Small Craft Advisory 802, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
230 PM AKST MON DEC 5 2011

BLACK ICE TONIGHT FOR NORTHERN SECTIONS. SEE SPECIAL WEATHER
STATEMENT ON OUR HOME PAGE UNDER FORECASTS...TEXT...SPECIAL WEATHER
STATEMENT EIGHTH ITEM DOWN.

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS A COLD FRONT
FROM THE ICY STRAIT AREA PUSHING SOUTHWARD. THIS FRONT WILL
CONTINUE TO DRIFT SE THROUGH TONIGHT AND BE OUT OF THE AREA BY
LATE TONIGHT. THE CLOUDS WILL DECREASE ALONG WITH THE RAIN AS THE
FRONT MOVES THROUGH THE AREA. THERE IS PARTLY CLOUDY SKIES OVER
THE NORTHERN THIRD OF THE PANHANDLE ALONG WITH OVER THE NORTHERN
GULF ATTM. THE PARTLY CLOUDY TO MOSTLY CLEAR SKIES WILL DRIFT
SOUTHWARD THOUGH TONIGHT WITH MUCH DRIER AIR ADVECTING OVER THE
AREA BEHIND THE FRONT. THERE IS SOME ALTO-CU DEVELOPING OVER THE
GULF THAT WILL MOVE OVER THE COASTAL AREAS THROUGH TUE TO PRODUCE
MOSTLY CLOUDY WITH A FEW ISOLATED SHOWERS THAT WILL BE MIXED WITH
OR BE ALL SNOW. THERE IS RAIN FALLING ATTM OVER THE SOUTHERN HALF
OF THE PANHANDLE BUT AS THE FRONT DRIFT SOUTH THE RAIN WILL
DIMINISH THROUGH THIS EVENING OVER THE CENTRAL AREAS AND THEN OVER
THE FAR SOUTHERN AREA LATE TONIGHT. THE FORECAST AREA WILL BE ON
THE DRY THROUGH TUE AFTERNOON WITH NOT MUCH UPPER LEVEL DYNAMICS
AND WEAK ANTICYCLONIC ROTATION.

THE STRONG WINDS OVER THE INNER CHANNELS ARE SLOWLY DIMINISHING
FROM NORTH TO SOUTH BEHIND THE FRONT BUT IT WILL NOT BE UNTIL LATE
EVENING THAT THE WINDS WILL CALM COMPLETELY. THE STRONGEST WINDS
THIS AFTERNOON ARE NEAR CROSS SOUND AND ICY STRAIT AS THE WESTERLY
WINDS ARE GALE FORCE WITH VERY HIGH GUSTS. THESE WINDS WILL SLOWLY
DIMINISH THROUGH TONIGHT. THE REST OF THE MARINE WATERS WILL SEE
THE SMALL CRAFT WINDS DIMINISH TO BE LESS THAN 20 KT THIS EVENING
THEN BE ON THE LIGHTER SIDE THROUGH TUE WITH A WEAK PRESSURE
GRADIENT. OVER THE GULF THE WEST WINDS 30 TO 35 KT WILL SLOWLY
DECREASE AS THE SURFACE FRONT AND UPPER LEVEL TROF DRIFTS EAST AND
INTO CANADA.

TEMPS WILL FALL ACROSS SE AK TONIGHT AS WITH LARGE BREAKS
DEVELOPING OVER NIGHT ACROSS THE AREA ALONG WITH CAA FROM THE WNW
LOWS TONIGHT WILL RANGE FROM LOWERS 20S OVER THE NORTHERN AREAS TO
MID 30S OVER THE SOUTHERN AREAS. WITH ALL OF THE RAIN ACROSS THE
REGION AND TEMPS FALLING BELOW FREEZING THERE WILL BE AREAS OF
BLACK ICE AND MAY PRODUCE HAZARDOUS DRIVING CONDITIONS. ABJ

&&

.LONG TERM...
OVERALL WEATHER PATTERN FOR ALASKA AND UPSTREAM REMAINS A CASE OF
HIGH AMPLITUDE TROFS AND RIDGES BUT STILL PROGRESSIVE. WINTRY COLD
AIR ALOFT BELOW -40C AT 500 MB REMAINS OVER SIBERIA AND IN THE
ANCHOR LOW OVER GREENLAND. THE RESULT IS THAT WAVES ORIGINATING IN
THE WEST ARE SUPPORTED BY THE COLD AIR BUT CONTINUE TO TRANSPORT
HEAT EACH TIME ONE APPROACHES SE ALASKA.

A RIDGE WILL OVER 140W WED AFTERNOON FOR A BRIEF SHOT OF COLD AND
CLEARING. RADIATIVE COOLING THROUGH CLEAR SKIES PLUS COLDER AIR
MOVING FROM INTERIOR PASSES IS GOING TO GIVE SE A FEELING OF WINTER
AGAIN WITH SOME MORNING MINIMUMS IN THE SINGLE DIGITS IN THE NORTH.

STARTING WED NIGHT ALL OPS MODELS AGREE THAT MOISTURE AND WARMER
AIR ALOFT WILL MOVE OVER OUR AREA STARTING AS SNOW. USED 12/05
AK-GFS-40 TO FORECAST THE SNOW FOR MOST AREAS ON THU WITH SOME
AREAS ESPECIALLY TO SOUTH CHANGING TO RAIN. STAY TUNED BECAUSE THE
SNOW AMOUNT IS VERY DIFFICULT TO CALL YET BUT SHOULD EVENTUALLY
TURN TO RAIN. NEXT BREAK LOOKS TO BE SAT NIGHT AND THEN MORE WARM
AND WET IN SW FLOW ALOFT. USED HPC PROGS SAT THRU MON. CONFIDENCE
MODERATE DUE TO TIMING OF FAST MOVING SYSTEMS. SNOW FORECAST
MODERATE BUT WILL WAIT TO SEE AMOUNTS AND RAIN CHANGE-OVER. JC

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND TIL 3 PM AKST THIS AFTERNOON AKZ018.
MARINE...GALE WARNING PKZ022-036-051-052.
         SMALL CRAFT ADVISORY PKZ011>013-021-031>035-041>043.

&&