Small Craft Advisory 116, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
349 PM AKST MON FEB 1 2016

.SHORT TERM...RATHER QUIET DAY ACROSS THE AREA WITH SOME AREAS OF
LOW CLOUDS AND FOG/LIGHT SNOW TODAY. A WEAK UPPER LEVEL WAVE
MOVING THOUGH THE EXTREME NORTHERN PANHANDLE IS RESPONSIBLE FOR
THE LIGHT SNOW THAT HAS BEEN OBSERVED IN PLACES LIKE HAINES,
SKAGWAY, JUNEAU, AND GUSTAVUS THIS MORNING. ACCUMULATIONS HAVE
BEEN LIGHT WITH MOST PLACES SEEING ONLY AROUND A TENTH OF AN INCH.
THE EXCEPTION IS HAINES WHERE 1.4 INCHES FELL LAST NIGHT.
OTHERWISE MOST PLACES ARE DRY. AS FOR WINDS, INNER CHANNEL AREAS
ARE EASTERLY OR SOUTHERLY WINDS AT 20 KT OR LESS. HIGHEST WINDS
ARE IN LYNN CANAL WHERE ELDRED ROCK IS BLOWING AROUND 20 KT AS OF
MID DAY.

THE PERIODS OF LIGHT SNOW IN THE NORTH WILL GRADUALLY BE
DIMINISHING TONIGHT AS THE WEAK WAVE MOVES OFF TO THE EAST. ANY
ADDITIONAL ACCUMULATIONS WILL BE LESS THEN 1 INCH AS THERE IS
HARDLY ANY MOISTURE FOR THE SYSTEM TO WORK WITH.

FOCUS THEN SHIFTS TO THE BOUNDARY THAT CONTINUES TO LINGER IN THE
GULF TODAY. A DEVELOPING LOW ALONG THE BOUNDARY NEAR 50N 140W,
WILL PRESS THE FRONT INTO THE PANHANDLE ON TUE. THE LOW ITSELF
WILL STAY OFFSHORE AND EVENTUALLY WEAKEN TO AN OPEN WAVE BY TUE
AFTERNOON. AS THE FRONT APPROACHES THE SOUTHERLY WINDS ACROSS THE
NORTHERN INNER CHANNELS WILL CHANGE TO MORE OF A NORTHERLY
DIRECTION EARLY TUE AS PRESSURE GRADIENTS FLIP. WINDS FARTHER
SOUTH SHOULD STAY SOUTHERLY (AND WILL INCREASE TO 30 KT IN
CLARENCE STRAIT) AS SYNOPTIC FLOW IS ENOUGH TO OVERPOWER THE
PRESSURE GRADIENT FORCING.

AS FOR PRECIP, SOUTHERN OUTER COAST WILL SEE IT FIRST LATE
TONIGHT OR EARLY TUE WITH THE REST OF THE PANHANDLE, EXCEPT THE
EXTREME NORTH (PRECIP HAS NOT GOTTEN THAT FAR NORTH YET) AND
EASTERN PANHANDLE (BRITISH COLUMBIA RIDGE PUSHING MOST OF THE
PRECIP WEST), GETTING INTO IT BY TUE AFTERNOON. SOUTHERLY FLOW
ACCOMPANYING THIS FRONT SHOULD PUSH ENOUGH WARM AIR INTO THE INNER
CHANNELS THAT MOST SOUTHERN AND CENTRAL PANHANDLE AREAS WILL SEE
RAIN WHEN THE PRECIP STARTS ON TUE. THE NORTHERN INNER CHANNEL
AREAS MAY SEE SOME LIGHT SNOW BEFORE CHANGING OVER TO RAIN DURING
THE AFTERNOON WITH LITTLE OR NO ACCUMULATION EXPECTED. PRECIP
AMOUNTS WILL MAINLY BE AFFECTED BY THE INTERACTION WITH THE RIDGE
IN BRITISH COLUMBIA, LOW PRECIPITABLE WATER VALUES ASSOCIATED
WITH THE SYSTEM, AND THE FRONT ITSELF BEING RELATIVELY WEAK. SO
FORECAST AMOUNTS WILL BE AROUND A QUARTER INCH OR LESS WITH THE
HIGHEST AMOUNTS EXPECTED ALONG THE OUTER COAST.

SHORT RANGE MODELS HAD SOME MINOR ISSUES ON WHERE THE LOW ON THE
FRONT IS ACTUALLY DEVELOPING. THE GFS WAS A LITTLE TOO FAR TO THE
WEST AND MOVES IT TO THE NW FASTER THEN THE OTHERS. ECMWF AND NAM
SEEMED TO HAVE A BETTER HANDLE ON THE MOVEMENT AND POSITION OF THE
FEATURE TODAY SO DECIDED TO USE THEM FOR ANY UPDATES TODAY.

