Small Craft Advisory 330, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
821 AM AKDT SUN APR 17 2016

.SYNOPSIS...A LOW WEST OF THE DIXON ENTRANCE WILL TRACK NORTHWEST
ALONG THE OUTER COAST THROUGH SUNDAY EVENING...THEN DISSIPATE
INLAND WEST OF YAKUTAT BAY SUNDAY NIGHT.

&&

.SHORT TERM...A 1009MB LOW JUST WEST OF THE DIXON ENTRANCE AS OF
EARLY THIS MORNING IS PRODUCING STRONG WIND GUSTS ON PRINCE OF
WALES ISLAND AS WELL AS IN THE KETCHIKAN AND METLAKATLA AREAS. THE
LOW IS TRACKING NORTH OVER THE EXTREME EASTERN GULF AND WILL
PRODUCE GUSTY CONDITIONS ALONG THE OUTER COAST THROUGH THE DAY.
INTERIOR LOCATIONS MAY SEE SOME GUSTS AS WELL TODAY, BUT NOT AS
STRONG AS ALONG THE OUTER COAST AND NEAR CLARENCE STRAIT. THE LOW
WILL SLOWLY PULL AWAY FROM THE COAST BEGINNING THIS AFTERNOON AND
IS EXPECTED TO DISSIPATE INLAND TONIGHT JUST WEST OF YAKUTAT.

ACCOMPANYING THE LOW IS A FRONT THAT HAS ALREADY PRODUCED HEAVY
RAIN OVER THE SOUTHERN PANHANDLE. MODERATE TO HEAVY RAIN WILL
OCCUR OVER THE SOUTHERN TWO THIRDS OF THE PANHANDLE TODAY. BY THIS
EVENING AS THE LOW BEGINS TO MOVE MORE TO THE WEST, A WEAKNESS IN
THE FRONT WILL FORM ALONG THE CHATHAM STRAIT / LYNN CANAL
CORRIDOR. HEAVY RAIN WILL CONTINUE TONIGHT EAST OF THIS LINE AND
SOUTH OF FREDERICK SOUND AND LIKELY CONTINUE INTO THE EARLY PART
OF THE EXTENDED RANGE FORECAST PERIOD BEFORE AN UPPER TROUGH
DISPLACES IT TO THE EAST INTO CANADA.

UPDATED PRESSURE AND WIND WITH GFS22 TODAY. POP UNCHANGED BUT QPF
UPDATED WITH THE LATEST NAM DNG5. TEMPS ADJUSTED USING GFS MOS AND
RESULTED IN WARMER HIGHS FOR A FEW LOCATIONS BY 1 TO 3 DEGREES.
OVERALL FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...PERSISTENT WEST COAST UPPER RIDGE CONTINUES TO BE
THE MAJOR PLAYER IN THE LONG RANGE FORECAST. THIS TIME INSTEAD OF
BEING THE CAUSE OF A LOT OF WET WEATHER FOR THE PANHANDLE, IT
WILL ACTUALLY BRING SOME DRY WEATHER TO THE AREA FOR MID WEEK.
HOWEVER, WE STILL HAVE ONE LAST SHORT WAVE TROUGH RIDING NORTH
ALONG A STALLED FRONT OVER THE SOUTHERN PANHANDLE TO DEAL WITH.

