Small Craft Advisory 266, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
328 PM AKDT THU APR 19 2012

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A
DEVELOPING GALE FORCE LOW MOVING INTO THE SOUTHERN AK GULF WITH
FIRST FRONTAL BAND MOVING OVER THE SOUTHERN PANHANDLE. THE GALE
FORCE LOW WILL TRACK NORTHWARD ALONG THE PANHANDLE COAST AND THEN
WEAKEN BY FRIDAY AFTERNOON. A RIDGE OF HIGH PRESSURE WILL BUILD
OVER THE PANHANDLE FRIDAY WITH FLOW SHIFTING FROM OFFSHORE TO
ONSHORE.

 MAIN ISSUE WITH THE ADVANCING LOW WILL BE WINDS OVER THE
SOUTHERN PANHANDLE AND COASTAL WATERS. EXPECT GALE FORCE WINDS TO
DEVELOP THIS EVENING AND INCREASE OVERNIGHT OVER THE COASTAL
WATERS AND SOUTHERN INNER CHANNELS. HAVE ALREADY SEEN WINDS PICK
UP THIS AFTERNOON BUT HIGHEST WINDS WILL OCCUR WENT THE SECONDARY
WRAP MOVES IN LATER TONIGHT. WINDS FOR CRAIG, KLAWOCK, KETCHIKAN
AND METLAKATLA WILL CONTINUE TO INCREASE THROUGH THE EVENING WITH
WIND GUSTS PICKING UP TO 40 MPH. AS THE LOW MOVES NORTH AND BEGIN
TO WEAKEN WIND OVER THE SOUTHERN REGIONS WILL BEGIN TO DIMINISH
IN THE LATE MORNING AND AFTERNOON.

 EARLIER IN THE MORNING A SURFACE TROUGH PASSED OVER THE
PANHANDLE WITH SOME SCATTERED SHOWER ACTIVITY AND CLOUDY SKIES.
AS THE TROUGH EXITED THE AREA SAW PRECIPITATION FOR THE CENTRAL
AND NORTHERN PANHANDLE DIMINISH. OFFSHORE FLOW HELPED TO INCREASE
SUNNY BREAKS THROUGH THE DAY BUT THESE WILL DECEASE AS CLOUD
SHIELD AHEAD OF THE FRONT ADVANCES NORTHWARD. A SHORTWAVE DID
MOVE OVER THE FAR NORTHERN PANHANDLE THIS AFTERNOON BRINGING SOME
SHOWER ACTIVITY TO SKAGWAY AND HAINES BUT THE WAVE LOOKS TO BE
QUICKLY MOVING NORTHEASTWARD INTO THE YUKON SO ONLY EXPECT
ISOLATED SHOWERS FOR THE REST OF THE EVENING. FORE THE SOUTHERN
PANHANDLE OVERCAST SKIES WITH PERIODS OF RAIN THROUGH THE DAY
WILL INCREASE THIS EVENING BECOMING STEADY RAIN THROUGH THE DAY
FRIDAY. THE CENTRAL AND NORTHERN PANHANDLE WILL SEE INCREASING
CLOUD COVER WITH SCATTERED SHOWERS OVERNIGHT AND THEN RAIN
DEVELOPING THROUGH THE DAY FRIDAY. NOT SEEING MUCH IN THE MAY OF
MOISTURE FEEDING MECHANISM WITH THIS FRONT SO MAJORITY OF PRECIP
WILL FALL OVER THE SOUTHERN REGIONS WITH 6 HOUR QPF VALUES
RANGING FROM 0.20 TO 0.40 INCHES OVERNIGHT. AS THE FRONT MOVES
NORTH AND WEAKENS THE CENTRAL AND NORTHERN REGIONS WILL SEE LESS
QPF, WITH 6 HOUR TOTALS LESS THAN 0.20 INCHES.

 MODELS WERE IN FAIRLY GOOD AGREEMENT FOR THE FIRST 12 HOURS WITH
DIFFERENCES IN THE TIMING OF THE LOW BECOMING MORE OF AN OPEN
WAVE TROUGH DEVELOPING. ECMWF AND NAM WERE QUICKEST TO WEAKEN THE
LOW WITH GFS AND UKMET KEEPING A WEAK CLOSED LOW CENTER A BIT
LONGER. THERE WERE NO SIGNIFICANT DIFFERENCES IN MODEL
INITIALIZATION BUT NAM WAS SHOWING A MUCH STRONGER NORTHERLY
GRADIENT DEVELOPING COMPARED TO THE GFS AND ECMWF. USED A BLEND
OF 12Z GFS AND 00Z EC WITH INHERITED GRIDS. MAIN CHANGES WAS A
SLIGHT DELAY IN TIMING OF WINDS TONIGHT WITH A DELAY IN THE
SECONDARY WRAP MOVING IN. FORECAST CONFIDENCE IS ABOUT AVERAGE.

.LONG TERM...MINOR DIFFERENCES BETWEEN MODELS BEGIN TO SHOW OVER
THE WEEKEND WITH THE GRADUAL WEAKENING AND EASTWARD PROGRESSION OF
THE UPPER LEVEL LOW IN THE GULF OF AK. THE ECMWF IS A LITTLE
QUICKER THAN THE GFS TO WEAKEN THE ASSOCIATED SURFACE LOW JUST
OFF THE CENTRAL SE AK COAST BUT A BLEND OF THE TWO MODELS STILL
BRINGS GALES AS FAR NORTH AS CAPE FAIRWEATHER WITH SMALL CRAFT
WINDS OVER THE REMAINDER OF THE SOUTHEAST AK OUTER COASTAL WATERS.
RAIN WILL SPREAD NORTHWARD OVER MOST SECTIONS OF THE PANHANDLE FRI
THOUGH SAT.

MODEL DIVERGENCE GROWS SIGNIFICANTLY WITH THE NEXT UPPER LOW THAT
MOVES INTO THE GULF OF AK MON NIGHT. THE GREATEST ENSEMBLE SPREAD
IS ON EITHER SIDE OF MEAN POSITION SUGGESTING MOST OF THE
UNCERTAINLY IS WITH THE TRACK AND SPEED OF THE SYSTEM RATHER THAN THE
DEPTH. SO FAR FORECAST CONSENSUS WOULD STILL SUGGEST THE THE
UPPER LOW WILL TURN SOUTHEASTWARD TOWARD SOUTHERN B.C. AND THE
PACIFIC NW. THIS WOULD LEAD TO A TAPERING OFF OF PRECIPITATION IN
THE EASTERN GULF NORTHERN INNER CHANNELS EARLY NEXT WEEK BUT RAIN BANDS
WILL LIKELY STILL SPREAD OVER SOUTHERN SE AK. WINDS ARE NOT
EXPECTED TO BE SIGNIFICANT IN THE EARLY HALF OF NEXT WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 1 AM AKDT FRIDAY THROUGH FRIDAY AFTERNOON FOR
     AKZ027.
         STRONG WIND FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR AKZ028.
MARINE...GALE WARNING FOR PKZ033-035-036-041-042.
         SMALL CRAFT ADVISORY FOR PKZ021-022-031-032-034-043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051-052.

&&

PRB/CFD