Small Craft Advisory 165, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
228 PM AKST THU FEB 17 2011

.SHORT TERM...THE LOW OVER HECATE STRAIT CONTINUES TO MOVE SE
THROUGH TONIGHT. HIGH PRESSURE REMAINS OVER NORTHWEST CANADA BUT
IS EXPECTED TO START TO SLOWLY WEAKEN AND DRIFT EAST THIS
AFTERNOON THROUGH TONIGHT. A FAIRLY HIGH AMPLITUDE, POSITIVELY
TILTED UPPER RIDGE AXIS PASSES PAYA FRIDAY MORNING AND REACHES
DIXON ENTRANCE LATE FRIDAY NIGHT. A STRENGTHENING SHORTWAVE
TROUGH DIGS SE INTO THE NORTHERN GULF LATE FRIDAY NIGHT AND SPINS
UP A 1005 MB LOW NEAR PRINCE WILLIAM SOUND. THE ASSOCIATED WARM
FRONT PUSHES INTO THE EASTERN GULF FRIDAY EVENING AND GOES ALOFT
JUST OFFSHORE SOUTHEAST ALASKA BY LATE FRIDAY NIGHT.

EXPECTING ANOTHER CLEAR COLD NIGHT ACROSS SOUTHEAST ALASKA.
NORTHERLY OUTFLOW WINDS WILL BE GREATLY DIMINISHED AND EXPECTED TO
STAY BELOW GALE FORCE AND EVEN DROPPING BELOW SMCR IN THE NORTHERN
ZONES. TEMPERATURES WILL BE A FEW DEGREES COLDER ACROSS THE
SOUTHERN PANHANDLE BUT A FEW DEGREES WARMER ACROSS THE NORTHERN
PANHANDLE.

CLOUDS WILL SPREAD INTO PAYA EARLY FRIDAY...ACROSS NORTHERN
SOUTHEAST ALASKA FRIDAY AFTERNOON...WHILE SUNNY SKIES PERSIST
FRIDAY FOR SOUTHERN. HAVE SNOW BEGINNING IN PAYA IN THE AFTERNOON
WITH 1 TO 3 INCHES POSSIBLE. SNOW BECOMES LIKELY AS FAR SOUTH AS
CROSS SOUND BUT WILL LEAVE OUT OF INNER CHANNELS THROUGH 3PM OR
THE END OF THE GRIDDED DAY PERIOD. WITH A TROUGH DEVELOPING IN THE
SOUTHERN YUKON DO EXPECT TO SEE THE WIND TO SHIFT SOUTHERLY ACROSS
NORTHERN HALF FRIDAY AFTERNOON WHILE IT STAYS NORTHERLY AND
DIMINISHES THROUGH THE AFTERNOON FOR SOUTHERN.

PRETTY GOOD AGREEMENT AMONG SHORT TERM MODELS WITH OVERALL
SYNOPTIC SITUATION AND CYCLO/FRONTAGENISIS IN GULF BUT TIMING OF
FRONTAL MOVEMENT STILL VARYING BY 6 HOURS. OPTED TO STAY WITH THE
SLOWER UKMET/NAM SOLUTION FOR PRES/WIND BUT USED A BLENDED
SOLUTION FOR POP/SKY/TEMPS.

.LONG TERM...SNOW EVENT AT PAYA 00Z SAT WILL WILL SPREAD SE ALONG
PNHDL AND EXTEND TO THE SRN PNHDL 00Z SUN. THE SHUTOFF IN THE SNOW,
ALONG WITH THE ONSET OF A NEW ARCTIC OUTBREAK, WILL OCCUR IN A N
TO S SEQUENCE BEGINNING ABOUT 06Z SUN.

FIRST CANDIDATE FOR HEAVY SNOW IS FOR PAYA. THE CONFIDENCE IS LIMITED
BY THE GRADUAL WARMING OF THE LOW LEVEL AIRMASS THERE WITH 1298 DAM
FOR THE 1000 - 850 MB LAYER EARLY SAT. A MIX OF RAIN AND SNOW COULD
OCCUR AND THEREFORE LIMIT THE SNOW ACCUMULATION.

MAJOR SNOW EVENT WILL GENERATE MOST OF THE PRECIPITATION FROM
A WATER VAPOR PLUME THAT IS OVR THE EASTERN CHAIN AS WELL AS THE
AK PEN, AND THE PRECIPITABLE  WATER VALUES FROM THE ADVANCED
MICROWAVE SOUNDING UNIT HAVE BEEN REASONABLY APPROXIMATED IN THE
MODELS.

ARCTIC OUTBREAK WILL REPLACE THE SNOW EVENT, AND BY ABOUT 12Z SUN
THE N WINDS IN LOWERING TEMPERATURES WILL HAVE SPREAD S TO
FREDERICK SOUND.

MODELS: OBVIOUS INTEREST IN THE ZONALLY-TRACKING LOW FOR FRIDAY
NIGHT AND SATURDAY. GFS IS FINE FOR INITIAL CONDITIONS SUCH AS
PRECIPITATELY WATER, BUT THE GFS SEEMS TO BE BLENDING TWO LOWS
TOGETHER IN THE GULF FOR 00Z SUN AND THE BEST AT KEEPING THEM
DISTINCT IS THE UKMET WITH A TIE FOR SECOND PLACE GOING TO THE
ECMWF AND NAM. SREF AND ECMWF FOR POPS 00Z SAT THROUGH 18Z SUN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY
     EVENING FOR AKZ024-026.
         WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY EVENING
     FOR AKZ025.
         WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
     MORNING FOR AKZ017-022.
         WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING
     FOR AKZ019>021.
         WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY
     EVENING FOR AKZ029.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-031>036-041>043-051-
     052.

&&

MM/JBT