND LAND AREAS.
EXPECT WINDS OF 25-35 MPH WITH GUSTS TO 45 MPH OVERNIGHT SATURDAY
FOR THE CRAIG/KLAWOCK REGION AND SPREADING FURTHER INLAND THROUGH
EARLY SUNDAY MORNING. RAIN WILL ARRIVE WITH THE WIND...BECOMING
HEAVY AT TIMES...LEADING TO THE RISK OF MUDSLIDES.

FOR THE CENTRAL PANHANDLE NORTHWARD THIS LOW WILL HAVE THE OPPOSITE
AFFECT. MID LEVEL WINDS WILL BE OFFSHORE...ALLOWING FOR
DOWN-SLOPING AND DRYING. AS A RESULT THE NORTHERN AREAS WILL HAVE
MORE BREAKS IN THE CLOUD COVER SATURDAY NIGHT...LEADING TO COOLER
MIN TEMPS. THE FIRST HALF OF SUNDAY LOOKS TO HAVE SUNNY BREAKS AS
WELL. WINDS THROUGH THE N-S INSIDE WATERS WILL TURN OUT OF THE
NORTH TOWARD THE LOW CENTER AND INCREASE TO SMALL CRAFT LEVEL. THE
LOW IS EXPECTED TO FILL THROUGH SUNDAY TO AN OPEN WAVE AS IT LIFTS
NORTH. THIS WILL ALLOW WINDS TO EASE FOR A SHORT PERIOD SUNDAY
NIGHT...ALTHOUGH WITH GALES IN CLARENCE STRAIT LASTING SLIGHTLY LONGER.

THE NEXT LOW PRESSURE SYSTEM WILL MOVE INTO THE WESTERN GULF
MONDAY. WINDS WITH THIS SYSTEM WILL INCREASE TO A STRONG GALE
OFFSHORE AND SPREADING INTO THE OUTSIDE WATERS THROUGH THE DAY
WITH STRONG WINDS REACHING THE COASTAL LAND AREAS MONDAY AFTERNOON
AND INLAND OVERNIGHT. RAIN ASSOC WITH THIS SYSTEM WILL SPREAD
ACROSS THE REGION MONDAY MORNING...BECOMING WIDESPREAD AND HEAVY
AT TIMES MONDAY NIGHT. WINDS WILL EASE INTO TUESDAY...HOWEVER RAIN
WILL CONTINUE INTO MID WEEK.

NUMERICAL MODELS HAVE DEPICTED VERY DIFFERENT SOLUTIONS FOR THE
LOW ON SUNDAY OVER THE PAST SEVERAL DAYS. SOLUTIONS FOR THIS HAVE
COME MORE IN LINE IN THE BROAD SCALE...HOWEVER SLIGHT DIFFERENCES
IN PLACEMENT OF THE LOW CENTER RESULT IN VASTLY DIFFERENT WINDS
THROUGH THE INNER CHANNELS. HAVE GONE MAINLY WITH THE GFS TODAY
AS IT MATCHED WELL WITH THE GEM/UK AND WAS IN THE MIDDLE OF THE
ECMWF AND NAM. MODELS ARE IN BETTER AGREEMENT FOR THE NEXT LOW
PRESSURE SYSTEM ON MONDAY BUT DIVERGE WITH ANOTHER SYSTEM
DEVELOPING TO THE SOUTH FOR WEDNESDAY. FROM WEDNESDAY ONWARD
TRENDED TOWARD THE HPC SOLUTION.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-041>043-051-052.

&&

FRITSCH/HANNON