Small Craft Advisory 806, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
2 PM AKST TUE DEC 6 2011

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS MOST OF THE
FORECAST AREA MOSTLY CLEAR TO PARTLY CLOUDY. THERE IS SOME MID TO
LOW LEVEL CU OVER THE COASTAL AREAS NEAR PASI AND ALONG POW. MOST
OF THESE CLOUDS WILL SLOWLY DISSIPATE BUT THERE IS A WEATHER
SYSTEM THAT IS TRACKING ACROSS THE NORTH PACIFIC THAT WILL
INCREASE CLOUDS OVER THE SOUTHERN AREAS TO NIGHT WHILE THE NORTH
AREAS WILL REMAIN MOSTLY CLEAR. WINDS WILL BE ON THE LIGHT ACROSS
MOST OF THE FORECAST AREA WITH VERY WEAK PRESSURE GRADIENT THROUGH
WED MORNING. TEMPS WILL FALL AS THE SUN GOES DOWN AND THE LACK OF
CLOUDS SO LOW TEMPS WILL RANGE FROM THE TEENS OVER THE NORTHERN
HALF TO LOW 30S OVER THE SOUTHERN AREAS.

THE UPPER AND MID LEVEL RIDGE OVER THE GULF TONIGHT WILL SLOWLY
DRIFT TO THE EAST THROUGH WED AFTERNOON AS A WARM FRONT LIFTS INTO
THE NORTHERN GULF. AS THE ONSHORE FLOW INCREASES THROUGH THE DAY
HIGH CLOUDS WILL INCREASE ACROSS MOST OF THE NORTHERN TWO THIRDS
OF THE PANHANDLE WHILE THE SOUTHERN THIRD WILL BECOME PARTLY
CLOUDY. THE FRONT WILL INCREASE THE WINDS OVER THE NORTHERN GULF
TO MIN GALES WITH 20KT FROM THE SE INCREASING OVER THE EASTERN
GULF BY THE AFTERNOON. THE INNER CHANNELS WILL SEE THE LIGHT NORTH
WINDS VEER AROUND TO THE SE BY THE AFTERNOON AND INCREASE TO 15
KT. THE E/W CHANNELS WILL SEE THE WINDS INCREASE TO BE 20 KT BY
THE AFTERNOON.

FOR THE MOST PART THE FORECAST AREA WILL REMAIN ON THE DRY SIDE
THROUGH THE NEXT 24HRS. THE EXCEPTION TO THIS WILL BE OVER THE
NORTH GULF COASTAL AREAS AS WITH THE INCREASING ONSHORE FLOW AND
MOISTURE TRANSPORT FROM THE SOUTHWEST THERE WILL SOME MINOR OVER
RUNNING. SO WITH THAT SAID INCREASE THE POPS TO HIGH CHANCE BY WED
AFTERNOON FOR THE PAYA AREA AND THE P-TYPE WILL SNOW. AMOUNTS WILL
BE GENERALLY NEAR 1 INCH BY THE END OF THE WED AFTERNOON TIME
FRAME. -ABJ

.LONG TERM...ON THE LARGE SCALE SE ALASKA REMAINS IN A PROGRESSIVE
PATTERN BUT THE AMPLITUDE OF THE SHORT WAVE RIDGES ARE FORECASTED
BY MODELS TO BE FLATTER THAN THE LAST WEEK. THE MEAN POSITION OF
THE UPPER RIDGE STILL APPEARS TO BE ON AVERAGE AT 140W THRU FRIDAY
BUT SYSTEMS ARE SO TRANSIENT THAT WE WILL HAVE RAPID CHANGES WITH
FEW BREAKS.

TRANSITION TIME PROBLEMS ARE PRECIPITATION TYPE AND WIND STARTING
WED EVENING. THERE ARE MIXED SIGNALS IN THE 06/12Z OPS MODELS BUT
FAIRLY CONFIDENT ABOUT STARTING PRECIP AS SNOW NORTHERN ZONES WED
NIGHT INTO THU MORNING. THERE IS SOME CHANCE THAT THE SNOW WILL
LAST WELL INTO THE DAY BUT NOT CONFIDENT ENOUGH TO GO WITH ALL SNOW
DUE TO THE WIND DIRECTION ALOFT BEING SW AND LOW LEVELS SE. A QUICK
LOOK AT THE 06/12Z NAM QPF SEZ LOTS OF WATER IN THE BUCKET THU INTO
FRI. EVEN MORE CHALLENGING IS TO KEEP RAIN OR SWITCH BACK TO SNOW
THU NITE. WILL INSIST ON AT LEAST MIXED RATHER THAN ALL RAIN. FRI
WILL BE RAIN EVERYWHERE LOOKING AT ANY MODEL THICKNESS OR MOS
TEMPERATURE FORECASTS. FRI NITE HAS WESTERLIES FOR SHOWERS MOST
LIKELY MIXED.

SAT IS THE BREAK BETWEEN SYSTEMS AS ALL OPS MODELS AGREE THAT THE
LAST UPPER RIDGE WILL BUILD UPSTREAM. THIS RIDGE IS AGAIN
PROGRESSIVE AND ALLOWS THE SW FLOW ALOFT ON SUN AS THE UPPER RIDGE
AXIS MOVES EAST OF THE PANHANDLE. CONFIDENCE BELOW AVERAGE ON
PRECIP TYPE AND SNOW ACCUMULATION BUT MODERATE TO HIGH ON THE
PATTERN.

THOU SHALT NOT DENY UPPER LEVEL ONSHORE FLOW. IT BRINGETH MOISTURE
AND OFTEN WARMTH WHEN IT BECOMETH SW. LONGER RANGE MODELS SHOW THAT
THE MEAN POSITION OF THE UPPER RIDGE WILL BE FARTHER EAST WHICH
WOULD FORECAST WARM & WET IF TRUE. CANT BET THE RANCH ON THAT YET
BUT IT BODES ILL. HPC CURRENT 500 MB PROGS AGREE WITH SW FLOW ALOFT
OVER SE ALASKA MON & BEYOND. - JC

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ051.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

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