Small Craft Advisory 598, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
444 PM AKDT TUE OCT 16 2012

.SHORT TERM...CURRENT WATER VAPOR IMAGE TODAY SHOWS A WEAK
TROUGH MOVING THROUGH THE PANHANDLE AT THE MOMENT WHICH IS
RESPONSIBLE FOR THE NUMEROUS SHOWERS AFFECTING THE AREA. A
SPOTTER AT POINT BAKER CALLED IN THIS MORNING WITH SOME SMALL
HAIL OR ICE PELLETS FROM ONE OF THESE SHOWERS SO SOME OF THE
SHOWERS THIS AFTERNOON COULD STILL HAVE SOME SMALL HAIL OR EVEN A
RUMBLE OR TWO OF THUNDER AS WELL BEFORE THE TROUGH MOVES
COMPLETELY THROUGH THIS EVENING. ALSO BEING AFFECTED BY THIS
TROUGH IS A DECENT SOUTHERLY PRESSURE GRADIENT OVER LYNN CANAL
THAT IS SPARKING SMALL CRAFT WINDS THERE.

 INTO TONIGHT, SHOWERS WILL CONTINUE OVER MUCH OF THE AREA AS SW
ONSHORE FLOW CONTINUES BUT THE FREQUENCY WILL DIMINISH A BIT THIS
EVENING AS A WEAK RIDGE BRIEFLY BUILDS OVER THE PANHANDLE.
ANOTHER TROUGH CURRENTLY OVER THE WESTERN GULF WILL THEN MOVE IN
LATE TONIGHT INCREASING THE FREQUENCY OF THE SHOWERS ONCE AGAIN.
ALSO ACCOMPANYING THIS TROUGH IS THE LEADING EDGE OF THE COOLER
AIR THAT IS WORKING SOUTH AND THEN EAST AROUND THE NORTHERN GULF
LOW. BY EARLY TOMORROW, 850 MB TEMPS WILL BE AROUND -6 TO -8C
OVER MOST OF THE NORTHERN PANHANDLE. LOW LEVEL TEMPERATURES
SHOULD BE TOO WARM FOR SNOW AT SEA LEVEL IN MOST AREAS EXCEPT FOR
YAKUTAT (ESPECIALLY IF THEIR WIND TURNS TO THE E OR NE TOMORROW
MORNING), HAINES AND SKAGWAY (MOSTLY IF THEIR SOUTHERLY WINDS
DROP OFF). SNOW ACCUMULATIONS, IF ANY, WILL BE LIGHT. YAKUTAT AND
THE HAINES AND KLONDIKE HIGHWAYS WILL BY THE PLACES THAT WILL BE
MOST LIKELY TO SEE ANY SNOW ACCUMULATION LATE TONIGHT.

 IN ADDITION TO THE SHOWERS, WINDS WILL BE STARTING TO PICK UP IN
THE SOUTHERN PANHANDLE TOMORROW AFTERNOON AS THE TROUGH STARTS
MOVING THROUGH. THESE WINDS WILL BE HIGH ENOUGH TO WARRANT STRONG
WIND HEADLINES FOR HYDABURG AND KETCHIKAN ZONES, AND GALES FOR
CLARENCE STRAIT FOR TOMORROW AFTERNOON. THESE WINDS WILL STAY
HIGH INTO THE EVENING AS THE NEXT LOW COMES UP FROM THE SW.

 SHORT RANGE MODELS ARE IN SOMEWHAT DECENT AGREEMENT BUT SUFFER
FROM SOME STRENGTH AND TRACK DISAGREEMENTS WITH THE LOW THAT IS
JUST ENTERING THE FORECAST DOMAIN AT THE END OF THE SHORT TERM
PERIOD. THE 12Z EC SEEMED TO HAVE A GOOD HANDLE ON THE STILL
DEVELOPING SYSTEM AND USED THAT FOR THE PRIMARY GUIDANCE
PARTICULARLY FOR TOMORROW AFTERNOON. FORECAST CONFIDENCE IS ABOUT
AVERAGE.

