Small Craft Advisory 12, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
539 AM AKST TUE JAN 4 2011

.SHORT TERM...OCCLUDED FRONT ALONG THE OUTER COAST WILL MOVE
INLAND TODAY. A LOW WILL DEVELOP OVER THE NE PAC AND MOVE NE
TOWARD THE FAR SE GULF TONIGHT. A LOW WILL MOVE NE TO NEAR KODIAK
ISLAND BY THIS EVENING.

 MAIN FORECAST CONCERNS ARE WINDS AND WHETHER THERE WILL BE ANY
SIGNIFICANT BREAKS IN PRECIP. OCCLUDED FRONT WILL MOVE THRU THE
AREA TODAY...AND PRESSURE GRADIENTS BEHIND IT WILL WEAKEN FOR
MOST AREAS. EXCEPTION WILL BE OVER LYNN CANAL...WHERE SLY
GRADIENTS WILL INCREASE SIGNIFICANTLY. MODELS OFTEN UNDERESTIMATE
THE STRENGTH OF THE GRADIENT ESPECIALLY IF THERE IS STRONG SW
FLOW AROUND 700 MB. 700 MB FLOW IS FORECAST TO BECOME SW 30-40 KT
BY LATE THIS MORNING AND CONTINUE INTO THIS EVENING. THIS WILL
ENHANCE THE SLY SFC PRES GRADIENT AND AM EXPECTING ADVY LEVEL
WINDS TO DEVELOP AROUND PAGY LATE THIS MORNING...CONTINUING INTO
THE EVENING WHEN FLOW ALOFT SHOULD START BACKING IN ADVANCE OF
THE LOW MOVING TOWARD THE SE GULF. WILL BE ISSUING WIND ADVY FOR
PAGY FOR THE 18Z-06Z PERIOD TODAY. ELSEWHERE...WINDS ARE
DECREASING EVEN AHEAD OF THE FRONT SO WILL ALLOW THE WIND ADVYS
FOR ZONES 27 AND 28 TO EXPIRE AT 5 AM THIS MORNING. WILL STILL
HAVE BREEZY TO WINDY THOUGH FOR SOME PLACES...MAINLY FOR THE
MORNING HOURS.

 AS FOR PRECIP...ONSHORE FLOW WILL LIKELY KEEP AT LEAST SPOTTY
PRECIP GOING EVEN AFTER FROPA TODAY FOR MOST OF THE AREA. IT WILL
TREND A LITTLE MORE CONVECTIVE THIS AFTERNOON...BUT MAY BECOME
MORE STRATIFORM LATER TONIGHT IN WARM ADVECTION AHEAD OF THE LOW
MOVING TOWARD SE GULF. WILL KEEP IT SIMPLE AND KEEP STRATIFORM
TERMINOLOGY THRU TONIGHT. MAY BE A DECENT BREAK OVER THE SRN AREA
LATE THIS AFTERNOON AND TONIGHT AS WEAK RIDGING BETWEEN SYSTEMS
MOVES THRU...SO POPS THERE DROP OFF SOMEWHAT DURING THAT TIME. AT
THIS POINT AM EXPECTING PTYPE TO REMAIN RAIN ALTHOUGH HYDER MAY
HAVE SOME SNOW THIS MORNING BEFORE THEY WARM UP. AIRMASS BEHIND
FRONT IS NOT ALL THAT COLD SO EXPECT PTYPE TO REMAIN RAIN AT SEA
LEVEL TONIGHT.

&&

.LONG TERM...MAIN FEATURES IN THE EXTENDED RANGE FORECAST PERIOD
INCLUDE A FAST MOVING GALE FORCE LOW EARLY ON...AND A RETURN OF
COLDER TEMPS BEGINNING NEXT FRIDAY NIGHT.

THE DEVELOPING GALE IS STILL AN OPEN WAVE ALONG AN EXISTING
FRONTAL BOUNDARY LOCATED ALONG 160W WELL SOUTH OF THE GULF. A
SURFACE CIRCULATION WILL CLOSE OFF LATER TODAY AND BY EARLY
WEDNESDAY MORNING IT WILL BE JUST ENTERING THE FAR SOUTHEASTERN
GULF AND TRACKING NORTHEAST. SURFACE WINDS WILL INCREASE RAPIDLY
WEDNESDAY MORNING OVER THE SOUTHERN COASTAL MARINE ZONES AND
SOUTHERN INNER CHANNELS AND REACH PEAK INTENSITY LATE WEDNESDAY
AFTERNOON. THE LOW ITSELF WILL BE JUST ABOUT FULLY OCCLUDED BY THE
TIME IT ARRIVES OVER THE OUTER COAST VICINITY SITKA AND WILL FILL
RAPIDLY AFTER MAKING LANDFALL. AS A CONSEQUENCE...SURFACE WILL
WILL DIMINISH JUST ABOUT AS ABRUPTLY AS THEY INCREASED...SO
ASSOCIATED GALES...SMALL CRAFT ADVISORIES...AND POSSIBLY WIND
ADVISORIES...WILL BE SHORT LIVED EVENTS. LOW LEVEL WARM SECTOR
ASSOCIATED WITH THE OCCLUDED FRONT IS NOT THAT LARGE AND WHAT
LITTLE THERE IS WILL BE CONFINED TO LOCATIONS SOUTH OF FREDERICK
SOUND DURING THE DAY ON WEDNESDAY. AS A RESULT...SNOW WILL RE-
ENTER THE FORECAST FOR MANY LOCATIONS WEDNESDAY NIGHT INTO
THURSDAY AND SOME LOCATIONS MAY SEE FROM 2 TO 4 INCHES BEFORE
LINGERING PRECIP WINDS DOWN FRIDAY NIGHT.

BEYOND THAT TIME...COLD LOW LEVEL AIR RETURNS TO THE PANHANDLE AS
A MID AND UPPER LEVEL RIDGE AXIS CENTERED OVER THE GULF TIPS TO
THE NORTHEAST AND GENERATES LOW LEVEL OFFSHORE FLOW FOR SOUTHEAST
ALASKA BEGINNING THIS NEXT WEEKEND. AM EXPECTING HIGHS IN THE MID
20S NEAR THE COAST MOUNTAINS TO MID 30S NEAR THE OUTER COAST.
OVERNIGHT LOWS IN THE MID TEENS TO MID 20S ALONG SIMILAR SPATIAL
DISTRIBUTIONS. IN ADDITION TO DRYING THE PANHANDLE OUT...THE
OFFSHORE FLOW SHOULD ALSO BRING US SOME PARTLY CLOUDY SKIES. GOOD
POTENTIAL FOR A COLD...CLEAR...AND DRY WEEKEND.

USED ECMWF FOR UPDATES TO WEDNESDAY AND THURSDAY PRESSURE AND
WINDS. BLENDED VARIOUS AMOUNTS OF GFS...ECMWF...AND GEM FOR POP.
NUDGED TEMPS TOWARDS GFS ENSEMBLE VALUES. FORECAST CONFIDENCE IS
AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM 9 AM THIS MORNING TO 9 PM AKST THIS EVENING
     FOR AKZ018.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-034>036-041>043-051.

&&

RWT/FRITSCH