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791
FXAK67 PAJK 192346
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
346 PM AKDT FRI SEP 19 2014

.SHORT TERM...LOW PRESSURE OVER THE NW GULF WILL WEAKEN THERE
TONIGHT...THEN DISSIPATE SAT. A LOW WILL DEVELOP AND MOVE NNE INTO
THE SE GULF LATE TONIGHT...THEN MOVE ACROSS THE N-CENTRAL
PANHANDLE SAT. ASSOCIATED FRONT WILL MOVE THRU ALL BUT THE FAR
SERN AREA...WHERE IT WILL STALL SAT AFTERNOON AS ANOTHER LOW
STARTS TO DEVELOP OVER THE NE PAC. USED BLEND OF THE 12Z ECMWF AND
NAM AS THEY WERE VERY CLOSE ON HANDLING THE LOW MOVING ACROSS THE
AREA LATE TONIGHT AND SAT. GFS APPEARED TO BE TOO FAST WHILE THE
GEM LOOKED TOO STRONG AND TOO FAR W WITH IT.

MAIN FORECAST CONCERNS WILL BE WINDS AND PRECIP POTENTIAL/AMOUNTS.
WINDS REMAIN LOCALLY STRONG OVER THE FAR NRN INNER CHANNELS BUT
THEY SHOULD DIMINISH THIS EVENING. MEANWHILE...WINDS WILL INCREASE
OVER THE SERN AREA TONIGHT AS LOW AND FRONT MOVE IN. WINDS COULD
APPROACH STORM FORCE OVER THE FAR SERN GULF AND CLARENCE STRAIT
BETWEEN 12-18Z SAT...BUT WILL PEAK THEM AT 45 KT FOR NOW AS
CONFIDENCE IN ULTIMATE STRENGTH OF THE LOW/FRONT IS NOT VERY HIGH
DUE TO MODEL DIFFERENCES AND POOR RUN TO RUN CONTINUITY. WILL HAVE
STRONG WIND HEADLINES FOR ZONES 26..27..AND 28 FOR LATE TONIGHT
AND SAT MORNING. WINDS COULD APPROACH HIGH WIND LEVELS IN ZONE 27
12-18Z. WILL NEED TO KEEP AN EYE ON ZONE 28 FOR END TIME OF THESE
STRONG WINDS AS THEY COULD HANG ON LONGER THAN CURRENTLY FORECAST
DUE TO FRONT STALLING OVER THEM.

AS FOR PRECIP POTENTIAL AND AMOUNTS...SHOWERS OVER THE NRN HALF OF
THE AREA SHOULD DIMINISH OVER ALL BUT THE NE GULF COAST AREA AS
WARMER AIR ALOFT MOVES IN AHEAD OF APPROACHING LOW AND FRONT.
STRATIFORM RAIN SHIELD WILL SPREAD N ACROSS THE SRN PANHANDLE THIS
EVENING AND REACH MOST OF THE NRN AREA LATE TONIGHT. AFTER TRAILING
COLD FRONT MOVES THRU MOST OF THE AREA SAT...PRECIP SHOULD BECOME
SHOWERY NW OF FREDERICK SOUND BY SAT AFTERNOON. THE HEAVIEST RAIN
SHOULD OCCUR OVER THE SERN THIRD OF THE AREA...WHERE STRONGEST SLY
LOW LEVEL JET WILL BE. RAINFALL THERE COULD BE IN THE 1.5 TO 4
INCH RANGE BY LATE SAT AFTERNOON...WITH THE KETCHIKAN AREA HAVING
BEST SHOT AT THE 4 INCHES OF RAIN BY LATE SAT AFTERNOON. THIS RAIN
SHOULD CAUSE AREA RIVERS AND STREAMS TO RISE QUICKLY...BUT AM NOT
EXPECTING ANY FLOODING THRU SAT AFTERNOON. THE COMBINATION OF
HEAVY RAIN AND STRONG WIND COULD LEAD TO MUDSLIDES NEAR STEEP
TERRAIN S OF THE FREDERICK SOUND AREA LATE TONIGHT AND SAT.

