Small Craft Advisory 891, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
403 PM AKST THU DEC 29 2011

.SHORT TERM... CURRENT SATELLITE HAS AN UPPER LEVEL DISTURBANCE
IN THE NORTHEAST GULF MOVING TOWARDS THE FAIRWEATHER GROUNDS THIS
EVENING. THE  DISTURBANCE WILL CONTINUE THE SNOW SHOWERS ALONG
THE OUTER COAST FROM ICY BAY TO NORTHERN BARANOF ISLAND AND
INLAND FROM THE HOONAH AREA NORTH TO HAINES TONIGHT. SNOWFALL
AMOUNTS FROM 2 TO 4 INCHES ARE EXPECTED. A LOW IN THE NORTHEAST
PACIFIC WILL TRACK NORTHEAST TOWARDS HAIDA GWAII TONIGHT. THIS
LOW WILL BRING LOW-LEVEL OFFSHORE FLOW FROM PETERSBURG ON SOUTH
AND INHIBIT SHOWER ACTIVITY TO ONLY BE SCATTERED SNOW SHOWERS OR
LESS, BUT THE UPPER LEVEL FLOW WILL CONTINUE TO BE ONSHORE ABOVE
850 MB. RAIN MIXING IN SHOULD REMAIN IN THE DIXON ENTRANCE JUST
SOUTH OF THE PANHANDLE. A SHORTWAVE WILL MOVE ACROSS YAKUTAT LATE
TONIGHT AND OVER THE PANHANDLE ON FRIDAY. THIS TROUGH WILL
PRODUCE SNOW SHOWERS OVER THE NORTHERN PANHANDLE AS MORE UNSTABLE
AIR MOVE ONSHORE. SCATTERED SNOW SHOWERS WILL MOVE OVER THE
SOUTHERN PANHANDLE AS THE TROUGH MOVES OVER THE AREA IN THE AFTERNOON.

WINDS OVER THE GULF WILL INCREASE AS THE DISTURBANCE AND TROUGH
MOVE THROUGH THE AREA TO SMALL CRAFT LEVEL LATE TONIGHT INTO
TOMORROW MORNING. SEAS WILL LINGER AROUND 10 TO 15 FEET WITH THE
LOWEST SEAS NEAR CAPE SUCKLING AREA. IN THE INNER CHANNELS, WINDS
WILL BE MAINLY 20 KTS OR LESS EXCEPT FOR NORTHERN LYNN CANAL AND
CROSS SOUND THIS EVENING. THERE WILL BE A SPLIT FLOW LATE TONIGHT
INTO TOMORROW WITH SOUTHERLY WINDS MAINLY NORTH OF FREDERICK
SOUND. TYPICALLY DIURNAL WIND PATTERN NORTH OF FREDERICK SOUND
WITH WINDS DECREASING OVERNIGHT AND INCREASING AGAIN TOMORROW
AFTERNOON. FROM FREDERICK SOUND ON SOUTH, THE WINDS WILL INCREASE
FROM THE NORTH OVERNIGHT BECAUSE OF THE HIGH IN CANADA AND THE LOW
OVER HAIDA GWAII.

A MIX OF THE 00Z AND 12Z EC WERE USED TO UPDATE THE FORECAST.
ONLY THE HIGH RESOLUTIONS MODELS WERE ABLE TO PICK UP THE UPPER
LEVEL DISTURBANCE IN THE GULF THE BEST. THE TRACK AND ARRIVAL
TIMES ARE SLIGHTLY QUESTIONABLE AND WILL BE SOMEWHERE BETWEEN
YAKUTAT TO PELICAN AREA. THE SNOW SHOWERS WILL BECOME LESS
FREQUENT AS THEY MOVE INLAND TOWARDS THE COAST MOUNTAINS EXPECT
FOR HAINES AREA. THERE WILL BE A DRY SLOT OVER PETERSBURG AND
WRANGELL AREA WITH POSSIBLE PARTLY CLOUDY SKIES LATE TONIGHT.

FORECAST CONFIDENCE OVER THE NEXT 24 HOURS IS AVERAGE TO ABOVE
AVERAGE.

.LONG TERM...WE WILL HAVE A SEVERAL DAYS OF A SIMILAR SEQUENCE:
A LAND FALLING LOW IS FOLLOWED BY A COOLER AIRMASS WITH THE NET
RESULT OF FALLING TEMPERATURES AND THE SNOW LEVEL FALLING TO
SEA LEVEL IN A N TO S SEQUENCE. THE OVERALL THE FORECAST CONFIDENCE
IS AVERAGE.

THE SHORT RANGE SECTION ABOVE DESCRIBES A LOW IN THE NORTHEAST
PACIFIC TRACK NORTHEAST TOWARDS HAIDA GWAII TONIGHT.  WE WILL
THIS THE NAME "SYSTEM ONE".

SYSTEM 2: THE NEXT POLAR FRONT ZONE WAVE WILL TRACK NE INTO THE
GULF WHILE DEEPENING TO ABOUT 970 MB WITH A CENTER REACHING A
POINT ABOUT 240 NM S OF PADQ 12Z SUN. THIS SECOND SYSTEM WILL SEND
A LARGE AND STRONG OCFNT ONSHORE, AND WILL BE A SNOW EVENT FOR THE
PANHANDLE ESPECIALLY N OF FREDERICK SOUND.

MORE ON SYSTEM 2: THE NEWEST RUNS (29.12) OF THE GFS AND EC CAME
IN WITH LARGE CHANGES FOR THIS SYSTEM ENTERING THE GULF AND HAVE A
CONSENSUS THAT HAS BEEN LACKING. THE FORECASTS FOR THE PERIOD OF
00Z SUN TO 00Z TUE REFLECTS THIS CONSENSUS: A TRIPLE POINT LOW
MOVING NE INTO THE GULF TO 55/143 FOR 12Z SUN WITH A CENTER OF A
987 MB. THE GFS AND EC ARE TRENDING TO AN AGREEMENT FOR SUCH A
FEATURE (THE GFS HAS AN INVERTED TROUGH BAG WITH A THICKNESS
FEATURE LIKE THE TRIPLE PT LOW IN EC).

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-041>043-051-052.

&&

NCB/ABJ JBT