Gale Warning 280, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
359 PM AKDT WED SEP 9 2015

.SHORT TERM...A GALE FORCE OCCLUDED FRONT WILL MOVE INTO THE
CENTRAL GULF THIS EVENING...THEN COME ASHORE OVER THE NRN
PANHANDLE THU. A LOW PRESSURE WAVE WILL DEVELOP ON THE FRONT AND
MOVE NE INTO THE ERN GULF THU AFTERNOON. THE MODELS DIFFERED A BIT
ON THE TIMING OF THE LOW PRESSURE WAVE...WITH THE 12Z NAM AND
ECMWF BEING FAIRLY CLOSE ON IT. USED THE 12Z NAM THRU THU.

MAIN FORECAST CONCERNS WILL BE PRECIP POTENTIAL/AMOUNTS AND
WINDS. RIGHT NOW...RAIN IS OCCURRING OVER THE NE GULF INCLUDING
THE PAYA AREA. EXPECT THE RAIN TO SPREAD INTO THE NRN PANHANDLE
THIS EVENING...THEN REACH ALL BUT THE FAR SERN PANHANDLE BY LATE
TONIGHT. THAT AREA SHOULD GET INTO THE FRONTAL RAIN THU MORNING.
THE FAR SERN AREA MAY GET SPRINKLES OR A LITTLE LIGHT RAIN BEFORE
THAT AS LOW LEVEL MOISTURE FROM REMAINS OF IGNACIO IS STILL IN
THAT AREA...ALTHOUGH MOST OF THIS PRECIP WILL LIKELY STAY TO THE
SE OF THERE.

AS FOR RAINFALL AMOUNTS...GIVEN THE VERY HIGH PRECIP WATER
VALUES AND STRONG S-SW UPSLOPE FLOW DEVELOPING AHEAD OF THE
FRONT...IT IS LOOKING LIKE A HEAVY RAIN EVENT FOR THE NW 2/3RDS OF
THE PANHANDLE THRU THU. RAINFALL OF 1.5 TO 3.5 INCHES IS POSSIBLE
BY LATE THU AFTERNOON...WITH SRN AND SWRN SLOPES OF THE CENTRAL
AND NRN PANHANDLE GETTING THE MOST RAINFALL. THE HEAVIER RAIN WILL
STAY N OF THE FAR SERN AREA THRU THU AFTERNOON...WITH ONLY 0.2 TO
0.5 INCHES OF RAIN EXPECTED THERE.

AS FOR WINDS...GALE FORCE S-SE WINDS ARE EXPECTED AHEAD OF THE
FRONT. THESE SHOULD REACH THE FAR WRN MARINE AREAS THIS
EVENING...THEN MOST OF THE REMAINDER OF THE ERN GULF MARINE AREAS
BY LATE TONIGHT. 25-35 KT WINDS WILL LIKELY REACH THE NRN AND
CENTRAL INNER CHANNELS LATE TONIGHT AND THU MORNING...THEN REACH
THE FAR SERN AREA THU. WITH PEAK 925 MB FLOW OF 40-50 KT ALONG
THE CENTRAL INNER CHANNELS THU...WENT WITH STRONG WIND HEADLINES
FOR ZONES 25 AND 26 THU. MAY ALSO SEE STRONG WINDS ALONG THE OUTER
COAST. DID PUT IN STRONG WIND HEADLINE FOR ZONE 27 THU MORNING
DURING THE CLOSEST APPROACH OF THE FRONT BEFORE IT DRIFTS A BIT
NWD AS LOW PRESSURE WAVE MOVES NE ALONG IT. IT WILL BE CLOSE TO
STRONG WIND HEADLINES FOR THE CENTRAL COAST AND ADJACENT INNER
CHANNELS...AND LATER SHIFTS MAY NEED TO ADD THEM IN.