AT THE START OF THE LONG RANGE, THE FRONT STALLED OVER THE
SOUTHERN PANHANDLE WILL BEGIN TO MOVE OUT OF THE AREA AS THE LAST
SHORT WAVE MOVES THROUGH. STEADY RAIN FROM THE FRONTAL BANDS WILL
CHANGE OVER TO SHOWERS AS WE GO THROUGH MON. THESE SHOWERS IN TURN
WILL RAPIDLY DRY UP AS A PROGRESSIVE RIDGE ALOFT ALLOWS THE WEST
COAST UPPER RIDGE TO EXPAND WESTWARD AND BUILD A SURFACE RIDGE
INTO THE AREA BY TUE. EXPECT MOST AREAS TO BE DRY WITH DEVELOPING
HOLES IN THE CLOUD COVER BY TUE. ONE CHANGE OVER THE PREVIOUS
FORECAST IS A STRONGER PRESSURE GRADIENT BETWEEN THE RETREATING
FRONT AND THE BUILDING SURFACE RIDGE DEVELOPING OVER THE PANHANDLE
ON MON INTO MON NIGHT (FORECAST PRESSURE GRADIENTS REACHING AROUND
2 TO 2.5 MB BETWEEN JUNEAU AND SKAGWAY AT THAT TIME). DECIDED TO
RAISE SOME WIND SPEEDS IN THIS TIME PERIOD WITH LYNN CANAL SEEING
THE MOST DRASTIC CHANGE (INCREASED WINDS TO 30 KT MON AFTERNOON
INTO MON EVENING IN NORTHERN LYNN). ALSO CONTINUED THE TREND OF
RAISING HIGH TEMPS FOR WED AND THU AS AN AREA OF HIGH THICKNESS
VALUES WILL BE MOVING INTO THE AREA THEN.

THERE ARE SOME NEW DEVELOPMENTS IN THE EXTENDED PERIOD AS FAR AS
WHAT THE LONG RANGE MODELS ARE SUGGESTING. THE ECMWF IS NOT AS DRY
AS IT ONCE WAS NOR IS THE GFS AS WET AS IT WAS FOR THU INTO FRI AS
THEY ARE COMING INTO BETTER AGREEMENT ON HOW TO HANDLE THE SHORT
WAVE ENERGY IN THE NE PACIFIC. BOTH MODELS NOW FEATURE A WEAK
SHORT WAVE TROUGH AND VORT MAX SNEAKING INTO THE PANHANDLE FROM
THE ESE THU EVENING BRINGING THE CHANCE OF RAIN WITH IT. FEATURE
IS NOTICEABLY STRONGER IN THE GFS THEN THE ECMWF AT THIS MOMENT.
THINGS RAPIDLY DIVERGE FROM THERE AS THE GFS BRINGS ANOTHER SHORT
WAVE IN FROM THE SAME DIRECTION AND ALSO BRINGS AN UPPER LOW INTO
THE SE GULF FOR NEXT WEEKEND (WETTER FORECAST) WHILE THE ECMWF
DOES NOT (DRIER FORECAST). NEEDLESS TO SAY THAT THE EXTENDED
FORECAST PAST THU REMAINS RATHER UNCERTAIN SO ELECTED TO KEEP THE
CHANCE POPS AND MOSTLY CLOUDY SKIES IN THE FORECAST FOR THU NIGHT
AND BEYOND.

&&

.AVIATION...MAIN IMPACT TO AVIATION OPERATIONS WILL BE LOW LEVEL
TURBULENCE AND WIND SHEAR TODAY AS THE LOW DISCUSSED IN THE SHORT
TERM PARAGRAPH TRACKS NNW ALONG THE OUTER COAST. WIND SHEAR AND
TURBULENCE WILL NOT BE LIMITED TO JUST THE OUTER COAST, AS THE LOW
LEVEL JET WITH WIND SPEEDS TO 50 KTS COVERS MOST OF THE PANHANDLE
SOUTH OF THE ICY STRAIT CORRIDOR BY LATE THIS MORNING. WIND SHEAR
AND LOW LEVEL TURBULENCE WILL HIT THE YAKUTAT AREA BY LATE
EVENING. OTHERWISE, MVMC CONDITIONS DUE TO CIGS AND VISIBILITY
REDUCTIONS IN HEAVIER RAIN / SHOWERS WILL PREVAIL THROUGH TONIGHT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 1 PM AKDT THIS AFTERNOON FOR AKZ027-028.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-034>036-041>043-051.
&&

FRITSCH/EAL

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