.LONG TERM...RATHER ACTIVE WEATHER PATTERN FOR THE EXTENDED RANGE.
A SERIES OF LOW PRESSURE SYSTEMS AND FRONTS WILL CROSS OVER THE AK
GULF AND PANHANDLE UNTIL THE WEEKEND WHEN HIGH PRESSURE RIDGE
MOVES OVER THE AREA...FOLLOWED BY ANOTHER FRONT. MODELS ARE JUST
STARTING TO SHOW SOME AGREEMENT FOR WAVE DEVELOPMENT OVER THE
GULF LATER IN THE WEEK, BUT STILL LARGE VARIATIONS IN EXACT TIMING
AND STRENGTH. FOR THE LARGER LOW PRESSURE SYSTEM ON THE WESTERN
PERIPHERY OF THE GULF AND ASSOCIATED FRONTS MOVING EAST MODELS
HAVE SHOWN BETTER AGREEMENT. WHAT IS NOW EXPECTED FOR THE WEEK IS
STRONGER WINDS, MORE PRECIP AND HIGHER QPF. TEMPERATURES HAVE
BEEN TRICKY WITH MOS GUIDANCE HAVING A RAIN SNOW LINE SOMEWHERE
OVER THE CENTRAL PANHANDLE, WHICH MEANS THERE IS POTENTIAL FOR
SNOW ACCUMULATION IN THE 2 TO 4 INCH RANGE THURSDAY INTO FRIDAY,
AND POSSIBLY MORE.

AFTER THE FIST WEAK FRONT EARLY TUESDAY EVENING DISSIPATES A GALE
FORCE FRONT CROSSES OVER THE EASTERN GULF THROUGH WEDNESDAY. MOST
ENERGY AND LOW LEVEL WINDS HOLD MORE OFFSHORE WITH THIS FRONT, BUT
PRECIP BANDS WILL MOVE OVER THE ENTIRE PANHANDLE. THIS WEDNESDAY
FRONT NOT PRODUCING SIGNIFICANT QPF AMOUNTS AND WITH TEMPS AT OR
ABOVE FREEZING NO REAL SNOW ACCUMULATION. FOR THURSDAY THE
QUESTION WAS IF A WAVE WOULD DEVELOP ALONG FRONTAL BOUNDARY AND
MOVE INTO THE GULF. THE 12Z MODELS ALL STARTED TO SHOW THIS WAVE,
GFS STILL FASTER WITH A DEEPER CLOSED LOW. HIGHER CONFIDENCE THAT
THIS WAVE WILL AT LEAST PRODUCE GALE FORCE WINDS BUT POTENTIAL FOR
HIGHER WINDS. AS THIS WAVE CENTER IS CLOSER TO THE COAST GETTING A
STRONGER LOW LEVEL JET MOVING OVER THE PANHANDLE AND THUS
PRODUCING HIGHER INLAND WINDS, MAINLY FOR THE SOUTHERN AND
CENTRAL PANHANDLE. NORTHERN INNER CHANNEL WINDS PICKING UP AS THE
WAVE PRODUCES A NORTH-SOUTH GRADIENT WHEN PREVIOUS MODEL RUNS HAD
A MORE PARALLEL GRADIENT. FOR NOW EXPECT GALES FOR THE INNER
CHANNELS WITH POTENTIAL OF HIGHER VALUES IF THIS WAVE IS DEEPER.
GETTING MUCH HIGHER QPF VALUES FROM BOTH GFS AND ECMWF ALONG WITH
NAEFS ENSEMBLE PRECIPITABLE WATER VALUES FOR THIS TIME UPWARDS OF
+1.5. WARM AIR MASS MOVING UP WITH THE WAVE MAY MOVE FAR ENOUGH NORTH
TO HAVE THIS HEAVIER PRECIP FALL MAINLY AS RAIN, BUT STILL BIT
EARLY TO NAIL THIS DOWN. BY THE WEEKEND THE RIDGE BUILDING OVER
THE GULF AND MOVING EAST WILL KEEP ONSHORE FLOW AND PRECIP UNTIL
DRY SLOT ON LEE SIDE MOVES OVER, BUT THIS MAY BE VERY SHORT LIVED
AS THE NEXT FRONT ASSOCIATED WITH A LOW TO THE WEST MOVES IN FOR
MONDAY.

12Z MODEL RUNS WERE STILL ON TRACK AND IN LINE WITH INHERITED
FORECAST EARLY ON, SO LEFT GRIDS AS IS UNTIL WEDNESDAY NIGHT. USED
A BLEND OF 12Z ECMWF/GFS FOR THE DEVELOPING WAVE IN THE GULF. GFS
WAS ON THE STRONGER SIDE BUT WANTED TO KEEP SOME OF THAT
POTENTIAL MENTIONED IN THE FORECAST. REST OF THE LONG RANGE USED
NEW WPC WHICH CONTINUED A GFS/ECMWF ENSEMBLE BLEND. FORECAST
CONFIDENCE IS BIT BELOW AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-033-035-036-041>043-051-052.
&&

EAL/PRB

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