.LONG TERM...MAIN FORECAST CHALLENGE IN THE LONG TERM ARE THE
EXACT PLACEMENT AND TRACK OF TWO WAVES OF LOW PRESSURE FORECAST TO
DEVELOP ALONG THE FRONTAL BOUNDARY ON THURSDAY AND RIDE NORTHEAST
ALONG THE FRONT THROUGH FRIDAY. MODELS HAVE BEEN TRENDING FARTHER
NORTH WITH THE FIRST WAVE WHICH IS FORECAST TO COME ONSHORE THE NE
AND E GULF COAST ON THURSDAY EVENING. AS THIS HAPPENS...RAINFALL
RATES SHOULD INCREASE SIGNIFICANTLY OVER THE NORTHERN AND CENTRAL
PANHANDLE AS A MID LEVEL SHORTWAVE...COMBINED WITH SOME LEFT EXIT
REGION DYNAMICS FROM A 130 KT 300MB JET LIFT AIR THAT IS RICH IN
TROPICAL MOISTURE. AS MENTIONED YESTERDAY...PRECIPITABLE WATER
VALUES WITH THIS SYSTEM ARE AROUND 2 STANDARD DEVIATIONS ABOVE
NORMAL FOR THIS TIME OF YEAR FROM THE GFS ENSEMBLES AND THIS IS
SUPPORTED BY HIGH SATELLITE DERIVED RAIN RATES SEEN EARLIER TODAY
OVER THE GULF WITH THIS WAVE.

THIS SHOULD BE A FAIRLY QUICK MOVING SYSTEM AND AS THE FIRST WAVE
PUSHES THROUGH THE PANHANDLE ON THURSDAY NIGHT...THE SECOND AND
WEAKER WAVE IS AIMED MORE AT THE SOUTHERN ZONES FOR FRIDAY. THIS
IS ALSO A VERY MOIST SYSTEM...ALTHOUGH IT DOES LOSE SOME OF THE
DYNAMICAL SUPPORT OF THE FIRST WAVE AND SO EXPECT RAINFALL RATES
TO PICK UP IN THE SOUTH LATE THURSDAY NIGHT AND CONTINUE THROUGH
THE DAY ON FRIDAY. WINDS WILL CONTINUE TO BE AN ISSUE WITH A
STRONG LOW LEVEL JET DEPICTED ON MOST OF THE GUIDANCE TO LAST
THROUGH EARLY MORNING ON FRIDAY AND EVEN THROUGH EARLY AFTERNOON
DOWN SOUTH AS THE SECOND WAVE MOVES ON SHORE. 925 MB WINDS ON THE
NAM ARE NEAR 50 KT ON THURSDAY NIGHT FROM JUNEAU SOUTH AND SO WENT
WITH WIDESPREAD GALES OVER THE INNER CHANNELS WITH STRONG WIND
HEADLINES IN SKAGWAY...JUNEAU...AND PETERSBURG...WRANGELL THROUGH
THURSDAY NIGHT. MENTIONED HIGHER GUSTS IN THE SOUTHERN ZONES ON
THURSDAY NIGHT THROUGH FRIDAY WITH THE OPTION OF GOING WITH STRONG
WIND HEADLINES ON LATER SHIFTS.

FROM SATURDAY NIGHT ONWARD...CONTINUED WITH THE TREND OF WPC
GUIDANCE AS WITH THE FAST FLOW AND MODELS WAFFLING BETWEEN HOW TO
HANDLE REMNANT TROPICAL SYSTEMS CONTINUES.

&&

.HYDROLOGY...WITH HEAVY RAIN EXPECTED FOR MUCH OF THE NRN AND
CENTRAL PANHANDLE...RIVERS AND STREAMS WILL RISE SIGNIFICANTLY.
AFTER COORD WITH RFC...A FLOOD WATCH WAS ISSUED FOR ALL BUT THE
FAR SERN PANHANDLE FOR THU INTO FRI. ALSO MENTIONED MUDSLIDE
THREAT DUE TO COMBINATION OF HEAVY RAIN AND STRONG WINDS. RAINFALL
UP TO 6 INCHES IS POSSIBLE THRU FRI.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
     FOR AKZ025-026.
         FLOOD WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY AFTERNOON FOR
     AKZ017>026.
         STRONG WIND FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON FOR
     AKZ027.
         STRONG WIND FROM THURSDAY AFTERNOON THROUGH FRIDAY MORNING FOR
     AKZ018.
MARINE...GALE WARNING FOR PKZ031-032-034-036-042-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-033-035-041-053.

&&

RWT/LEVIN

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