Small Craft Advisory 166, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
301 PM AKST FRI FEB 18 2011

.SHORT TERM...UPPER LEVEL, POSITIVELY TILTED RIDGE AXIS OVER
SOUTH CENTRAL SOUTHEAST ALASKA TODAY CONTINUES SOUTH AND WILL
CLEAR DIXON ENTRANCE BY LATE TONIGHT. AN INTENSIFYING SHORT WAVE
WILL DROP SOUTHEAST INTO THE NORTHERN GULF TONIGHT AND SPIN UP A
LOW DEVELOPING IN PRINCE WILLIAM SOUND TONIGHT THAT DEEPENS TO
995 MB AS IT TRACKS EAST TO JUST SOUTHWEST OF YAKUTAT SATURDAY
AFTERNOON. THE ASSOCIATED WARM FRONT MOVES TO THE COASTAL WATERS
THIS EVENING AND IS EXPECTED TO GO ALOFT OVER SOUTHEAST ALASKA
TONIGHT. THE ASSOCIATED MODERATELY STRONG COLD FRONT WILL MOVE
ONSHORE THE NORTHERN SOUTHEAST ALASKA COAST BY SATURDAY
AFTERNOON.

EXPECT WIDESPREAD SNOW ACROSS SOUTHEAST ALASKA STARTING IN THE NW
TONIGHT AND SPREADING SE TO COVER ALL PANHANDLE BY SATURDAY
AFTERNOON. STRONG LIFT ASSOCIATED WITH FRONT COMBINED WITH A LONG
FETCH OF MOISTURE IN SOUTHWEST FLOW AND THE SLOW EASTERLY
PROGRESSION OF JET STREAM WILL ADD UP TO WINTER STORM SNOWFALL
AMOUNTS FOR MUCH OF THE PANHANDLE. HEAVIEST SNOW WILL FALL JUST IN
ADVANCE OF FRONT SATURDAY AFTERNOON AND COULD SEE RATES AT 1 INCH
PER HOUR. FOR THE INNER CHANNELS, THE EVENT IS EXPECTED TO STAY
ALL SNOW. PRECIPITATION TYPE BECOMES TRICKY ALONG THE IMMEDIATE
COAST AS WHEN WINDS SHIFT TO S OR SW COULD SEE TEMPS WARM AND
PRECIP GO TO RAIN. BY LATE TONIGHT AND CONTINUING THROUGH SATURDAY
CAA IN WESTERLY FLOW IS FORECAST SO THE PLACES THAT DO GO TO RAIN
WILL CHANGE BACK TO ALL SNOW ON SATURDAY OR SATURDAY NIGHT FOR
EXTREME SOUTHERN ZONES.

GOOD AGREEMENT IN QPF AMOUNTS OF 1-2 INCHES LIQUID WITH THIS
SYSTEM. PAYA AREA WILL SEE MOST PRECIP BUT WITH SOME OF THIS
FALLING AS RAIN SO SNOW AMOUNTS WILL BE ABOUT THE SAME AS PLACE
THAT ONLY RECEIVE 1 INCH LIQUID BUT HAVE HIGHER WATER EQUIVALENT
RATIOS. IN GENERAL GRIDS CARRY 7 TO 14 INCHES FOR THE 24-36 HOUR
EVENT. EXPECT TEMPS TO RISE OVERNIGHT FOR NORTHERN AND COASTAL
AREAS THAT THEN FALL THROUGH THE DAY SATURDAY.

WIND STARTING TO SHIFT TO THE SOUTH THROUGH NORTHERN INNER
CHANNELS TODAY AND WILL SEE THEM INCREASE TO NEAR SMCR LEVELS ON
SATURDAY. GRADIENT ORIENTATION IS FAVORABLE FOR WINDS THROUGH
INNER CHANNELS HOWEVER WITH DEEP STABLE BOUNDARY LAYER WILL HOLD
BACK SOME ON SPEED AND INTRODUCE WIND SHEAR IN THE LOWER LAYERS.

.LONG TERM...SHUTOFF IN THE SNOW WILL OCCUR ALONG WITH THE ONSET
OF A NEW ARCTIC OUTBREAK IN A N TO S SEQUENCE FROM 00Z TO 12Z SUN.

MODELS: QUITE HARD TO GO AGAINST A LONG RANGE CONSENSUS BETWEEN
THE GFS AND ECMWF. MODEL CONSENSUS ENCOURAGED USING A POP FIELD
BLEND OF SEVERAL MODELS IN WITH THE PRE-EXISTING FORECAST INC NAM,
SREF, GFS AND ECMWF.

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 WARNING FROM 9 AM SATURDAY TO 3 AM AKST SUNDAY FOR
     AKZ026.
         WINTER STORM WARNING FROM 3 AM SATURDAY TO 3 AM AKST SUNDAY FOR
     AKZ024.
         WINTER STORM WARNING FROM 3 AM TO 9 PM AKST SATURDAY FOR AKZ025.
         WINTER STORM WARNING UNTIL 3 PM AKST SATURDAY FOR AKZ017-022.
         WINTER STORM WARNING FROM 3 AM TO 3 PM AKST SATURDAY FOR
     AKZ019>021-023.
         WINTER WEATHER ADVISORY FROM 3 AM TO 9 PM AKST SATURDAY FOR
     AKZ018.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-033-034-041>043-051-052.

&&

MM/JBT