.LONG TERM...THERE IS SOME LARGE CHANGES IN THE FORECAST FROM WED
NIGHT THROUGH NEXT WEEK. THE AMERICAN MODELS(NAM/GFS) INITIALIZED ON THE
POOR SIDE WITH THE WEATHER SYSTEM MENTIONED IN THE SHORT TERM
WHILE THE THE UKMET/CANADIAN/EC DID MUCH BETTER AND THERE WAS
GOOD ENSEMBLE AGREEMENT. THE NAM/GFS TRACKED THE LOW MUCH FURTHER
SOUTH AND WEAKER ALONG WITH MUCH COLDER AIR BEING ADVECTED OVER
THE GULF AND PANHANDLE THROUGH THIS WEEK. THE PREFERRED MODEL WAS
THE EC THROUGH THE MID RANGE AND THEN HPC FROM DAY 5 THROUGH DAY 8
AS THERE WAS GOOD RUN TO RUN CONSISTENCY AND THERE WAS SMALL SPREADS
IN THE ENSEMBLES INTO THE WEEKEND.

THE TACK OF THE LOW AT THE START OF THE FORECAST PERIODS WAS VERY
TRICKY BUT IT LOOKS LIKE THE TRACK WILL MOVE THE LOW OVER THE
SOUTHERN AREAS AND THEN INTO CANADA THROUGH WEDNESDAY EVENING.
THERE IS VERY STRONG UPPER LEVEL SUPPORT THAT WILL PRODUCE STRONG
SHOWERS AND THEY MAY BE HEAVY AT TIMES THROUGH THE EVENING. ONCE
THE LOW WILL PRODUCE SOLID GALES OVER CLARENCE STRAIT WITH THE
NORTHERN HALF SEEING WINDS FROM THE NORTH NEAR 15 KT BUT AS THE
RIDGE BUILDS IN OVER THE AREA THE SOUTHERLY PUSH WILL MOVE THROUGH
THE INNER CHANNELS. THIS WILL INCREASE THE WINDS FROM THE SOUTH TO
MAX SMALL CRAFT AND GUSTY WINDS OVER LAND AREAS. THE COLD FRONT
WILL MOVE OVER THE AREA WED NIGHT AND SHOWERS WILL PERSIST THROUGH
THE DAY ALONG WITH WEST WINDS OVER THE GULF TO 25KT. THE SOUTH
WINDS OVER THE INNER CHANNELS WILL SLOWLY DIMINISH AS THE RIDGE
WEAKENS SOME BUT SMALL CRAFT WINDS WILL PERSIST OVER LYNN CANAL
THROUGH WED NIGHT.

THERE WAS A CHANGE IN THE FORECAST THAT TOOK OUT THE SNOW OVER THE
INNER CHANNELS A IT DOES NOT LOOK LIKE THE COLDEST AIR WILL BE
OVER THE AREA WHEN THERE IS PRECIP. FROM WED THROUGH FRIDAY TEMPS
WILL BE ON THE COOL SIDE BUT WITH THE OCEAN WATER IN THE UPPER 40S
AND 850MB TEMPS AROUND -6 THE COLD AIR MOVING OVER THE GULF WILL
WARM AND KEEP TEMPS IN THE UPPER 30S TO MID 40S OVER THE
PANHANDLE.

THE UPPER LOW OVER THE GULF WILL BEGIN TO SLIDE TO THE SOUTHEAST
THROUGH FRIDAY AND PULL ALL THE SHOWERS SOUTH WITH IT. AS THIS
HAPPENS THE COLD/DRY AIR LOCKED UP IN THE INTERIOR WILL BEGIN TO SLIDE
SOUTH. SO THE SHOWERS OVER THE PANHANDLE WILL DIMINISH FROM NORTH
TO SOUTH THROUGH FRIDAY AND WITH THAT INCREASE THE NORTHERLY
WINDS. TEMPS WILL FALL BELOW FREEZING FRIDAY NIGHT AND THERE WILL
BE LOCALLY WINDY CONDITIONS DEVELOPING NEAR GAPS AND OVER MARINE
WATERS. THE OFFSHORE FLOW WILL PERSIST AND THE SKIES WILL BECOME
PARTLY CLOUDY OVER THE WEEKEND AND THAT MAY PERSIST INTO EARLY
NEXT WEEK. HIGH TEMPS WILL BE NEAR 40 WHILE OVERNIGHT LOWS WILL
DIP INTO THE 20S OVER THE NORTHERN AREAS WITH THE LOWER 30S OVER
THE SOUTHERN AREAS OVER THE WEEKEND.

THERE IS ABOUT AVERAGE FORECASTER CONFIDENCE THROUGH EARLY NEXT
WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR
     AKZ027.
         STRONG WIND FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY EVENING
     FOR AKZ028.
MARINE...GALE WARNING FOR PKZ036.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-033>035-041>043-051-
     052.

&&

EAL/ABJ