Flood in Alaska, September 11 to 12, 2013

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
347 PM AKDT WED SEP 11 2013

.SHORT TERM...A WEAKENING OCCLUDED FRONT OVER THE FAR ERN GULF
WILL MOVE ONSHORE OVER THE NRN PANHANDLE THIS EVENING...THEN
DISSIPATE OVER THE CENTRAL PANHANDLE EARLY THU MORNING. HIGH
PRESSURE WILL BUILD OVER THE ERN GULF AND SE AK THU. USED BLEND
OF LATEST ECMWF/UKMET/GEM WITH PREVIOUS GRIDS FOR TONIGHT AND
THU.

 MAIN FORECAST ISSUES WILL BE PRECIP POTENTIAL AND WINDS. RIGHT
NOW PRECIP IS BASICALLY LIMITED TO THE ERN GULF AND PAYA
AREA...WITH MODERATE RAIN FALLING IN PAYA ATTM. THIS BAND OF
PRECIP SHOULD PUSH TO THE NRN OUTER COAST BY EARLY THIS
EVENING...THEN REACH THE PAJN AREA BY LATE EVENING. AS PRECIP
MOVES EWD...THE RAINFALL RATES WILL BE DECREASING AS THE FRONT
WEAKENS. THERE COULD BE A SHORT DURATION BURST OF MODERATE RAIN
AROUND PAEL/PAGS AREAS THIS EVENING AS FRONT MOVES THRU. LOOKS
LIKE PRECIP BAND WILL FALL APART LATE TONIGHT AND EARLY THU
MORNING OVER THE CENTRAL AREA AS THE FRONT DISSIPATES.

 AS FOR WINDS...RIGHT NOW WINDS OF SCA LEVEL ARE CONFINED TO NRN
LYNN CANAL. THINK THIS WILL CONTINUE THIS EVENING AS STRONG SW
MID-LEVEL FLOW WILL REMAIN THERE UNTIL LATE EVENING...WHEN
PASSAGE OF MID-LEVEL TROF SHOULD DIMINISH THIS FLOW. WINDS ARE
NEAR SCA LEVEL AROUND CAPE SPENCER...WITH AROUND 20 KT S-SW WINDS
THERE. THESE WINDS SHOULD WEAKEN SOME LATE THIS AFTERNOON...THEN
AFTER FRONT PAST THEM A WNW TIP JET MAY DEVELOP THERE THIS
EVENING. AT THIS POINT ONLY GOING FOR 20 KT WLYS LATER THIS
EVENING IN CROSS SOUND...BUT IT IS POSSIBLE THEY MAY HAVE A SHORT
PERIOD OF STRONGER WINDS. OVER THE FAR SERN AREA...HAVE NW
15-20 KT WINDS GOING ON IN CLARANCE STRAIT...AND THESE MAY
DIMINISH TO AROUND  15 KT TOWARD DAYBREAK THU. AS HIGH PRESSURE
RIDGE BUILDS OVER THE ERN GULF THU...NW WINDS SHOULD PICK UP OVER
THE SE GULF TO AROUND 15 KT.

 OTHERWISE...WILL HAVE PATCHY MARINE FOG ALONG THE CENTRAL OUTER
COAST AHEAD OF THE FRONT...BUT ONCE THE FRONT PASSES THRU LATER
TONIGHT...SHOULD SEE THAT GET MIXED OUT. COULD BE SOME FOG AROUND
PAYA AND OVER THE SRN AREA TONIGHT AND THU MORNING AS WELL. BEST
CHANCE TO GET THICKER FOG IS AROUND PAPG/PAWG AREAS WHERE CLOUDS
SHOULD HOLD OFF LONG ENOUGH AND WINDS BECOME LIGHT ENOUGH FOR FOG
TO DEVELOP THERE BY LATE EVENING. A BAND OF LOW CLOUDS TRAPPED
UNDER AN INVERSION WILL LIKELY SPREAD SE INTO THE SRN INNER
CHANNELS OVERNIGHT TONIGHT...DESPITE THE NW LOW LEVEL FLOW.
SHOULD SEE THESE CLOUDS DISSIPATE THU AS INVERSION WEAKENS AND
DRIER AIR MOVES IN FROM THE NW. FOR MUCH OF THE AREA THU
AFTERNOON IT LOOKS LIKE IT WILL BE FAIRLY NICE AS CLOUDS
ASSOCIATED WITH REMNANT OF THE FRONT DISSIPATE BY AROUND MIDDAY.

.LONG TERM...OVERALL THERE IS NOT MANY ISSUES WITH THE FORECAST
MODELS THROUGH THE MID RANGE BUT BY SATURDAY INTO EARLY NEXT WEEK THE
MODEL BEGIN TO GO IN THEIR DIFFERENT WAYS WITH LARGE SPREADS IN
THE ENSEMBLES. NOT MANY CHANGES WERE DONE THROUGH SAT MORNING WITH MAINLY
DRY CONDITIONS WITH THE WETTEST AREA OVER THE NORTH GULF COAST.
THE BIGGEST CHANGE WAS SKI COVER AND TEMPS OVER THE SOUTHERN
AREAS. THERE WILL BE MOSTLY SUNNY SKIES OVER THE SOUTHERN HALF
FROM STRONG SUBSTANCE PRODUCED BY THE BUILDING RIDGE AND WITH 850MB
TEMPS NEAR +14 TEMPS WILL RISE INTO THE 70S TO BE ABOVE NORMAL
FROM FRIDAY INTO SUNDAY. WINDS WILL REMAIN ON THE LIGHTER SIDE
THROUGH MOST OF THE LATE WEEK BUT THERE WILL BE SOME STRONGER
NORTHERLY WINDS THAT WILL DEVELOP SATURDAY INTO SUNDAY AS HIGH
BUILDS INTO THE INTERIOR. AT THIS TIME SPEEDS WILL BE LESS THAN 15
KT BUT THEY COULD GET AS HIGH AS 20KT IN NORTHERN LYNN.

A UPPER LOW WILL MOVE INTO THE FAR SOUTHERN GULF OVER THE WEEKEND
FROM THE WEST AND SLOWLY DRIFT ALONG 50N TO BE OVER THE FAR
SOUTHEAST GULF BY SUNDAY NIGHT. THERE WILL BE A LEAD FRONT THAT
WILL BE WEAKENING AS IT DRIFT EAST ACROSS THE NORTHERN GULF WITH A
CHANCE OF SOME PRECIP. THIS FRONT IS WEAKENING SO DO NOT EXPECT
THERE WILL MUCH RAIN BUT THERE WILL BE A CHANCE LATE SAT INTO SUNDAY.
AS THE LOW MOVES INTO THE SE GULF ON SUNDAY MAY SEND BANDS OF
PRECIP OVER THE AREA FROM THE SOUTH TO NORTH BUT THERE IS
UNCERTAINTY WITH THE TRACK OF THIS SYSTEM SO THERE IS LOW
FORECASTER CONFIDENCE FROM SAT INTO NEXT WEEK. UPDATED THE
EXTENDED FORECAST WITH THE LATEST WPC.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

RWT/ABJ