Small Craft Advisory 896, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
339 PM AKST FRI DEC 30 2011

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS WIDESPREAD SNOW
SHOWERS OVER THE GULF DRIFTING OVER SE AK. THESE SHOWERS ARE
ASSOCIATED WITH A UPPER TROF ADVECTING VERY COLD AIR ALONG WITH
STRONG SHORTWAVE ENERGY. THE COLD AIR MOVING OVER THE RELATIVE
WARM GULF IS PRODUCE VERY UNSTABLE CONDITIONS AND VERY STRONG
SNOW SHOWERS. THESE SHOWERS HAS THE POTENTIAL TO PRODUCE
1-4 INCHES OVER THE NORTHERN HALF OF THE FORECAST AREA WITH
1-3 OVER THE SOUTHERN HALF. THE NORTHERN GULF HAS THE GREATEST
POTENTIAL FOR THE MOST SNOW WITH THE STRONGEST ONSHORE FLOW. SO
WITH THAT SAID CONTINUED TO THE WINTER STORM WARNING FOR ZONE
17 THROUGH MIDNIGHT.

THE MAIN UPPER TROF WILL LIFT NORTH OF THE AREA THROUGH TONIGHT
WITH A UPPER RIDGE BUILDING OVER THE GULF THEN OVER THE PANHANDLE
THROUGH SAT. ALONG WITH THE RIDGE THE WINDS WILL BACK AROUND TO
THE SE SO THE SNOW SHOWERS WILL SLOWLY BECOME SCATTERED ACROSS THE
FORECAST AREA BY SAT AFTERNOON. SNOW AMOUNTS THROUGH SAT WILL
RANGE FROM 1 TO 3 INCHES WITH THE HIGHEST AMOUNTS OVER THE
NORTHERN HALF AND COASTAL AREAS.

AS FOR WINDS...THE STRONG WEST WINDS OVER THE GULF WILL SLOWLY
DECREASE THROUGH TONIGHT AND BECOME SE OVER THE EASTERN GULF WITH
SMALL CRAFT WINDS DEVELOPING OVER THE FAR SOUTHEAST AREAS. THE
INNER CHANNELS WILL SEE A WEAK RIDGE BUILD OVER THE PANHANDLE
THROUGH THIS EVENING AND INCREASE THE SE WINDS TO GENERALLY AROUND
20 KT. THE STRONGEST WINDS WILL BE OVER LYNN CANAL WITH SMALL
CRAFT WINDS ALONG WITH SMALL CRAFT WINDS NEAR CROSS SOUND. THERE
WILL BE HIGHER GUSTS NEAR STRONG SNOW SHOWERS AND NEAR THE COASTAL
AREAS. LAND AREAS WILL SEE WINDS MOSTLY LESS THAN 15 MPH BUT MAY
SEE HIGHER GUSTS ALSO NEAR SNOW SHOWERS. THE FAR NORTHERN ZONES
WILL SEE STRONG SOUTH WINDS DEVELOP EARLY THIS EVENING/LATE
AFTERNOON WITH GUSTS NEAR 35 MPH. THESE WINDS WILL SLOWLY DIMINISH
THROUGH SAT AS THE PRESSURE GRADIENT WEAKENS. THE FAR SOUTHERN
AREAS WILL SEE THE SE WINDS INCREASE LATE SAT AFTERNOON AS THE
NEXT STRONG LOW PRESSURE SYSTEM BEGINS TO LIFTS OUT OF THE NORTH
PACIFIC.

.LONG TERM...THERE ARE TWO IMPORTANT WIND EVENTS IN THE LONG RANGE.
THE FIRST IS FOR THE SRN PANHANDLE FOR SUNDAY (NEW YEARS DAY) AND
SUNDAY EVENING. PLEASE NOTE THE HIGH WIND WATCHES FOR ZONES 27 AND
28. THE SECOND WIND EVENT SHOULD OCCUR MON NIGHT AND TUE AND INCLUDE
MUCH OF THE CENTRAL AND SRN PNHDL AS WELL AS MOST OF THE THE OUTER
COAST.

CONFIDENCE FOR THE LONG RANGE FORECAST IS A LITTLE LOWER THAN
AVERAGE. THE GOES LOOP THROUGH 23Z SHOWS A COMPLEX LOW SYSTEM ABOUT
600 NM S OF THE AK PEN. THE FAMILIAR CONCEPTUAL MODELS FOR A MATURING
OCCLUSION DURING A CYCLONE EVOLUTION DOES NOT WORK WELL FOR THIS
SYSTEM. AS MANY AS FOUR CYCLONES HAVE DEVELOPED ALONG A LINE ABOUT
800 NM LONG, AND THIS LINE PARALLELS THE AK PEN ABOUT 600 NM TO
THE S. THE MODEL CONSENSUS HAS BEEN STYMIED BY THIS SYSTEM AND THEY
HAVE BEEN GENERALLY MAKING LARGE RUN-TO-RUN ADJUSTMENTS. NOW WE
HAVE AN IDEA WHY: THESE DIFFERENT MODELS AND MODEL RUNS HAVE BEEN
PICKING DIFFERENT SUBSET COMBINATIONS OF THESE LOWS.

THE 30.12 EC CAME IN WITH A SOLUTION THAT APPEARS TO DEPICT A NEW
TRIPLE POINT DEVELOPMENT ALONG THE LINE DEPICTED ABOVE. THE LOCATION
ON THE 00Z GOES AT 40N/146W AND THIS LOCATION SEEMS CONSISTENT WITH
A NEW TRIPLE POINT FEATURE AND WILL UNDERGO CYCLOGENESIS SLOWER THAN
THE PRIOR LOWS.

BEYOND 00Z TUE THE CHANGES MADE TO THE FORECAST WAS TRIVIAL. THERE
SEEMED LITTLE VALUE WOULD BE ADDED GIVEN THE LARGE SCALE OF THE
REGION OF LOW CONFIDENCE AS DESCRIBED IN THE PARAGRAPH IMMEDIATELY
ABOVE. FOR THE SAKE OF CONVENTION, WE WILL LABEL THE COMPLEX LOW
DISCUSSED ABOVE AS SYSTEM ONE. SYSTEM TWO IS TO PROVIDE AN ADDITIONAL
STRONG WIND EVENT, AND BASED ON THE EC WILL HAVE A LARGER COVERAGE
OF HIGH WINDS IN SE AK. THE CONFIDENCE IN THE FORECASTS ASSOCIATED
WITH SYSTEM TWO IS ALSO AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING FOR
     AKZ027-028.
         WINTER STORM WARNING UNTIL MIDNIGHT AKST TONIGHT FOR AKZ017.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-041>043-051-052.

&&

ABJ/JBT