Small Craft Advisory 268, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
352 AM AKDT THU MAR 17 2016

.SHORT TERM...UPPER RIDGE OVER THE ERN GULF AND SE AK WILL BE
FLATTENED BY NRN STREAM TROF MOVING ACROSS S-CENTRAL AK INTO THE
SW YUKON THRU TONIGHT. A WARM FRONT OVER THE SRN GULF WILL DRIFT N
TO THE NRN GULF TONIGHT. THE FRONT WILL BEGIN TO WEAKEN LATE
TONIGHT. USED BLEND OF THE 00Z GFS AND NAM THROUGH TONIGHT AS THEY
HAD GOOD HANDLE ON THE MAIN FEATURES.

MAIN FORECAST CONCERNS WILL BE PRECIP POTENTIAL/PTYPE AND WINDS.
THERE ARE SOME SPOTTY SHOWERS OVER THE NRN AREA ATTM...BUT THESE
WILL DIMINISH THIS MORNING AS LOWER LEVELS DRY OUT SOME DUE TO A
MORE ELY FLOW DEVELOPING. PRECIP WITH THE WARM FRONT WILL MOVE N
ACROSS THE GULF AND MAINLY AFFECT THE NE GULF COAST THIS AFTERNOON
AND TONIGHT...BUT SOME PRECIP CANNOT BE RULED OUT OVER THE NRN
THIRD OF THE INNER CHANNELS AS THICKER MID-LEVEL CLOUDS MOVE
ACROSS THE AREA IN WARM ADVECTION PATTERN ALOFT LATE THIS
AFTERNOON AND TONIGHT. DECIDED TO GO WITH CHANCE POPS TO HANDLE
THIS AREA FOR THAT TIME PERIOD. AM NOT EXPECTING PRECIP FURTHER S
AFTER ANY EARLY MORNING SHOWERS AS THE DEPTH OF THE MID-LEVEL
MOIST LAYER WILL BE LESS DUE TO PROXIMITY OF UPPER LEVEL RIDGE
AXIS.

PTYPE WILL BE A TRICKIER CALL. BOUNDARY LAYER TEMPS ARE CURRENTLY
MARGINAL AT BEST TO ALLOW SNOW TO REACH SEA LEVEL. TEMPS SHOULD
SLOWLY WARM THROUGH THE DAY OVER THE NE GULF COAST AND NRN
PANHANDLE...ENOUGH SO TO MINIMIZE THREAT FOR SNOW THIS AFTERNOON.
BIG QUESTION WILL BE TONIGHT ESPECIALLY NEAR PAYA. THINK PTYPE
WILL DEPEND ON PRECIP RATE THERE. ATTM...IT LOOKS LIKE THE
HEAVIER PRECIP RATES WILL STAY W OF PAYA TONIGHT...WITH ONLY 0.01
TO 0.03 IN/HR FOR PAYA. THINK THIS WILL BE TOO LIGHT FOR SNOWMELT
COOLING TO OVERCOME LOW LEVEL WARM ADVECTION...EVEN IN THE ELY LOW
LEVEL FLOW. IF THEY REACHED AT LEAST 0.05 IN/HR THOUGH...THAT
COULD BE JUST ENOUGH FOR SNOWMELT COOLING TO WIN OUT AND CAUSE
PRECIP TO BECOME AT LEAST MIXED IN PAYA. IF IT CAN GET CLOSER TO
0.10 IN/HR IT MIGHT BECOME ALL SNOW. THERE MIGHT BE A LITTLE SNOW
MIXED IN FOR THE FAR NRN PANHANDLE TONIGHT WITH A JUST COOL ENOUGH
BOUNDARY LAYER TO ALLOW FOR SOME SNOW IF PRECIP OCCURS THERE.

AS FOR WINDS...STRONGEST WINDS WILL BE OVER THE GULF NEAR THE WARM
FRONT. COULD SEE GALE FORCE WINDS OVER THE OFFSHORE WATERS AND SCA
LEVEL WINDS OVER THE REMAINING COASTAL WATERS BEGINNING THIS
AFTERNOON. ABOUT THE ONLY OTHER AREA THAT LOOKS LIKE IT WILL REACH
SCA LEVELS IS CROSS SOUND TONIGHT AS ELY GRADIENT TIGHTENS A BIT.
REST OF THE INNER CHANNELS SHOULD STAY 20 KT OR LESS FOR THE MOST
PART ALTHOUGH LOCAL EFFECTS COULD CAUSE HIGHER WINDS WHERE ELY
FLOW IS FAVORED.

.LONG TERM...RELATIVELY QUIET WEATHER EXPECTED OVER SOUTHEAST
ALASKA THROUGH THE EXTENDED RANGE. THE STRONGEST UPPER LEVEL
DYNAMICS WILL BE WELL SOUTH OF THE AREA IN THE CENTRAL PACIFIC. THE
MAIN FEATURE OF INTEREST WILL BE A BROAD UPPER LOW OVER THE
NORTHERN PACIFIC THAT WILL GRADUALLY WEAKEN AND PUSH EAST THROUGH
THE WEEKEND. FLOW AROUND THE UPPER LOW WILL PUSH A FEW WEAK
IMPULSES OVER THE PANHANDLE. WETTEST DAY OF THE LONG TERM WILL BE
LATER SATURDAY AND EARLY SUNDAY AS A SHORTWAVE MOVES NORTH INTO THE
AREA WITH SHOWERS DEVELOPING FROM NORTH TO SOUTH THROUGH THE DAY.
HOWEVER AM NOT EXPECTING THIS TO BE A SIGNIFICANT RAINMAKER WITH
AMOUNTS STILL UNDER A QUARTER OF AN INCH. AS THE UPPER LOW SLIDES
SOUTH OF THE PANHANDLE LATE WEEKEND AND EARLY NEXT WEEK EXPECT FLOW
TO SHIFT MORE OFFSHORE WITH DRY WEATHER ANTICIPATED. COULD SEE
SEVERAL LOCATIONS REACH THE 50 DEGREE MARK EARLY NEXT WEEK. ALONG
WITH A LACK OF SIGNIFICANT RAINFALL, WINDS ARE EXPECTED TO STAY
BELOW SMALL CRAFT LEVEL FOR THE MOST PART AS A WEAKER PRESSURE
GRADIENT RESIDES OVER THE AREA.

USED THE 00Z NAM/ECMWF FOR UPDATES TO THE FORECAST THROUGH DAY 4
THEN UTILIZED THE LAST WPC GUIDANCE FOR THE REMAINDER OF THE
FORECAST. FORECASTER CONFIDENCE IS AVERAGE.

&&

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

RWT/TPS

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