OTHERWISE...WILL LEAVE IN ISOLATED TSTMS FOR THE PAYA AREA FOR THE
EARLY EVENING PERIOD (THRU 03Z). WARMING AND PASSAGE OF VORT MAXIMA
ALOFT WILL LIKELY END THIS THREAT LATER IN THE EVENING.

.LONG TERM...UPPER LEVEL TROUGH EXTENDING FROM THE AK INTERIOR INTO
THE N PACIFIC WILL WIND TO THE EAST THROUGH SUNDAY SWINGING
ANOTHER STRONG SURFACE LOW NORTHWARD INTO THE AK GULF. MODELS ARE
BEGINNING TO FALL MORE IN LINE WITH THE TRACK OF THIS LOW HOWEVER
THERE IS A LARGE DIFFERENCE IN STRENGTH, AT LEAST 10 MB. THUS THIS
LOW WILL AT LEAST BE MAX SMALL CRAFT WITH THE POTENTIAL OF
REACHING STORM FORCE. SEAS WILL BUILD INTO THE 12 TO 18 FOOT
RANGE WITH THE ADVANCING LOW AND FRONT. MODERATE TO HEAVY RAINFALL
WILL AGAIN PUSH OVER THE PANHANDLE FROM SOUTH TO NORTH WITH THE
ADVANCING FRONT WITH INCREASING WINDS OVER THE INNER CHANNEL.
STRONG WIND GUSTS WILL DEVELOP OVER THE COASTAL PANHANDLE ON
SUNDAY INTO SUNDAY NIGHT. WINDS WILL SHIFT FROM SOUTH TO NORTH
THEN BACK AGAIN AS THE LOW MOVES NORTHWARD. THERE WILL BE DROPS IN
SPEEDS AS THE WINDS FLIP BUT SPEEDS WILL PICK UP FAIRLY QUICKLY AS
GRADIENTS INCREASE.

THE LOW WILL TRACK TO THE NORTHWEST THROUGH MONDAY MORNING NEARING
PRINCE WILLIAM SOUND AS A RIDGE OF HIGH PRESSURE BUILDS OVER THE
PANHANDLE INTO TUESDAY. TO THE SOUTH A 980 MB LOW WILL TRACK EASTWARD
SOUTH OF 50 N TOWARD THE WASHINGTON COAST. INDICATIONS THAT THIS
SYSTEM COULD PUSH NORTHWARD AND REACH THE SOUTHERN PANHANDLE AND AK
GULF LATER IN THE WEEK, BUT WITH THE RUN TO RUN VARIATIONS HAVE
LOW CONFIDENCE ON THE OPERATIONAL MODEL SOLUTIONS.

WHILE 12Z ECMWF/GFS DIFFERED ON THE STRENGTH OF THE SUNDAY LOW,
AROUND 10 MB, THEY DID HAVE SIMILAR TRACKS. USED A BLEND OF THE
DEEPER ECMWF AND WEAKER GFS FOR NOW. WITH THE LARGE SPREAD IN
OPERATIONS MODELS KEPT WITH AN ENSEMBLE BLEND BY USING THE NEW
WPC. FORECAST CONFIDENCE IS AVERAGE BUT DROPS BY EARLY NEXT WEEK.

&&

.HYDROLOGY...RIVERS AND STREAMS IN SOUTHEAST ALASKA WILL SEE SHARP
RISES TO BANKFULL OVER THE NEXT 2 DAYS AS SEVERAL WAVES OF
PRECIPITATION PASS THROUGH THE PANHANDLE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM LATE TONIGHT THROUGH SATURDAY AFTERNOON FOR
     AKZ026.
         STRONG WIND FROM 1 AM AKDT SATURDAY THROUGH SATURDAY MORNING FOR
     AKZ027.
         STRONG WIND FROM 1 AM AKDT SATURDAY THROUGH SATURDAY AFTERNOON
     FOR AKZ028.
         STRONG WIND UNTIL 7 PM AKDT THIS EVENING FOR AKZ018-019.
         STRONG WIND FROM SATURDAY AFTERNOON THROUGH SATURDAY EVENING FOR
     AKZ018.
MARINE...GALE WARNING FOR PKZ012-033>036-041-042.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031-032-043-051-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

$$

RWT/PRB

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