Area Forecast Discussion
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000
FXAK67 PAJK 110018
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
418 PM AKDT THU JUL 10 2014

.SHORT TERM...LOW PRESSURE WILL DEEPEN AND MOVE N INTO THE FAR
WRN GULF TONIGHT. OCCLUDED FRONT OVER THE W-CENTRAL GULF WILL
MOVE TO THE ERN GULF FRI...BUT BEGIN TO SLOW ITS EWD MOVEMENT
LATE IN THE DAY.

 MAIN CONCERNS ARE THE DEVELOPING FLOOD SITUATION FOR MENDENHALL
LAKE AND RIVER...PRECIP POTENTIAL/AMOUNTS...AND WINDS. WILL
DISCUSS  THE FLOOD SITUATION IN THE HYDROLOGY SECTION BELOW. AS
FOR PRECIP POTENTIAL...MODELS HAVE TRENDED SLIGHTLY FURTHER E
WITH THE PRECIP THRU DAYTIME FRI. STILL SOME DIFFERENCES ON HOW
FAR E IT GETS BY LATE FRI AFTERNOON. DECIDED TO USE A BLEND OF
THE 12Z GFS/EC/GEM TO HANDLE THE PROGRESSION OF THE PRECIP TO THE
E AND FOR RAINFALL AMOUNTS. SHOULD HAVE PRECIP INCREASING IN THE
PAYA AREA TONIGHT...AND IT WILL LIKELY BE HEAVY AT TIMES LATE
TONIGHT AS STRONG SLY LOW LEVEL JET MOVES INTO THAT AREA. PRECIP
SHOULD REACH THE PAEL AREA EARLY FRI MORNING...AND WILL LIKELY
GET AS FAR E AS THE PAJN AREA BY LATE FRI AFTERNOON. THE HEAVIER
PRECIP SHOULD GRADUALLY SHIFT TOWARD THE PAEL AREA FRI AFTERNOON
AS LOW LEVEL JET AXIS SHIFTS EWD WITH THE FRONT. RAINFALL AMOUNTS
COULD BE OVER 3 INCHES IN THE PAYA AREA THRU FRI AFTERNOON...AND
1-2 INCHES AROUND PAEL BY LATE FRI AFTERNOON. AMOUNTS SHOULD DROP
OFF RAPIDLY TO THE E...WITH GENERALLY LESS THAN A TENTH OF AN
INCH IN THE PAJN AREA BY EARLY FRI EVENING.

 AS FOR WINDS...LOOKS LIKE GALE FORCE WINDS WILL SPREAD NE INTO
THE CENTRAL AND NRN GULF TONIGHT AS FRONT MOVES IN. THE WINDS
AHEAD OF THE FRONT SHOULD SLOWLY WEAKEN AS IT MOVES FURTHER E AND
AWAY FROM THE MAIN LOW CENTER OVER THE FAR WRN GULF...BU STILL
EXPECT SCA LEVEL WINDS OVER MUCH OF THE REMAINDER OF THE GULF.
DOES NOT LOOK LIKE THE STRONGER WINDS WILL REACH THE INNER
CHANNELS THRU FRI AFTERNOON. LYNN CANAL WILL SEE STRONGEST WINDS
OVER THE INNER CHANNELS DUE TO THERMALLY ENHANCED S FLOW...WITH
20 KT WINDS DURING THE AFTERNOON AND EARLY EVENING PERIODS...BUT
DIMINISHING TO 10 KT DURING THE OVERNIGHT HOURS. THE 15-20 KT NW
WINDS OVER THE FAR SERN AREA SHOULD WEAKEN TO ABOUT 10 KT
TONIGHT.

 OTHERWISE...WILL HAVE A THIN LAYER OF STRATOCU CLOUDS HANG
AROUND OVER THE NW 2/3RDS OF THE AREA TONIGHT. THE SERN THIRD
WILL LIKELY SCATTER OUT CLOUD WISE BY EARLY EVENING...ALTHOUGH
SOME THIN HIGH CLOUDS WILL DRIFT IN FROM THE W OVERNIGHT. SHOULD
SEE CLOUDS INCREASE SLOWLY OVER THE WRN PART OF THE SRN PANHANDLE
FRI. LOOKS LIKE A FAIRLY WARM DAY OVER THE SERN AREA FRI...WITH
MANY AREAS GETTING INTO THE 70S. HYDER LOOKS LIKE IT COULD GET
INTO THE LOWER 80S. DID LOWER MAX TEMPS SOME OVER THE MORE ERN
PART OF THE NRN INNER CHANNELS FRI DUE TO FASTER ONSET OF PRECIP.



 &&

 .HYDROLOGY...SUICIDE BASIN IS CURRENTLY EMPTYING OUT INTO THE
MENDENHALL LAKE AND RIVER SYSTEM. GIVEN THE AMOUNT OF WATER THAT
WAS IN THE BASIN AND WHAT THE LAKE AND RIVER LEVELS WERE WHEN
EVENT STARTED...RECORD FLOODING IS EXPECTED FOR BOTH THE LAKE AND
RIVER. CURRENT FORECAST MAX STAGE IS 11.7 FEET FOR THE LAKE AND
14.6 FEET FOR THE RIVER. EVENT IS UNFOLDING FASTER THAN PAST
YEARS...AND IT LOOKS LIKE THE PEAK OF THE FLOOD WILL BE SOMETIME
FRI NIGHT. CURRENT FORECAST HAS WATER LEVELS DROPPING RAPIDLY ON
SAT. WILL UPDATE THE FLOOD WARNING TO INCLUDE OTHER IMPACTS SINCE
THE WATER IS EXPECTED TO BE SO HIGH. THE BANKS OF THE MENDENHALL
RIVER WILL BE A DANGEROUS PLACE TO BE WHEN THE FLOODING BEGINS AS
THEY WILL BE VULNERABLE TO EROSION DUE TO THE HIGH AND SWIFT
WATER. WILL ALSO HAVE TO KEEP AN EYE ON THE CHILKAT AND TAIYA
RIVERS FOR FRI NIGHT THRU SAT NIGHT WITH THE RAIN COMING INTO
THAT AREA.

 &&

.LONG TERM...MAIN EFFORT TODAY WAS ON THE BEGINNING OF THE
EXTENDED PERIOD FRI NIGHT TO SUN. EVENTS TO WATCH DURING THIS
PEIOD ARE THE MENDENHALL FLOOD AND WAVY FRONTAL SYSTEM CAUSING
TRICKY POP/QPF DETAILS IN THE GRAPHIC FORECASTS. LIKE SHORT TERM
FORECAST... I TENDED TO USE A BLEND OF THE 12Z GFS/GEM/EC.

FLOOD WARNING DETAILS COVERED WELL IN HYDRO SECTION ABOVE. THE
FRONT APPROACHING THE COAST TONIGHT WILL HAVE A TIGHT GRADIENT OF
RAINFALL RATE WITH IT. ALONG AND JUST AHEAD OF THE FRONT THERE
WILL BE HEAVY PCPN. THE WAVY NATURE OF THE FRONT MAKES IT HARD TO
SAY BUT DECIDED TO BRING A BRIEF PERIOD OF MODERATE RAIN AS FAR
EAST AS JUNEAU TO ANGOON TO SITKA LINE LATE FRI NIGHT AND EARLY
SAT MORNING THEN PULL HEAVIEST PRECIPITATION BACK TO THE WEST
CLOSER TO THE COAST. THE PERIOD OF HEAVIEST RAINS LATE FRI TO EARLY
SAT COINCIDES WITH THE PREDICTED PEAK WATER LEVELS AND FLOW WITH
THE MENDENHALL FLOOD. RAIN TOTALS IN THE MENDENHALL BASIN FROM FRI
AFTERNOON TO SAT AFTERNOON SHOULD BE AROUND ONE INCH. ALSO IN
THAT SAME TIME FRAME WILL BE HIGH TIDE /130 AM SAT/ WHICH WILL
LIKELY BACK THE WATER IN LOWER MENDENHALL RIVER. THE GOOD NEWS IS
THERE IS A MINUS TIDE SAT MORNING SO FLOOD WATERS SHOULD RECEDE
QUICKLY SAT.

LITTLE CHANGE MADE TO THE REST OF THE EXTENDED PERIOD FOR NEXT
WEEK. I DID GRADUALLY REDUCE THE CHANCE OF RAIN FROM MON TO WED
THAN THE PREVIOUS FORECASTS HAD.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...AREAL FLOOD WARNING UNTIL 10 PM AKDT SATURDAY FOR AKZ025.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ042-043-051.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041.

&&

$$

RWT/TA





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